The use of a characteristic damage variable in the study of transverse cracking development under fatigue loading in cross-ply laminates

A two dimensional shear lag analysis of a cracked cross-ply composite laminate subjected to uniaxial loading, taking into account residual thermal stresses, has been developed. This analysis has led us to introduce a characteristic non-dimensional damage variable η, which is a function of the crack density, material properties, and lamina stacking sequence. This analysis has been applied to a CFRP composite material (T300/914). The use of the characteristic damage variable has led to phenomenological laws that allow accurate prediction of the number of fatigue cycles necessary for the initiation of the first matrix cracks, and the kinetics of this damage, up to the “saturation” stage, in any cross-ply laminate subjected to a uniaxial fatigue loading.