Fracture Toughness Analysis of Non-Conventional Specimens: Some Key Issues

The specimens used to characterize the interfacial fracture toughness may be grouped as conventional and non-conventional. We call conventional a specimen cut from, for example, a symmetric composite or a similar adhesive joint. Analyzing the fracture toughness using conventional specimens is a common practice guided by existing standards. In contrast, we call non-conventional a specimen resulting from, for instance, bi-material joints, thin laminates that need to be stiffened before testing, or laminates with an elastically coupled behavior or residual stresses. Here, we collect such cases of peculiar specimens and highlight issues related to the following three steps of the process of fracture toughness analysis: specimen design, testing, and data reduction. Our particular focus is on making suggestions for a proper evaluation of the fracture toughness.