Questioning the universal motion equation of cracks in dynamic fracture: inertia matters too.

Objectif

Crack propagation is the primary mechanism by which materials break. This topic has been the subject of intense research due to its fundamental theoretical importance and wide range of practical applications. Brittle solids, such as polymers and glass, as well as other engineering and geological materials, tend to break abruptly, resulting in high-speed crack propagation. Despite considerable scientific progress, the complex dynamics of high-speed cracks cannot yet be fully explained by classical theories of dynamic brittle failure. These theories are based on the existence of a universal crack motion equation which was confirmed from steady-state experimental evidence. While recent models that are agnostic to this assumption confirm this idea, they too are pushed to their limits in cases involving significant variations in crack velocity. My aim is to advance the understanding and modelling of dynamic fracture by focusing on the expression of inertial crack propagation phenomena. I hypothesise that the motion of a crack's tip is driven not by a 'constitutive' relationship, but by a hyperbolic partial differential equation, which is characteristic of systems with kinetic energy and thus subject to inertial effects. To this end, I will: i) establish experimental evidence for the expression of these inertial phenomena by performing unconventional dynamic fracture tests and developing cutting-edge multi-physics instrumentation; ii) investigate the origins of these phenomena at smaller scales; iii) propose a rigorous modelling framework embedded in an efficient and generic implementation; and v) compare model predictions with experiments for calibration and validation. My immediate deliverables are a reformulation of dynamic fracture and its numerical implementation, as well as providing the community with a complete database exploiting ultra-high speed imaging and dedicated full-field measurement techniques for calibrating and validating dynamic fracture models.