Validating Griffith fracture propagation in the phase-field approach to fracture: The case of Mode III by means of the trousers test

At present, there is an abundance of results showing that the phase-field approach to fracture in elastic brittle materials — when properly accounting for material strength — describes the nucleation of fracture from large pre-existing cracks in a manner that is consistent with the Griffith competition between bulk deformation energy and surface fracture energy. By contrast, results that demonstrate the ability of this approach to describe Griffith fracture propagation are scarce and primarily restricted to Mode I in the setting of infinitesimally small deformations. Aimed at addressing this lacuna, the main objective of this paper is to show that the phase-field approach to fracture describes Mode III fracture propagation in a manner that is indeed consistent with the Griffith energy competition. This is accomplished via direct comparisons between phase-field predictions for fracture propagation in the so–called trousers test and the corresponding results that emerge from the Griffith energy competition. The latter are generated from full-field finite-element solutions that — as a second main contribution of this paper — also serve to bring to light the hitherto unexplored limitations of the classical Rivlin-Thomas-Greensmith formulas that are routinely used to analyze the trousers test.