CompositesWorld
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16 CompositesWorld DESIGN & TESTING OCTOBER 2015 strain in the notched test section of the specimen. Te latter has important implications for accurate shear modulus determina- tions. To calculate the shear modulus, the average shear stress τ ave (calculated as the applied force divided by the specimen cross-sectional area between the notches) is divided by the measured shear strain γ, or G = τ ave /γ. Because the average shear stress is used in the shear modulus calculation, the average shear strain between the notch tips, γ ave , also must be used to obtain the correct shear modulus. When relatively small strain gages are centered between the notches, the measured shear strain can be 5-10% lower than γ ave when testing 0° unidirectional specimens. Terefore, the measured value of shear modulus will be 5-10% too high. Te use of cross- ply specimens results in greater shear strain uniformity and more accurate measurement of shear modulus. Note that if 0° unidirectional specimens are to be used, specialized shear strain gages 4 that extend the entire distance between the notch tips may be used to record accurate values for the average shear strain, γ ave , and thus the shear modulus, G. Te V-notched rail shear test fxture (Fig. 1b) loads the specimen through its faces, allowing for greater load transfer and the testing of higher shear strength composite laminates. Face-loading of the 76-mm long by 56-mm wide V-notched specimens is accomplished by gripping the outer 25 mm of each specimen end, using clamping bolts. Up to 500 MPa shear strengths have been obtained from [0/±45/90] ns quasi-isotropic and [±45] ns laminates 5 , but specimens must be kept relatively thin to avoid slipping in the grips. Te V-notched rail shear specimen also has a central test section that is three times larger than that of the Iosipescu specimen, allowing proper shear testing of relatively coarse textile composites with large unit cell sizes. Te test method also is suitable for unidirec- tional and cross-ply composite laminates. As with the Iosip- escu shear test, the use of cross-ply laminates is recommended to produce a robust specimen and a more uniform state of shear strain between the notches. Although the V-notched rail shear test fxture is capable of higher specimen loadings than the Iosipescu shear test fxture, there is increasing interest in testing the thicker, high-shear- strength laminates used in structural applications. For such Looking for the most compettve and performing soluton for increase your productvity? Nidaplast is your ideal partner for high strength, low weight and cost efectve sandwich panels NIDAPL AST LLC - 315 NW Peacock Blvd - Port St. Lucie - 34986, Florida – USA - contact : Tel : +1 772 342 4991 - Fax : +1 772 621 6393 - mdan@nidaplast.us - www.nidaplast.com 30 years of experience - Nidaplast innovates for daily applicatons - Nidaplast imagines the most performing concept in composites - Nidaplast ofers a wide range of honeycomb products as core material - Nidaplast ofers various ways of implementaton - Nidaplast has an important potental of development Building Wind turbine Transportaton Marine NIDAPLAST LLC 315 NW Peacock Blvd., Port St. Lucie, Florida 34986 USA Tel: +1.772.344.0034 • Fax: +1.772.934.3663 mdan@nidaplast.us • www.nidaplast.com The use of cross-ply specimens results in greater shear strain uniformity and more accurate measurement of shear modulus.