Fatigue Damage Evolution in Unidirectional CFRP

Cyclic tests were conducted on unidirectional carbon-epoxy composite specimens loaded at 45oto the fibre axis, using a stress ratio R (minimum/maximum stress)of 0.1. Matrix damage wasmonitored through measuring strain changes in the direction perpendicular to the fibres and inthe loading and transverse directions. Hysteresis loops were constructed for the loading,longitudinal, transverse and shear directions. Ratchetting of the loops indicated that cycliccreep in the matrix was dominant. A parameter based on cyclic creep allowed damageevolution to be described and fatigue life to be predicted.