Yielding and irreversible deformation below the microscale: Surface effects and non-mean-field plastic avalanches

TL;DR

This paper investigates how surface effects and size influence yielding and plastic deformation in microscale crystals, revealing size-dependent yield stress and altered avalanche statistics due to the absence of dislocation storage.

Contribution

It provides a theoretical framework for understanding size and surface effects on plasticity and introduces new insights into the statistical behavior of plastic events at small scales.

Findings

Yield stress depends on system size and geometry.

Plastic deformation occurs via abrupt stress drops.

Absence of dislocation storage alters avalanche statistics.

Abstract

Nanoindentation techniques recently developed to measure the mechanical response of crystals under external loading conditions reveal new phenomena upon decreasing sample size below the microscale. At small length scales, material resistance to irreversible deformation depends on sample morphology. Here we study the mechanisms of yield and plastic flow in inherently small crystals under uniaxial compression. Discrete structural rearrangements emerge as series of abrupt discontinuities in stress-strain curves. We obtain the theoretical dependence of the yield stress on system size and geometry and elucidate the statistical properties of plastic deformation at such scales. Our results show that the absence of dislocation storage leads to crucial effects on the statistics of plastic events, ultimately affecting the universal scaling behavior observed at larger scales.