Measurement of Textile Deformation by the Moiré Method

Measurement of Textile Deformation by the Moire Method

By Atsuko Osada*,Fumiko Nawata** and Masanobu Miki**

*Faculty of Domestic Science, Osaka International Universityfor Women * *Faculty of Human Science, Osaka International Universityfor Women,Moriguchi, Osaka

Based on the Journal of the Textile Machinery Society of Japan, Vol.46, No.5, T118-T124(1993)

Abstract In this study,we discuss the applicability of the Moire method for measuring the mechanical deformation of textile end-use products. The results can be summarized as follows: (1)The application of the Moire method made it possible to describe the 2-dimensional deformation of the distance between adjacent loop centers and the skew angle of loops of knitted fabric at any point. The case of tensile stress on knitted cotton fabric was reported. (2)The Moire method can thus be applied to detect the inhomogeneity ofloops and the skew angle,or the cover factor of knitted fabric. (3)The Moire method will offer some suggestions for improving the production and construction of knitted fabric,when the measuring systemis improved to get higher precision and further 3-dimensional measuring is applied.

1. Introduction In addition, thedeformation is also considered to be caused by mechanical force at the time of washing, and Since the consumer judges the purchase from the by the weight itself and so on. viewpoint of the "second quality" of the "textile end-use Therefore, we think it is extremely important that we products" such as (color, figure, design and so on), few know various problems concerning the shrinkage, d on- "claims" are done after using their purchases . However, gation, loss of shape, wrinkle and so on which is caused the consumer judges the purchase from the viewpoint of at the time of above-mentioned handling, and in order the primary quality such as (comfort, easy handling , loss that we prevent it beforehand, we check in detail, inves- of shapeand so on) of the textile end-use products, tigate conditions in mechanical deformation. claims are frequently done after using their purchases. Accordingly, we decide to apply the Moire method in Therefore, we interest in the investigations of its causes order to study these problems. The measurement by the and preventive measures for mechanical deformation, Moire method has various merits as follows : 1) Because which has the apparent characteristics, particularly dis- of noncontact measurement, there is no disturbance of tortion and slippage of yarn, loss of shape, bagging and the thing which is measured. 2) It is convenient that a so on. dynamic strain can be taken. 3) Because the strain distri- The cause of the deformation of this kind in the textile bution of the whole sample can be easily grasped through end-use products are mainly the plasticity deformation in the method, it is possible to check these deformation the distance between adjacent woven textured yarns or from macroscopic viewpoint. For these merits,it has been the distance between adjacent knitted loop centers and used for 2-dimensional deformation measurement of the crossing angle of the yarn structuring them. As to the metal and high polymeric material[1lbefore. But, there other factors, there are the residual deformation of the has been no case in which it was applied to 2-dimen- material itself and the deformation added at the time of sional deformation of the textile end-use products. cutting, sewing and finishing in manufacturing process of Moreover,it came to be utilized in 3-dimensional form these end-use products (for example, the deformation by measurement in the 1970"sand it began to be applied to cutting gap, seam slippage, unreasonable finish set and the field related to clothing : it is applied to body meas- so on). In addition, the deformation is also considered to urement[2I, a grasp of drape formE3I,baggingform[4I, be caused by the relaxation of stress given in such textile wrinkle form[51and so on. end-use products manufacturing processing. Moreover, Then, grasping 2-dimensional deformative condition the deformation is also considered to be caused by added and 3-dimensional deformative conditions of the textile external force in the case of both putting on and taking end-use products and at the same time applying the off clothing and also exercising. And, in the caseof using Moire method which has separately been used as above- a shoulder bag, distortion and slippage of yarn by which mentioned, we studied the deformation behavior of the an external load is concentrated on a shoulder and an arm. textile end-use products, and aimed to suggest for the

120 Journal of the Textile Machinery Society of Japan bsin0 c?o a2+b2-2abcos0 sink _ b sin 0 (3) ~<0 a2+b2-2ab cos 0

Figure 2 shows the distance between adjacent loop centers and the skew angle of loops in the knitted products for practical use, the former is represented by "a", the latter is represented by " 8 ". (The skew angle of loops as shown above is equal to the curve of wale.) Then, when applying the Moire method to the measurement of mechanical deformation of textile end-use products, a set of grating is assumed to be that which forms the knitted loops . The distance between gratings is assumed"the Fig. 1 The formation of Moire fringe distance between adjacent loop centers of knitted fabric": : master grating --- : Moire fringe which has the value of "a". And a set of the other grating -- - - - : loops grating is assumed a set ofimster grating which is given the a : distance of loops known distance between gratings. The distance between b : distance of master gratings gratings is assumed to be "the distance between master d : distance of Moire fringes 0 : skew angle of loops gratings" : which has the value of "b". By overlapping c5 : skew angle of Moire fringe these two sets ofgratings, the system which forms the Moire fringe is realized. Therefore, the relational equation (1),(3) in the formation of Moire fringe is solved by "a"( distance between improvememt of these consumption quality. adjacent loop centers of knitted fabric ), by " 6 "( skew Since the cotton knitted products recently came to be angle of loops ), then equation (4), (5) such as follows abundantly utilized in various uses such as outer wears are obtained. besides inner wears, the latent claims came to be obvious. When a plus sign in equation (4) is adopted, the restric- In this report, from this background we selected the cot- tion becomes as follows : ton knitted product as a sample. First of all, by applying bsa(q s0). the Moire method we study a possibility to grasp 2-di- mensionaldeformation condition of the sample given a simple stress through measuring both the distance betwen -+ 2d b cos ¢ + 1 a=b Cb/z adjacent loop centers and the skew angle of loops of d 2 (4) sine knitted fabric. ~Cb)2-1}2+4 b

2. Principle of Analysis 0=+sin-' d sin (5) The Moire fringes are detected by uneven intensity of light which is brought out when two sets of grating overlap at a certain angle.This is shown in Figure 1. The equation of the formation of Moire fringe is expressed by equation(1),(2)(0 s qS< r )[6l.

ab d= a2+b2-2ab cos 0 (1)

b sin 0 sin= (2) a2+b2-2ab cos 0

Fig. 2 The distance of loops and the skew angle In this report, we assume that - 7t/2 S q5 < ~z-2. Equa- of loops tion (2) becomes equation(3). (See the figure caption of Fig.l )

Vol. 40. No. 4 (1994) 121 The value of "b" in equation (4),(5) is distance between master gratings which was given in the beginning. The value of "d" in equation (4),(5) is the distance between Moire fringes measured from the formed Moire fringes, and the value of " q " is the skew angle of Moire fringe.Since these three values are known, the distance between adjacent loop centers (a) and the skew angle of loops ( 8 ): the factors in the mechanical deformation of knitted products, can be calculated. In this report, the experimental condition is as follows : bsa<1.5b. Therefore, in equation (4) including a plus-minus sign, a plus sign is adopted, then "a" and " e " can be calculated.

Fig. 4 The method to pick up many Moire fringes 3.Measuring Method on the same specimen (See the figure caption of Fig.l ) As shown Figure 1, if each fringe in two sets of fringes causing Moire fringe form is parallel, and, at the same time, each distance between gratings is unifom,the ample of the condition as follows : formed Moireefringes illustrate a well-regulated ar- b sa < 1.5b. rangement. Therefore, by shifting the master grating, the The measuring point is shown by the cross point of the distance between Moire fringes (d) and the skew angle of measured line and the Moire fringe. The skew angle of Moire fringe ( q ) can be measured at any point, and rea- Moire fringe is measured at each measuring point by the sonably these values are equal at all points. But,in the range as follows: -r/2<

122 Journal of the Textile Machinery Society of Japan greater angle, the number of the Moire fringes increases. But the Moire fringe does not clearly appear. As a result measurement becomes difficult. And,when the Moire fringe formed by the above-mentioned method is measured, the calculated distance between adjacent loop centers approaches practical value. But, the skew angle of loops needs the correction in the skew angle of the master grating (r). The corrected equation is shown by the equation (6).

0=-sin d sin +r (6) Fig. 6 The outline of the apparatus for experiment L : light S : specimen 4. Experiment G : master grating C : camera

4.1 Experimental material

A specimen was made of the home sewing machine as follows: Brother knitted machine Derika KH-120. The condition of the specimen is shown in Table 1. The specimen was dyedin black for easy detection of the Moire fringe. This treatment was done in order to use the transmission light for the measurement of Moirefringe. The specimen prepared thus was assumed to be a front neck line. The specimen was sewn by a home sewing machine. The polyester thread forknitted products was used as the sewing thread. The neck line was made with the bias- faced fabric. Figure 5 shows the outline of the sewn specimen.

Table 1 The condition of specimen

Fig. 7 The condition of fixed specimen

4.2 Experimental apparatus

Figure 6 shows the outline of the experimental apparatus. This is the apparatus with which the Moire fringe formed by setting up the master grating in front of the specimen was photographed from the side of the master grating in front of the specimen. The testing machine was "Simadzu AUTOGRAPH AG -500B" made by Simadzu Manufacturing Company Limted. The specimen was clamped with the grab on the testing machine. In this report, the master grating was the makeshift grating which was printed on the film of the overhead projector at intervals of every 1.24mm. In the optical system, parallel ray was appropriate to the principle of the formation of Moire fringe. However, in this report, the dif- Fig. 5 The outline of the sewed specimen fusion reflection ray was temporarily applied : fluores-

Vol. 40. No. 4 (1994) 123 cent lamp,white,15-Watt > 2. Consequently, the interval The above-mentioned matters shows that the knitted between the specimen and master grating is set as short loop conditions were almost the same throughout the as possible. area of the specimen. On the other hand, as the elongation of the specimen was increased by 5,10, 15 4.3 Experimental method ... %,respectively, the changes in the Moire fringes were detected. Some resulting change in the condition of the Experimentalprocedure was as follows :1) The speci- knitted loop of the specimen was estimated. Figure 9 men shown in Figure 5 was hung with the knitting nee- shows the Moire fringe of the same specimen in the dles of accessories of the above-mentioned knitting ma- condition of 25% tensile field along the vertical axis. The chine, and that was clamped with the grab on the above- measuring method of this Moire fringe (Figure 9) is mentioned testing machine such as in Figure 7. 2) The shown in accordance with the above-mentioned 4.3 in master grating was fixed by the upper grab at the angle order as follows : First, Figure 10 shows the tracing of of 15 with the horizontal line. 3) The Moire fringe of the Moire fringes in Figure 9. The lines shown the specimen in both non-stressand 5,10,15,20,25,30% with , , were the measured lines. Figures 11 to 13 tensile field condition along the vertical axis were photo- show the measured result on each measured line. In these graphed respectively. 4)The photographed both Moire figures, the abscissa shows the position of the measuring fringe and outline of the specimen were traced on the point on the measured line of the specimen, and the ordi- tracing paper. In this case, only the central part of Moire nate shows the distance between adjacent loop centers of fringe was traced in order to get its clear effect. 5) The knitted fabric and the skew angle of loop. In all measured lines were set in parallel with the master grat- cases,from Figures 11 to 13, the distance between adja- ing line at the angle throughout the area of the specimen. cent loop centers of knitted fabric doesn't show any great 6) The measurement was done with the method shown in above-mentioned 3.

Fig. 8 The Moire fringe under non-stress field of the specimen assumed neckline Fig. 10 The tracing figure of the Moire fringes on Fig.9

Fig. 9 The Moire fringe under 25% vertical axis tensile field condition of the specimen assumed neckline

4.4 Result

Figure 8 shows the Moire fringe of the specimen as- Fig. 11 The analysed result on measured lineO sumed to be the front neck line in non-stress field condi- ...... : distance of loops tion. The Moire fringes were detected almost uniformly. -A-A- : skew angle of loops

Journal of the Textile Machinery Society of Japan 124 5. Consideration

Until now, any examples in which the deformation of the knitted products is grasped by measuring the distance between adjacent loop centers and the skew angle of loop have not been seen except in this report. However,there already existed the idea in accordance with to thedistance between adjacent loop centers, and the skew angle of loop whichwas pointed out in this report. The former is the measuring method of the knitted fabric density with the densimeter. The latter is that of the bowing to be in "JIS L-1018 Testing Method for Knitted Fabrics". That is the method in which the shift of the wale line in a point to be about 1 meter ahead along a direction of wale of the knitted fabric is measured. However, in any measur- Fig. 12 The analysed result on measured lines ing methods the knitted products are regarded as uniform (See the figure caption of Fig.ll ) ones, so that it is impossible to measure at any local part. Therefore, the method in this report is thought to be useful with respect to the following matters. Both the distance between adjacent loop centers and the skew angle of loops of knitted fabric can be measured simultaneously. Moreover, local measurement in the knitted products is possible. Furthermore, applying the Moire method to the deformation measurement of the knitted products makes it possible not only to measure the 2-dimensional deformation shown in this report, but also to grasp the 3-dimensional deformation simultaneously. The above-mentioned matter is thought to be greatly useful in the viewpoint of measuring the deformation of the knitted products. But, the measuring method in this report leaves room for improvement asfollows : The process of the measure- Fig. 13 The analysed result on measured line® ment of the Moire fringe has the disadvantage that hand- (See the figure caption of Fig.l l ) work tracing of the Moire fringes and so on are neces- sary. In addition this method takes fairly long time for change depending on the position. But, in the vicinity of measuring. the apex of the neck line, the distance between adjacent loop centers of knitted fabric increases a little. This result 6. Conclusion is thought to be because of the stress concentration on the apex of the neck line. And, in the vicinity alongthe neck 1)The applying of Moire method to the 2-dimensional line, the distance between adjacent loop center of knitted deformation measurement of the knitted products makes fabric decreases.This result is thought to be caused by the it possible to measure the skew angle and the distance stressed loops on the diagonal alongthe neck line. On the between adjacent loop centers at any point of the other hand, the skew angle of loops is as follows: At the specimen. place approaching nearer the neck line, the skew angle of 2)By applying the Moire method, the inhomogeneity of knitted loop tends to increase. This phenomenon is loops is clearly detected, so this method can be applied to thought to be the result caused by the increase of the the inspection of the inhomogeneity of loops. Further, angle of the neck line in accordance with the elongation since this method can measure the skew angle and the of the specimen. From the above-mentioned matter, the distance between the loops, this method can be applied to result was obtained as follow : The 2-dimensional de- the measurement of the cover factor and the inspection formation in the case of tensile condition along the verti- of the skew angle of the knitted products. cal direction for the cotton knitted products can be 3)This method will offer some suggestions for improv- grasped by measuring the distance between adjacent loop ing the production and construction of the knitted fabric, centers and the skew angle of loops of knitted fabric. when the measuring of Moire fringe is improved to get

Vol. 40. No. 4 (1994) 125 higher precision, and computer image processing is ap- References plied to this measuring method and also further 3- dimensional measuring is combined with this method. [1IP.S.Theocarisand C.Hadjhossiph;Engineering 4)In this report, the measurement was carried out for Fracture Mechanics,12,241(1974) the knitted products. The deformation measurement of [2Higuchi,]Otsuka, Yamada and Ninomiya; J.Home the woven fabric, which has thegrating form, can also be Econ. Japan.,35,117(1984) applied to this method. [3ISuda and Takahashi; Jpn. Res. Assn. Text. End- Uses.,5,51(1983) (Acknowledgment) [4]Matsuoka, Nagae and Niwa; Japan. Res. Assn. Text. We would like to thank Mr.Shiro Okano of director of End-Uses.,25,502(1984) The Japan KnittingInspection Institute Foundation IslMatsuoka, Niwa and Nagae; Japan. Res. Assn. Text. (presently: The Japan Textile Products Quality and End-Uses., 25,34(1984) Technology Center) for valuable discussion. [6]Edited by Journal of the Machinery Society of Japan ; " Hikari -ouyou -kikai -keisoku -gi jyutsu",p.19 Asakura-syoten (1985)

126 Journal of the Textile Machinery Society of Japan