S. Samborski and H. Dębski
Lublin University of Technology, Poland
Keywords: composite laminate, mechanical coupling, FEM, VCCT, fracture toughness
The continuous fiber-reinforced polymer (CFRP) composites are commonly used in the aircraft industry due to their advantageous strength-to-weight ratio and the possibility to design the final product's mechanical properties. In particular, it applies to the mechanically coupled, multidirectional composite laminates. Unfortunately, this group of structural materials – equally wide and unexplored - remains prone to the occurrence of various defects, among which delamination is one of the most common damage forms. Propagation of the initiated defect can follow one of the three classical fracture modes, as well as their combinations. In case of the unidirectional (UD) CFRP laminates the fracture toughness tests are standardized by the ASTM and the ISO organizations - see ASTM D5528, ISO 15024, ISO 15114, ASTM D7905. However, the multidirectional laminates exhibit non-symmetry in the strain energy release rate (SERR) distribution along delamination front and different mode mixities. It impedes direct application of the standardized test methods with their data reduction scheme. Luckily, the finite element (FE) codes available today with the virtual crack closure technique (VCCT) enable proper planning of the experiments. The work paper was financially supported by the Ministerial Research Project No. DEC-2016/21/B/ST8/03160 financed by the Polish National Science Centre.