Time limited self-organised criticality in the high rate deformation of face centred cubic metals

Plastic deformation is a fundamentally important physical process, ultimately determining how materials can be used. Metal plasticity is governed by dislocation dynamics and lattice twinning. Although many continuum constitutive models exist, plasticity is now known to occur in discrete events arising from the self-organisation of dislocations into 'avalanches' under applied stress. Here we extend avalanche plasticity to high strain rates, by introducing time limitation to self-organisation. At high rates large avalanches fail to form; the system must self-organise around new constraints. Various macroscopic consequences include an increasing rate of work hardening with strain rate. We perform new measurements on high purity copper that distinguish between instantaneous and permanent strength contributions across a strength transition at 10^4 s^-1, showing the transition to be a change in structural evolution. Strong model agreement validates our time limited self-organisation approach. Our work results in a unified, physically realistic framework for plasticity, with wide applicability.

Lewis Lea, Lawrence Brown, Andrew Jardine