Abstract
Damage initiation and growth under quasi-static and cyclic loading of cross-ply and multidirection laminates are presented. Damage states such as initiation of matrix cracking, onset of delamination and fiber fracture are identified. A linear relationship is found between the maximum applied cyclic stress and logarithm of number of cycles for each damage mode. The effect of transverse cracks on the stiffness reduction has been quantified. Again a linear relationship between the normalized stiffness and crack density is shown to be a good representation of the test data, irrespective of the applied maximum cyclic load. Under cyclic loading matrix cracks initiated at a lower stress compared to the quasi-static loading. Also higher crack densities were observed under cyclic loading than that of quasistatic one. A major difference between the two types of loading is in the initiation and growth of delamination.
