Energy Partitioning During Subcritical Mode I Crack Propagation Through a Heterogeneous Interface

The energy budget during the propagation of tensile fractures typically includes two major energy dissipation modes: the fracture energy to create a new interface and the radiated energy. Since seismic hazard is related to the amount of seismic energy released, it is important to evaluate precisely the energy budget during fracture propagation and see in particular if it is constant or not. However, two aspects are typically limiting a precise estimate of the energy budget: first, the measurement of the nonseismic energy release and second, the rock heterogeneity‐like asperities or barriers. We conducted here laboratory experiments, using an analog material (Polymethyl methacrylate (PMMA)), of a stable mode I interfacial crack propagation close to brittle‐creep transition through a heterogeneous interface for different macroscopic rupture velocities to evaluate carefully their energy budget. Both acoustic and optical advances of the crack front were measured simultaneously, providing precise estimates of both types of dissipated energy. We computed the radiation efficiency η R (ratio of the radiated energy to the available energy for driving the fracture) and observed a nonlinear increase of η R with the average fracture propagation velocity v over 2 orders of magnitude independently of the initial quenched disorder. The experimental observations are supported by a model based on the fluctuations of the local rupture velocity induced by the crack front pinning on local asperities which leads to η R  ∝  v 0.55 . We discuss implications for slow shear rupture modes, seismicity rate evolution, and induced seismicity.