MECHANICAL AND STRESS-OPTICAL PROPERTIES OF PHOTOELAS!IC MATERIALS by YOSHIO TESHIMA
A THESIS submitted to OREGON STATE COLLEGE
in partial fulfillment of the requirements for the degree or MASTER OF SCIENCE
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,, : ACKNOWLEOOMENT
Sincere appreciation is expressed to H. D. Christensen, Assistant Professor of Mechani cal Engineering, who sug eated the thesis subject, and under. whose direction this thesis was com pleted. TABLE OF CONTENTS Page
I. I NTRODUCTION • • • • • • • • • • • • • • • • • l
II. THE PROTOBLASTIC METHOD OF STRESS ANALYSIS • • 4 III. BASIC REQUIREMENTS OF PHOTOELASTIC MATERIALS • 9
IV. PHOTOELASTIC MATERIAI,S • • • • • • • • • • • • 1. Gl ass • • • • • • • • • • • • • • • • • • • 15 2. Cellu1oid • • • • • • • • • •. • • • • • • • 16 3. Cata1in 61-893 • • • • • • • • • • • • • • 18 4. Fosterite • • • • • • • • • • • • • • • • • 21 5. Homa1ite CR-39 _ • • • • • • • • • • • • • • 22 6. Y...ris ton • • • • • • • • • • • • • • • • • • 24 7. Pl ex1g1nss and Lucite • • • • • • • • • • • 25 6. l!arb1ette • • • • • • • • • • • • • • • • • 26 9. Viny11te • • • • • • • • • • • • • • • • • 27 10. Summary of the Properties of Photoelastie Materials • • • • • • • • • • • • • • • • ~ 26
V. CASTING ND TESTING SEL: ~CTED POLYESTER RESINS • 31 1 • . Selection of Resins • • • • • • • • • • •. • 34 2. Mixing the Res infl • • • • • • , • • • • • • 35 3. Mol d Prepars. tion • • • • · • • • • • • • • • 38 4. Cas ting and Curing the Resins •••••• ~ 39 5. Machinability of the Resins • • • • • • • • 46 6. Tension Tests • • • • • • • • • • • • • • • 47 7. Strain Creep Tests • • • • • • • • • • • • 55 8. Optical Creep Tests • • • • • • • • • • • • 59 9. Stress Fringe Relationships • • • • • • • • 71 10. Determination of Fringe Constants • • • • • 72
VI. SUMJ~RY OF RESULTS • • • • • • • • • • • • • • 77 VIr. RBCO liDA'riONS FOR FU'IURE INVESTIGATIONS • • 81
VIII. COlWLUSIONS • • • • • • • • • • • • • • • • • 85
IX. BIBIIoGTIA.diY • • • • • • • • • • • • • • • • • 87
APPENDIX •• • • • • • • • • • • • • • • • • • 90 LIST OF FIGURES Figure Page 1. Polariscope Arrangement • • • • • • • • • • • • 5
2. :Mold Assembly •••••• • • • • • • • • • • • 40
3. Lindberg Furnace and Control Panel • • • • • • 42 • 4. ethod of Removing Gaskets • • • • • • • • • • 43
5. Method of Machining Test Specimens • • • • •• 49 6. Test Specimen Templates •••••••••••• 49
7. Arrangement for Tension Tests • • • • • • • • • 51 B. Tension Test of Laminae 4116-4134 (Stress- Strain Curve) ••••••••••••••••• 53 9. Tension Test of Marco MR-2BC (Stress-strain Curve) • • • • • • • • • • • • • •. • • • • • • 54
10. Arrangement for Strain Creep Tests • • • • •• 56 11. Strain Creep Test of Laminae 4116-4134 and Marco MR•2BC (Strain•Creep Curves} •••••• 57
12. Loading Jig for Beam-in-Pure-Bending • • • • • 60
13. Arrangement for Optical Creep Test • • • • •• 61 14. Isochromatic Fringe Patterns for Laminae 4116M4134 CUred for 4 and 6 Hours at 150 F • • 53 15. Isochromatic Fringe Patterns for Laminae 4116-4134 Cured for B Hours at 150 F, and :Marco NR-2BC • • • • • • • • • • • • • • • • • 64
16. Fluorolite Analyzer •••• • • • • • • • • • • 65 17, Optical Creep Test of Laminae 4116-4134 Cured for 4 Hours at 150 F • • • • • • • • • • • • • 66 18. Optical Creep Test for Laminae 4116-4134 Cured tor 6 Hours at 150 F ••••••••••••• 67 19. Optical Creep Teat for Laminae 4116-4134 Cured for 8 Houra at 150 F • • • • • • • • • • • • • 68 LIST OF FIGURES (CONTINUED) Figure Page
20. Optical Creep Test of Marco iffi-280 • • • • • • 69 21. Optical Creep Characteristics of Laminae 4116-4134 and Marco MR-28C • • • • • • • • • • 70 22. Stress Fringe Relationships for Laminae 4116-4134 and Marco MR-280 • • • . • • • • • - 73
LIST OF TABLES Table Page I. Properties of Photoelastic Materials • • • • • 29 II. Cr1tical Temperature Properties of Materials used for Three-Dimensional Photoelasticity • • 30
III. Properties of Liquid Resins • • • • • • • • • 35 IV. Mechanical Properties ot Laminae 4116-4134 and arco MR-280 Compared to Catalin 61-893 • 52 V. Total Strains for Laminae 4116-4134 and Marco MR-280 over the Time Interval of 5 Minutes . to 180 Minutes • • • • • • • • • • • • • • • • 58 VI. Optical Creep Characteristics of Laminae 4116-4134 and Marco !!R-280 • • • • • • • • • • 71 VII. Fringe Constants for Laminae 4116-4134 and Marco MR-280 obtained from Bending and Tension Teats • • • • • • • • • • • • • • • • 76 MECHANICAL AND STRESS-OPTICAL PROPERTIES OF PHOTOELASTIO MATERIALS
I, INTRODUCTION
The discovez-y of the photoelastic effect resulting. from stressing a transparent, optically isotropic material is credited to Dav·id Brewster, who observed this phenome•, non using glass 1n 1912, and published accounts· of his eltperiment in 1818. Although this discovery marked the birth of photoelasticity, which ha·s .become one of the moat powerful tools in present-day stress analysis, the possibility of applying this method to engineering appli cations was not recognized at that time. The basic concept that optical retardations producing color effects were proportional to the principal stresses existing in a stressed ma.terial, the stress-optic law, was formulated independently by F. E. le'Ulttan ttnd Clerk Maxwell in 1841 and 1853 respoet1vely. No practical appl1.cat1ons were made with th1.s me·thod until 1891, when Olarus Wilson published results concerning photoelastie investigations conducted on a s1mply-suppol'"ted beam subjected to a point load. Further applications of this method ere made by Mesnager· in 1901 (ll~ p629; 18; p4). Early workers in this field were seriously hand1• capped by the lack of a suitable .material with which the required models eould be mB.de. Glass, the only material 2 available, was relatively insensitive and was very diffi cult to machine. Progress in the development of photo elasticity was slow until 1920, when E. G. Coker introduced Celluloid as a model material (10, p325). This plastic was used extensively until the development of Bakelite in
the early twenties. Bakelite BT~61•893, which is now manufactured by the Catalin Corporation under the trade name of Oatalin 61-893, bas become the standard material for use in two-dimensional photoelastic studies. In the
.. ~· . years since the development of Catal1n 61-893, an entirely new world of synthetic resins has been born. Since all transparent plastics are potential photoelastic materials, it becomes of interest to investigate the suitability of these materials for photoelastic use. A great number of these resins have been used tor stress analysis work, but there are still many which have yet to be investigated. In the field of three-dimensional photoelastioity, a new material, Fosterite, has been ·eveloped by the Westinghouse
Research La..boratory1 and it appears that this resin will soon replace Catalin 61•693 for use as a model material 1n this particular type of study. Although the mechanical and str sa-optical properties data of photoelastic materials are available in texts devoted to the subject of photoelasticity, it was believed that any single text did not contain information on many of the materials which have been used and can be used. 3 This paper attempts to summarite all such information, obtained through a survey of available literature, so that it will be available in one work. Also included 1s a report of the preliminary studies for an investigation hose ultimate goal is to find a low cost, easily cast resin which could be substituted for the more expensive Catalin 61-893 for use as a model material in the photoelasticity courses offered at Oregon State College. The prtmary objective of thi& study was to determine the feas1b111.ty of casting several of the com• mercially available polyester resins with the equipment available in the engineering laboratory, and to test the resulting cured resin in an effort to evaluate their worth as photoelastio materials. Recommendations for future 1n• vestigationa on materials which proved successful are also presented. 4 II. THE PROTOBLASTIC ETHOD OF STRESS ANALYSI S
So that a clearer understanding of the principles in volved in the photoelastic method of stress analysis may be obtained, a short discussion on this subject is included in this paper. Som6 crystals such as mica and calcite exhibit the phenomenon of double refraction, ie, a beam of light fall• ing at normal incidence on the crystals is resolved into two components and transmitted on planes at right angles. Almost all other transparent materials such as glass and the synthetic resins show this effect when the material is subjected to a stress and examined under polarized light. This effect is only temporary since, upon removal of the load, the material once again becomes optically isotropic (11, p8~7, 839). The primary objective of the photoelastic method, therefore, is to measure the double refraction induced throughout the structural model when applied loads deform the material fram which the model is made, and to translate this effect into terms of stress by use of suitable mathematical relationships (18, pl60). The equipment and lens arrangement necessary to produce the required circularly polarized light is shown in figure 1. This polariscope arrangement is available for photoelastic investigations condu.cted at Oregon State College. 5
..
Fig. 1. Polariscope Arrangemen~ 6 The photoelastic method of stress analysis is a use... ful tool for promoting better and economical designs of structural and machine parts.. In many cases, especially in parts utilizing ductile materials where the design is based on the maximum shear stress theory of failure, all that 1s required from a stress analysis is the distribution of tbe maximum shearing stresseLh In such instances, the photoelastic method offers a rapid and simple means of obtaining the desired information which cannot be rivaled by an'Y other type of analytical procedure (22, p70). Briefly, the method consists of loading a scale model in a manner similar to that e.x1st1r~g 1n the prototype and observing the stressed model unaer circularly polarized 11ght. The r.esult1ng fringe patterns may have a light or dark background depending upon the orientation of the transmission axes of the lens system , Light background patterns e.ra obtained eithe-r by having (l) parallel polarizer and analyzer with crossed qua~ter wave plates, or (2) crossed polarizer and analyzer with parallel quarter wave plates. Dark background patterns are obtained by eithel' having (l) crossed polarizer and analyzer with crossed quarter wave plates., or ( 2) parallel polarizer and analyzer with parallel quarter wave plates. i'i1th a light. background,- the dark bands, or isochromatic fringes ap.. pear1ng on the model 1nd1ea.te. odd n'Un1bers ot one...half' wave lengths of retardation, while with a dark background, these 7 fringes indicate an integer number of wave lengths of retardation. The r e tardation produced at any point in the model is given by the equation (10, pl$6) .
R • Ot(p-q) (1)
where, R • relative retardation in wave lengths, Angs tram. un1ts 0 • stress•optieal coefficient, in./psi t • thiekne.ss ot the material, in. ( p-q) • difference. in principal stresses, psi.
In practice, however, the material fringe value, "f," is used instead of the stress•opt1ea.l ooeffie1ent "C" where "f" is defined as the stress difference in psi required to change the retardation at a point in a model one inch thick by one fringe. Then, if nn" 1a the fringe order at a point in the model of th1eknes,s '"t"
(p•q) : nf/t (2)
On the tree boundaries, one of the principal stresses disappears so that the stress pattern yields the tangential boundary stresses directly as
s ·• nf/t (3)
Since in many instances the ms.x1lnulu shearing stre s·es occur at the free boundaries, generally tto further information is required. Thus, by simply counting the number of fringes, multiplying by the material fringe value, and dividing by the thickness of the model, the stresses at these points can be easily determined. If, however, the stress distribution and the stress values are required for the interior points of the structure, isoolinios must be obtained from the stressed model and the stress trajectories· determined. Isoclinic lines are obtained using \'1hi te light in place of the monochromatic sourc·e used in the polariscope for obtain ing isochromatic fringes. With the information thus obtained, principles of the theory of elasticity must b~ applied to complete the solution to the problem. 9
III. BASIC REQUIREMENTS OF PHO'I'OELABTIC MATERI ALS
Although the ideal photoelast!e material has yet to be developed,. many plastics, which have been produced for general industrial p'L'lrpose.e, have been used as model materials . Only two have been developed specifically as photoelast1c materialat namelr Catalin E51•893, which ha& long been the standard material tor two-dimensional photoelastic studies, and the rec6'1tly developed Fosterite resin,. which has proved s.uccesfltul for' use in studying stresses in the three-dimensional syste.m. In many instances, the type of material selected for the model is dictated by the needs of the particular problem- under in... vestigation, which often leads to a compromise of securing the largest nuniber of desirable propel-ties with the fewest undesir~ble charaeter1st1cs. However, there are several properties which should be sought for even if they cannct~ be obtained. These pr.operties, not necessarily in the order of importance, are listed below: Transparencz. The m.Odel must t"an$m1t light;
.unless tbe material is t~ansparent, 1t is un• suited for photoelast1c models. Clear materials are the moat preferable since theJ transm1t the maximum amount of light; colored or opaque. materials should be avoided if possible.
~achinabilit,:. The materials should be easily 1·0 machined by means of or dinarily available machine tools to keep expenses of producing models at a minimum. Fabrication of models by other means such as casting and welding should be considered. High Optical Sensitivity. A loM fringe constant is desirable in photoelastic materials so that models under load will show the maximum amount of fringes, thereby increasing the accuracy of the resulting stress values, but this requirement ill have to be sacrificed for the mechanical strength properties required. Fringe orders should be high enough at moderate loads so that their value ean be determined by a mere counting process without resorting to the use of special instruments auoh a.s compensators. . , Linear Stress-Strain and Stress-Fringe Relationships. This requirement is essential since the material must conform to the elastic theory on which the photoelastio method is dependent for similarity in stress patterns betl'leen the model and prototype . Linearity of stress....fl'inge relationships allows the use of one fringe eonstant for all fringe orde·rs. ll High Modulus£( Elasticity and Proportional Ltmit. The modulus of elasticity should be hi h enough so that the models suffer only smal l deformations under load and still retain the same shape. A high proportional limit is desirable so that reasonably h i gh loads can be applied to the model .
~ Strain-Cree2 ~ Optical Creep. The effects of creep must be negligible within the limits of the stresses to be applied. For the stress-optic law to hold) it is absolutely necessary that fringe order bo dependent only on the model and the loads applied and not on changes in time. Freedom from I nitial Stress. Since the stress patterns result from loads applied) any initial stress in the mater 1al will result in errors in determining fr.inge values. If the initial stresses are un avoidable~ they should be capable of being removed by annealing . Isotropy. The material must be isotropic to conform to the elastic theory. Constancy Bf Properties with M·oderate Changes
~ Temperature. Properties must remain essentially constant at normal variations
in room temperatures so that test results will not be affected by changes in tempera tures~ I at the time of testing.
Availability at Moder ate ~· The material should be one that ia fairly inexpensive, and also available in large sheets with polished surfaces so that the time required to prepare models may be kept at a minimum. Freedom !.£..2!u Time-Edf;e Effects. All materials suitable for photoelast1c1ty appear to be susceptible to the formation of residual stresses shortly afteP .being machined. This
I effect is pronounced in some materials, while in others, 1t is not quite as noticeable (10, p892-893; 29, p767•77l).
The last-named property, freedom from time•edge effects, constitutes probably the greatest difficulty encountered in the use of synthetic resins for photoelastic studies. Ttme-edge stressesJ which can be observed in mod.els examined under pola~ized light as the appearance or fringes at the free edges, are a: tuncti,on primarily of t1me, temperature, and humidity. These resulting fringes are highly undesirable since they interfere with the ae curae,. of the boundary fringe counts, which normally are 13 the most critical. Leaf (15, pl09; 16, p20), in his in• vestigationa concerning this effect, has shown that moisture, either absorbed or lost by the material, is the pJ'inc1pal cause of this phenomenon. For Catalin 61-893, the process best suited to pre vent the occurrence or time-edge stresses is to machine
the model jus~ prior to examination in the polariscope, or it this is not possible, s·torage in light oils or a desiccator will retard the tormation of these fringes. In celluloid, coating the freshly-cut edges with Vaseline has been found to be beneficial in retarding these stresses (11, p894), while it has been reported that covering the lubricated edges with thin aluminum foil has proved successful 1n preventing these effects in Dekorit, a German phenol-formaldehyde resin, possessing stmilar properties to that of Trolon (11, p246). 14
IV. PHOTOELASTIC MATERIALS
With the development of the synthetic resins industry, there became available to the photoelastie1an literally hundreds of plastics,nany of which were potential photoelastic materials which could be used tor making the models required 1n the determination of stresses by the photoelastic method. Many of these materials have been thoroughly investigated and found satisfactory for this purpose, but the resins which have yet to be investigated far outnumber those that are in actual use. Before entering into the discussion on photoelastic materials, it may be well to defin·e some of the chemical terms used.1n connection with plastics. These terms are: Polymerization. A chemical change resulting in the formation of a new compound whose molecular weight is a multiple of the original substance. Condensation. The union of molecules accomplish ed by the elimination of water or stmple by product to form the large complex molecules. This definition is usually restricted to include those organic reactions in which a carbon atom unites with another carbon atom, Monomer. The simplest form of molecule capable of conversion to larger molecules, as for
example, through additional pol~erizat1on . .15 Pold'!er. Multiples of monomers, or compounds with the same proportionate composition of elements, but with different molecular weights (5, p35).
Brief commentaries on the more common photoelastic materials which have been used are presented 1n the pages following. These discussions are concluded with Table I; which shows the mechanical and stress•opt1cal properties of photoelastic materials, and Table II, which lists the properties of materials which h ve been found successful for use in three-dimensional studies. 1. Glass. Glass is the original model material used in the determination of stresses by the photoelastio method. Invest1ga.tors frequently mentioned in connection with the use of this material are Coker, who used it in many of his earlier experiments, and notably Kesnager, who in 1913, studied the distribution of stresses in a bridge photoelastically using a model made entirely of glass. Glass has many of the requisite properties of the ideal photoelast1c material. It may be obta1ned in a great number of varietie• in either large plates or thick blocks; it is a homogeneous ~tert ·al which is perfectly transparent, rigid, and stress free. It has a high modulus of elasticity, a large linear loading range, and unlike the synthetic resins, its stress and optical properties 16 are not affectod to any great extent with time or ordinary variations in tomperature or atmospheric conditions {13,. pll9). Glass also has the advantage of showing clearly defined isoclinic lines, and in addition, is one of the few materials which is not affected by the formation of time-edge effects (11, p895). Even with all these attributes, glass is now used only to a very limited extent, it at all, because of the
difficulty encountered in machining to even the s~plest shapes, and because it ie relatively insensitive optically in comparison to the synthetic resins now available. Due to its extreme fragility, there is also the danger of chipping occurring at the, load points. Possibilities of casting glass models have been suggested, but these would be neither homogeneous nor isotropic and would also show large initial stresses. Although these stresses could be annealed out, the high temperatures and the time required for the annealing pro• cess, in addition to the danger of fracture occurring, would not make this feasible for practical use. In this country, glass has very seldom been used as a photoelastic material (10, p324). 2. Celluloid. Great advances were made in the development of the photoelast1c method of stress analysis following the introduction ot this material in 1906. This material was used extensively in the early photoelastic 17 research work of Coker which led to the publication of the first compr,ehens1ve treatment on the s,ubject, ! Treatise ,£a Photoelasticity, by Coker and Pilon 1n 19Sl. Celluloid, also known by other names such as viscoloid, pyralin, and xylonite~ is a nitrocellulose compound that is e~s1ly machined, optically five times as sens1t1ve as glaes 1 and pos,sesaes good transparency. Al• though this material was a decided improvement over glass, it still lacked the elastic properties desirable in a good photoelastic material. Investigations by Edmonds and McMinn indicated wide variations in the properties of this matel'1al, but that age appeared to b.a ve a beneficial effect on these properties (6, pl9) . They also reported that for Celluloid there appeared to be evidence that a true proportionality between stress and strain did not exist under any condition of loading. Several factors must be taken into consideration when using this material for , photoelastic studies. These are, namely. change in proper• ties with age, its susceptibility to optical and strain... creep under sustained loads, and the variations in proper ties which vary with the rate of loading and with the t ,empe:rature at the time of the test (8, pl45). Although Celluloid and the other types of cellulose• nitrate type of resins hav~ been replaced t,o a large extent by Catalin 61-893, it must still be considered as a lS photoelastic material. It is eheap ~ available 1n sheets as large as 20 by 50 inches, and in thieknes'tuls varying from 0.005 inches to 1.00 inch. It ean be easily cemented to itself by means of such solvents as acetone, ethyl acetate, and butyl acetate. This property is advantageous in simplifying the construction of complicated models suoh as bridges trusses and other types of two ... d1mens1ona1 models (11# p325) . 3. Catalin 61•893. This material ia a glycerin phthalic anhydride type of thermosetting resin. It was formerly produced by the Bakelite Corporation under the trade name or Bakelite BT•61-893, but now it is manu factured by the Catalin Corporation under the designation Catalin 61•893. Since its introduction in the early twenties, it has become the standard photoelastio material for two-dimensional studies in the United States because 1ts p:rop$rt1es approach closest to those o.f the idea'l photoela.stic material. Cata.lin is available in semi-finished standard plates 6 inches by 12 inches, in thicknesses of 1/4 inch to 1 l/4 inch inclusive, at a cost of $17 .60 per pound at the present time, a pound ot the mat$r1al being equivalent to the 1/4 inch plate in the standard size. Principal dis advantages of this material are ita relatively high cost, size limitations of available plates, its susceptibility ·'
19 to t1me•edge effects, and the unpolished surface condition which requires considerable work to obtain the glass smooth surfaces preferable for use in photoelastic studies. In general• the material is water clear, machinable with standard tools, yet hard enough for practical handling. It is an isotropic material having a linear stress-strain relationship to 6,000 psi, a linear stress• fringe relationship to 7,000 psi, a modulus of elasticity of about 615,000 psi, a tensile strength of 1'7,000 psi for a five minute loading, and a Poisson's ratio of 0.365, Its optical sensitivity is high, approximately four times that of celluloid, so that thin models can be safely stressed to produce the rich fringe patterns required for accurate stress determinations (3, pl). At normal variations in room. temperature, 60 F 85 F, the maximum change in stress-optical coefficient is approximately 2.5 per cent, or a change of about 2 to 3 psi per fringe per inch, while variations in the modulus ' or elastic1ty amount to 3 per cent, a change from 630 , 000 psi to 615 1 000 pal . Poisson's ratio ith1n these temperature
limits remains constant (19 1 pAll). For increasing temperatures, both the fringe values and the 1nodulus continue to decrease, but at 230 F, the critical temperature, the effect of temperature on the properties disappears, and the material once again becomes -~~----~
20 p rfectly elastic, ie, there is com lete recovery of deformations and optical ef octs when loads are removed and stress-strain and stress-fringe relationships become linear. At the critical temperature, the modulus of elasticity of the material drops to 1,100 psi, and the fringe value to approximately 3.33 psi per fringe per inch. The ability of certain resins to regain their elastic properties at elevated temperatures is the phenome non that permits th use of th se materials for three dimensional photoelasticity. Briefly1 this method consists of heating themodel to the critical temperature, applying the desired loads, and allowing the material to cool slowly to room temperature with the loads acting. This permits the retardation, or fringes , resulting from the loading to be "frozen" into the material. After tlle material has cooled, slices are removed from the model and analyzed in a manner somewhat similar to that employed tn two-dimensional photoelastioity. Cutting the models into which stress patterns have been frozen does not produce any effects other than local effects of the cutting process (10, p327-337). However, the theory of three-dimensional photoelasticity is much more complicated and lengthier than that of the two-dimensional type.
Catalin 61-893 has been used for three-d~ensional photoelast1c1ty because ot the lack of a more suitable 21 material, but size limitations of available lates, its relatively high deformat ion and resultin distortion at t he critical temperature, and its susce tibility to time edge effects, which are more critical in this type of photoelasticity, have proven to be seri:ous limitations for use of this material in such studies (20, pl9}. 4. Fosterite. This is a newly-developed resin espec1all1 compounded for use as a model material in three dimensional photoelasticity by the Westinghouse Research Laboratories. Several types of Poster!te were pr·oduced initially, but now, photoelastic Fosterite has been standardized for manufacture as a styrene- alkyd resin in which 50 per cent of styrene is copolymerized witp an alkyd consisting of sebasi o and maleic acids and diethylene glycol (20, pl9). Fosterite is available in cylinders of 4, 6, and 8 inch dtameters and in bars ranging from 2 by 8 inches to a by 8 inches. The 4-inch cylinder is available in 18· and 36•1nch lengths, while the others maybe obtained in
15- and 30~inch lengths. As waa mentioned previously, Catalin 61-893 has been used for three-dimensional photoelasticity because of the lack of a better mater1a1 even though it possessed un desirable characte.riat1cs for this purpose. The use of Fosterite complet.ely eliminates the size limitationa and 22 the time-edge effects and reduces the e:t'ormations and resulting distortions to 65 per cent o:t' those experienced lith Catalin 61-893. The availability of Fosterite in the larger sizes results in two distinct advantages: 1 . More accurate and intricate models can be made. 2. The slices removed from the models may be made thinner in proportion to the overall dimensions of the model. Using thick slices results in errors, since the stresses, in general. vary in the direction of the thick ness of the slices and the added effect or these varying stresses are obtained photo elastically (22, p90). The use of Fo.sterite for ordinary photoelastic tests at room temperature is precluded by the excessive amount of creep \Vhich the material exhibits under load ( 20, p22) • Although the cost of this material is slightly higher than Ca.talin ol-893, it appears that this resin will replace it for tbree•d:lm.ensional photoelastiaity.
5 . Homalite CR... 39 . This resin, formerly produced by the Columbia Chemical Division of the Pittsburgh Plate
Glass Company under the trade name of Columbia Resin CR-39~ is now manufactured by the Bomal1te Company of Wilmingto.n , Delaware, under the designation of Homalite CR-39 . CR- 39 is chemically termed an allyl diglycol carbonate and belongs to the thermosetting class of 23 synthetic resins. This plastic is available in sheets 40 by 50 inches and in thicknesses of l/16 inch to 1/2 inch. Investigations conducted on this resin by Coolidge indicated that the material showed excessive optical and strain-creep under loads. Tests conducted at elevated temperatures to determine the suitability of this .material for three-dimensional photoelasticity proved unsuccessful because ot the large drops in strength and the relatively small deformations resulting from the high rigidity of the material (4, p74•82). The advantages of this material over Catalin 61•893 arec 1. It is available in larger sheets and has about the same optical sensitivity. 2. The material is manufactured with polished surfaces and is less inclined to contain residual stresses. 3. It is less susceptible to t !me-edge effects than Catalin 61-893. The disadvantages of this material are: 1. It possesses a lower limit of elasticity than Catalin. 2. It is more sensitive to creep and oall?ot be as easily or as satisfactorily annealed. 24 3. It is far more brittle than catalin 61-893 (17, plOO).
6. Kriston. This resin is an allyl-ester monomer, available from the B. F. Goodrich Chemical Company, which can be cast through the use of' suitable molds and techni ques into a thermosetting resin. Kriston possesses many advantages for photoelastic use, but suffers from one serious detect, namely, poor machinability. It is excessively brittle and extreme
c~re must be exercised in machining it to prevent chipping and cracking. Otherwise, this material has proved suc cessful for use in both two- and three-dimensional photo elasticity. One of' the principal advantages of' this material is that the catalyzed monomer may be used to weld other pieces of' the cast material. The resulting joints are relatively stress free, and the strengths of' these joints are equal to or greater than the strength of' the standard section. With regards to time-edge effects, Kriston has very desirable properties, since re~lts have shown that little or no time-edge effects were experienced in frozen stress patterns or specimens tested at room temperature (31, pl55-l'72 ) • 25 7. Plexiglass and Lucite. These two resins are representative of the acrylic, or methyl methacrylate. type of thermoplastic resins. Plexiglass is the product of the Robm and Haas Company, while Lucite is produced by the duPont Company. These materials are easily machined and have the requisite elastic properties, but their low optical sensitivities, as in the case of Celluloid and Vinylite, have prevented their wide acceptance as photoelastic materials for general use. Ho~ever, because of their low optical sensitivities, these materials have proved superior to other resins in cases where a complete stress analysis of structures was desired. In such instances, isoclinic lines must be obtained, and the presence of fewer iso chromatic& permits clearer identification and accurate tracing of the isoclinios. The advantages of using less optically sensitive materials for obtaining isoclinics are: 1. Ease of identifying the isoclinios when photographic records are desired because of fewer interfering isochromatics. 2. Models made from high optically sensitive materials show time-edge effects to a greater extent (in shorter times) than those of lower sensitivities. 26 Both glass and Celluloid have been used for ob taining isoclinics, but the fragility of glass under loads and the difficulties encountered in the machining process eliminate the use of glass.. Although Celluloid has been the next choice of investigators in securing isoclinic patterns, a comparison of its properties with those of Plexiglass and Lucite shows that the latter possess certain advantages over Celluloid. These advantages are: 1. Optical sensitivities of Plexiglass and Lucite are 1.25 times as great as glass while Celluloid is 3.9 times greater. 2. Plexiglass and Lucite, unlike Celluloid, possess water-clear transparency equal to that of glass. 3. Creep effects in Plexiglass and Lucite are smaller than in Celluloid under the same conditione of stress. 4. achinability of both materials is equal to that of Celluloid. 5. Plexiglass and Lucite possess higher elastic constants than Celluloid (30, p423-424). 8. Marblette. Marblette is a cast phenolic type of thermosetting resin available from the Marblette Corpora tion of New York. This material is easily machined, possesses an elastic limit of 2,750 psi, an ultimate strength of 2'7 4,500 psi, and a .modulus of elasticity of 250,000 psi in the as-received condition. Tnesc values can be increased considerably through adequate annealing processes (ll, p897). arblette, in spite ot its several desirable qualities, possesses high creep characteristics and proportionally higher residual double retraction and permanent set., if comparison is made under the basis ot equal stress with other materials. However, for equal fringe numbers in stress patterns, the stress intensities being in inverse ratio to the optical sensitivities of the two materials, relatively lower stresses are necessary with Marblette and hence, use of the material for models subjected to uniformly distributed loads is possible. With respect to time-edge affects, Marblette shows lese time-edge stresses than does Catal.in 61-893 (29, p767-77l.).
A liquid cement is available from the manufacture~ for cold cementing Marblette; this cement has also been found successful with Ba~~lite. ' 9. Vinylite. V1n~l1te 1s a polyvinyl butyral compound manutaotured by 'the Bakelite Corporation. This resin has been found susceptible to crazing effects upon the application or loads producing stresses fran 20 to 30 per cent of the normal ultimate strength. This effect has also been observed in Plex1glass and Lucite. Although this material has suitable strength properties, its low optical sensitivity or 226 psi per 28 fringe per inch places it in a class with Celluloid, which precludes ita use as a satisfactory material for general photoelaatic use (9, p65).
10~ Summ$-r'Y of the Properties of Photoelast1o Materials. The mechanical and stress-optical propert1e& or the materials mentioned in the preceding section, together w1 th othera, · are shown 1n Tables I and II. It will be noted that there are some discrepancies existing between the values given for the same material. This is to be expected since var·lous factors such as temperature, humidity, rate of ·testing, and variations in the manu• faoturing process itself, all have an effect on the resulting values. The values shown in the tables should be used _only- as a guide in selecting the desired material. For best results, investigators should conduct their own mechanical and stress-optical tests on sample pieces of material to determine the required values. TABLE 1 PROPERTIES OF PHOTOELASTIC MATERIALS
MAX CHEMICAL TENSILE ELASTIC MOD OF POISSON'S FRINGE OPTICAL SOURCE CREEP STOCK OF MATERIAL CLASSIFICATION STRENGTH LIMIT ELAST RATIO CONSTANT THICK . (psi) (psi) (psi) (psi I fr I in.) (in) DATA
BAKELITE BT-41-001 PHENOL FORMALDEHYDE 14,000 - 620,000 0 . 36 6!1 - - (II, p894) " • . . 13,900 - 61 !1, 000 0 . 36!1 6!1 . 2 - - (IO,p348) BAKELITE BT-46-001 - 16,000 - 615,000 0 . 365 B3 - - ( . ) ~ • - 16,000 - 620,000 0. 36 B3 - - ( ll,p B94) BAKELITE BT- 48-004 - - - - - 40.2 VERY HIGH - ( 9-,p 63) BAKELITE BT-48-005 - - - 300,000 - 55 - - (II ,p894) CATALIN PHENOL FORMALDEHYDE 2,100 1,850 200,000 - 45 HIGH - ( 9,p 63) . . . 4,000 - 200,000 - 45 - I (II, p 894) !13, pi81-2J CATALIN 800 (ENGL .) - 2-3,000 - 187,000 - 47-50 - - 7 ,p232 GLYCERIN PHTHALLIC 14,500 ( 9,p 63) CATALIN.. 61-893 ANHYDRIDE 5,500 630,000 0.36 87 LOW 1.25 • . ( 13 1 P 181-2) .. .. 17,000 - 630,000 0.36 84 - - . 15,000 - 620. 000 0 . 36 89 - - (18,pl72) . . • 17,000 - 615, 000 0.365 86 - - (IO,p348) 4900 3900 220 2001 000 I (IO,p325) CELLULOID CELLULOSE NITRATE 8500 7500 3 90,000 0 . 33-0.38 380 - .. . • 7,500 4,000 350,000 - 295 - - (29,p768) ...... 7,000 - 300,000 - 230 - - (22,p 73) . " . 7,000 - 280, 000 - 22.. - - (ll,p894) CR- 39 (ENGL.) ALLYL STYRENE 7,000 - 280,000 - 100 LOW - (13,pl81-2) 350,000 FOSTERITE STYRENE ALKYD (Ste Table ][) (22,p 73) ( 9, p63) GELATIN 65% H2 0 - 14% GLYCER. - - 15 - 0 . 19 - - (II, p894) • 13% H 0 - NO GLYCERIN - - 6 - 0.14 - - (IO,p350) GLASS - 10,000 - 9,000,000 0.40 1150 NEGL. - ( 13. pl81•2) . - 4-12,000 - 9,000,000 0 . 2-0. 27 800 - - ( . ) " - 10,000 - 10,000,000 0 . 40 1150 - - (ll,p894) 980 - ~ - . - 9,000, 000 0.25 3000 - (IO,p350) HOMALITE CR-39 ALLYL DYGLYCOL CARS. 1,000 3,000 250,000 - 77 HIGH Q50 ( 4,p 81) . • ~ • • - - 350,000 - 85 - - (II, p894) KRISTON ALLYL ESTER MONOM. 8,200 - 540,000 - 80 - ·- (31,pl63) LUCITE METHYL METHACRYL. 7-9,000 - 500,000 - HIGH - 0.375 ( 9,p 63) • • • 8,000 - 300,000 - HIGH - - (ll,p894) • • • 10,000 4,000 420,000 - 920 - - (30,p424) L'ORCA (FRANCE) - - - - - 80 - - (29,p768) MAR8LETTE PHENOL FORMALDEHYDE 4,500 2,750 274,000 - 51 HIGH I ( 9,p63) . (Annld) . • - - - - 75 - - (18 .P 172) . • .. . - - 500,000 0.40 70 - - (II, p894) • • . • 4,500 - 530,000 - 75 - - {22,p 73') .. " " " - - 530,000 0.41 76 - - (IO,p350) ...... (Unannld) - - - - 50 - - (18,pl72) ...... 4,500 - 160,000 -0 .40 42 - - (ll,p894) . . 4,500 2,750 2102000 0.35-0.46 23-48 - - (IO,p350) ...... 50,000 . 4,500 2,750 250,000 - 23 - - (29,p768) --MONSANTO CN 2050 CELLULOSE NITRATE 5-10,000 - 286,000 - 224 - 0. 25 ( 9 ,P 63) NORTON RESIN METHYL METHACRYL. 8-10,000 - 475,000 - 6310 - 0.125 ( • ) PERSPEX (Pioaticized) (E) .." " 7,000 - 450,000 - VERY HIGH - - (13, pl81-2) " ( Unplasticized) . 10,000 - 470,000 - 500 UP NEGL. - ( • ) PHENOLITE (JAPAN) - 10,700 4,300 525,000 - 65.2 - - (IO,p350) • - 8,500 7,000 1,000,000 - 55 - - (29,p768) POLLOPAS - - - - - 180 - - ( . ) PLEXIGLASS METHYL METHACRYL. 8,800 - - - 500 UP NEGL. - (13, pl81-2) " • . 10,000 4,000 400,000 - 920 - - (30,p424)
PYRALIN - 5-10,000 - 318,000 0. 30 226 - 0.50 ( 9, p63) RUBBER - - - - 0.50 8.10 - - ( .. ) TROLON (GERMANY) - - 1,420 355,000 - 63 - - (10, p350) : VI NY LITE vs 1310 VINYL COPOLYMER HIGHER 8-10,000 - 474,000 - THAN CELL. - 0.25 ( 9,p63) ~ XYLONITE CELL. NITR. CAMPHOR 5-8,000 - 300,000 0.3 ~ 300 MOD. - (13, p 181-2) 30
TABLE II Critical Temperature Properties of trateriala Used tor Three-Dimensional Photoelast1c1ty
Catalin 61-893 Fosterite Kriston Critical Temperature, F 248 194 275 Fringe Constant, t, ps1/fr/in. 3.30 3.25 6.25 odulus of Elasticity, E, psi 1200 1950 13,000 Ulttmate Tensile Strength, psi 400 430 680 Figure of erit (E/f) 121. 132 2080 Time-edge Effects Very Large Small Small 31 V. CASTING AND TESTING SELECTED POLYESTER RESINS
With the development of nlow-pressure" or contact thermosetting resins, it has become possible to cast plastics in sheet form at a minimum cost without using expensive, specialized equipment . These contact resins, which are classified under the generic term of · "polyesters," are a group of clear, liquid, thermosetting resina of adjustable viscosities, which when catalyzed and subjected to heat, cure to an extremely hard, stable solid without the use of pressure and at moderate tempera tures. More recently, through the use of accelerators, cure can be accomplished even at room temperatures (23, pl). These polyesters include unsaturated alkyd resins, copolymerized with a monomer such as styrene, as well as the polyallyl resins, suoh .aa d1allyl phthalate and allyl diglycol carbonate. The unsaturated alkyds are not specific chemical compounds but are condensation products of varying composition and varying chain length, whereas moat of the allyls are definite chemical compounds. In general, the pure allyl resins polymerize much more slowly than do the unsaturated alkyds. The polymerization of polyesters takes place without the formation of water, acids, ammonia or any other volatile compound, unlike the polymerization of the phenolic,
• 32 urea, melamine, and saturated alkyd resins, which is a condensation reaction (27, p353-354). The various polyesters on tbe market today differ from one another in several respects. Some are air in• hibited; others are nGt. Some may be cured at room temperatures, others mar not. They also differ in electrical and physical properties. The principal advantage ot this group of resins lies in their ability to be east without the application of pressure and extl'eme curing temperatures which permits the use of low•eost molds and eliminates the need of e.x
pensi~e baking ovens, autoolavee, and sim.ilar heating units. Thus, it has become feasible to east and 1nvest1... gate the mechanical and stress-optical properties of these contact resins in the possib111t7 that a material possessing equal or: superior prope:t>t1es than Catal1n 61•893 could be found. The objectives ot the investigations presented herein were to determine the posa1b111t1Cls of successf\1lly casting several of the commercially available polyester resins with the ex.1st1ng rae111t1ea at the Oregon State College Engineering Laboratory, and to conduct mechanical and stress•opt1oal tests for the purpose of evaluating the worth of these resins as sttitable photoelast1c materials. Although the t ·est results are compared to published data on Oata.l1n 61•893, the primary purpose was 33 not to find a resin superior in all respects to this specially compounded resin, but more generally, to find a castable resin which possessed satisfactory properties, and, in addition, was more economical to use in the elementary photoelasticity courses offered at the College. As was mentioned previously, the present cost of Catalin 61-893 is $17.50 per pound, whereas the prices of the polyester resins used in this investigation ranged from 0.53 to 1.05 per pound. It must be pointed out, however, that the latter prices are for the liquid resin only and do not take into account the cost of catalysts and accelerators required. Considering the small amounts used, the addition of these constituents would not raise the total material cost by more than a tew cents. Although labor and power costs have not been considered, it is believed that these resins, if successful, could be cast at a fraction of the cost ot Catalin 61..893. Aside from the principal advantage of o tability at lower cost, a secondary consideration involves the availability of optically clear surfaces in the as-cast condition of these materials, which would eliminate the tedious and time-consuming grinding and polishing opera tions required iith the use of catalin 61-893. This resin was formerly available only in rough sawed sheets which required a oonsider.able amount of work before the finished model was obtained, but now it is available in 34 a semi-finished condition which eliminates a few of the intermediate grinding operations. It should be pointed out that by immersing the model in a suitable fluid having an index of refraction identical with that of the model material, it is possible to use the models in an unpolished condition, but optimum results are obtained ueing models with highly polished, glass-like surfaces. Mechanical difficulties encountered in designing a loading arrangement in hich the immersion fluid can be used has also prevented ~ide acceptance of this method. 1. Selection of Resins. The resins selected for this investigation were all of the polyester type, with the criteria of selection being based on optical clarity, color, and strength property data as obtained from manu facturers' bulletins. Sample quantities of the resin were ordered, and upon receipt, were placed under refrigeration since all thermosetting resina are subject to a slow cure reaction even ithout the accelerator added. This is especially true for small quant1tie~ of resin which can change temperature rapidly. Trade names of the resins selected and their manufacturers are listed below, while Table III gives pertinent information on the properties of the resins in their as-received forms (2, pl; 25, p5-6; 26, pl) . 35 Resin Manufacturer Laminae 4116 American Cyanamid Company Laminae 4134 Plastics and Resins Division 30 Rockefeller Plaza New York 20, N. Y.• Marco MR-260 Marco Chemicals, Inc Marco MR-280 Sewaren, New Jersey Vibrin 100 Naugutuck Chemical V1br1n 114 Division of the US Rubber Co Baugu.tuck, Connect1out
TABLE III Froperties o.f the Liquid Resins
Per cent Viscosity Shrinkage SE Gr ( c;es) durins cure Laminae 4116 Clear Light 1.,ua 300-600 6-7 Straw Laminae 4134 Clear Light 1.12 300-600 6-.7 Straw
Marco lffi-260 Light st:r·aw 1 ,.24 l.O,OOO -- ~ - to 12,000 Marco MB-2SC Light Straw 1.12 650 -- V1br1n 108 Water Clear 1.12 600 10.2 Vibrin 114 Olear Straw 1.14 400 8 .'1
2. Mi.x1ns; the Resins. In mixing the resins in pre• paration to casting, the following formulations recommended by the respective manufacturers were used: (All parts by weight) 36
Laminae 4116•413~ (Oven Cure) 80 parts Laminae 411 6 r,a s in 20 parts Laminae 4134 r esin 0.4 parts Laminae 347 Catalyst
Marco WR-26C (Oven Cure) 100 parts MR-26C r esin 20 par,ts Styrene 2.5 pa:rts MC •l Paste Catalyst
Marco MR-280 (Room Temperature Cure) 100 parts MR-280 resins 2 parts !0-1 Paste Catalyst -· 5 parts· Accelerator E
Vibr1ns 108 and 114 (Oven Gure) 100 parts Vibrin lOS or 114 2 parts Luperco JDB Catalyst
In general, the mixing procedures followed for the above rosins were relatively simple, and in most eases were identical, the exceptions being Marco MR•26C in which Styrene is used, anCl ltarco MR - 280 in which an Ac celerator is used. The procedure followed, with dit' .ferences in methods for the Marco resins noted, 1s out• lined below; a. Remove the required amounts of resin from refrigeration and allow to reach r .oom temperature. b. Add the requ1red' amount of catalyst which will d1ssolve.readily 1n the resin under 3 7 stirring action . The catalyzed mix should be stirred thoroughly to assure uniform distribution of the catalys t 1n t he r esin. In the case of Marco MR-260, the required 20 parts of Styrene monomer should be added to the resin and mixed thoroughly before the catalyst is added- a. Allow the catalyzed resin to stand for an h.our or two to perm1t entrapped air bubble·s resulting from stirring to escape. For' Marco MR-28C, the Marco Accelerator E should be added at this point and the mix ture again stirred thor oughly . Some care tm1st be exercised 1n stirring the mixture now since the time available for the air bubbles to escape 1s 11m1 te·d by the gelling
action which begins approximately 45 minutes after the introduction ot the acceleratol" to the .resin mix. d. The catalyzed and/or accelerated resina are then ready to be poured into prepared molds. e. Mixing beakers may be cleaned using acetone to remove the bulk of the remaining resin
followed by cleaning with a detergent such as Labtone Glass Cleaner. 38 3. Mold rel!aration. The mater al selected for molds was common pl te glass sheets since this material is readily available at relatively low cost, and bas the high finish on the surfaces which is essential for imparting the required surf ces on the resin. Although there was some doubt as to whether ordinary plate glass would with stand the temperatures at which curing took place without fracturing, subsequent experience showed that there were no failures resulting from this cause: Containing gaskets for the plate glass molds were made from sponge rubber strips cut from sheet material of the type available from athletic supply houses. These strips were covered with sheet cellophane to prevent contact of the liquid with the rubber gaskets; a condition which inhibits the cure of the resin. Sponge rubber was selected since the resiliency of the gaskets permitted minor adjustments in the thickness of the space between the mold faces. Before assembling the mold, a lubricant was applied to the inner surfaces of the mold . Initial castings were made using Johnson's Glass 1ax as the lubricant, but subsequent castings were made using Marco ML-2 Concentrated Lubricant dissolved in acetone in the ratio of five parts by weight of lubricant to 95 parts by weight ot acetone . This solution was applied to the mold faces with a clean 39 cloth so that a film of lubricant ~as visible on the surfaces. Generally, two to three coats were found to be sufficient. Although partin qualitlos using Glass Wax were satisfactory, better results were obtained with the Marco lubricant. To assemble the mold, the cellophane covered gaskets. were placed between the lubricated faces of the mold at three edges . Four one-inch "C" clamps were then placed at the corners and adjusted to hold the mold at the desired thickness . The assembled mold is shown in figure 2. 4. Casting and Curing the Resins. In pouring the catalyzed resins, the assembled mo ld was held at a 45 degree angle and the rosin allo~od to flow down the side of the mold. This minimized the possibility of entrapping air bubbles in the resin. After pouring, all resins, with the exception of Marco MR-28C, were allo ed to gel at room temperature overnight. The arco MR-260 resin and Laminae 4116-4134 gelled completely during this period, but in the Vibrin resins, approximately one-half inch of the resin at the exposed surface of the mold remained in liquid form . The occurrence of these air-inhibited sur faces was reduced to some extent by lacing a cover of cellophane bet oen the glass plates in contact with the resin surfaces . All resins gelled crystal clear except f or Vibr1n 114, which had a tendency to cloud upon gelling. 40
.------~~------~------~ I
J ------~
J'ig. 2.. a,ld Assembly
I ' 41
All attempts to obtain a clear gel with ttis resin wer~ without success; therefore, V1brin 114 was eliminated from. further investigation. In the ease of Marco MR..280, which 1s a room temperature curing resin, the gelling action begins ap• proximately 45 minutes after the accelerator is added to the catalyzed resin. During the next two hours, an ' exothermic heat r -eaction takes place. After this h_eat of reaction has been dissipated, the finished resin may be removed-from the mold . The total time required between pouring the resin and the removal of the finished plate was approximately 4 to 5 hours • . Curing for all other resins was conducted in .a Lindberg circulating air annealing furnace, shown in figure 3. Controls provided on this oven consisted of a thermocouple actuated on-off- type controller and an Electrol proportional controller, also thermocouple actuated. Range of the proporti-onal controller was from 150 F to 1500 F. Prior to placing the gelled resins in the oven for curing, the "cu clamps holding the mold are removed together with the rubber containing gaskets. Here again, care must be exercised, since any hurried attempts to remove the gaskets w111 result in separation of the glass plates :from the resin. Once separation hs.a occurred, it is practically impossible to place the glass mold surface in perfect contact with the gelled resin li&. 3. Lindberg Furnace and Control Panel 43 ithout lr spaces being present at the resin-mold boun ary. In one instance, after such an occurrence, the resin wa pl ced in the curing oven with the top plate removed an subjected to the regular curing cycle. This resulted in a fin shed plate having very uneven surfaces and showing some evidence of surface checking. T.he pro cedure ua·ed in removing the gaskets can be more easily explaine by referring to the sketch and accompanying text shown in figure 4 .
Fig. 4. Method of removing gasket 1. Cut and remove gasket at (a). 2. Grasp exposed end of rubber gasket and remove in the directions shon1 by arrows (b). . 3 . Remove "C" clamps from mold.
Cracking of the resins on curing was the major dif ficulty encountered in the casting of Marco MR-260 and Vibrin 108 resins. arco MR-260 was cured for three hours at 210 F, while Vibrin lOB was given a two-step 44 cure, l/2 hour at. 190 F followed by 1 hour at 250 F. Possibly at this point, it would be well to explain the problem involved in the action which oceurs when the gelled resin is cured at the elevated temperatures. The curing of thermosetting polyester resins is basically an exothermic heat reaction. lienee, if the casting is large, or if the mold is of such a material which does not absorb and oonduet the heat rapidly, the temperature of the resin mass during the curing period rapidly in• creases. This heat in turn speeds up the rate o.f polym:er1zation s·o that the reaction may literally "run away" and generate excessive heat. In most materials, such a heat build-up or increase in temperature is
~ accompanied by e.xpe.nsion of the material. In the curing resins, this expansion is o.pposed by the shrinkage action or the resin as .it is in the process of curing to its final state. Thus, it ean b& seen that during curing two forces are working in direct opposition, which, 1t not controlled,. will result in fractured cast.ings or one that is under strain. Therefore·,. temperature rise must
be controlled during the period. when exotb$~1c heat is
being produced moet rapidly ('?,7 1 pl} ,. The failures experienced. with the two resins were possibly due to the high heating rate characteristics of the oven. In an attempt to minimise the rapid heat 1n ex-ease, the mold containing the gelled resins wel"e 45 sandwiched between two l/4-1nch steel plates during the curing period. Tbis· did not alleviate the cracking tendencies of Vibrin 100, and therefore, this resin was eliminated from further study. Thus far, both Vibrin resins 100 and 114 were found unsatisfactory for casting; the former because of cracking during cl.lr1ng with the facilities used, and the latter due to difficulties 1n obtaining a clear gel . Investigations on Marco MR-·260 were also d1seontinued since most of the early castings in which failures \¥ere encountered were with this resin, which resulted in the depletion of the small quantities of th:e resin available for study. To minimize the risk of losi.ng additional material through fracture, the steel plates we·re also used with Laminae 4116-4134. Results of casting this particular formulation proved very successful; therefore, three dif ferent curing pel'iods were used with this resin to determine the effects ot different curing periods on the properties of the material. Temperature of curing for Laminae 4116-4134 resins was 150 F for periods of four, six,. end. eight hours. After holding the resins for the spee.ified times at the ·curing temperature, the resins were allowed to o.ven cool until the following mo.rnlng. This was done to avoid rapid temperature changes, which could lead to fracture of' th$ finishEid plates. Upon removal trom the 46 oven, the resins were separated from the molds. Extreme care must be exercised at this stage since fracture can occur in either the finished resin or in the glass plates comprising the mold.. Adhesion between the mold surfaces is too great to allow removal of the plates b7 pr1ing \Vi thout danger of cracking or chipping one or both of the glass plates. The procedure used was to scribe around one surface of the resin at the junction of the edge of the · resin and the plate glass with the point of a sharp knife. Continued scribing will result in rainbow-colored areas appearing at the surface of the resin where separation begins. These multi-colored areas will spread aoross the resin-mold surface until finall7, the mold and resin will separate with a sharp cracking sound. Once the first plate has been removed, it is a simple matter to remove the remaining plate following the same procedure just out lined. Surfaces of the cured resin were optically clear, and measurements with a micrometer showed that the surface variation amounted to 0.005 inches or less, 5. Machinability ot the Resins. The machinab1litr of the Laminae 4116-4134 resins was tound to be slightly better than Marco MR-260, although both materials appeared to be more bri.t.tle than Catalin 61·893. Standard tools were used 1n machining the models , and by exercis1ng the normal amount of care, chipping at the edges and machining stresses can be avoided. For drilling, however, 47 it was found necessary to use a lubricant, either water or light oils, to prevent the formation of machining stresses around the holes. The test specimens were end-milled to shape using metal templates as shovm in figure 5 . The plastic blanks, previously cut 1/16-ineh oversize on the band saw, were sandwiChed between the templ ate and the baseboard• clamped, and then milled to shape by runni ng the assembly against the tnilling cutter. A case- hardened steel collar attached to the cutter, whi ch bore against the edge of the template during the final cuts, assured perfect edges on the finished models. The metal templates used were milled from mi. l d steel stock and were case-hardened by carburizing for 8 hours a t 1750 F, followe by quenching 1n water. These templates are shown in fi~re 6 . 6. Tension Tests . For the purpose of determining the stresa·strain relationships , tension tests were con ducted on specimens of Marc o MR- 280 and the three types of Laminae resins. The tensile models used in these tests were or the pin- end type which were end-milled to shape using the templ ate shown previously in figure 6 . Brass bushings with a pres s fit were also used to minimize the pos s i bil1t1 of fracture occurring a t the pins, thereby in creasing the load~carrying capacity of the models . 48
Fig. S. ethod. of achini.ng Test Specimens ,.. 49 Drill 2 Holes fD. 4 D.
a -ICI) ,..,.. ~
I 1·~,..,,CI) 'J .....,. I{)
: -ICil U) I : ~ - I _l - ~ - '" (\J (c) Strom- Creep Specimen """----+---'_j_ L~ _J (b) BendinQ Specimen Dr i ll 8 To JJ _/ l 0 . 0312" . for 10-24 : ~.:: .~"i l - l--It_ ___J ~IfJ~@f' sc,ew (o) Tensile Specimen (d) Bross Bushings for (e) E nd M i ll Note : All Steel Parts Case Tensile Spec imen C o il or Hardened FIG. 6 TEST SPECIMEN TEMPLATES 8 ACCESSORIES SC AL E : FULL SIZE MATERIAL = MILD STEE L EXCEPT AS NOTED 50 A 3000-lb capacity T1nius·01sen lever-type testing machine was used for these tests. Loads were increased in increments of 50 pounds from zero load to fracture of the specimen. The strain measurements ere made using Type A-1, SR-4 electric resistance strain gages in con junction with a Young Testing Machine Company Type A Strain Indicator. After completing the first few tests, it was found desirable to use the entire 20,000 microinch r~nge of tha indicator. This was accomplished by intro• ducing a four-ohm resistance in series with the compensa· ting gage circuit and utilizing the range extender provided on the indicator. Even with this arrangement, strain measurements in the vicinity of the ultimate strength could not be measured, but adequate data were obtained to determine the cardinal points of interest obtainable from a tension test. The testin arrangement used is shown in figure 7. Two specimens each of Marco MR-280 and Laminae 4116- 4134 cured for four hours at 150 F, and one each of Laminae 4116-4134 cured for six and eight hours at 150 F ere tested. In all but one case, fracture occurred within the critical section of the model. The values ot the ultimate strength, proportional limit, and the modulus of elasticity resulting from these tests, together with those of catalin 61-893, are given in Table IV. 51
(
Fig. 7. Arrangement tor Teftsion Testa 62
Stress•str in ou,r'Yes for the tamin c and .,~c.rco r 1ns are shown 1n fig'lltt'&e 8 end 9.
TABLE IV
Mechanieal Properti, o.r L mint..~ 4ll -4134 and t oo mt-280 Compared to Catal1n 6l-S98
Ultimate Proportion l. ~o 1psl_l. I (ps1J tPe1l . 4-hr-Laminae 910 4000 440.000 6-hr Lbl1nac 9000 4000 404,000 ' B-ht' La.m!:nac 9400 4000 40 ,ooo aroo. M.ft•2SO 6400 3000 $04,000 catal1n el-a93 13500 5500 663,000 In genoral, the tam1nac r sins po seas higp r strength propettt1os than Ul"CP MR•ESC, but both D.l'e 1nfet91 o:r to c tal1n 6l•a93 in this re.epcot. 1th1n the Lam1ttao group. the high~st ntrength prop rt1ea of the three types tested ,.,fU' exhibited by th Lam1n e 4116-4134 re 1n cured ~ .or tour hour . at 150 F, w1 th th lo .eat &tren th being .xh1o1t d bJ the resin .cured r r s1x hours at the sam temper:tdnJ.ro.. The str ngth of tho rosin o.tJ.red rox- e1gb.t hours laJ pprox ately td.dwe.y b&tw on the otb r two. Thus, 1t c b s en that no aet1n1t · trend of the e.ftflct ot curing t on tr~ngth prop ~tte as estublish d by these testa. It was not dote 1ned wbetbel- the slig,bt ! . . ,, :~ . .. -t-:-·- IA-·n -+~h-n +- I :·-1. -. -+--+-:-::t-:-::-::t-:::..+-_.. +-_ -+'-+.;.;.·+~-'-+--+- ...... I ... -'-f'-· bJn: :.: :::: :.': :::: :::: :::. :::: ...... I ·.. _.: :::: :::: :;:: ;::: :::. :::: ... -1--t- I ...... ::: ::: ~r.- ~ni~~ : :::. :> ><: :::: :::: :::: ::: ::: :: · • • t • - .'I . ·-·· ···· ...... / " / '" ...... :.:. l:"'r~n · ~:: :~:: :::: :::~ :::: :::: :::: . : :.:: .. ·:- .. : . : ·: . . ·: :· .: :::: :::· :::: :~:: ...... ·• ...... ' ...... "l ' ...... ~·· · ....~J '",.....~"·" ' -!~ r:1~1N. ·.• ' i"' l! •" ~~t ' · 'in ...... , 11...... :~< ,••••...... • ~- ·-·'!"··:: .::!'I! :.: :::: :~:: ;r~: :::-: :~!r :::: ::_r:: ~:i-- ... ~: . t .•!: . , : .. t ~ .:- .• r:.: ::_:: :.:!: :!:.;.. ~;:: ·-·-·m··~u....~ tm:Jttili"'--. ._ · · .. · .,...... ,...... 'Jl'l ...... ·rt .. ,. '1' ·• ... · ...... , . ., !"' .. ,. _ .. 1"1 •·u;;_fi- ~" 1 '~ H.Jtttw.~ ' .. ' " .,., .. ,. "!i .... 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Strain-GreeR Tests . Short-time strain-creep tests ~ere conducted on all resins to determine their respective creep characteristics . For these tests, tensile specimens ·ere subjected to a constant load, hich produced z;ooo psi within the test section of the specimen. Strain readings were then taken at intervals of 5, 10• 15, 201 30, 45, 60, 90, 120, 150, and 180 I t inutes after the application of the load. These rondings 'ere obtained using Huggensberger tensometers measuring over a one-inch gage length attached to both sid~s of the specimen. An average value of the strain readings of both gages was used to determine the value of strain. Because of their limited capacity, the gages ere not attached to the specimen until after full load had been applied. Although it , was realized that this procedure would produce errors in the actual total strain recorded over the specified period, it was believed that an indication or the overall creep characteristics could still be obtained in this manner. The testing arrangement is shown in figure 10. The resulting strain-creep curves, figure 11, show th t all Laminae resina possess similar creep rates. Rapid increases in strain are shown during the first 45 minutes, after which the creep rates become f irly 56 Pig. 10. A.J"rangement tor Strain C~ep testa 58 constant. ~1e creep curves for Marco MR- 28C , on the other hand, show a much more uniform creep rate over the three- hour period. It should be pointed out that the curves plotted from the data show only the increase in strain after apvlication of the lo&d) and do not t ke into consideration the initial strain due to loading. The total increases in strain between the time interval of 5 minutes and 18 0 minutes after the appl ication of the load is shown in T ble V. So that the magnitude of the strains involved may be more easily visualized, the strains have been converted to equival ent stresses in psi. The per centage increases in stress over the actual applied stress are also shown . TABLE V Total Strains for Laminae 4116-4134 and Marco MR•28C ovQr the !l'ime Interval of 5 Kinutes • 180 M1nutes Total ModulU3 of Equiv Per cent Strain Elasticit)' stress Increase {in.) (psi) (psi) in Stress 4-hr Laminae 0 . 00203 440,000 894 44 . 6 6-hr Laminae 0.00207 404, 000 836 41.7 8 - hr Laminae 0 . 00189 404,000 764 38 .1 Marco .~; -280 0 . 00202 394, 000 795 39. 7 'l'he above results indicate that all resins tested sh ow excessive amounts ot strain-creep to be used 59 satisfactorily as a photoelastic mat erial. Even for the time interva l of 5 minutes to 60 minutes, the strain resulting from creep expressed in terms of equivalent stress ·amounts to 22.5 per cent, 23,6 per cent, 19.7 per cent, and 17.5 per cent over the applied stress for the resins in the order shown in the table. a. Optical Creep Tests. A study was also made of the optical creep obaracter1stics of the various resins to determine whether there was any correlation between optical creep and strain creep. For these tests, the beams were end-milled to shape as previously outlined, and loaded through holes located on the neutral axis of the beams by a linkage system to produce pure bending in the central portion of the beam. This loading arrangement is advocated by Frocht (10, p38l) as being preferable t'Q the more commonly used method of applying the load through pins placed at sui table points on the upper and lower edges of the beam. Figure 12 shows a modified form ot the loading jig used in this test~ which is to be made for future use in the Oregon State College Photoelasticity Laboratory. •, ·. All beams were subjected to a constan't 'bending moment of 112.5 lb-1n. by applying a 300-lb load through a lever .system. This arrangement is shown in figure 13. Photographs of the· resulting fringe pat.terns were taken ~ed1ately after loading and at intervals of 51 10, 15, 10 3 Drt l l and Rtom All Holts ~D. 8 Links Reqd . No. 48 Dri II 2 Holes for Cotter Pins Pin Detail Full Size FtG . 12 LOADING FIXTURE FOR PURE BENDING Scale : One- Half Size Except A• Noted All Dimensions In Inches 61 Pig. l3. Arrangement for Optical Creep !est ·' - 62 30, 60, 120, and 180 minutes after application of load. The initial and final fringe pattern photographs for all beams are shown 1n figures 14 and 15. Negatives of the . sequence fringe patterns were analyzed using the GE Fluorolite measuring device pictured in figure 16. The measured distances between fringes, shown plotted against fringe order in figUres 17 through 20, do not take into consideration the magnification !'actor introduced by the lena arrangement. The fringe orde~s at the tension edge ' of the beam were determined by extrapolation, and the changes in these fringe o:rdera • .i th re•pect to time were used as the criterion or optical creep. A ·comparison of the overall optical creep character istics ot the various resins is shown in figure 21. It is evident that the greates.t amount of creep is exhibited by the Marco resin while the Laminae 4116-4134 resin cured for eight hours at 150 F shows the least, being practically negligible over the three-hour period. Within the Laminae group, increased cure times appear to have a beneficial effect in reducing the optical creep tendenci.es of the resin. Table VI lists the total change in fringe order in terms of tr1nges and equivalent stress for the various resina. 63 (a) 4 HR LAMINAC Al L OADING - (b) 4 HR LAMINAC AT 180 MIN lei 6 HR LAMINAC AT LOADING - (d I 6 HR LAMINAC AT 18 0 MIN FIG. 14 ISOCHROMATIC FRINGE PATTERNS FOR OPTICAL CREEP TEST OF LAMINAC 4116- 4134 CURED FOR 4 HRS (a,b) AND I HRS (c,d) AT 150 F. APPLIED LOAD AND BENDING MOMENT FO.. ALL BEAMS• 300 LIS AND 112.~ LB-IN RESPECTIVELYi STRESS • 2730 pti (a,b) 1 · 2710 psi (c,d) . - 64 (a) 8HR LAMINAC AT L OADI NG (b) 8 HR LAMINAC AT 180 MIN (c) MARCO MR:-28C AT LOADING (d) MARCO MR-28C AT 180 MIN FIG. 15 ISOCHROMATIC FRINGE PATTERNS FOR OPTICAL CREEP TEST OF LAMINAC 4116- 4134 CURED FOR 8 HRS AT 1!50 F (a,~) AND MARCO Mft-21C CUR£D AT ROOM TEMPERATURE (c,d). APPLIED LOAD AND BENDING MOMENT FOR Al.L BEAMS= 300 lBS AND 112.5 LB- IN. RES PECTIVELY; STRESS • 2690 psi (a,b), 2780 psi (c,d). ------ I I l ------· J'ig. 16. 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J'l ~ ~~~ ••••. .. .•.. :: ..... : ... :::: .::;-::;:::. ric: : ' L.t.w~H~.ei ; ~ ...... ·:.· ::· :: ~ Mr: :::.. ~ttttJt~ ·. -: .. 71 TABLE VI Optical Creep Characteristics of Laminae . 4116-4134 and Marco MR•28C Fringe Values Equiv At At Stress % Loading 180 Min -Diff {psi) Change 4•hr Laminae 5.60 4 .85 0.75 394 15.5 6-hr Laminae 4.65 4.30 0.35 189 8.15 8-hr Laminae 4.85 4.90 0.05 27.4 1.03 Marco MR-280 6 .15 5.25 0.90 351.9 17.1 There appears to be no correlation in the magnitudes of the strains involved between strain creep and optical creep of the various resins. However, in both cases, in creased curing time appears to decrease the creeping tendencies or the Laminae r esins. 9. Stress-Fringe Relationships. For this series of tests , tensile specimens of the four types of plastics ere viewed in the field of the polariscope while slowly being loaded. Because of the lack of material, the speci• mens used were t hose which had b een previously used for the strain creep tests. For this r eason, there is some doubt as to the worth of the r eported r esults, but under the circumstances, it was assumed that previous loadings would have little or no eff ect on the optical properties of the material. This assumption may be justified since the applied loads produced only 2,000 psi, a stress which was within the straight-line portion of the stress-strain 72 curve , and because sufficient time was allowed to elapse between the two tests for the material to regain its original dimensions through elastic f l ow . The test procedure consisted of observing the pass ing of al'"ernate light and dark fringes across the region of pure t(~nsion , and recording the load increment required to cause n complete cyclic change , ie, from dark fringe to dark fringe . No effort was made to control the time factor · or to study the effects of creep during this test . The time taken to reach either the breaking point of the material ()r the final load was approximately 15 minutes. Fi~lre 22 sho s the r sults of this test, and taking the foregc>ing qualifications into consideration, the results indicated that all materials possessed linear stress-fringe relationships to 7, 500 psi plus . Lack of capacity of testing facilities prevented the determination or the stress at Which fringe relationships ceased to be linear. 10. Determination of the Fr1nge Constants . The fringe constants of the photoelastic materials may be obtained by utilizing the initial data obtained from the optical creep tests, in which a bending specimen waa used, or from the data of the stress-fringe relationship tests, in which a tensile specimen was used. Considering the beam- in- pure-bending, elementary beam theory shows that only axial stresses exist in the .. : .. ~· r - ; ...· .:... ·.. :· ~·.c·~:.±..~. f-.~.--+~. . . ~~+-~. .. ~1- ._ ...... · .... -·.. . .. , . I I · · ···· ... · · ·· :; • ,:-:: :::: :. -::::::: :;;: :-:-;: :::: :::: :.: :.· .. 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I ....i '· ·...··. ·.. · ... : · :·:·: : : :::~ :~:: :: :::: 1 ' r~l l---'-:-r-·::~:.:..:....:.·+:1·~·· _.· +-+--·+-'-:.-+:::c=:-~F:::+: :.,.:.:-:::!-:'-:.+: :...:c.,:::r-:.+. ~:--:-:.. +..-'--+.-:..+-+~ - ~odo : :_:- :·:: :=' 1f cif ·· .. · · · .. · ·· · t---r--+-i ·· :: ·. l I ·.=: =: i~)~ : ...... . ~ v1 :. : i --f--f-r+-t-+-+-+-.+1~-. -1_-t--t-+--1f--t-l : I ~ . : . . . . . I" . I~ ~~ · I ~~ . • . ~ ' :2 0 f-1 .-i :. .· -r--~- --f·-' ~~ -'--t.:..-+-f---4'::,...:·+c·:-=-:1· 1 r-+'-==r--+--+--+-''-'+"-:-+ ~- .I ·1.::: :. ·. I lfRI"GE D1 Ri. ; : ...... ! .. ,·. I I I . i . .. . ! ; -l l .. 1.:...... -L..:....;. ..L.:c..:J--l...·-'-·.1.'-. __,·. --:: :' ....___... 74 region of pure bending and that these stresses are defined by the equation, S = Mo/I. Equating this to the photo• elastic stress equation, S • nf/t, we have S = Mc/I • nt/t or, t • Mot/In where, ! • the fringe constant, ps1 per fringe per inch M • the bending moment, lb-in. c • distance from the neutral axis, 1n. t • the thickness of the material, in. I • the moment of inertia of the section, in.4 n • the fringe order Since "t" is constant tor a given material, it becomes evident that this constant is determined by the proportionality of nc," the distance of the fringe from the neutral axis, and "n," the fringe order. A plot ot fringe distance versus fringe value will result in a line whose slope is c/n, providing a simple means for computing the fringe constant. The principal advantage or this method is the speed with which the constant can be determined, which eliminates the possibilities of creep effects entering into the results. All that is required is to load the beam and to photograph the resulting fringe 75 pattern for future analysis. However, despite the tbepretieal simplicity of pure bending; it is rather difficult technically to produce a stress pattern of pure bending of known bending moment (10, p360). Aside from the machining effects which cause a slight shift in the position of the neutral axis, or cause resulting increases and decreases of the boundary stresses on the compression and tension sides of the beam, there is also a decrease in the applied bending moment resulting from the friction forces developed if the loads are applied through pins at the ed es of the beam. These friction forces may be reduced by using the loading arrangement shown in the section on Optical Creep, but here again, another factor, the accuracy with which the loading jig is constructed, enters into consideration. In the second method, using the tensile speciihen, the increments of load required to cause fringe changes must be recorded together with the corresponding fringe value as the loading progresses . Although this method .. is more time consuming than the former, it has been found that tension testa provide the moat consistent results and the bending tests the least consistent results unless special care is exercised. Correlation of the results obtained from both methods is satisfactory where the stresses involved are small, but for h1gh ntresses, the agreement is not so good (10, pl62). 76 For the tensile specimen, the fringe constant equation becomes S a P/A a nf/t f = Pt/An The fringe constants for the Laminae 4116-4134 and Marco UR-280 resins as calculated using both methods are shown in Table VII. TABLE VII Fringe Constants for Laminae 4116·4134 and Marco MR-280 Obtained from Bending and Tension Tests Fringe Constants {psi por inch per fringe) % Tension Test Bendins Test Diff Laminae 4116-4134, 4hr 162 . 5 139 14.5 Laminae 4116-4134, 6hr 166.5 161.5 3.0 Laminae 4116-41341 Bhr 172.5 169.0 2 .03 Marco MR-280 121.1 128.5 6.1 The percentage difference ia baaed on the fringe constants as obtained from the tension tests. Good cor relation exists between the constants as determined from both methods for all resins except the 4-hour Laminae where the discrepancy amounts to 14.5 per cent. Con ider• ing the fair degree of agreement existing between the constants of other resins, no reasons could be found for the wide variation in values obtained. 77 VI. SUL!t!ARY OF R::-'SULTS An investigation was conducted into the possibilities of casting several polyester r esins with the equipment available at the Oregon State College Engineering .Labora tory. Resins studied included Laminae 4116-4134, Marco MR-280 and ~m-26C, and the Vibrin resins 108 and 114. or the five resins with which this investigation was begun, only two, namely, Laminae 4116-4134 and Marco MR-2BC, were found to be castable with little or no difficulty. Vibrin 114 was eliminated due to diff iculties encountered in obtaining a clear gel, while V1brin 108 proved susceptible to fracture during the curing process . Studies on Marco MR-260 were discontinued because or lack of sufficient raw materials to complete the studies. For all resins except Marco KR·29C, a two-step curing opera tion was used, namely, gelation at room temperature fol lowed by curing at an elevated temperature, In t he case of Marco MR-280, both gelation and cure were accomplished at room t emperature. Mixing methods, mold preparation, and casting techniques used are fully discussed. Mechani cal and stress optical tests were conducted on materials successfully cast in an effort to evaluate their worth as photoelastic materials. The results of these tests are summarized below. Tension tests conducted on the resins selected for 79 1 ~est1gati n ho that ultimat tronzths are consido~ blJ lowe:r than tor (J.atEa.lin Gl•S93. Whil th ultimate strength ot tL1 - resin 1a 1Z.,800 pa1 1 the Latd.nao 4116-413 r 1n exhibited breaking stresses ranging trom ;.ooo pal to 9 1 910 p 1 depending upon: the lensth ot curing t11110 allowe4 for the ll1 tet-1$1, wh1lo ~arGo 14R-29C sbo '04 a atreneth ot 61 400 pa1 at fa!lure. ¥or tht Ltantino.e res1ns1 no dof1n.1ta trends ot tho etrects of Qur1ne t1tn on stl"ongth, 1c, higher atl'engths \11th lonc•X' cur1ng t1mee. ere indS.cc.ted. Uodul1 ot ~ ,aat1c1ty ot all Da ter1a.la tested were o.lso ' correspond1ncly lowet.. than fo~" Ce.tatin 01...09 • '1" et results. !.ndtoatocl tbn t atxHt$G...stl'a1n x-ele.tiorushipe t~ero l1nenr to 4.000 pe1 ftJr th r. . nac roein and to 3 1 000 p 1 tor lt el> m-2SC, as c:ompn1'$d to 5, 600 ps! tor 61•893•· St:rain cl'e&p oxh1bit~d by the minae resins and t•attco lt -me appear& to b$ rathex- exc ssive for theas 11ater!als to be t>One 1dered euitable tor photoelast1c tUUh Re ults or three-hour atttaln ere p teet indio te that incre se 1n et:raln, ,expreeaed in terms ot equivalent streseo • r ns f'r~ sa per oent to 44 pe:- cent o~er the applied etres tol' ·all :restnl'l te&-ted. ven at tho end ·ot th tlr$t hour" th&tJ.o inaroase re.ne;e !rom 17.6 par cent to 22.5 pel' cent. Ov r the tbree•hour p riod, LD.m1n o 4116·4134 cured for oleht boure at 150 F howe the mblbllUJ~ mount ot train or. ep, W1 thin th Laminae srou , in- ere os 1n oux-ing ttm flppear to decrea!te the strain 79 creep tendencies of the material. Laminae 411G~4134 cured for eight hours at 1 50 F possessed the least optical creep characteristics, show i ng only a gain of 0 . 05 fringes over the three-hour test period. This increase, which occurs during the first 10 minutes after application of the load, amounts to 1 . 03 per cent over the initial fringe conditions . This compares favorably to the optical creep characteristics of Catal1n 61-893, which are considered negligible at stresses under 5, 000 psi over a two-hour teat period. For the other materials tested, percentage changes in fringe order amounted to 15.5 per cent, 8.1 5 per cent, and 17 . 1 per cent for the Laminae 4116-4134 cUl~ed for four and six hours at 150 F and the Marco MR-280 resins respectively. As in the case of strain creep, increased curing times appe r to have a beneficial effect in reducing optical creep in the Laminae resins. Stress-fringe relationships can be considered linear to 7 , 500 psi plus for all resins. catalin 61 -893 exhibits linear stress- fringe relationships to 7, 000 psi . The stress optical coefficients as determined from tensile tests for the Laminae resins in the order of in creasing curing periods were 162 . 5, 166. 5, and 172 . 5 psi per fringe per inch of thickness while that of Marco MR- 23C was 121 . 1 psi per frinse per inch of thickness . In general, these val ues indicated that the resins test ed 80 were less sensitive optically than Catalin 61-893. 81 VII.. BC01;MEND IO..!S FOR FUTURE INVESTIGATIONS I It is .fully l~oalized by the author that the investi gations conducted and reported in this paper, especially the t.est results, do not fully evaluate the materials which were found to be castable with the available equip ment. This was primar1.ly·due to the small amount of liquid resin available to investigate both the casting techniques required and the 3Ubsequent testing of the cured resins. For the two resins which were found to be castable, namely Laminae 4116·4134 and Marco MR-·280, the following recommendations are made for any fut.ure investigation that may be conducted on these two resins. 1. Finished plates should be la:rge:r than the ' 5 x 7 inch s1~e uaed in these investigations. This is necessary s.o that all test specimens l'equired for a given series of tests may be cut from the srune sheet, thereb7 allowing some measure of control 1n determining the reprodueib:llity of test values resulting. from one casting to the next. A plate 10 x 14 inches, or larger, is re.co:mmend.ecl. 2. Since there is a question as to whether or not the tensile strength values reported in this paper S.l"'~e typical of the values which 82 are to be expectc 1 a series of tensile tests should be conducted on these resins. At least five specimens (lt p591) should be taken front each of several different plates to determine the ultimate tensile strength, the propoi•t1onal limit, and the modulus of elasti,city for each material. After these values have been established, the effect of the rate of loading should be investigated. 3. For strain creep tests, instead of the Huggensberger tensometers used in this in vestigation, SR•4 electric resistance strain gages should be used. In this manner , the complete strain history from application of load,. strain during extended loading, and the resulting permanent set mar be obtained. Strain creep tests should be conducted at different level s of stress within the proportional limit to dete~ine whether creep rates remain constant for all degrees of stress. I 4 .. Optical creep tests should be carriea out at the same time a.s ,the strain creep tests in the manner reported previously in this paper. However, instead of extrapolating to 83 determine the frinbe value at the extreme edge of tl: o beam, a tension compensator should be constructed so that an accurate determination of the fringe order may be obtained. 5 . For Laminae 4116·4134, the optimum curing time at the curing temperatv.re should be determined. This .may be done by increasing the curi ng periods and testing the result ing material until strength properties be come oonst ant . The curing period for which the strength properties first approach constancy shoul be the optilnum curing time .. 6 . Although Marco MR-28C exhibited excessive optical and strain creep, because of the cas~ with whiCh this resin can be cast, the cffe.ot of cl1.anges in oatalyst and accelerator content, and also the effect of' subsequent annealing on the strene;th and optical properties should be investigated. 7 . To conduct the tests mentioned above, 10 pounds of Marco - 2BC and 20 pounds of' . Laminae 4116..4134 should be sufficient to make a complete and thorough investigation on the resins . 84 8 . With e a.rds to custin · facilities, it is believed that a lo~-cost oven constructed cs ecia.lly for curing purposes, or a cam I!l.Orci.al oven, would gr atly aid in the casting of these resins . Such an oven should have a ranGe from room tc.mperaturc to approximately :?50 F, \'lith a fairly close temperature control, either manual or auto matic, so that the heating rates can be regul tod. It should also bo insulated well enough to cool at the desired rate . If the oven is provided with transparent sides on t least t;ro stU'f&.ces , frozen stress tests, in which observation of the loaded specimen is deuirable, can be conducted. esistance he&tin elements should consist of coils having cifferent speeds and should be covered by a thick steel pl&to to e u&llze the heat distribution in the oven . controllable circulating air fun is essential to prevent s tratification of hee. t within the oven. 5 VIII. . N LUSIONS From the results obtained during the preliminary studies conducted on the casting and testing of the selected polyester resins, the following conclusions were reached. I 1. Laminae 4116•4134, an oven-cured resin, and Marco MR-28C, a resin cured at room tempera• ture, were found to be easily cast resins. These plastics may be cast at a fraction of the cost of Cata.lin 61-893, and have the added advantage of possessing glass smooth surfaces thereby eliminating the work required with the Catal1n resin in obtaining a finished model. 2. Further investigations are warranted by these two resins; the- former because of acceptable strength and optical properties, and the latter _because of the s1mpl1c1 ty with which it may be cast. Optimum curing times should be determined for the Laminae resin while the effects of annealing on th~ strength and optical properties should be investigated for the Marco resin. 3. Laminae 4116-4134, cured for eight hours at 150 F, was found to be susceptible to strain 86 ereep, but the negligible amount of opti cal ereep exhibited will permit its use for elementary photoelasticity problems where the applications ot load are for short periods only. 4. Stress-strain and stress•fringe relation ships are linear to 4 1 000 psi and 7,500 psi respectively for Laminae 4116•4134, cured for eight hours at 150 F; as compared to 6,000 psi and 7,000 psi respectively for Catalin 61-893. The fringe constant for the former is approx~tely twice that ot catal1n 61-893. 5. T.be preliminary investigations conducted on Laminae 4116-4134 indicate that this resin may have properties equal to those of Catalin 61•893. Further investigations may prove this resin to be a very satis factory photoelastie material for two• dimensional studies. 87 IX. BIBLIOGRAPHY 1. American society for testing materials. 1949 book of ASTM standards: including tontatives, part 6. Philadelphia, American society for testing materials, 1950. l374p. 2. American cyanamid company. Casting laminae resins. New York, American cyanamid company. 3p. 3. Catalin corporation of America. Catalin cast resins for photoelastio analysis of stress. New York, Catalin corporation of America. 3p. 4. Coolidge, D. J. Jr. An investigation of the mechani~ cal and stress optical properties of columbia resin OR-39. Proceedings of the society for exper~ental stress analysis 6, 1:74~82. 1948. 5. Delmonte, John. Plastics in engineering, 3d ed. Cleveland, Ohio, Penton publishing company, 1949. 646p. 6. Edmonds, Robert Harold Gray and Bryan Towne McJiinn. Celluloid as a medium for photoelast1c invest!• gat1ons. Seattle, Washington, bulletin of the University of Washington experiment station, April 5, 1932. 2lp. (Exper~ent station series bulletin no. 63) 7. Fisher, w. A. P. Basic properties relied upon in frozen stress techniques. Proceedings of the institution of mechanical engineers (London) 158:230-235. 1948. S. Fried., Bernard.. Some observations on photoelastio materials stressed beyond the elastic ltm1t. Proceedings of the society for expertmental stress analysis 8, 2:117-128. 1951. 9. Frigon, R. A. Report of the easte~n photoelastic1ty conference committee on materials research. Proceedings of the thirteenth semi-annual eastern photoelasticity conference, Cambridge, Massachusetts, p62-66. June 1941. 10. Frocht, Max Mark. Photoelastioity, vol l. New York, John Wiley and sons, inc, 1947. 4llp. 11. Hetenyi, M. ed. Handbook of experimental stress analysis. New York, John Wiley and sons, inc, ( 1950. 1077p. 12. Heywood, R. B. Modern applications of photo elasticity. Proceedings of the institution of mechanical engineers (London) 158:235-240. 1948 .. 13. Jessop, R. T.. and F. c. Harris. Photoelasticity: principles and methods.. London, Cleaver•Hume press ltd, 1949. l84p .. 14. Leaf, alter. Additional data on time-edge effects. Proceedings of the sixteenth semi-annual Eastern photoela.st!eity conference, Illinois institute of technology,. November 13 and 14. 1942. 15. Lear, Walter. Edge-effects critical in photo elasticity. Mach1p.e design 15:109•111. March 1935. 16. Leat, Walter . The time-edge effect: its cause and prevention. Proceedings of the fifteenth semi• annual Easte:rn photoelasticity conference, cambridge, ~iassaohusetts, June 20, 1942. 17. 'tee, Barron R., Roscoe Meadows, Sr, and Vla.l ter E. Taylor. The photoelaat1city labora tory a.t Newport News shipbuilding and dry dock company. Proceedings of the soo.iety for experimental stress analysis 6 1 1:83-106. 1948. 18. tee, George Hamor. An introduction to experitnenta.l photoelastic1ty. New York, John Wiley and sona. ino, 19·50.- 3l9p. · 19. Lee, George Hamor and Armstrong. Effect of tempera• ture on the physical and. optical properties of photoelastic m.a terials. Tranaactions of the American society of mechanical engineers 60t All•l2 . 1938. 20. Leven, M. M. A new mAterial for thrtJe•cU.meneiona.l photoelasticity. Proceedings for the societ1 ot experimental stress analysis 6, 1:19•28. 1948. 21. Leven, }4. M. Further properties of photoelastic fosterite at elevated temperatures.. Proceedings of the society for experimental etresa analysis 6, 2:lQ6-llO. 1948. 22. Leven, Y.. 14 . Photoelastic stress analysis useful tn the design or ma,oh1ne parts. Materials and methods 33:70-73, Uaroh 1951. 89 23. Leven, M. 14. Photoelastte stress analysis useful in the design ot machine parts. Materials and methods 33:89•92. April. 1951~ 24. Marco chemicals 1n<:orporated. Casting bulletin RC-250. Sewaren_, New Jersey, Marco chemicals incorporated. 5p.• - 25. Jlareo chemicals incorporated. Resin pamphlet 'l'P-550. Sewaren* New Jersey, 1.tarco chemicals incorpora ted. 5:P• 26. Naugutuck ehemleal division of the United Sta.tea rubber company. Weehnical bulle·tin; general propertitiUil of standard v1brins • Naugutuek; Oonneeticut, Naugutu.ck chemical division or the United States Rubber company. 6p. 27. Naugutuck chemical d.i.v1s1on of the United States rubber company.. Technical bulletin; v1br1n •. Nausutuok, Connecticut, Naugutuck chemical division of the United States rubber co. 4p. 28. Schack., W!lliSlll . A manual of plastics and resina., Brooklyn, New York, chemical publishing company, inc,· 1950. 647p., · 29. Solakian; Arshag G. A new photoelastic material .. properties of ma.rblette compared to those of other photoela.stic materials • Mechanical engineering :57t'16'7.,..771. 1955. 5C>* Solakia.n, Arshag G~ Optically less sensitive .mater1a:;ts in photoelasticity.,. Mechanical eng1.neer1ng 59:423.. 424 i 1937. 31. Taylor, C. E~ , E. o. Stitz, and R. e. Belsheim. A casting material for tnree-dimensional photo• elasticity. Proceedings ot the society of experimental stress analysis 7, 2:155-172. 1950 •. APPENDIX 90 TENSION TEST OF LAMINAC 4116-4134, CURED 4 BR AT 150 F Specimen No. 1 Section Size 0.255 in. x 0.310 in. Area 0.0790 in.2 ·SR•4 Gage Factor 2.07 Load stress Strain Strain Corr Strain (1b) (psi) (m1cro1n.) (microin. per in.) 0 0 ..... 30 379 7180 50 633 7560 380 1580 100 1266 8740 1560 2760 150 1899 9950 2770 3970 200 2532 11450 4270 5470 250 3165 12080 4900 6100 300 3798 14640 7460 8660 350 4431 16200 9020 10220 400 5064 17950 10770 11970 450 5697 19930 12750 13950 500 6330 21910 14730 15930 550 6963 24040 16860 18060 600 7596 26500 19320 20520 650 8229 29160 21980 23180 700 8962 ...... 750 9595 -· _,. - 785 9940* ------ *Fracture 9l. TENSION 'fEST OF LAMINAC 4116•4154, CURED 4 BR AT 150 F Specimen No. 2 Section Slzt 0~250 1n. x 0.310 1n. Area 0.0775 1n.2 SH-4 Gage Faetor 2.07 toad Stress Strain Strain Corr Strain .illl (psi~ ~m1oro1:n.} (m1cro1n• l?er in.) 0 0 .,,...... 20 258 640 - 50 645 1270 61() ·-1830 l.OO .1290 2350 1710 2910 150 1935 3950 3310 4510 200 2580 5020 4380 5580 250 3225 6'700: 6060 7260 300 3870 7980 7340 8540 350 4515 9650 9010 10210 400 5160 11350 10710 11910 460 5805 13350 12710 13910 500 6450 15500 14860 15060 550 7095 17650 16990 18190 600 7740 20300 19660 20860 650 8385 23750 23110 24310 700 9030 27780 27J,40 28340 750 9675 .... -- _,_ ·- 76~ 9880-* -- -- *Fracture 92 TENSION TEST OF LAMINAC 4116-4134, CURED 6 HR AT 150 F Section Size 0.255 in. x 0.310 in. Area 0~0'790 1n.2 SR•4 Gage Factor 2.07 Load Stress Strain Strain Corr Strain illl (psi) (microin_.l (m1eJ'o1ni! per in.) 0 .... 30 --379 1550 •• -_.,.. 50 633 2130 560 1780 100 1266 3640 2090 2190 150 1899 4740 3190 4310 200 2532 6480 49:30 6150 250 3165 8070 6520 7720 300 3799 9740 8190 9390 350 . 4431 11'700 10150 11350 400 ...... ,...... 450 5697 ...... 500 6330 16860 17130-- 1833- 0 550 6963 20060 19510 19'720 600 7596 24440 22890 24090 G50 8229 28900 27350 28550 700 8962 ...... 710 9000* -- *Fraetur~ 93 TENSION TEST OF LAMINAC 4116-4134, CURED 8 HR AT 150 F Section Size 0.255 in. x 0.315 in. Area 0.0804 in. SB-4 Gage Factor 2.07 Load Stress Strain Strain Corr Strain illl (psi) (micro1n.) (m1cro1n. per 1n.) 0 0 50 622 --2380 -- · 100 1244 3720 1340- 2940 150 1866 5360 2980 4580 200 2488 6710 4330 5930 250 3110 8590 6210 7810 300 3732 10050 7670 9270 350 4354 11740 9360 10960 400 4976 13600 11220 12820 450 5598 15570 13190 14790 500 6220 1'7500 15120 16720 550 6842 19800 17420 19020 600 7464 22450 20070 21670 650 8006 26100 23720 25320 '700 8700 ...... 750 9330 .... - '755 9400* -· *Fracture 94 TENSION TEST OF MARCO MR-280 Specimen No. 1 Section Size 0.257 in. x 0.307 in. Area 0.0790 in.2 SR-4 Gage Factor 2.07 Load Stress Strain Strain Corr Strain il!U. (psi) ~m1croin.) (microin. per in.) 0 0 30 379 140-- -- 50 635 192 --52 202-- 100 1266 303 163 313 150 1899 440 300 450 200 2532 603 463 613 250 3165 762 622 773 300 3798 923 783 933 350 4431 1091 951 1101 400 .5064 1273 1133 1283 450 5697« *Broke through pin Specimen No. 2 Section Size 0.252 1n. x 0.310 1n. Area 0.0780 1n.2 SR-4 Gage Factor 2.07 Load Stress Strain Strain Corr Strain ill.l ~Esil ~microin.l (microin. ~er 1n.l 0 0 17 .... 50 640 152 169 149 100 1280 318 335 315 150 1920 467 484 464 200 2560 629 646 626 250 3200 918 835 815 300 3840 993 1010 990 350 4480 1176 1193 1173 400 5120 1385 1402 1382 450 5760 1616 1633 1613 500 6400 1872 1889 1869 705* 9030 *Broke 95 STRAIN CREEP TEST OF L INAC 4116-4134 (Cured 4 hours at 150 F) Section Size 0.310 in. x 0.3351n. Area 0.104 in.2 Load 203 lb Stress 2,000 psi Gage Faotore No. 1 l/833 No. 2 1/837 Strain Time . Gage Readings No. 1 No. 2 Ave Strain ~min~ No. 1 No. 2 ~in. Eer in.~ {in. 12er in. l 0 o.oo o.oo · o.oooooo o.oooooo 0.000000 5 0.59 0.45 0.000709 0.000537 0.000623 10 0.77 0.60 0.000931 o.ooo716 0.000823 15 0.90 . 0.70 0.00107 0.000036 0.000953 20 1.00 o.ao 0.00120 0.000995 0,.00108 25' 1.09 0.86 0.00131 0.00105 0.00118 30 1.15 0.94 0.00138 0.00112 0.00125 45 1.35 1.11 0.00162 0.00133 0.00147 60 ' 1.50 1.25 0.00180 0.00149 0.00164 90 1.80 1.52 0.00216 0.00182 0.00199 120 2.02 1.71 o.oo242 0.00204 0.00223 150 2.22 1.90 0.00255 0.00227 0,.00241 180 2.40 2.05 o •.oo2aa 0.,00245 o:oo266 96 STRAIN CREEP TEBT OF LAMINAC 4116•4134 (Cured 6 hours at 150 F) Section Size 0.305 in.• .x 0.335 in. Al-e a 0.102 in.2 Load eos.s lb Stress 2,000 psi Gage Factors No. 1 1/833 No. 2 l/837 Strain '1'1me Gage Readings No. l No. 2 Ave Strain (m1n} No,. 1 No. 2 ( 1n.• per. 1n.) ( 1n. per 1n.) I 0 0,.00 o.oo 0.000000 o •.oooooo o.oooooo 5 Ol48 0.48 0 . 000576 0.000574 0.000575 10 0.70 o.ee 0 . 000840 04>000789 0 .•000814 15 0.89 0.74 0.00107 0 .. 000884 0.000977 20 0.96 0,90 0.00ll5 C.00108 0.00110 25 1 •.06 0.99 0.00127 o.OOllS o.oo122 30 1.14 1.05 0 •.00137 0.00126 0.00131 45 1.34 1.25 o.oOl6l 0 •.00149 0.00155 60 1.51 1.41 0.00181 0.00168 0.00174 90 1.81 . 1~67 0.00217 o.ool99 0.00208 120 2.01 1.86 0.00242 0.00211 0.00226 150 2.18 2.01 0.00259 0.00240 0.00249 180 2.30 2-ll o.o0276 0.00252 0.00264 97 STRAIN CREEP TEST OF LAtDlAC 4116- 4134 (Cured 8 hoUl~s at 150 F) Section Size 0 . 315 in. x 0 . 340 in. Area 0.107 in. 2 Load 214 1b • Stress 2, 000 pai Gage Factors No . 1 1/ 833 No . 2 1/ 837 Strain Time Gage Readings No . 1 No . 2 Ave Strain ~min l No . 1 No . 2 ~in . Eer in . ~ ~ in . 12er in. ~ 0 o.oo o.oo 0.000000 0 . 000000 0 . 000000 5 0,55 0 . 43 0 . 000660 0 . 000514 0 . 000587 10 0,71 0 .. 56 0 . 000052 0 . 000824 0 . 000761 15 0.85 0 . 69 0 . 00102 0 . 000824 0 . 000922 20 0 . 90 0 , 75 0 . 00108 0 . 000896 0 . 000988 25 0 . 99 0 . 83 0 . 00119 0 . 000990 0 . 00109 30 1.06 0 . 90 0 . 00127 0 . 00107 0 . 00117 45 1 . 25 1 . 07 0 , 00150 0 . 00128 0 . 00139 60 1 . 39 1 . 21 0 . 00168 0 . 00144 0 .. 00156 90 1 . 65 1 . 45 0 . 00198 0 . 00173 0 , 00185 120 1.85 1 . 63 0.00222 0 . 00195 0 . 00208 150 2 . 03 1 . 81 0 . 00244 0 . 00206 0 . 00225 180 2 . 19 1 . 96 0 . 00263 0 . 00234 0 . 00248 98 STRAIN CREEP TEST OF UARCO l!R-2SC Section Size 0.308 in. x 0.335 in. Area 0.103 1n.2 Load 206 1b Stress ·s, 000 psi Gage Factors No . 1 1/833 No . 2 1/837 strain Time Gage Readings No . 1 No . 2 Ave Strain (min) No . l No . 2 (in. per in.) (in. per in.) 0 o.oo o.oo 0 . 000000 0.000000 o.oooooo 5 0.59 0 . 29 0 . 000696 0 .000346 0.000521 10 0 . 70 0.39 0 . 000840 0 .• 000466 0.000653 15 0 . 80 0 . 46 0 . 000961 0 . 000550 o.ooo705 20 0.89 0.54 0.00107 o.oooe45 0.000805 25 0.95 o.6o 0 . 00114 0 . 000716 0 . 000928 30 1.01 0 . 66 0 . 00121 0 . 000789 0 . 000999 45 1.21 0 . 85 0 . 00146 o . oo102 0 . 00123 60 1 . 36 1 .oo 0.00163 0 . 00119 0 .00141 90 1.63 1 . 25 0 . 00196 0 . 00152 0 . 00174 120 1,.92 1 . 50 0 . 00230 0 . 00179 0 . 00204 150 2.13 1 .70 0 •.00256 0 . 00203 0 . 00229 18 0 2 . 34 1 . 91 0 . 00281 0 . 00228 0 . 00254 OPTICAL CREEP TEST LAMINAC 4116-4134, CURED 4 RR AT 150 F Time 0 min 5 min 10 min 15 min 30 min 60 min 120 min 180 min Dist Dist Dist Dist Diat Dist / Dist Dist Fringe (em) (em) (em) {em) (em) {em) (em) (em) 5.5 0.075 o.oao 0.0'70 0.070 0.090 0.085 0 .075 0.035 5.0 0.155 0.165 0.170 0 .165 0.165 0.170 0.150 0.160 4.5 0.260 0.275 0.270 0.265 0.285 0.280 0.270 0.240 4.0 0.350 0.360 0.360 0.360 0 ..365 I 0.365 0.350 0.350 3.5 0.470 0.475 0.470 0.465 0.480 0.470 0.470 0.440 3.0 0.550 0.560 0.555 0.555 0.560 0.560 0.545 0.555 2.5 0.670 0.670 0.660 0.660 0.685 0.660 0.670 0.635 ~.o 0.750 0.765 0 .760 0.765 0.765 0.765 0.750 0.750 1.5 0 .865 0.870 o.a55. 0.855 0.885 0.860 0.870 0.830 1.0 0.955 0.970 0.965 0.965 0.975 0.970 0.950 0.955 0.5 1.075 1.075 1.055 1.055 1.005 1.065 1.065 1.030 o.o 1~150 1.160 1.160 1.155 1.165 1.165 1.150 1.145 0.5 1~290 1.295 1 ..275 1.275 1.. 300 1.290 1.285 1.250 1~0 1.465 1.365 1~365 1.355 1.370 1.370 1.355 4.360 1~5 1.500 1.505 1.490 1.485 1.525 1.500 1.500 1 ..465 2~0 1.585 1~595 1.590 1.590 1.600 1.690 1.590 1.585 2~5 1.720 1.735 1.'715 1.715 1.755 1.735 1.730 1.705 3.0 1.810 1.820 1.820 1.815 1.830 1.830 1.820 1.835 3.5 1.945 1.965 1.945 1.940 1.985 1 •.970 1.975 1.955 4~0 2.040 2~050 2.060 2.060 2.075 2.000 2.090 2.100 4.5 2.175 2.200 2.180 2.190 2.230 2.220 2.250 2•240 5.0 2.265 2.315 --- io'Ee: Frfnge distances measured on negatives .from top of beam (compression edge). , <0 <0 OPTICAL CREEP TEST LAMINAC 4116-4134, CURED 6 HR AT 150 F Time 0 min 5 min 10 min 15 min 30 min 60 min 120 min 180 min Diet · Dist Dist Dist Dist D1st Dist Dist Fringe (em) (em) (em) (em) (em) {em) {em} (em) 5.0 0.060 0.060 0.050 0.040 0.;045 0.050 0.050 4.5 0.190 0.150 0.195 0.200 0.175 0.125 0.180 0.190 4.0 0.275 0.275 0.275 0.265 0.265 0.260 0.260 0 .265 3,.5 0.400 0.425 0.405 0.-420 0 .400 0.400 0.390 0.410 3.0 0.495 0.490 0.490 0.475 0.480 0.480 0.480 0.480 2.5 0.630 0.650 0.625 0.640 0.610 0.610 0.615 0.635 2.0 0.700 0.710 . 0.705 0.690 0.700 0.690 0.695 0.700 1.5 0.855 0.875 0.855 0.860 0.835 0.835 0.835 0.855 1.0 o •.930 0.925 0.950 0.900 0.900 0.910 0.900 0~920 0.5 1.000 1.105 1.075 1.075 1.060 1.050 1.055 1~075 o.o 1.175 1.180 1.175 1.155 1.150 1 .•150 1.155 1.160 0.5 1.300 1 '~330 1.300 1.150 1.300 1.300 1.300 1.320 1.0 1.425 1.415 1.425 1.400 1.400 1.400 1.415 L.420 1.5 1~530 1~575 1~540 1~560 1.535 1.535 1.540 1~575 2.0 1.660 1~655 · 1~660 1.645 1~640 1~650 1~660 1.675 2 . 5 1~785 1~820 1~795 1~810 1~790 1~800 1.805 1.845 3.0 1.930 1.905 1.920 1~900 1~900 1.915 1.930 1.950 3.5 2.045 2.085 2.060 2.080 2~070 2.075 2.095 2~145 4.0 2.170 2.180 2.185 2.170 2.185 2.20 2.235 2.260 4.5 2.335 -- Hote: Fringe distances measured on negatives from top of beam (compression edge). . 1-J 0 0 OPTICAL CREEP TEST LAltiNAC 4116-4134, CURED 8 HR AT 150 F Time 0 min 5 min 10 min 15 min 30 min 60 min 120 min 180 min Dist Dist Dist Dist Dist Dist Dist Dist Fringe (em) (em} (em) (em) (em) (em) (em) (em) 5.0 0~040 . 0.050 0.030 0~035 0.075 0.075 0.065 0.055 4.5 0.200 0·.210 0.205 0~210 0.210 0~220 0.210 o:190 4~0 0~260 0.265 0~265 0.260 0.270 0.280 0.280 0.255 3.5 0.415 0 .. 420 0 .420 0.430 0.435 0~440 0.425 0.415 3~0 0~480 0.480 0~490 0~480 0.500 0.495 0.495 0.480 2~5 0~.650 0~660 0•650 0~660 0~660 0.680 0.655 0.640 2.0 0.710 0~705 0~710 0~700 0.720 0 .720 0.715 0.695 1.5 0.895 0~900 0~790 0~900 0~900 0.900 0 ~900 0.885 1~0 0.955 0~940 0.950 0.945 0.955 0~955 0~950 0.930 0.5 1.170 ------1:175 1.160 1.150 0~0 1.200 1.190 1.. 200 1.185 1.205 1.200 1.195 1.180 0.5 1.315 --- 1.315 1.335 1.325 1.0 1.455 1.440 1~455 1~445 1 ~455 1~455 1~450 1:440 1.5 1.565 1.580 1.580 1.. 575 1.580 1:590 1:575 1:580 2.0 1.695 1 -~685 1~685 1~ 685 1~700 1~700 1.695 1~690 2.5 1.825 1.840 1.835 1~830 1~840 1.850 1.840 1.840 3.0 1.930 1.920 1.930 1.925 1.935 1.950 1.940 1~940 3.5 2.080 2.100 2.095 2.100 2.105 2.100 2.105 2.100 4.0 2.190 2.180 2.190 2.185 2.200 2~215 2.205 2.205 4.5 2.360 2.360 2.360 2.355 2.370 2.375 5.0 Bote: Fringe distances measured on negatives from top of beam (compression edge)...... 0 ~ OPTICAL CREEP TEST KARCO MR-28C Time 0 m1n 5 min 10 m1n 15 min 30 m1n 60 min 120 min 180 min Dist Dist Dist Dist Dist Dist Dist Dist Fringe (om) (om) (om) (om) (om) (om) (om) (em) 6.5 0.060 o.ooo 0.060 0~065 0.070 0.060 0.060 0.065 6.0 0.155 0.140 0.150 0~160 0~065 0~155 0.155 0.155 5~5 0.213 0~240 0~230 0~255 0 .235 0~245 0.235 0.240 5.0 0.325 0~310 0.315 0.320 0~330 0 .. 325 0.325 0.325 4~5 0.390 0~400 0~395 0 .420 0.395 0.410 0.400 0~400 4~0 0~490 0.480 0~480 0.645 0 .495 0 .485 0.490 0.490 3.5 0.560 0~565 0.555 0 .575 0~565 0.565 0.560 0.560 3~0 0.660 0~650 0~650 0 ~645 0.655 0 .650 0~655 0.655 2.5 0~730 0~730 0~725 0~ . ?45 0~730 0~730 0~720 0.725 2.0 0~830 0 ~820 0 .815 0~8 15 0~830 0~820 0~810 0~815 1.5 0~900 0~900 0.885 0~905 0~895 0 .790 0.885 0.885 1.0 1.020 1.000 0~995 1.000 1.000 0~990 0.985 0.990 0.5 1.075 1~075 1.075 1~100 1~060 1~075 1~060 1~060 o.o 1.155 1;.145 1.145 1.150 1~150 1.135 1~135 1~140 0.5 1.260 1.240 1~235 1~265 1.240 1~245 1.230 1~225 1.0 1.295 1.300 1~300 1.300 1~310 1~310 1~305 1~310 1.5 1.420 1.415 1~415 1~430 1~415 1~415 1~410 1~405 2.. 0 1.500 1 .•500 1.500 1.500 1~515 1~505 1.500 1.505 2.5 1.620 1.615 1.610 1.630 1.620 1 . 610 1~600 1~605 3.0 1.700 1.700 1.700 1.700 1.715 1.710 1~'710 1~715 3.5 1.820 1 .810 1~815 1.835 1.825 1 ~81.5 1.835 1~820 4.0 1.910 1.811 1.900 1~910 1.925 1.g:so 1.930 1.950 4.5 2.030 2.015 2.030 2.050 2.045 2.045 2.090 2.075 5.0 2.150 2.125 2.120 2.130 2.165 2.180 2.200 2.235 5.5 2.240 2 .24 2.260 2.290 2.290 2.310 6.0 Note: Fringe distances measured on negatives from top of beam ....., 0 (compression edge). (\) 103 STRESS FRINGE RELATIONSHIP OF MARCO MR-28C Sect.!on Size 0.203 1n• .x 0.308 in. Area 0.,0631 in.2 Load Stress Fringe lli1 {psi) 0 0 o- . 1 30 475 2 55 870 3 80 1268 4 105 1661 5 130 2060 6 155 2450 7 180 2850 a 205 3245 9 230 3640 10 255 4140 11 280 4430 12 305 4820 13 330 5220 14 355 5615 15 380 6010 16 405 6405 17 430 6800 18 4$5 7200 19 485 7680 20 525 8300 104 STRESS FRINGE RELATIONSHIP' OF LAMINAO 4116-4134 CU'RED 4 H'R AT 150 F Section Size 0.202 1n. 1 0,30'7 in. Area 0.0620 1n4J · Load St:rees Fringe (-lb) (psi) Q '0 0 l 32.5 524 2 60.0 967 3 95.0 1530 4 180.0 2095 5 160.0 2580 6 19th0 3140 7 225.0 3630 a 260.0 4195 9 290,0 4670 10 320~0 5160 11 355,0 5720 12 390,0 6290 13 425.0 6850 14 460.0 7410 15 495.0 7990 16 54Q~() 8700 105 STRESS FRINGE RELATI ONSHIP OF LAMINAC 4116•4134 CURED 6 HR AT 150 F Section Size 0.210 in. x 0.312 1n. Area 0.0655 1n.2 Load Stress Fringe illl (psi) 0 0 0 l 35 534 2 70 1069 3 105 1603 4 135 2060 5 170 2595 6 205 3130 7 235 3585 8 270 4120 9 305 4650 10 350 5340 11 365 5880 12 415 6340 13 450 6860 14 490 7480 15 540 8025 ) 106 STRESS FRINGE RELATIONSHIP OF LAMINAC 4116-4134 CU~~ S HR AT 150 F Section Size 0.205 in. x 0.315 in. Area 0.0645 1n.2 Load Stress Fringe (lb} (psi) 0 0 0 1 35 542 2 70 1087 3 105 1630 4 140 2170 5 170 2635 6 205 3180 7 240 3720 8 270 4180 9 305 4730 10 335 5200 11 370 5740 12 405 6280 13 440 6820 14 495 7670