[SY-E14] Stability Controlled Crack Evolution in Staggered Laminate Bio-material
Nacre that is a bio-material with a staggered laminate micro-structure of hard and soft constituents shows a good performance of strength, stiffness, and toughness. The toughness of nacre with 95% hard and brittle phase and less than 5% soft collagen phase remarkably increases with cracking. Recent research shows that cracking in the bio-material is a stable process in macroscopic point of view, in which the fracture process zone widely spreads and in space, rather than the unstable process in many brittle/quasi-brittle materials, and that the high performance of the material is achieved by a shear ligament toughening mechanism. In this study, we solve a problem on cracking process under tensile test of model specimen with staggered micro-structure by using FEM and a simplified model, and discuss the relationship between the macroscopic behaviour and the fundamental properties of micro-structure. We find that the crack initiation in such staggered micro-structure originates from the loss of macroscopic stability and the following strain concentration. Coupling the normal debonding and shear sliding at interface of hard phases, a stable behaviour is achieved globally before a globally unstable point in stress-strain space, in which locally unstable domains do not contribute to the macroscopic instability. This mechanism can be considered as a stability enhancement, i.e. a kind of toughening. The cracking behaviour of our model shows size effect. The macroscopic stable stage is significantly affected by both the model and grain size of hard phase. Our research offers a different angle of view in exploring the microscopic mechanism of cracking process of staggered laminate bio-material.