Vendredi 22 mai 2026 à 11h, salle des séminaires IRPHE
Abstract: How to describe fracture processes that evolve under slow external loading but release energy through sudden internal events?
Crack bursts, sudden damage localisation, fragmentation, or rapid crack extension are not captured by first-order equilibrium alone. A configuration may satisfy force balance and yet be mechanically unrealisable: if it has lost stability, it cannot be observed.
I will discuss an energetic framework for instability-driven jumps in irreversible fracture systems. The main claim is that the onset of a burst is governed by loss of (second-order) stability under the constraint of irreversibility. Once such an instability is reached, the system cannot continue along a smooth path. Instead, physical time freezes, the transition unfolds in an internal time scale, resulting in a jump.
Viscosity plays a key role in this phenomenon, resolving the apparently instantaneous jump into a finite-mobility constrained energy-gradient flow. Along this trajectory, the system dissipates exactly the energy released across the discontinuity, and the jump terminates when energy release is exhausted. This provides a local and global energetic account of burst transitions, and numerically testable tools to describe a mechanically admissible evolution satisfying a global energy balance.
This framework is motivated by experiments showing velocity-dependent apparent toughness in soft brittle materials. My goal is to clarify what minimal theoretical structure is needed to confront experimental observations and to identify simple benchmark experiments where the distinction between stable growth and instability-driven bursts can be made visible and measured.