JUL 2018


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11 Combined Load Shear Testing ultimate shear strength. Additionally, predicted shear strengths are highly dependent on the ply failure theory used. As an example, combined loading shear testing and lami- nated plate theory strength analyses were performed using a [0/±45/90] 4S quasi-isotropic carbon fiber/epoxy laminate. e laminate shear strength was predicted using three ply-failure theories: maximum strain, Tsai-Wu and Hashin. Ply damage produced during incremental shear loading was modeled by reducing associated stiffness properties of the damaged ply 4 . e three failure theories predicted ply-level damage initiating at applied shear stress levels of 250-443 MPa. e ultimate shear strength measured from shear testing was 346 MPa 3 , whereas the predicted strengths were 250-564 MPa. e post-failure condition of the quasi-isotropic shear speci- mens (Fig. 3, p. 10) showed a complex failure mode, with different failure planes produced in the various ply orientations. Knowing that the maximum shear stress is produced on the vertical plane connecting the V-notches, it is logical to expect that a proper shear failure would occur on this vertical plane. However, shear loading of a multidirectional laminate produces a complex, multi- axial stress state that is different for each ply orientation. us, the rather complex failure mode observed in the quasi-isotropic shear specimen is less surprising. Interestingly, isotropic materials also can provide somewhat unexpected failures under shear loading. For example, Fig. 4 (p. 10) shows the post-test condition of a V-notched epoxy shear specimen. e specimen failed along 45° planes, which, as shown previously (Fig. 2b, p. 10), is the plane on which the maximum tensile stress occurs. us, even some isotropic materials do not fail on the plane of maximum shear stress when subjected to shear loading. REFERENCES 1 ASTM D5379/D5379M-12, "Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method," ASTM International (W. Conshohocken, PA, US), 2012 (first issued in 1993). 2 ASTM D7078/D7078M-12, "Standard Test Method for Shear Properties of Composite Materials by the V-Notched Rail Shear Method," ASTM International (W. Conshohocken, PA, US), 2012 (first issued in 2005). 3 Litz, D. J. "Development of the Combined Loading Shear Test Method and Shear Strain Measurement in the V-notched Rail Shear Test," M.S. Thesis, Department. of Mechanical Engineering, University of Utah, 2012. 4 Gibson, R. F. "Principles of Composite Material Mechanics," 4 th Edition, CRC Press, 2016. ABOUT THE AUTHOR Dr. Daniel O. Adams is a professor of mechanical engineering and has been the director for 21 years of the Composite Mechanics Laboratory at the University of Utah and vice president of Wyoming Test Fixtures Inc. (Salt Lake City, UT, US). He holds a BS in mechanical engineering and an MS and Ph.D in engineering mechanics. Adams has a combined 38 years of academic/ industry experience in the composite materials field. He has published more than 120 technical papers, is vice-chair of ASTM Committee D30 on Composite Materials and co-chair of the Testing Committee for the Composite Materials Handbook (CMH-17). He regularly provides testing seminars and consulting services to the composites industry. Preferred by manufacturers of FAA certifi ed airframes, space launch, rotorcraft, and UAV structures •

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