A numerical study on toughening laminated composite materials against delamination by initiating multiple interlaminar cracks is presented. Different configurations of interface toughening and weakening patches, that modify the interface properties at selected locations, are investigated as a way to trigger multiple delaminations. Both interface toughening and weakening patches can be configured to toughen the laminated material by initiating multiple delaminations. The initiation of multiple delaminations and the increase in toughness depend on the interface strengths and toughness of the patches. The main mechanisms behind the initiation of multiple delaminations for both cases are presented. An adaptive refinement method implemented within a Matlab Finite Element Analysis code that models the interfaces of the laminate with cohesive elements is used for the analyses. The adaptive refinement framework allows efficient analysis of multiple delaminations with very fine meshes at the wake of the crack tips. A discussion on the overall performance of the toughening concept, and the main parameters affecting the results, i.e. the length of the interface toughening or weakening patches, the distance of the substrate between the affected interfaces, and the material's mechanical properties, is carried out. The results presented in the paper show that a toughening effect against delamination can be achieved using interface toughening or weakening patches to onset multiple delaminations.

A numerical study on the feasibility of using patches of interface weakening or toughening material to trigger multiple delaminations toughening laminated composite structures against delamination is presented. The studies use an adaptive refinement formulation that uses cohesive elements to model delamination initiation and propagation. A DCB specimen is loaded under displacement control with two cohesive interfaces and a single pre-crack is introduced in one of them. The studies show that multiple delaminations can be initiated in the secondary originally uncracked interface by placing interface toughening patches at the main pre-cracked interface or interface weakening patches at the secondary one. The energy dissipation significantly increases compared to a standard DCB specimen featuring a single delamination.