Fracture of disordered materials

Par Elisabeth Bouchaud, Mardi 18 octobre 2011, 9:00-10:30

Because the mechanical properties of materials are controlled to a large extent by their microstructures, it is important to build up predictive models of fracture which take explicitly disorder into account. While there indeed exists a unified theoretical framework to describe the failure of homogeneous materials, understanding and modeling the mechanical properties of heterogeneous media is still an open problem. In the vicinity of cracks, classical homogenization methods become inefficient, because of high stress gradients, and because fracture is governed by rare events statistics. Recent approaches coming from the study of out-of-equilibrium phenomena in statistical physics may be able to take up the challenge. After introducing some basic concepts of Linear Elastic Fracture Mechanics, I will review experiments characterizing the roughening of fracture surfaces and crack fronts, and the intermittent dynamics of the latter. Striking observations concern the existence of universal morphological features, independent of both the material and the loading conditions, reminiscent of interface growth problems. In this context, I will analyze models which describe the crack front as an elastic line that propagates in a random potential. In these models, the onset of crack propagation is interpreted as a dynamic phase transition, while sub-critical crack growth is assimilated to thermally-assisted depinning. While these models describe quite accurately what happens at scales large enough so that the material behaves elastically, they fail to be quantitative at smaller scales, where non linear elastic effects come into play.

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Mis en ligne le samedi 9 juillet 2011