Fatigue behavior of notched carbon epoxy laminates during reversed cyclic loads

Abstract

The relationships between fatigue damage, stress redistribution, and residual stiffness and strength were investigated for notched graphite epoxy laminates during fulIy-reversed cyclic loads. Two material systems, AS4/3501-6 and AS4/1808, two lamination arrangements, (0,45,90,-45)s₄ and (0,45,0,-45)s₄, and two notch configurations, central hole and opposing semi-circular edge notches, were used to obtain a fundamental understanding of the fatigue effect in specimens under low and high cycle lifetimes. Damage was evaluated with penetrant-enhanced X-ray radiography and Iaminate deply. Tensile and compressive residual strengths were measured at three stages of damage development. A recently developed nondestructive testing technique, Stress Pattern Analysis by Thermal Emission, was implemented to obtain full-field measurements of surface stresses during damage initiation and growth. A new micromechanical theory of the adiabatic thermoelastic effect in Iaminated fiber composites was conceived to assist the interpretation of SPATE measurements.