Matrix-Dominated Damage in Notched Cross-Ply Composite Laminates: Experimental Observations

The matrix-dominated damage in three highly transparent notched cross-ply laminates with double-edge-semicircular notches were experimentally investigated under a monotonously increasing quasi-static tensile load. A newly designed computer controlled digital camera-video recorder system was successfully used to record the "real time" damage development due to the enhanced stresses around the notches. The damage states were quantitatively characterised as a function of the nominal strain or stress. It was observed that the notches have significant influences on the formation and propagation of the matrix-dominated subcritical damage. The damage states, which depend on the type of the laminate and the size of the notches, appeared to be highly reproducible. Instead of the conventional longitudinal cracks (splits) and the free-edge delamination in unnotched specimens, notch-induced splits (NISs) and notch-induced delamination (NID) were observed. The notches speed up the transverse damage growth in the areas near the notches, both in density and in length. The ultimate strength of the laminates with different notch size is significantly different, due to the diversities of the final failure mechanisms. The notch size and the laminar thickness are two key parameters determining the mode of the matrix damage and the final failure mechanisms of the laminates.