Cracking the case on fracture
Designers and engineers need to be constantly aware of failure modes in materials. Material breakdown often involves fracture, and the ways in which cracks propagate must be understood to prevent their initiation and ensure safety margins. Many material engineering studies are carried out within a model of continuum plasticity, yet such models often lack sufficient microscopic detail to account for crack propagation and fracture resistance. Writing in Physical Review Letters, Srinath Chakravarthy and William Curtin of Brown University in the US report computer simulations showing more clearly what processes influence fracture in plastic deformation, and on what length scales.
The authors model plastic deformation as the movement of discrete dislocations along slip planes. Specifically, a set of “obstacles” arrayed with some selected spacing restricts the movement of dislocations and modifies the plasticity. They then examine fracture by including an initial crack in the material and observing it propagate as a function of material cohesive strength, fracture energy, and obstacle spacing. Chakravarty and Curtin find that it is the obstacle spacing length scale that most strongly affects fracture toughness. Moreover, they propose that their model could serve as a more general simulation environment for fracture studies in various materials. –David Voss