Improving the crack propagation response of layered and bonded structures through dissipation mechanisms at different length scales

Abstract

The wide use of layered and bonded parts in structural applications is limited by the brittle crack propagation response of the weak interface zones. A vast body of literature has focused on the improvement of the bond properties, often focusing exclusively on the increase of fracture toughness and without a detailed definition of the design requirements in terms of macroscopic interface properties or structural response. In this work, macroscopic interface properties are defined in terms of Cohesive Zone Models (CZM), and the capital role of the cohesive length in determining the more or less gradual nature of the damage and crack propagation behaviour at the structural level is highlighted through examples on a Double Cantilever Beam (DCB) test. A concept based on a two-mechanisms CZM response with very different cohesive lengths is proposed to ensure a gradual crack propagation behaviour at the structural level, without significantly decreasing the initial damage threshold. A possible strategy to obtain such a macroscale interface response, based on the creation of bridging ligaments, is analysed and the link between the ligament elastic and failure response and the macroscopic interface response are discussed.