Strain intermittency in shape-memory alloys

TL;DR

This study investigates the intermittent strain behavior during martensitic transformations in a Cu-Al-Be shape-memory alloy using full-field measurements, revealing power-law strain avalanching and transformation asymmetries.

Contribution

It introduces an experimental method combining full-field strain measurement with controlled monotonic loading to analyze strain intermittency in shape-memory alloys.

Findings

Strain avalanches follow a power-law distribution over six decades.

Hysteretic superelastic behavior observed during phase transformation.

Asymmetry between forward and reverse transformations detected.

Abstract

We study experimentally the intermittent progress of the mechanically induced martensitic transformation in a Cu-Al-Be single crystal through a full-field measurement technique: the grid method. We utilize an in- house, specially designed gravity-based device, wherein a system controlled by water pumps applies a perfectly monotonic uniaxial load through very small force increments. The sample exhibits hysteretic superelastic behavior during the forward and reverse cubic-monoclinic transformation, produced by the evolution of the strain field of the phase microstructures. The in-plane linear strain components are measured on the sample surface during the loading cycle, and we characterize the strain intermittency in a number of ways, showing the emergence of power-law behavior for the strain avalanching over almost six decades of magnitude. We also describe the nonstationarity and the asymmetry observed in the forward versus reverse transformation. The present experimental approach, which allows for the monitoring of the reversible martensitic transformation both locally and globally in the crystal, proves useful and enhances our capabilities in the analysis and possible control of transition-related phenomena in shape-memory alloys.