The current publication deals with the fracture toughness of polymeric multi-layer materials. In detail, the crack initiation and growth, crack arrest, and crack re-initiation of a multi-layer material are examined. The aim is to develop a numerical model for crack initiation and incremental crack growth of a three-layer single edge notched bending specimen that features one brittle layer in a plastically deforming matrix. Crack initiation and crack propagation are modeled using the finite fracture mechanics concept and the energy concept, respectively. No delamination is accounted for and the crack grows in one plane. The experimental observation of a crack initiating in the brittle layer (at 61.4 ± 2.2 N) while the initial crack is blunting can be reproduced well with the numerical model (at 63.6 N) with a difference of <3.6%. The model is ready to be used for different layups to predict toughening mechanisms and damage tolerances in multi-layer materials.
Keywords: crack initiation; elastic-plastic fracture mechanics; finite fracture mechanics; multi-layer materials; polymer materials.