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-pl y laminates, (0/90(n)/0)(n = 4, 8, 12), were investigated at room temp erature and 80 degrees C. Materials systems used were roughened T800H/ 3631 and conventional T300/3601 carbon/epoxy composites. In situ obser vation of the microscopic failure process was conducted by using a sca nning acoustic microscope (SAM) and a scanning electron microscope (SE M) with instrumented tensile loading devices and by the replication te chnique. Progressive damage parameters such as the transverse crack de nsity and the delamination ratio were measured. Thermal residual strai ns which had important effects on the failure process were measured by the ply separation method. On the basis of the above data, a simple m odified shear-lag analysis including the thermal residual strains was conducted to obtain the transverse crack density as a function of lami nate strain, considering the constraint effect and the strength distri bution of the transverse layer. The analysis was also extended to the system containing delamination.