Statistical mechanics of cracks: Fluctuations, breakdown, and asymptotics of elastic theory

We study a class of models for brittle fracture: elastic theory models that allow for cracks but not for plastic flow. We show that these models exhibit, at all finite temperatures, a transition to fracture under applied load similar to the first-order liquid-gas transition. We study this transition at low temperature for small tension. Using the complex variable method in a two-dimensional elastic theory, we prove that the energy release in an isotropically stretched material due to the creation of an arbitrary curvy cut is the same to cubic order as the energy release for the straight cut with the same end points. We find the energy spectrum for crack shape fluctuations and for crack surface phonons, under a uniform isotropic tension. For small uniform isotropic tension in two dimensions, we calculate the essential singularity associated with fracturing the material in a saddle point approximation including quadratic fluctuations. This singularity determines the lifetime of the material ~half-life for fracture!, and also determines the asymptotic divergence of the high-order corrections to the zero temperature elastic coefficients. We calculate the asymptotic ratio of the high-order elastic coefficients of the inverse bulk modulus, and argue that the result is unchanged by nonlinearities—the ratio of the highorder nonlinear terms are determined solely by the linear theory. @S1063-651X~97!02706-2#