Fatigue Damage Evaluation through Stiffness Measurements in Boron-Epoxy Laminates

Abstract

Stiffness reductions, resulting from fatigue damage, were measured for unnotched [±45]_s, [0/90] _s, and [0/90/ ±45 ] _s boron/epoxy laminates. Deg radation in the various in-plane stiffnesses (E_xx, B_yy, G_xy) were measured using a combination of uniaxial tension, rail shear, and flexure tests. An attempt was made to predict stiffness loss at failure from a secant modulus criterion. Damage growth and stiffness loss were load-history dependent, hence, the secant modulus criterion is not a valid criterion for general application.