Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture

Abstract

A planar crack generically segments into an array of "daughter cracks" shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in-situ microscopy observations of fracture surfaces at different stages of quasi-static mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. They further show that facet coarsening is a selfsimilar process driven by a spatial period-doubling instability of facet arrays with a growth rate dependent on mode mixity. Those results have important implications for understanding the failure of a wide range of materials.

Configurational stability of a crack propagating in a material with mode-dependent fracture energy – Part II: Drift of fracture facets in mixed-mode I+II+III

“…Pons and Karma (2010)'s numerical simulations, based on Karma et al (2001)'s phase-field model that reproduces standard crack propagation laws of Linear Elastic Fracture Mechanics (LEFM) (Hakim and Karma, 2009), revealed that a crack loaded in mode I+III gradually evolves from a planar configuration to a fragmented one, through unstable growth of helical perturbations. Chen et al (2015) and Pham and Ravi-Chandar (2014) provided a detailed picture of the coarsening mechanism that leads to the merging of adjacent facets into larger ones as the crack propagates. Yet, several features of the fragmentation patterns remain poorly understood.…”

“…A possible interpretation of the discrepancy between theoretical and experimental values of the threshold was recently provided by Chen et al (2015), who extended Pons and Karma (2010)'s simulations based on Karma et al (2001)'s phase-field model by performing an extensive study of non-coplanar solutions. In this work the bifurcation accompanying the transition from coplanar to fragmented front was shown to be strongly subcritical, which suggested that jumps from the stable branch to the unstable one could be induced well below the theoretical threshold by large enough perturbations.…”

Numerical methods for hydraulic fracture propagation: A review of recent trends

“…No general criteria to handle such a case is yet recognized as fully satisfactory although a number of recent advances have been made (Lin et al, 2010;Lazarus, 2011;Pham and Ravi-Chandar, 2016;Leblond et al, 2015;Chen et al, 2015) on that particular problem by the mechanics community.…”

Crack front instabilities under mixed mode loading in three dimensions

“…6-a. As a result many disconnected crack fronts can begin to propagate, leading possibly to discontinuous crack fronts propagation and eventually coarsening as reported for instance in [20].…”