Proposal for the Testing of Weld Metal from The

REPORT No. 121 S October 1968

NEDERLANDS SCHEEPSSTUDIECENTRUM TNO NETHERLANDS SHIP RESEARCH CENTRE TNO SHIPBUILDING DEPARTMENT LEEGHWATERSTRAAT 5, DELFT

PROPOSAL FOR THE TESTING OF WELD METAL FROM THE VIEWPOINT OF BRITTLE FRACTURE INITIATION (EEN VOORSTEL VOOR HET BEPALEN VAN DE WEERSTAND VAN GELASTE VERBINDINGEN TEGEN HET ONTSTAAN VAN BROSSE BREUKEN)

Jr W. P. VAN DEN BLINK Philips' Welding Electrodes Factory

and

Jr J. J. W. NIBBERING Ship Structures Laboratory Delft Technological University

Issued by the Council © Netherlands Ship Research Centre TNO, 1968 VOORWOORD PREFACE

In het kader van de vraag naar optimale constructies wordt veel In the scope of the demand for optimum structures much research onderzoek verricht naar het sterktegedrag van scheepsconstruc- is performed into the strength behaviour of ship structures sub- ties onder invloed van een realistisch optredende belasting. jected to a reaslistic load. In dit licht bezien is het eveneens van belang met meer zeker- In this respect it is also of importance to obtain more reliable heid dan thans mogelijk is de sterkte van lasverbindingen in deze information on the strength of welds in these structures. The constructies te kunnen bepalen. De in het algemeen optredende generally prevailing dynamic loads and weld defects have to be dynamische belastingen en het voorkomen van onvolkomen- taken account of. heden in de las en overgangszone dienen mede in beschouwing The results of research in this direction are reportes in this te worden genomen. publication in the form of a proposal for a new testing method De resultaten van daarop gericht onderzoek zijn in dit rapport of weldments. The method is based on present stage experience gegeven in de vorm van een voorstel voor een nieuwe beproevings- and practical application possibilities for industrial laboratories. methode van laswerk. Rekening is gehouden met de verkregen Of course the proposed method has been subjected also to ervaring en overwegingen voor een praktische uitvoering in in- extensive discussions in some commissions of the International dustriele laboratoria. Vanzelfsprekend is de voorgestelde me- Institute of Welding (1.1.W.). thode ook onderwerp geweest van diepgaand overleg in enige In principle the testing method comprises the requirement of werkgroepen vanhet InternationalInstituteof Welding" a specified ductility of the weld metal at the root of a sharp (1.I.W.). notch. The dimensions, a standard notch and the loading have In principe komt de beproevingsmethode neer op het eisen been specified. van een bepaalde vervormbaarheid van het lasmetaal aan de In connection with the important aspects of the proposal, a voet van scherpe kerf. De afmetingen, een standaardkerf en general acceptance of this NIBLINK test may be strongly de belasting worden gespccificeerd. advocated. Gezien de belangrijke aspecten van het voorstel, mag een alge- NETHERLANDS SHIP RESEARCH CENTRE TNO mene aanvaarding van deze NIBLINK beproevingsmethode ten sterktste worden aanbevolen.

NEDERLANDS SCHEEPSSTUDIECENTRUM TNO CONTENTS

page

Summary 7

1 Introduction 7

2 Description of test . . . 7

3 Test piece and test procedure . 8

4 Determination of critical C.O.D. values 11

5 Alternative procedure for the testing of type T test piece . 12

6 Additional observations with regard to the operation of the test . . 13

7 Discussion of arguments leading to the proposed test 13

8 Summary of qualities of the proposed test method particularly with reference to the

Charpy-impact test 16

References . 17

Appendix I I 8

Appendix II 19 7

PROPOSAL FOR THE TESTING OF WELD METAL FROM THE VIEWPOINT OF BRITTLE FRACTURE INITIATION

by Jr. W. P. VAN DEN BLINK and Jr. J. J. W. NIBBERING

Summary A method of testing weldmetal for its sensitivity to brittle crack initiation is described. The method is based upon considerations derived from the present stage of experience and on considerations of feasibility by industrial laboratories. Interested parties are invited to carry out tests on the basis of the proposal in order to investigate the practicability of the test and eventually to contribute to a collection of data necessary to improve testing requirements.

1 Introduction necessary to provide the possibility to test the weld in its two main directions, longitudinal and transverse. The proposal presented in this paper is the result of a A consideration in designing the test method has Netherlands investigation in the framework of a joint also been that the method should enable to provoke working programme of the International Institute of fractures in mild steel welds at temperatures not too Welding (1.1.W.)-Working Group "Brittle Fracture far below environmental temperature without general Tests for Weldmetal" (W.G. 2912). One of the main yielding of the weldment. tasks of this working group, in which members of With the aim of ensuring a wide practicability of commissions II, IX, X and XII are cooperating, is to the test, its design has been chosen such that the test device evaluation tests for weld metal from the view- may be expected to be feasible for any interested in- point of brittle fracture danger. This task setting has dustrial laboratory. emanated from a wide-spread conviction that the The subdivision of the report is such that the first 6 mechanical properties that determine the service be- sections mainly deal with the operation of the test, haviour are in many cases not adequately reflected while in sections 7 and 8 the underlying philosophy is by the results of conventional small scale brittle frac- given. ture tests. Important: as a result of the discussions on the proposal As a result of its studies the working group has con- in Warsaw in 1968 some important modifications, par- cluded that for the majority of structures the investi- ticularly with regard to the drop heights and the critical gation of the brittle fracture initiation properties of the Crack Opening Diplacements (C.O.D.), have been weld are relatively more important than that of crack introduce& see section 2 and table I. arresting properties. Moreover results for actual welds and information A further conclusion has been that an evaluation about the influence of variations in drop height and test for the weld metal should preferably involve a notch sharpness can be found in the appendices. parent metal/weld combination of the full plate thickness to be applied. 2Description of test Itis generally agreed upon thatbrittle fracture initiation in a steel weldment normally involves the Essentially the method comprises the drop-weight presence of a crack-like defect, and that, therefore, loading by a series of consecutive blows of increasing crack initiation tests should use test pieces containingand defined height, and defined weight on a sharply crack-simulating sharp notches. Crack initiation thusnotched specimen containing the weld metal to be is equivalent to "crack extension". investigated. A matter of careful consideration has been how to Each subsequent blow results in an increased plastic account for an unequality in yield value of parentdeformation in the notch tip region of the test piece. metal and weld metal, which may be particularlyThe amount of local plastic deformation before frac- noticeable in mild steel weldments. This unequalityture is used as a measure of the ductility. The usual type results in different behaviour of the weld metal, de-of drop-weight test equipment, modified in some de- pending on the direction of the weld in a structure tails as will appear later, is suitable for the execution relative to the main service stresses. Likewise it was of the test. 8

For evaluation purposes the test is carried out at different temperatures. Two types of welded test Assumed stress pieces may be used: distribution .1 Type T containing a Transverse weld, notched in the centre line of the weld in the weld direction (figure 2a). Type Lcontaining a Longitudinal weld, notched perpendicularly to the weld direction with the notch extending to the centre of the weld 325 (figure 2b). When the test is used as an acceptance test, only one Critical residual C.O.D. for drop weight test = Total C.O.D. at test temperature will normally be necessary. Three incipient yield in static test on base material. specimens are thought to be sufficient. As will be ex- Incipient yielding is defined to occur at the load at which the calculated nominal bending stressinthe notched section is plained further, for acceptance testing type T has been equal to the minimum specified Gy (kg/min') chosen as the standard specimen. proof stress value ---,P=116,.t t (mm) P (kg) When stress relieving is effectuated by heat-treatment, the drop- The critical amount of deformation to be required weight specimens should be subjected to the same treatment is chosen as the total deformation undergone by a before testing. test piece of unwelded plate material (type P), loaded The critical C.O.D. then is half of the value indicated above. I to a calculated nominal stress equal to the minimum Fig. 1Determination of critical residual C.O.D. for modified specified proof stress value in a static bend test (see drop-weight test with the aid of static bend test. figure 1). This applies to non-stress-relieved structures; For stress-relieved structures half of that value is con-total deformation to which high strength steels are sidered to be sufficient, of course the specimens should subjected and with a view to the higher residual also be heat-treated. stresses. The test method implies the necessity of measuring It will be clear that the results obtained with the the deformation at the notch tip before or at fractureproposed method will show a certain amount of scatter as advocated in particular by Wells. Several methodsas a consequence of the inhomogeneity of weld metal. can be used, such as the measurement of the plasticIn principle for a pure initiation test, as the present zone size, of the lateral contraction at the notch root,one, any specimen out of the prescribed number (3) of the total crack opening displacement or of the resi- should fulfill the requirement. On the other hand the dual crack opening displacement (C.O.D.). test method as well as the criterion have the character The latter method mentioned has been chosen.of a compromise in order to be applicable to all kinds Tests in the Delft Ship Structures Laboratory haveof practical situations. On account of this it is thought shown that when the deformations are small there isto be reasonable to allow that for acceptance-testing an essential difference between the type of deformation one out of three specimens shows a critical C.O.D. in notched bars in static and in drop-weight testingslightly below the required one, provided that the respectively. In a static test the residual contraction other two results are significantly better. This can be in way of the notch is rather wide-spread and relativelymet satisfactorily by prescribing that shallow. For the same amount of C.O.D. the contrac- C.O.D., x C.O.D., x C.O.D.3 > (C.O.D.cr;,)3 tion caused by drop-weight loading is much larger and Assuming that for general application the residual occurs in a smaller region (pit-like). On account of thisC.O.D. measuring iswidely acceptable and easily it has been decided that for drop-weight-specimens theapplicable (see figure 5), in the following sections use of C.O.D. measurements should be preferred toreference will be made mainly to this method. contraction measurements. Of course the only practical possibility is measuring the C.O.D.'s after each blow 3Test piece and test procedure is given (residual C.O.D.'s). In the static test (figure 1) the total C.O.D. at yieldThe test piece T and the test set-up are represented pointand not the residual C.O.D. after unloading schematically in figure 2a. The test piece L is shown in is used for the critical residual C.O.D. value in the figure 2b. The V-butt weld is by way of example. The drop-weight test. In this way the effect of residual test piece of the unwelded plate (P) has the same dimen- welding stresses is also taken into account (see sect. 7). sions as the pieces T and L but machining of the surface Consequently welds in steels of higher yield point will in the notched region is not necessary except when spe- always have to meet a more severe notch deformation cial measurements or observations are desired in this criterion which is reasonable with a view to the higherregion; the rolling direction of the plate should be ipz 0.91 1.1 t (kg ,)1

Rounded! edges

Machined; flush with plate (both -sides/ !Hardened steel See detail. Center of weld

Bridge piece LI lt U11(1 ((MIL_

Fig.2bTest piece t,

Hardened steel Rounded edges 3.25

11 02 360

Fig. 2cTest piece ?'

L2Detail of notch !region see also i.5 ) Conditions for maximum thickness t=65 mm 2 When t> 65 mm the total height of the test piece should be f+2A/r mm., The bridge piece is omitted, the flat bottom part of the drop-weight should have a diameter of 75 mm and the span should be made 007t2. Fig.. 2ateat piece 'T and the way of loading (proposed for acceptance testin,g)5

1;1

MOS r]

1. ii

4,-e --rmeszrart-A,, Fig.. 3 Test-equipment

= 10

noted. As indicated in figure 2a, the test piece is sub, Although any type of static displacement measure- jected to 4-point-bending in order to have pure bendingment is, in principle, suitable, those methods which of the notched part. The "bridge-piece" can best beallow a measurement without removing the test piece, clamped to the test-specimen so that both are cooledfrom the anvil are preferable. at the same time (figure 3). The supports are flattened For general application a mechanical dial gauge in order to limit the amount of energy lost by plasticextensometer of the type shown in figure 5a measuring, deformation at the place of impact. the widening of a milled slot in the notch or a drilled A rigid foundation of the supports is required' with hole, can be used. Figure 5b shows an alternative la view to the reproducibility of the test results (fi-.method which is more accurate but less easily to per-, sure 3). form. The dimensions Of the' test piece are shown in figures 2a and 2b. As will be seen, the notch depth is made proportional to the square root of the plate thickness and equal to 2.,/t, where t is the plate thickness in mm. This relation has been chosen as a practical compromise between a constant notch depth and a notch depth proportional to the plate thickness, as will be

,explained in section 7. J. AA The 0,2 mm notch can be made by hand sawing Very reliable results Cheap specime (Adjusting of pin of ((Pin of extensometer with a saw-blade ground to the reguired thickness or extensometer easy( adjusted from origi- nal circular section a jeweler's saw. to Indicated section The drop-hammer mass is related to the plate thick- This is difficult to do without impairing ness and corresponds to a weight in kg equal to the the accuracy,). plate thickness in mm with a tolerance of + 10%. (See appendix I.c). In figure 4 a device is shown which allows quick and safe manipulating with the drop- hammer..

-Figure 5a

Figure 5bi

Small balls into the material jpressed'

Fig :,5'Possible methods of measuring C.O.D. When testing at a series of temperatures, it is practical to start with the lowest temperature envisaged. When the test piece is at the 'desired temperature, the test starts by measuring the initial distance for the C.O.D.-measurement. A first blow is then given from a height of 250 mm and after that the reference distance is measured. The rig. 4Magnetic safety clutch (when current is switched on difference with the intial distance iwthe residual C.O.D. pin in magnet goes down) Table I. Dropheight sequence Beforeiubjecting a test piece to drop-weight loading the notch has to be prepared for the measurement of Hl. 112 H3 H4 11-5 H6. H7 H8 H9in mm 25030035040014505005506001 700etc. the residual C.Q.D.'

_____.;__IL!II 11

The second blow is given from a height of 300 m (seeNext the fracture C.O.D..'s are plotted as a function of table 1), and the C.O.D. is measured again, This is'temperature (figure 7). continued with the height 'increasing in steps of 50 A direct comparison between different weld metals mm under 600, mm height and in steps of 100 mmin the same steel is possible in a diagram as given in height until fracture occurs. The C.O.D. measured at'figure 7.. the last blow before fracturing is noted as the fracture It will' be obvious that for steels in which cracks, CO. D'. at the test temperature. in the zones adjacent to the weld are a real possibility, During the test the temperature of the test piece the quality of these zones may be decisive for the quality should be watched and corrected by cooling if necessa- of the weldment and may be determined in a similar way. ry. For evaluation testing, for instance when comparing different weld metals, test pieces are tested the same 4.Determination of critical C.O.D. values way at temperatures 10° and 20. ° higher respectively. A static 'bend test is carried out at -the intended test At these higher temperatures the C.O.D. measure-temperature on a test piece of the steel (type P), using, ments for the lower blow energies may be omitted asthe same span and loading fixture as for the drop- far as they did not fracture the piece at a lower tem-weight tests. The total C.O.D. value at incipient yielding perature. is determined. This is defined to occur at the load In figure 6 the procedure is given diagrammatically. value at which the "nominal maximum stress value", The temperature T is plotted at the abcis and the drop- 'calculated by taking the remaining cross section in C.O.D.'s are height H at the ordinate. The residual way of the notch as the cross section of a hypothetical plotted 'with -the temperature ordinates as a base::bend test piece, equals the minimum specified proof Fracture)( so....-. stress value. For the dimensions of figure 2 and four point bending the load computed with a 1111W is:

.18 mmi 70 P = flay't ay: kg/mm' (yield-stress) t':. Slow Ur mm (plate-thickness) ric '092 P:kg (load) 8 .60 m.

I racture Fracture Or.068 -if S5 N In figure 8 not only the CO. D. at incipient yielding but

Fructure Q.051 m 50 - 111050 ll C.O.D.'s measured from zero-load on are given for

450 040 mm 10.045 1.045 i1103W 5 _. . tests at two different temperatures. The enormous

Fracture 10,03 10.033 031 11.028 capacity for 'deformation of this material is obvious. 40 ,*aumm 0.02710.025 41022 In thestatictest at 50°C the total C.O.D.. at fracture 3 lk 35 Atte1st, 2,nd 0.073 0.012 0.016 and3rdblow is more than twenty times as large as the residual 2E 30 C.0 II. not mea- drop-weight 0.00 6.007 0.008 'surfd. C.O.D. at fracture in a test at a tempera- 25 1, o. ture 50° higher (figure 7).

1 i In figure 8 one of the curves is obtained with a 1 1 specimen containing a fatigue-crack. Even this one behaved quit satisfactorily at 50.°C. Figure 8 shows

1 further that for loads below yield point the C.O.D. in

-10° -5° + 5 +10 creases approximately linearly with the load. For loads Test .temperature OD) between the one for which a calculated nominal' stress Semi-killed steel 37' of yield point value exists and the one at which a Isotherm Robertson arrest temp. +20°C 'plastic hinge is formed the C.O.D. progressively in- Claarpy 3.5 kgm/cm2 (20 ft.lb) ± 3°C creases with the load. At stiff higher loads a very rapid 5.2 kgm/cm2 (30 ft.lb) ± 7°C 7 kgm/cm2 (40 ft.lb) ± 9°C increase of C.O.D.. occurs. 50% Crystalline ±17°C Originally it has been considered to use. theresidual Fig. 6Example of testing 'diagram for given mild steel C.O.D.-value after unloading from the load at which ta plastic hinge is formed as a measure for the critical # 0.20 drop-weight C.O.D. However this value cannot be

r 0./5 Critical; C.0 0.4 see fig. 9 ); determined easily and accurately because itis very .0.10 sensitive for small differences in the load applied (see I 0.05 figure8)1.. Therefore the much more accurately to

+.5° .810°' determinetotalC.O.D..,at incipient yielding was chosen; it is about equal to theresidual"plastic hinge" C.O.D. Fig,7' Maximum C.O.D.% before fracture derived from results of figure 6 (see figure 8) for the test conditions chosen. 12

111 No fracture at C.0.D.055mm

.c No fracture at 16 covs=1,5mm

4500 Ti7n-rn-57w 15 ,c - ;4 14 saw cu 4000 2 13 Plastichinge 3500 12 Calculated 1.5 Cy tPlastic 11 1 3000 10

2500 ViSual Incipient yielding Calculated 2200 minimum "E 2000 specified proofstress) 6 4c C.O.D. at incipient yield to be 1500 used ascritical value for residual C.O.Dindrop weight test.

1000

5 2 Residualcan.after unloading 500 from Loadat which plastic hinge is formed.

01 0.2 0.3 04 0.5 0.6 C.O.D. (mm)-

Semi-killed steel 37 Isotherm Robertson arrest temp. +20 °C Charpy 3.5 kgm/cm2 (20 ft.lb)+3°C 5.2 kgm/cm2 (30 ft.lb) + 7°C 7 kgm(cm2 (40 ft.lb) 9°C 50% Crystalline +17°C Fig. 8C.O.D. values obtained with static bend-tets at 5°C and 50 C for given mild steel

It is obvious that the establishment of critical C.O.D.pective of the yield value ratio of steel and weld metal. values is a procedure that can be carried out separately For longitudinal welds, with the main service stress from any weld metal testing. in the direction of welding, the validity of this assump- It is to be expected that the C.O.D.'s at incipienttion was confirmed by tensile testing of notched plates yielding are un-ambiguously defined by yield point [6]. In this case the deformation of the plate is imposed and plate thickness. After some experience has beenon the weld, regardless of its yield value. For the L-test gained there is no need for further static bend testing. piece, therefore, there is no doubt that equal performance of different weld metals means equal defor- Important:C.O.D. measurements are carried out inmation of the test pieces, i.e. equal C.O.D. various ways in different laboratories. The configu- For welds in the transverse direction, however, ration of the notch might be made different from whatthere are cases in which the deformation of the weld is given in this report. Also the place where the C.O.D. is not governed by the overall deformation of the measurements are taken might be chosen different weldment but by the ratio of stress to weldmetal yield from what is proposed. value. It is obvious that the deformations at notches All these variations are acceptable provided that inin an uninterrupted weld, loaded perpendicularly to its the static bend test exactly the same C.O.D. measuringdirection by a uni-axial stress field will be governed is applied as in the drop-weigth testing. In this way theonly by the magnitude of the applied. stressIf the influence of measuring techniques on the final resultyield value of the weld is lower than that of the plate, can be eliminated. a notch in the weld will start to deform plastically at a lower load than the plate and vice versa. Alternative procedure for the testing of type T test To take account of these conditions, an alternative piece mode of evaluation is possible, which will be denoted The procedure as described above is based on the T,. assumption that welds in a structure are subjected to To start with, the procedure involves the drop- the same amount of strain as the plate material, irres-weight loading of unwelded test pieces with the aim 13

of finding the drop-height at which such a test piece The number of blows necessary to give a certain shows a C.O.D. equal to the critical value. The weldedC.O.D. in a given test piece may depend on the rigidity test piece T is then loaded by the same number ofof the foundation of the supports. But the final C.O.D. stepwise increasing drop-heights, resulting in corre- to fracture will hardly be influenced by small variations sponding nominal stress fields as in the unwelded P-spe-in rigidity. A satisfactory set-up is shown in figure 3. cimen. If the test piece does not fracture it is considered It sometime happens during a test that at a certain to have fulfilled the T' test requirement. blow the residual C.O.D. increases far more than It will be obvious that for mild steel weldments theduring the preceding steps. This can be due to the for- T' procedure will normally be milder than the regularmation of an internal crack ("tunnel-crack-) not T-test, because the higher yield point of the weld metalvisible from the outside. will give rise to a smaller deformation in the weld When this is suspected to have occurred itisre- metal as compared with the base material for thecommended to insert ink in the notch, after which the same drop-height. For alloy steels, however, the T' specimen can be fractured in order to inspect the frac- procedure may be more severe than the regular test, ifture-surface. the yield value of the weld metal happens to be lower In the foregoing sections the testing of the parent than that of the steel. steel is included mainly to have a basis for relating the applied stress level to the resulting notch deformations. It has not been the intention to compare steel perfor- 6Additional observations with regard to the operations mance versus weld performance with the aimto of the test predict the actual performance in a structure. From the foregoing sections the impression may be For such a comparison not the parent metal but the gained that multiple drop-weight testing involves moremost critical zones surrounding the weld should be work than the determination of for instance a Charpyinvestigated preferably in the same way as proposed V temperature curve. for the weldmetal. This may be true in the present stage. It is to be expected however, that after some experience has been gathered, the procedure can be very much simplified. 7Discussion of arguments leading to the proposed test For instance the static bend tests will be very soon no longer necessary when for a few yield value classes a.In the study of brittle fracture phenomena it is of steel and plate thicknesses (and perhaps methods of necessary to differentiate between the propagation C.O.D. measuring) reliable data are obtained to make aspects, which concern the global weldability proper- "master-charts" for the critical C.O.D. ties, and the initiation aspects, for which local con- The choice between the L and T-type of test pieceditions are to be considered. It needs hardly to be can be easily made if there is no doubt about the waysaid that the most critical regions for crack initiation of loading of the weld in the structure. are the welds and the zones directly adjacent to it. A difference between the result of L- and 1-testing Even for those structures, for which the design and may be expected from the crystallisation texture of the choice of material is based upon considerations of weld, which may tend to favour fracture in the weld crack arresting, the safety of operation is improved by direction. measures that limit the danger of crack initiation. Apart from the relative severity of L- versus 1- For an important category of weldments the crack testing, it is worthwhile to consider what relative weight propagatingbehaviour of the weld metal is considered should be attached to the result of each test with a viewnot to be of primary interest for the safety of the to the type of defects to be expected in actual welds. structure as a whole. Both the statistical evidence from If defects transverse to the weld are expected to bebrittle fracture cases in service [1] and the experimen- virtually non-existent, it may be justified to omit thetal evidence from tests on large welded plates [2], [3]. L-testing altogether. [4] indicate that under certain conditions brittle frac- It may be taken for granted that by far most of thetures tend to avoid the weld proper. Although it is not defects resulting from the welding procedure itselfpossible to outline quantitatively the physical con- tend to be in the direction of welding, so that in gen-ditions which determine the fracture path, it isstill eral the T-type of test cannot be omitted. possible to distinguish in technical terms specific cases. For this reason testing of the T-type is proposed as the The following circumscription is considered to cover standard procedure.This simplifies the process and has those cases for which the existing evidence predicts the additional advantage that little material is con-that a brittle fracture, even if initiated in or in the vicin- sumed. ity of a weld, will not follow the weld proper: 14

Butt welds, welded through the complete plate thick- plates. Finally itis quite impossible to obtain some ness by means of conventional multi-layer processes, idea about the influence of weld faults, like lack of in nonstress relieved structures of ferritic steels with penetration (figure 9), porosity etc. on the resistance to minimum specifiedproof-stress values not greaterbrittle fracture with the aid of small size specimens. than 40 kg/mm2. These considerations have become more and more im- For these structures the safety of operation is bestportant in the last ten years when the welding of thick guarded by requiring crack arresting properties of theplates has become common practice. steel and freedom from crack initiation in the weld and Given this situation, a logical approach is to in- its environment. vestigate the metal under conditions which are more closely related to that under service conditions. From For structures outside this category, the crack arrest- a technical viewpoint the testing of structure simulating ing properties of the weld metal need consideration,elements is the best solution, but this method is not but it will be obvious that the prevention of cracksuited for general application. initiation remains a matter of importance. From the So there seems to be room for test methods on foregoing it may be clear that the I.I.W. Workingsmaller test pieces of which the results can be applied Group "Brittle Fracture Tests for Weld Metal" haswith more confidence to structural behaviour than concentrated first its activities on the initiation aspectsthat of conventional notch ductility tests. of brittle fractures. A test for crack initiation on relatively wide plates has been proposed and investigated by Ikeda et al. [5]. b.In the introduction to this paper it has been statedIn this deep-notch test, the loading is purely static, that there is a general conviction that conventionalwhich could explain the reported rather low initiation notch ductilitytesting,particularly Charpy-impacttemperatures. The test is not suited and not meant for testing, does not adequately reflect the expected service general application becauseitinvolves the use of behaviour of a weld. This does not mean that the con- expensive testing equipment. ventional testing results have no relation to the duc- On the other hand in a smaller test piece, such as tility properties of the metal but that there is no reli-proposed in the present paper, not all conditions able method to relate the results of conventional me-acting in structures, such as the effect of very deep thods with that to be expected in actual structures.notches and of residual stress fields, can be included. This uncertainty is basically caused by the difficulty to Therefore there remains room for tests on larger relate quantitatively the differences in behaviour of aassemblies to account for such influences. ductile metal under conditions of different geometry For most cases however the test procedure proposed and loading speed. will satisfactorily simulate the actual conditions to A practical difficulty encountered in Charpy testingwhich a weld is submitted in a structure. is that, in the transition range, a very large scatter in One of the crucial questions has been to what extent impact values is often found and that there is no uni-weld metal will be deformed in an actual structure if formity of opinion about the significance of this scatternotches are present. To get an answer to this problem from the viewpoint of material evaluation. Uncer-an investigation was carried out by Nibbering [6] with tainty also exists with regard to the different valuesthe aid of extensive measurements on a tensile loaded found in different regions of a multi-layer weld in heavy plate, welded in the tensile direction and provided with several notches, comprising different zones in the weldment. This test showed very clearly that the notch in the weld metal is plastically deformed to the same extent

as the virgin plate material.. It is obvious that transverse welds will mostly not behave in the same way, but it is believed to be a safe procedure to assume that in many cases a transverse weld as well will have to deform along with the plate. This may be the case for instance in transverse welds in flanges in composite beams and at weld crossings. Nevertheless the test procedure T' leaves room for those cases in which the design is such that transverse, uninterrupted welds are loaded by a linear stress field Fig. 9Specimen with lack of penetration over their entire length (see section 5). In that case the 15

weld should be subjected to a stress criterion rather proached than by single blow loading. This opinion is than a deformation criterion. In case the yield value based on the consideration that the blows that do not of the weld is lower than that of the plate steel the fracture the test piece, will cause a condition of defor- stress criterion (i.e. the T' procedure) is the more mation and stress around the notch tip, which will be severe one and should be applied. less different from the condition that results from static loading than in a one-blow test. The energy from c. A dynamic test has been chosen in the first placea next blow will mainly be consumed in the elastic to provoke fractures at temperatures not too fardeformation of the test piece and only a final fraction below room temperatures and this making the test of the energy will further deform the notch tip region less cumbrous for general application. This choice was plastically and eventually lead to fracture. Thus the supported by results of tests on specimens containing condition of fracture may be expected to be rather fatigue cracks reported by Nibbering et al. [7]. Static similar to what happens if a tensile loaded specimen or dynamic testing proved to make a difference of more is fractured by a blow of low energy. than 50 C in transition behaviour. A second reason In fact a compromise is obtained between pure for testing by an impact load was that for many struc- static loading and the high speed shock loading in- tures the occurrence of shock is a real danger; shocks herent to normal impact testing. Important is that in may happen either by accident or as result of small this way the phenomenon of strain hardening at the localbrittlefractures which may develop during notch tip is retained. fatigue loading, when the fatigue crack travels through The drop-height steps and the hammer weight, the various zones of a weldment (figure 10). A third which determine largely the speed of loading, have reason is that the test-equipment turns out to be simple been chosen on the basis of what is thought to be and in expensive. realistic and are connected with the experience obtained so far [7], [8]. The initial height is 250 mm for all steels. Conse- quently higher strength weld metals willsuffer a greater number of blows untilthe critical C.O.D. value is attained than lower strength weld metals. This might seem to be of advantage for the higher strength metals because in general the greater the number of blows the larger the C.O.D. before fracture,(see appendix lb). But it should be realized that at the moment of fracture higher strength metals are subjected to a higher speed of loading than lower strength metals because the final drop-height is larger. More- over the critical C.O.D. prescribed for higher strength steels is larger than for lower strength steels being prac- tically proportional to yield point. The main reason is that in structures the total C.O.D.' s at notches are higher for high strength steels as compared to mild steel. For non stress relieved structures the critical C.O.D. should of course be higher than in stress relieved structures. Static loading to yield point of a non-stress relieved structure will after unloading generally result in residual plastic deformations of a magnitude equal Fig. 10Fracture-surface of H.A.Z. (Heat-affected zone) ofto o,/ E. For the case of moderate dynamic loading the electro gas welded plate (result of fatigue loading at 20°C) presence of residual stresses will have a similar effect. That is why the critical C.O.D. has been defined as it is. The intermittent impact loading has been chosen For stress-relieved structures half of that value is con- partly in order to get more information out of one test sidered to be sufficient. piece than is possible by loading by a single stroke: The form of the notch is that of a machined slot the latter is essentially a go no go test. with a width of 0.2 mm at the bottom. A natural A second reason to chose intermittent loading by crack, for instance a fatigue crack, is obviously at- increased drop heights is that it is believed that in this tractive, but has the disadvantage of being more diffi- way real loading conditions are more closely ap- cult to make in a reproducible way. The speed of de- 16

formation at the bottom of a saw-cut is lower than of Quality has been definedinterms of directly a fatigue-crack, which meets once again the wish to measured local ductility (C.O.D.) instead of in

avoid a too extreme dynamic character of the test. An- terms of a complex figure like specific energy. I other disadvantage of fatigue-cracks for the type of Full plate thickness, so thickness-effect has been test used is that, after one or more blows, such a crack included and the inhomogeneous character of the is relatively much more blunted than a saw-cut notch, weld has been taken into account. resulting in an uncontrolled shift in the severity of the Notch size and acuity conform rather to realistic test. In appendix Id some information is given about cracks. the difference in behaviour of specimens containing saw-cuts or fatigue-cracks. The difference is partly a Strain hardening as occurs instatic loading, has result of the sharpness of the crack and partly of the been maintained by applying progressively in- deterioration of the material at the tip of the crack. creasing drop heights. On the whole it amounts to about 25 'C difference Realistic compromise between static and conven- in critical temperature. tional impact tests. (Strain rate is restricted by The depth of the notch has been chosen in propor- using low drop heights - stepwise increased - and tion to the root of the plate thickness. This is a com- a saw-cut notch instead of a natural crack). promise between a constant depth and proportionality to the thickness. A constant depth is attractive from Possibility of comparing weld and heat-affected the viewpoint of interpretation of the results. With a zone (H.A.Z.) view to the technological character of the test, how- Influence of weld defects, for instance lack of pene- ever, an increase of the notch depth with the plate tration, porosity etc. on resistance to brittle fracture thickness seemed appropriate in order to account for can be estimated. the fact that real defects normally will also tend to increase in length with plate thickness, if only by theApart from the aboveitis attractive that crack- decreased probability of detection. The square rootarresting properties of the weld can simply be estimated was chosen because it was assumed that a linear rela- with same specimens by applying large drop heights tion would exaggerate the effect of plate thickness on [7], [9]. defect size and also to keep the test piece within wield- Objections to the proposed method can easily be able dimensions for the greater plate thicknesses. found of course as always with compromises. The The overall dimensions have mainly been chosen inchoice of loading speed is arbitrary; the derivation of connection with the existing experience. The height ofthe critical C.O.D. value from a pure static test is the remaining section in way of the notch, the ligament,theoretically not wholly justified; the notch is not a has been made constant, 65 mm, because otherwise natural crack. However eventually the test can easily the testing conditions would have to be varied in abe adjusted to meet such objections if required. It is more complicated way. As it is now, only the drop- suggested that in order to limit the number of para- weight has to be varied in proportion to the platemeters and to maintain the possibility to compare the thickness to induce the same "nominal- stress field atresults without the need of applying confusing cor- the same drop height in different plate thicknesses. rections only drop height, drop weight and critical The deformation and stress at the notch tip will, ofC.O.D. value should be varied if necessary. course, vary with the plate thickness, butt this is exactly Some results with respect to the first two variables a cause of the size effect to be accounted for. A second are given in appendix I. To show the outcome of the reason to keep the ligament constant was to have amethod when applied to welded plates,results for constant gradient of the nominal bending stress in way submerged arc-, electrogas- and automatic CO3-welds of the notch for a given yield-value class. are collected in Appendix II. Comparisons with results The 65 mm for the ligament is believed to be suffi-obtained with Charpy-V-notch specimens can be made. ciently large, so that a plastic strain field in the tip It is hoped that the interested parties, notably those region is not strongly disturbed by the vicinity of therepresented in the I.I.W. Commissions If, IX, X and neutral axis and does not differ too much from nor-XI I will be willing to contribute to obtain experimental mal tensile conditions. data by carrying out testing programmes on the basis of the proposal presented in this paper. 8 Summary of qualities of the proposed test method One of the main reasons for giving the proposed particularly with reference to the Charpy-impact test testing parameters in rather great detail is to ensure the a.Initiation characteristics are clearly separated from possibility to compare testing results from different propagation characteristics. sources in a cooperative investigation. 1 17

References 5L,IKEDA, K., Y. AKITA and H. K !NARA, The Deep Notch Test and Brittle Fracture Initiation. 11W-doe. X-404-67. I.Aupica, A., Progress reports of Working Group _Brittle 6.NIBBERING, J. J. W., Plastic deformations at notches in welds Fracture in Service". IIW-doc. X-387-66, X-424-67 and of mild steel plates. S.S.L. rep. 129, (11W-doe. 29/2-/07 Welding in the World, 1965, pp. 58-67. 1968). KIHARA, H., Recent Studies in Japan on Brittle Fracture of NIBBERING, J. J. W., J. VAN LINT and R. T. VAN LEEMEN, Welded Steel Structure under Low Applied Stress Level. Brittle fracture of full-scale structures damaged by fatigue. Japan Institute of Welding, 11W-doe. X-291-61. Neth. Ship Researchcentr. Report no. 85 S. 1966.11W-doe. DECHAENE, R. and J. SEBILLE, Euratom Colloquium on Brittle X-374-66 and I.S.P. Nov. 1966. Fracture. Proceedings, pp. 445-478. VAN DEN BLINK, W. P., A crack extension test for weld metal. 4,SELANDER, L.. and L. TODELL, Brittle Fracture Propagation 11W-doe. IX-527-67/X-453-67. in Welded Joints. Institute of Welding Technology, Stock- MARQUET, F., Side bend test procedure. Steel times, Nov. 19, holm. 11W-doe. IX-573-68/X-567-68. 1965. 18 APPENDIX I

a.Influence of drop-height of first blow on test results b.Influence of step-magnitude on test results

,...-Fracture 550 500 nlow C.O.D. (mm) :/--Fracture no 500 0.049 0.054 550 Blowc.o.D.(mm)

450 --5 0.038 0.045 500 3-6 0.041 0.054

400 -4 0.027 0.033 450 5 0 045

350 -3 0.017 0.025 400 2-4 0.020 0.033

300 -2 0.009 0.016 350 3 0.025 Conclusions: Conclusions: 300 0.007 0.016 250 1 0.008 1 2 Influence is moderate, (about Influenceisdistinct,but 200 10% of critical C.O.D. for a 250 1 0.008 when the results are com- difference of 50 mm in ini- pared with those of figure 6 2 tial height) 200 can be seen that in "transi- Test temperature0 °C tion" temperature onlya Average of 2 "2 specimens difference of about 5°C is Test temperature0 °C obtained Average of2 x 2 specimens

C.O.D

C.O.D.

c.Influence of variations in drop-weight on test results d.Influence of sharpness of notch on test-results Comparison between saw-cut notch and fatigue-crack From the results d. to j. given in the following table it appears Fracture Conclusions: that the critical temperature for specimens containing fatigue- 1000 1 mm is about 30°C. (The Results conform if plottedcracks with a length greater than critical C.O.D. was 0.04 mm; see figure 8). For specimens con- Blow Carl(mm) onthebasisofenergy taining saw-cuts the critical temperature was about 0°C. (weight x height). Difference 900 -5 0.046 It is important to know if this large difference is only due to infracture C.O.D. isnot the difference in sharpness between saw-cuts and cracks or if it alarming (10%) is partly due to the deterioration of the material caused by the

800 4 0.033 fatigue-loading. The results for the specimens a, b and c, containing very small fatigue-cracks (0.5 mm) suggest that only 10°C of the total of 30°C were caused by the mentioned deterioration. 700 0.025

600 2 0.015

Fracture 500 i 1 0.010 :Blow COD. (mm) . nn 450I. 5 0.040

400W exi--4 0.031 ,.x C.O.D. 350 3 0.027 Height of Number r N Length of Temp. before frac-Observations crack (mm) (0 C) first step of blows 300 2 0.012 ture (mm) 0.

250 --1 0.007 a.50,000 0.5 + 5 25 6 0.035 l length of b.50,000 0.4 +10 25 9 0.240 fatigue-cracks 200 c.96,000 0.5 +20 30 5 0.360 J 0.5 mm Test temperature: -5 °C d.71,000 2.5 0 30 1 o Average of 2a2 specimens e.50,000 1 0 25 5 0.022 f. 70,000 2.2 +10 30 1 0 length of 100 g.98,000 1.5 +10 15 3 0.010 fatique-cracks h. 126.000, 3.5 +20 15 6 0.037 I mm i.101,500 1.8 +30 15 6 0.030 j.110,000 +2.5 +40 15 6 0 80 C.O.D. 19

APPENDIX II

Summary of tests on welded plates dElectrogas weld : (Dropweight 22 kg) T-test; gap 14 mm; one pass (enclosed CO2) solid wire 1.6 mm; 450 Amp; 5 cm/min aPlate material: (Semikilled, as rolled) Temp. C.O.D. mm thickness 25 mm; yield point 25 kg/mm2 10°C 0.11 critical temp. I 10°C I tensile strength 45 kg/mm2 Icritical C.O.D. 0.055 mm 10°C 0.165 (Charpy 3.5 kgm/cm2 : I + 25 °C ! I) 10°C 0.050 Results: (-10°C0.045) fracture at copper inclusion Temp. C.O.D. mm 0°C0.400 next to notch) 20°C 0.01 critical temp.I- 10°C 0°C0.140 10°C 0.045 (Charpy 3.5 kgm/cm 2 : I - 7 CI) 0°C0.190 10°C 0.070 50% cryst. + 7°C 0°C 0.280 v. d. Veen +8°C) e Automatic CO, weld : L-test; symm X; 60'; hor; root pass: basic electr. b Submerged arc weld: L-test Composite electrode (basic core) 2.4 mm Symm. double V, 90', two passes, resp. 800 and 450 Amp; 45 cm/min; 8 passes 1000 Amp. Weld speed 33 cm/min, wire 5 mm, cry = 35,8 kg/mm2,Temp. C.O.D. mm = 48,5 kg/mm2 30°C 0.160 critical temp. I < 30°C I Temp. C.O.D. mm 20°C 0.150 (Charpy 3.5 kgm/cm2: 55 °CI) 0°C 0.19 critical temp. 15°C I (estim.) 5°C 0.09 (Charpy 3.5 kgm/cm2: I -10°C 10°C 0.065 fElectrogas weld (enclosed CO2): 1-test Composite elestrode 2.4 mm; 450 Amp; 5 cm/min c Submerged arc weld: Temp. C.O.D. mm T-test; with lack of penetration (see figure 9) 40°C 0.041 critical temp. :I 18°C I Temp. C.O.D. mm 30°C 0.055 (Charpy 3.5 kgm/cm21 20 °C 10°C 0 critical temp. :I (estim.) 20°C 0.020 0°C 0.090 (Charpy 3.5 kgm/cm2: I 20°C ) 15°C 0.24 0°C 0.035 10°C 0.63 PUBLICATIONS OF THE NETHERLANDS SHIP RESEARCH CENTRE TNO (FORMERLY THE NETHERLANDS RESEARCH CENTRE TNO FOR SHIPBUILDING AND NAVIGATION) PRICE PER COPY DFL. 10.- M = engineering department S = shipbuilding department C=corrosion and antifouling department Reports ISThe determination of the natural frequencies of ship vibrations 37 M Propeller excited vibratory forces in the shaft of a single screw (Dutch). H. E. Jaeger, 1950. tanker. J. D. van Manen and R. Wereldsma, 1960. 3 S Practical possibilities of constructional applications of aluminium 38 S Beamknees and other bracketed connections. H. E. Jaeger and alloys to ship construction. H. E. Jaeger, 1951. J. J. W. Nibbering, 1961. 4 SCorrugation of bottom shell plating in ships with all-welded or 39 M Crankshaft coupled free torsional-axial vibrations of a ship's partially welded bottoms (Dutch). H. E. Jaeger and H. A. Ver- propulsion system. D. van Dort and N. J. Visser, 1963. beek, 1951. 40 S On the longitudinal reduction factor for the added mass of vi- 5 S Standard-recommendations for measured mile and endurance brating ships with rectangular cross-section. W. P. A. Joosen and trials of sea-going ships (Dutch). J. W. Bonebakker, W. J. Muller J. A. Sparenberg, 1961. and E. J. Diehl, 1952. 41 S Stresses in flat propeller blade models determined by the moire- 6 S Some tests on stayed and unstayed masts and a comparison of method. F. K. Ligtenberg, 1962. experimental results and calculated stresses (Dutch). A. Verduin 42 S Application of modern digital computers in naval-architecture. and B. Burghgraef, 1952. H. J. Zunderdorp, 1962. 7 M Cylinder wear in marine diesel engines (Dutch). H. Visser, 1952. 43 C Raft trials and ships' trials with some underwater paint systems. 8 M Analysis and testing of lubricating oils (Dutch). R. N. M. A. P. de Wolf and A. M. van Londen, 1962. Malotaux and J. G. Smit, 1953. 44 S Some acoustical properties of ships with respect to noise control. 9 S Stability experiments on models of Dutch and French standard- Part. I. J. H. Janssen, 1962. ized lifeboats. H. E. Jaeger, J. W. Bonebakker and J. Pereboom, 45 S Some acoustical properties of ships with respect to noise control in collaboration with A. Audige, 1952. Part II. J. H. Janssen, 1962. 10 S On collecting ship service performance data and their analysis. 46 C An investigation into the influence of the method of application J. W. Bonebakker, 1953. on the behaviour of anti-corrosive paint systems in seawater. 11 M The use of three-phase current for auxiliary purposes (Dutch). A. M. van Londen, 1962. J. C. G. van Wijk, 1953. 47 CResults of an inquiry into the condition of ships' hulls in relation 12IM Noise and noise abatement in marine engine rooms (Dutch). to fouling and corrosion. H. C. Ekama, A. M. van Londen and Technisch-Physische Dienst TNO-TH, 1953. P. de Wolf, 1962. 13 M Investigation of cylinder wear in diesel engines by means of labo- 48 CInvestigations into the use of the wheel-abrator for removing ratory machines (Dutch). H. Visser, 1954. rust and millscale from shipbuilding steel (Dutch). Interim report. 14 M The purification of heavy fuel oil for diesel engines (Dutch). J. Remmelts and L. D. B. van den Burg, 1962. A. Bremer, 1953. 49 S Distribution of damping and added mass along the length of a 15 S Investigations of the stress distribution in corrugated bulkheads shipmodel. J. Gerritsma and W. Beukelman, 1963. with vertical troughs. H. E. Jaeger, B. Burghgraef and I. van der 50 S The influence of a bulbous bow on the motions and the propul- Ham, 1954. sion in longitudinal waves. J. Gerritsma and W. Beukelman, 1963. 16 M Analysis and testing of lubricating oils II (Dutch). R. N. M. A. 51 M Stress measurements on a propeller blade of a 42,000 ton tanker Malotaux and J. B. Zabel, 1956. on full scale. R. Wereldsma, 1964. 17 M The application of new physical methods in the examination of 52 C Comparative investigations on the surface preparation of ship- lubricating oils. R. N. M. A. Malotaux and F. van Zeggeren, 1957. building steel by using wheel-abrators and the application of shop- 18 M Considerations on the application of three phase current on board coats. H. C. Ekama, A. M. van Londen and J. Remmelts, 1963. ships for auxiliary purposes especially with regard to fault pro- 53 S The braking of large vessels. H. E. Jaeger, 1963. tection, with a survey of winch drives recently applied on board 54 C A study of ship bottom paints in particular pertaining to the of these ships and their influence on the generating capacity behaviour and action of anti-fouling paints A. M. van Londen, (Dutch). J. C. G. van Wijk, 1957. 1963. 19 M Crankcase explosions (Dutch). J. H. Minkhorst, 1957. 55 S Fatigue of ship structures. J. J. W. Nibbering, 1963. 20 S An analysis of the application of aluminium alloys in ships' 56 C The possibilities of exposure of anti-fouling paints in Curacao, structures. Suggestions about the riveting between steel and Dutch Lesser Antilles, P. de Wolf and M. Meuter-Schriel, 1963. aluminium alloy ships' structures. H. E. Jaeger, 1955. 57 M Determination of the dynamic properties and propeller excited 21 S On stress calculations in helicoidal shells and propeller blades. vibrations of a special ship stern arrangement. R. Wereldsma, J. W. Cohen, 1955. 1964. 22 S Some notes on the calculation of pitching and heaving in longi- 58 S Numerical calculation of vertical hull vibrations of ships by tudinal waves. J. Gerritsma, 1955. discretizing the vibration system. J. de Vries, 1964. 23 S Second series of stability experiments on models of lifeboats. B. 59 M Controllable pitch propellers, their suitability and economy for Burghgraef, 1956. large sea-going ships propelled by conventional, directly coupled 24 M Outside corrosion of and slagformation on tubes in oil-fired engines. C. Kapsenberg, 1964. boilers (Dutch). W. J. Taat, 1957. 60 S Natural frequencies of free vertical ship vibrations. C. B. Vreug- 25 S Experimental determination of damping, added mass and added denhil, 1964. mass moment of inertia of a shipmodel. J. Gerritsma, 1957. 61 S The distribution of the hydrodynamic forces on a heaving and 26 M Noise measurements and noise reduction in ships. G. J. van Os pitching shipmodel in still water. J. Gerritsma and W. Beukelman, and B. van Steenbrugge, 1957. 1964. 27 S Initial metacentric height of small seagoing ships and the in-62 C The mode of action of anti-fouling paints: Interaction between accuracy and unreliability of calculated curves of righting levers. anti-fouling paints and sea water. A. M. van Londen, 1964. J. W. Bonebakker, 1957. 63 M Corrosion in exhaust driven turbochargers on marine diesel 28 M Influence of piston temperature on piston fouling and pistonring engines using heavy fuels. R. W. Stuart Michell and V. A. Ogale, wear in diesel engines using residual fuels. H. Visser, 1959. 1965. 29 M The influence of hysteresis on the value of the modulus of rigid- 64 C Barnacle fouling on aged anti-fouling paints ; a survey of pertinent ity of steel. A. Hoppe and A. M. Hens, 1959. literature and some recent observations. P. de Wolf, 1964. 30 S An experimental analysis of shipmotions in longitudinal regular 65 S The lateral damping and added mass of a horizontally oscillating waves. J. Gerritsma, 1958. shipmodel. G. van Leeuwen, 1964. 31 M Model tests concerning damping coefficient and the increase in 66 SInvestigations into the strenght of ships' derricks. Part I. F. X. P the moment of inertia due to entrained water of ship's propellers. Soejadi, 1965. N. J. Visser, 1960. 67 SHeat-transfer in cargotanks of a 50,000 DWT tanker. D. J. van 32 S The effect of a keel on the rolling characteristics of a ship. der Heeden and L. L. Mulder, 1965. J. Gerritsma, 1959. 68 M Guide to the application of Method for calculation of cylinder 33 M The application of new physical methods in the examination of liner temperatures in diesel engines. H. W. van Tijen, 1965. lubricating oils (Contin. of report 17 M). R. N. M. A. Malotaux 69 M Stress measurements on a propeller model for a 42,000 DWT and F. van Zeggeren, 1960. tanker. R. Wereldsma, 1965. 34 S Acoustical principles in ship design. J. H. Janssen, 1959. 70 M Experiments on vibrating propeller models. R. Wereldsma, 1965. 35 S Shipmotions in longitudinal waves. J. Gerritsma, 1960. 71 S Research on bulbous bow ships. Part II. A. Still water perfor- 36 S Experimental determination of bending moments for three mod- mance of a 24,000 DWT bulkcarrier with a large bulbous bow. els of different fullness in regular waves. J. Ch. de Does, 1960. W. P. A. van Lammeren and J. J. Muntjewerf, 1965.