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A comprehensive experimental study augmented by a finite-element analysis was performed to assess the influence of three Iosipescu shear test loading fixtures on the in-plane shear strain distribution in the specimen test section, and on the measured static shear modulus and shear strength of graphite-epoxy with different laminate layups. The three fixtures were designated WAF-1, WAF-2 (Wyoming asymmetric fixtures), and AFPB (asymmetric four-point bend). AS4/3501-6 graphite-epoxy laminates of [0°]n, [90°]n, [±45°]ns, [0/90°]ns, and [0°/±45°/90°]ns quasisotropic were used in the study. Additionally, isotropic specimens of a standard photoelastic resin were evaluated. The notch angle for all specimens in this study was 90°. Both photoelastic coatings and moire interferometry were used to determine the in-plane shear strain distribution in the test section.
The area of uniform shear strain was found to be small relative to the specimen size and depended on the laminae layup. Factors influencing scatter in the test results using the different fixtures are identified and discussed including the effect of edge and face tabs. Significant stresses on the notch flanks away from the test section were identified, which may initiate failure outside the test section.
composite materials, shear test, Iosipescu shear test, finite element, mechanical properties, test methods
Senior staff engineer, Hercules Aerospace Company, Magna, UT
Professor of mechanical engineering, California Polytechnic State University, San Luis Obispo, CA