Effects of matrix cracks on delamination of composite laminates subjected to low-velocity impact

This paper investigates delamination mechanisms of composite laminates subjected to low-velocity impact. To obtain delamination data between plies with different fiber orientations, thermal-deply tests were conducted on quasi-isotropic laminates after low-velocity impact. Regularities of delamination positions in different interfaces as well as the matrix cracks distribution through the laminate thickness were analyzed. It is found that delamination positions are influenced by matrix cracks and the distribution of matrix cracks is determined by the out-of-plane shear stress distribution. To illustrate the formation process of delamination, a novel micro-block finite element model was established. It is revealed that due to the interaction between adjacent cracks, inter-laminar cracks growing towards each other show higher stress intensity factors and are thus more likely to form delamination. This crack propagation pattern eventually leads to the formation of two centrosymmetric fan-shaped delaminations in each interface.