IN-SITU OBSERVATION AND PROBABILISTIC PREDICTION OF MICROSCOPIC FAILURE PROCESSES IN CFRP CROSS-PLY LAMINATES

The microscopic failure processes in three different types of cross-ply laminates, (0/90(n)/0)(n = 4, 8, 12), were investigated at room temperature and 80 degrees C. Materials systems used were roughened T800H/3631 and conventional T300/3601 carbon/epoxy composites. In situ observation of the microscopic failure process was conducted by using a scanning acoustic microscope (SAM) and a scanning electron microscope (SEM) with instrumented tensile loading devices and by the replication technique. Progressive damage parameters such as the transverse crack density and the delamination ratio were measured. Thermal residual strains which had important effects on the failure process were measured by the ply separation method. On the basis of the above data, a simple modified shear-lag analysis including the thermal residual strains was conducted to obtain the transverse crack density as a function of laminate strain, considering the constraint effect and the strength distribution of the transverse layer. The analysis was also extended to the system containing delamination.