Experimental and analytical study of fatigue damage in notched graphite/epoxy laminates

Fatigue damage development in notched graphite/epoxy laminates is investigated in both compression and tension, with tested specimens being examined for damage type and location using light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. Comparison of observed delamination locations with finite element calculations indicates that both interlaminar shear and peel stresses must be considered when predicting delamination. Fatigue loading generally caused only small stiffness losses, and residual strengths were in all cases greater than, or equal to, the virgin strengths.