An Assessment of the Double-Notch Shear Test For

Applied Composite Materials5: 289–304, 1998.© 1998Kluwer Academic Publishers. Printed in the Netherlands.

289

Erratum

An Assessment of the Double-Notch Shear Test forInterlaminar Shear Characterization of aUnidirectional Graphite/Epoxy under Static andFatigue Loading‡

MAHMOOD M. SHOKRIEH? and LARRY B. LESSARD??Department of Mechanical Engineering, McGill University, Montréal, Québec, Canada

(Received 5 August 1996; accepted 21 May 1997)

Abstract. This research explores a modified testing technique for measuring interlaminar shearproperties of orthotropic composite materials. An existing test method (double-notched test method)is examined here to characterize the interlaminar shear properties (strength and fatigue life) of aunidirectional ply under both static and fatigue loading conditions. No complicated fixture is requiredfor the testing method which is beneficial for fatigue testing of the materials. The testing methodis verified by a finite element technique where an optimized geometry for the specimen is found.AS4/3501-6 graphite/epoxy material is used in this study. The experimental results show that finalfailure occurs in the gage area for both static and fatigue loading conditions. Moreover, a reasonableamount of scatter for both the static strength and fatigue life is achieved.

Key words: composites, interlaminar shear test method, static, fatigue, characterization, double-notched test.

1. Introduction

Interlaminar shear strength is defined as the shear strength at rupture in whichthe plane of fracture is located between the layers of reinforcement of a plasticreinforced structure [1]. To measure the interlaminar shear strength of a material,a reliable and simple method must be found. The method must also be able todetermine fatigue properties of the material (such as fatigue life). In this research,a test method is devised to measure interlaminar shear strength (Syz) and fatiguelife of a unidirectional ply under interlaminar shear stress as a necessary contribu-tion to a complete set of three-dimensional material properties. Figure 1 depicts a

‡ Previously published inApplied Composite Materials5(1), 1998, 49–64. However, much to ourregret, due to a technical problem the last page of the article was omitted.? PhD Student?? Assistant Professor

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290 MAHMOOD M. SHOKRIEH AND LARRY B. LESSARD

Figure 1. Three-dimensional geometry of a layer of composite material.

specially orthotropic material showing that there are essentially two planes whichhave similar material appearance (x-y andx-z), thus shear strengthSxy andSxz aresimilar. The shear strengthSyz is different and tends to be weaker than the othertwo shear strengths. Accordingly, the test methods suitable for measuringSxy andSxz are not applicable toSyz, thus another test method must be utilized.

The four main methods for determining the interlaminar shear strength of amaterial are the short beam shear test [2–6], the four-point shear test [6, 7], theIosipescu test [6, 8–11] and the notched coupon [1, 6, 12–15]. Different authorshave shown that the short beam shear test [2–6], and four point shear test [6, 7]are not reliable test methods. Moreover, a pure interlaminar shear stress can not beinduced which results in a complex fracture [8]. Also to measure the interlaminarshear strength (Syz), by utilizing these methods, a 90◦ unidirectional ply must beused. It is clear that a 90◦ unidirectional ply can fail in matrix failure mode, causedby σyy, before failure ever happens under interlaminar shear stressσyz. Thereforeit is very difficult to use these methods to measure the interlaminar shear strength(Syz).

The Iosipescu testing method has been examined extensively [6, 8–11]. Manyinvestigators verified the Iosipescu testing method as a highly effective and reliablemethod. However measuring the interlaminar shear strength (Syz) of a unidirec-tional ply by this method is difficult. Notably, the fixture can be damaged duringfatigue tests. Furthermore, the type of specimen needed is complicated, as seen bytests performed by Gipple and Hoyns [16] for measuring the interlaminar shearstiffness and strength of a unidirectional AS4/3501-6 material system.

Unlike the Iosipescu test, the double-notched test method requires no extensiveset-up or fixture and the specimen (Figure 2) is simple. These features make thedouble-notched test method attractive for fatigue testing. Markham and Dawson[12] performed a study of the notched coupon test and they concluded that thespecimen always fails in shear. They also reported consistent results with fractureoccurring in a single plane unlike the complex fracture occurring with the short

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UNIDIRECTIONAL GRAPHITE/EPOXY UNDER STATIC AND FATIGUE LOADING 291

Figure 2. Specimen dimensions (all configurations are possible by varying notch depthd,notch widthw, notch distancel and specimen thicknesst , according to Table I).

beam shear test. These results and the simplicity of the testing method in staticand fatigue loading conditions led to the belief that this may be an appropriatetesting method. However, there are some disadvantages mentioned in the literatureabout this testing method which are summarized in the following. Munjal [6] foundthat it was difficult to control the notch depth in the notched coupon test and thushad quite a scatter in the results. Chiao et al. [8] postulated that the shear strengthdata obtained in by this testing method was lower than that by other methods.Tarnopol’skii and Kincis [13] discussed the disadvantages of this test method bytesting samples with nonsymmetrically placed notches. Fixtures for preventionof specimen bending were necessary and the results were highly sensitive to theaccuracy of cutting the notches.

This study examines all the disadvantages postulated by other authors, andshows that all these difficulties can be eliminated by selecting a proper specimengeometry found by finite element analysis.

2. Description of the Problem

The double-notched specimen test is selected as suggested in the ASTM StandardD 3846-79 reapproved 1985 [14] for reinforced plastics and further investigated inthe ASTM Standard D 2733-70 [1] for reinforced plastics at elevated temperatures.This standard suggests two methods for finding shear strengths. Method A, testedin compression, requires that a clamp be placed at the midsection of the specimenfor a distance of 65 mm and tightened evenly so as not to damage the specimen.This should result in an interlaminar shear-type failure. Method B does not requirea clamp and is tested in tension to failure. Method A will be referred to as clampedand method B will be referred to as unclamped. It is desired to study the behaviourof a double-notched sample under these two testing conditions. This is performedby applying a finite element analysis and through an experimental program.

The behaviour of the double-lap shear specimen is similar to the notched coupon,with interlaminar shear failure being introduced at the interface of two layers. Pre-vious results [15] showed a non uniform stress region over the failed area but wereinfluenced by large and almost equal shear stress concentrations at each end of thefailure plane resulting in a variation in the shear strength. It is thus desired to see

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Table I. Different configurations for the double-notched specimen.

a (mm) W (mm) d (mm) l (mm) t (mm)

w1, w2, w3 66.67 1.13, 2.29, 4.57 1.59 6.35 3.17

d1, d2, d3 66.67 2.29 1.52, 1.59, 1.66 6.35 3.17

l1 63.50 2.29 1.59 12.70 3.17

l2 66.67 2.29 1.59 6.35 3.17

l3 68.26 2.29 1.59 3.175 3.17

t16, t24, t32 66.67 2.29 1.06, 1.59, 2.17 6.35 2.12, 3.18, 4.33

whether these results also occur in a notched specimen and what effect variationsof the notch size has on the results.

In order to induce pure interlaminar shear (σyz) in the gage area of a double-notched specimen, a 90-degree lay-up must be used. However, the material isweaker in matrix tension than in interlaminar shear loading. Therefore, a ten-sile load applied to a double-notch specimen with 90-degree lay-up results in atensile matrix failure prior to failure in interlaminar shear. There are two solu-tions to this problem. The first solution is to use (0/90)s laminate instead of a90-degree lay-up. However, experimental evidence show that failure for this con-figuration occurs between the 0 and 90 degree layers. On the other hand, it isknown that the strength of the material in matrix compression loading is higherthan in matrix tension. Therefore, the second solution is to apply a compressiveload instead of a tensile load on a 90-degree lay-up. However, the disadvantageof the second method is the possibility of out-of-plane deformation, which can beavoided by using clamps. The clamp used in this study and clamp dimensions areshown in Figure 3. Various testing programs are also analyzed, including usinga specimen of pure 90 degree layers or a hybrid of 90 degree layers being sup-ported by 0 degree layers. Analysis is also performed of whether better resultsare obtained from testing the sample in tension or compression, with or withoutclamp.

The specimens of dimensions as given in Figure 2 and Table I were consideredfor analysis. The coupon was a laminated composite plate consisting of 16, 24 or32 layers. The composite plate configuration was (9016), (9024) or (9032) in theanalysis.

The effect of notch width was first examined by Tarnopol’skii et al. [13] whostated that the double-notch shear test is very sensitive to the accuracy of cuttingthe notches. To examine this difficulty, three different widths:w1, w2, andw3 areanalyzed in this study. Another disadvantage of the double-notched shear test givenby Munjal [6] and Chiao et al. [8], is said to be the difficulty in accurately cutting

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Figure 3. Clamp used to eliminate the out-of-place deformation (dimensions are in mm).

the notches to the prescribed depth (see Figure 2). Thus a study was undertaken toanalyze the depth effect by testing three different notch depths:d1, d2, andd3. Thesedepths correspond to half of the thickness of the specimen, an overcut (too deep),or an undercut (too shallow). The distance at which the notches are cut (see ‘l’ inFigure 2) is also variable due to the difficulty in machining the specimen accurately.Thus three distances between the notches were examined:l1, l2, andl3. The finalanalysis was to determine the effect of the specimen thickness. Three specimenthicknesses were examined:t16, t24, andt32, corresponding to either 16, 24, or 32

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plies. Due to the difficulty in manufacturing thick specimens, more than 32 plieswould not be feasible. Less than 16 plies, was also undesirable due to sensitivity toexternal effects, including out-of-plane deformation. Different configurations forthe notched specimen are summarized in Table I.

The material used in this study is AS4/3501-6 with the following materialproperties: longitudinal modulus (Exx = 150 GPa), transverse or normal modulus(Eyy = Ezz = 8 GPa), in-plane shear modulus (Exy = Ezx = 5 GPa), out-of-planeshear modulus (Eyz = 3 GPa, calculated by transversely isotropic assumption),Poisson’s ratios (νxy = 0.3, measured) and (νxz = νyz = 0.3, assumed), trans-verse or normal tensile strength (Yt = Zt = 53.98 MPa), transverse or normalcompressive strength (Yc = Zc = 203.69 MPa) and the interlaminar shear strength(Syz = 42 MPa, as measured in this study). The material properties were measuredin the Composite Materials Laboratory of McGill University.

3. Finite Element Analysis

To predict the behaviour of the notched coupon, a stress analysis is performed usingthe SDRC I-DEAS finite element software [17]. The specimen was modeled usingeight-node quadrilateral isoparametric elements. Since the stresses between the twonotches are of main interest, elements were concentrated in this area. Even thoughshear stresses are of great importance to the problem at hand, nonlinear materialproperties were not considered in this work. The softening effect of nonlinear shearstress/strain behaviour could have an impact on the final stress analysis.

3.1. BOUNDARY CONDITIONS

By considering plane stress conditions iny-z plane (Figure 2), a cross section ofthe specimen can be modeled by two-dimensional finite elements. Since there isno symmetry with respect toy-axis, the entire cross section of the specimen iny-z plane is modeled. The boundary conditions for the unclamped case are shownin Figure 4(a). One end of the specimen is fixed and an edge pressure is appliedto the thickness at the other end. Moreover, to simulate the gripped ends of thetesting machine, the displacement of the nodes in the gripped area were fixed inz-direction (Figure 4(a)).

The displacement field of the nodes in the gauge area is examined for theunclamped model (Figure 4(b)). The out-of-plane deformation, observed by fi-nite element analysis and by experimental techniques, is due to the antisymmetricgeometry of the specimen. To eliminate this behaviour, a simple clamp (Figure 3) isused. To simulate the clamped case in the finite element model, fixed displacementboundary conditions inz-direction are applied on appropriate nodes in the clampedregion (Figure 4(c)). Note that not all nodes under the clamped area are fixed.The induced bending due to loading means that only some parts of the clamp are

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Figure 4. Load and displacement boundary conditions.

applying pressure to the specimen to keep it from bending. The appropriate nodeswere found by an iterative process.

3.2. RESULTS OF FINITE ELEMENT ANALYSIS

The results of the finite element analysis are presented here for various notchwidths, depths, lengths and specimen thicknesses.

3.2.1. Loading Analysis

ASTM Standard D 2733-70 [1] suggests applying tensile loading on the notchedspecimen with or without a clamp (method A and B). The specimen in tensioncreated positiveσyy andσzz stresses whereas the specimen in compression creatednegativeσyy andσzz stresses. Since the material in the matrix direction is weakerin tension than in compression, it is desired to keep the normal stresses negative sothat they do not cause failure. Thus the compression version of the test was chosen.The results of the stress analysis of the specimen with or without a clamp undercompressive loading are shown in Figure 5. The stresses in the gage area, betweennotches, from point A to B (Figure 2) are plotted (Figure 5). The results indicatethat theσyy andσzz stresses in the gage area were reduced by adding the clamp andthe stress concentrations at the notch tips were reduced. As shown in this figure,the stresses are normalized with respect to their related strengths. To normalize

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Figure 5. Stress analysis of clamped and unclamped specimen.

Figure 6. The results of stress analysis for different notch widths.

σyy andσzz stresses, they were divided by the strength in transverse direction (Y )which is assumed to be equal to the strength in normal direction (Z). The tensilestresses are normalized by tensile strength and compressive stresses are normalizedby compressive strength. The interlaminar shear stress (σyz) is normalized by theinterlaminar shear strength. Theσyz stress exhibited the same behaviour with lowerstress concentrations at the notches and adding the clamp increased the shear stressin the gage area which is favored. With the clamp, interlaminar shear stress (σyz)becomes the dominant stress, thus most likely to cause failure. The clamped speci-men or method A tested in compression is thus the preferred case and is consideredfrom here on.

3.2.2. Effect of the Notch Width

The effect of the notch widthsw1,w2 andw3 was examined. Three different models(w1,w2 andw3) are considered with dimensions given in Figure 2 and Table I. Theresults of stress analysis for the clamped conditions show that the variation of thenotch width does not alter theσyy, σzz andσyz stresses significantly. For example,

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Figure 7. The results of stress analysis for different notch depths (overcutting and exact givenearly identical stress results).

the variation ofσzz for the three models is shown in Figure 6. This indicates thatthe notch width does not have an important influence on specimen strength.

3.2.3. Effect of the Notch Depth

The effect of the notch depthsd1, d2 andd3 was examined. Three different models(d1, d2 andd3) are considered with dimensions given in Figure 2 and Table I. Itwould seem likely that if the depth of the notch is more than half the depth ofthe specimen, or overcut, then bending stresses should occur in the gauge area.Also, if the depth of the notch is less than half the depth of the specimen, orundercut, then compressive stresses should occur in the gauge area. To examine theeffect of the notch depth, stress analyses for different notch depths are performedand it was determined that the change of depth did not effect the stresses in thegauge area, but alters the normal stressσzz near the notch locations (Figure 7).Undercutting causes higher magnitudes ofσzz normal stress at the notch location.Also it causes higher positiveσzz just inside the notch location which can lead topremature failure. Therefore, it is concluded that undercutting should be avoidedduring manufacturing. There is no significant change in the behaviour of transversestress (σyy) and interlaminar shear stress (σyz) with varying the notch depth.

3.2.4. Effect of the Length Between Notches

The effect of the length between notches was studied. Three different models (l1, l2andl3) are considered with dimensions given in Figure 2 and Table I. The results ofthe stress analysis indicate that if the distance between the notches is too close thenhighσyy andσzz stresses exist and the interlaminar shear stress,σyz, also increases.Normal and shear stresses are lowered by increasing the notch length. The variationof σzz for three cases is shown in Figure 8. Therefore, a proper notch length can beselected by examining the transverse and normal stresses (σyy andσzz) comparedto the strength of the material in these directions. Although doubling or halving

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Figure 8. The results of stress analysis for different notch lengths.

Figure 9. The results of stress analysis for different specimen thickness.

the notch length changes the state of stress, however the state of stress is not verysensitive to small variations of the notch length. Therefore the effect of a smallvariation of the notch length about a nominal value is not critical.

3.2.5. Effect of the Specimen Thickness

The specimen thickness effect was then investigated. For this study, three thick-nesses were examined which correspond tot16, t24, and t32, or 16 plies, 24 pliesand 32 plies. The dimensions are given in Figure 2 and Table I. It was determinedthat by increasing the amount of layers the transverse and normal stresses (σyy andσzz) remained the same. However the interlaminar shear stress (σyz) increases withincreasing the number of plies (Figure 9). It is concluded that to perform a bettertest, the number of plies should be as high as possible.

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3.2.6. Summary of Theoretical Findings

Based on the finite element analysis of different samples, the (9024) lay-up witha notch width ofw = 2.286 mm, notch depth ofd = 1.5875 mm, notch distanceof l = 6.35 mm, and total length ofL = 139.7 mm (Figure 2) was selected forthe experimental studies. It is also recommended that the notches be cut exactly(neither undercut nor overcut).

4. Experimental Program

To examine the analytical study an experimental program is conducted. The de-scription of the experimental setup and the results are explained in the followingsections.

4.1. MANUFACTURING OF SPECIMENS

The specimens used in this research were made of unidirectional AS4/3501-6. Theunidirectional prepreg sheets were aligned and processed in an autoclave. Theindividual specimens were then cut from the sheets to the length and width asdescribed in Figure 2 using a diamond impregnated saw. A critical aspect of themanufacturing was the cutting of the notches. Since some tolerance exists in thethickness from the curing process, the average thickness of the gage area of eachspecimen was found and divided in half. After clamping the specimen into a millingmachine the depth was then cut into the specimen at one end using a fast cuttingspeed (1500 rpm) and small depth increments to reduce microcracking. The sameprocess was then used on the other side to a depth of the total thickness minus thedepth of the existing notch. This ensured no overcutting of the notches.

4.2. EXPERIMENTAL SETUP

Tests were performed using an MTS 810 testing system, equipped with hydraulicgrips and computerized for data acquisition. Displacement and load were moni-tored for static experiments. In fatigue tests, maximum and minimum displace-ment, load as well as number of cycles were monitored. Static tests were per-formed under displacement control, while the fatigue tests were carried out underload control conditions. To avoid temperature effects, which could degrade thematerial properties, fatigue tests were performed at frequencies less than 10 Hz.All tests were performed in ambient temperature. The simple clamp was used toeliminate the out-of-plane deformation caused by the antisymmetric geometry ofthe specimen as described in Section 3.1 (see Figure 3). The nuts of the clamp weretightened by using a torque wrench to 0.113+ 0.000, −0.028 nm.

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(a) thickness too small

(b) overcut notches

(c) undercut notches

Figure 10. Final static failure mode of double-notched specimen (overcut and undercut) with(90)24 configuration.

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Figure 11. Final static failure mode of double-notched specimen (exact cut) with (90)24configuration.

4.3. TEST RESULTS

In the following sections, the results of experiments to verify the results of thefinite element analysis are summarized. Moreover, the results of static and fa-tigue characterization of AS4/3501-6 graphite/epoxy unidirectional material underinterlaminar shear stress are presented.

4.3.1. Verification of the Finite Element Results

To verify the results of the finite element study, an experimental program is con-ducted. Several static tests on double-notched specimens yielded unsuccessful re-sults, three of which are shown in Figure 10. Figure 10(a) shows the result of atest where the thickness was too small, i.e., the (90)16 configuration. As shown, thespecimen failed at the notch location rather than on the line connecting the notches.In Figures 10(b) and 10(c), thicker (90)24 samples are examined and overcuttingand undercutting are studied. As shown, failure occurs near the location of stressconcentrations and correct modes of failure in the gage area are not achieved forthese cases. Finally, samples with (90)24 configurations are manufactured by theexact cut procedure explained in Section 4.1, and tested under static loading con-ditions. The test result is shown in Figure 11. As shown, the specimen failed underinterlaminar shear stress, right in the gage area. The successful mode of failurefor this configuration verifies the results obtained by finite element analysis. Byachieving the successful mode of failure using the (90)24 ply specimens, sampleswith (90)32 configurations need not be manufactured.

4.3.2. Characterization of AS4/3501-6 Graphite/Epoxy Unidirectional Material

The results of static experiments for measuring the interlaminar strength of thematerial under out-of-plane shear loading using (9024) specimens are summarized.The results are shown in Figure 12, compared with the results of Gipple and Hoyns

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Figure 12. Static strength measurements for out-of-plane shear.

Figure 13. Final fatigue failure mode of double-notched specimen (exact cut) with (90)24configuration.

[16] using the Iosipescu method. The average magnitude for the interlaminar shearstrength is about 42 MPa which is about 30% higher than that of measured byGipple and Hoyns [16]. By considering the reasonable standard deviation achieved,it is concluded the experimental scatter is acceptable and test method is reliable formeasuring the interlaminar shear strength of the material.

Fatigue experiments were performed under load control conditions and the fa-tigue load was applied in a sinusoidal form. The fatigue tests were loaded withmaximum stress equal to 80% of the maximum strength, stress ratio (κ = σmin/σmax)equal to 0.1, and frequency between 1 to 10 Hz. An edge view picture of a speci-men, failed under out-of-plane shear fatigue loading, is shown in Figure 13. Notethat this type of test also shows a correct mode of failure, along the shear planebetween the notches.

The fatigue life of the material was measured for different samples by applyingthe maximum interlaminar shear stress (σyz) equal to various percentages of the

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Figure 14. Results of fatigue life tests.

maximum interlaminar shear strength and stress ratio equal to 0.1. Tests werecontinued until catastrophic failure was achieved. The results of fatigue life testsare shown in Figure 14. It is clear that to fully characterize the interlaminar shearfatigue properties of the material (e.g., fatigue life and residual strength) more testsmust be performed at different maximum stress and various stress ratios. Althougha limited number of fatigue tests are shown, a reasonable scatter was achievedwhich shows the reliability of the test method.

5. Conclusions

The double-notched test method is verified as a simple and reliable test methodto measure the interlaminar shear properties of composite materials under staticand fatigue loading conditions. No complicated fixture is required for this methodwhich is greatly beneficial in fatigue testing of the materials. Out-of-plane defor-mation, due to the antisymmetric geometry of the specimen, can be eliminated byusing a simple clamp. The results of a stress analysis, using a finite element tech-nique, of the double-notched specimen show that by selecting the proper geometry,a relatively uniform state of interlaminar shear stress (σyz) can be achieved in thegage area. Also, results show the magnitudes of the other stresses in the gage lengthregion (σyy andσzz) are not as critical compared to interlaminar shear stress (σyz).Tested specimens confirm that a reliable geometry has been found for further test-ing. The failed specimens under static and fatigue loading conditions show that thecorrect final failure mode occurs in the gage area. The results of the experimentalstudies for static and fatigue cases show reasonable scatter for the magnitude ofstatic strength and fatigue life of the material, which confirm the reliability of thetest method.

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Acknowledgements

The authors would like to thank graduate students Ms. Olivia P. Eilers, and Mr.Peter Kotsiopriftis for their help during the course of this study.

References

1. ASTM Designation D-2733-70, ‘Interlaminar shear strength of structural reinforced plastics atelevated temperatures’,ASTM Designation, 1970, 773–776.

2. ASTM Designation D-2344-76, ‘Apparent horizontal shear strength of reinforced plastics byshort beam method’,ASTM Designation, 1976, 361–364.

3. ASTM Designation D-2344-84 (Reapproved 1989), ‘Standard test method for apparent inter-laminar shear strength of parallel fiber composites by short-beam method’,ASTM Designation,1989, 43–45.

4. Ewins, P. D., ‘Techniques for measuring the mechanical properties of composite materials’,Composite-Standards Testing and Design, National Physical Laboratory, 1974, pp. 144–154.

5. Whitney, J. M. and Browning, C. E., ‘On short-beam shear tests for composite materials’,Experimental Mechanics25, 1985, 294–300.

6. Munjal, A. K., ‘Test methods for determining design allowables for fiber reinforced com-posites’, inTest Methods for Design Allowables for Fiber Composites, ASTM STP 1003,C. C. Chamis and K. L. Reifsnider (eds.), 1989, 93–110.

7. Sideridis, E., Ashton, J. N. and Kitching, R., ‘Measurement of the interlaminar shear strengthof glass-reinforced plastics of different construction using the off-axis four-point bending test’,Composite Structures18, 1991, 139–161.

8. Chiao, C. C., Moore, R. L. and Chiao, T. T., ‘Measurement of shear properties of fibrecomposites, Part 1. Evaluation of test methods’,Composites, 1977, 161–169.

9. Adams D. F. and Walrath, D. E., ‘Current status of the Iosipescu shear test method’,J.Composite Materials21, 1987, 494–507.

10. Ho, H., Tsai, M. Y., Morton, J. and Farley, G. L., ‘Numerical analysis of the Iosipescu specimenfor composite materials’,Composites Science and Technology46(2), 1993, 115–128.

11. Chang, F. K., Tang, J. M. and Peterson, D. G., ‘Effect of testing methods on the shearstrength distribution in laminated composites’,J. Reinforced Plastics and Composites6(4),1987, 304–318.

12. Markham M. F. and Dawson, D., ‘Interlaminar shear strength of fibre-reinforced composites’,Composites, 1975, 173–176.

13. Tarnopol’skii, Y. M. and Kincis, T., ‘Method of static testing for composites’, inHandbook ofComposites, Vol. 3, Mechanics of Composite Materials, Chap. 5, G. P. Sendeckyj (ed.), 1985,215–275.

14. ASTM Designation D-3846-79 (Reapproved 1985), ‘Standard test method for in-plane shearstrength of reinforced plastics’,ASTM Designation, 1985, 208–210.

15. Harding, J. and Li, Y. L., ‘Determination of interlaminar shear strength for glass/epoxy andcarbon/epoxy laminates at impact rates of strain’,Composites Science and Technology, 1992,161–171.

16. Gipple, K. L. and Hoyns, D., Measurement of the out-of-plane shear response of thick sectioncomposite materials using the V-notched beam specimen’,J. Composite Materials28(6), 1994,543–572.

17. SDRC I-DEAS, version VI, Integrated design engineering software,Structural DynamicResearch Corporation, 1991.

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An Assessment of the Double-Notch Shear Test For