Transverse Shear Stiffness of T300/5208 Graphite-Epoxy in Simple Bending

Evaluation of the complete set of elastic constants of a graphite/epoxy laminate, including the transverse shear moduli, was achieved by conducting tension, compression, and bending tests on square-section specimens cut 0° and 90° to the fiber axis from 64-ply unidirectional T300/5208 laminate. Axial test specimens were instrumented with tee gages to obtain data on ex tensional moduli and Poisson's ratios. Bending deflections were analyzed using rigorous finite difference solutions for stress distribution to derive the shear moduli along with the extensional moduli acting in bending. A self- consistent set of properties was determined which established the material as being transversely isotropic and conforming to the linear theory of elasticity. The values obtained for the elastic constants were in good agreement with published data except for the in-plane shear modulus, which was somewhat lower than indicated by other test methods. Calculations of the Timoshenko shear coefficient indicated a large variation with fiber orientation and span.