Accounting for localized deformation: a simple computation of true stress in micropillar compression experiments

TL;DR

This paper introduces a straightforward analytical method to accurately compute true stress in micropillar compression tests, accounting for localized deformation, thereby improving the interpretation of experimental data at micro- and nanoscale.

Contribution

It presents a simple, analytic formula for true stress calculation during localized deformation in micropillar experiments, avoiding complex finite element simulations.

Findings

Enhanced accuracy in stress measurement during localized deformation.

Applicable to homogeneous, isotropic materials and crystals.

Requires only standard experimental data.

Abstract

Compression experiments are widely used to study the mechanical properties of materials at micro- and nanoscale. However, the conventional engineering stress measurement method used in these experiments neglects to account for the alterations in the material's shape during loading. This can lead to inaccurate stress values and potentially misleading conclusions about the material's mechanical behavior especially in the case of localized deformation. To address this issue, we present a method for calculating true stress in cases of localized plastic deformation commonly encountered in experimental settings: (i) a single band and (ii) two bands oriented in arbitrary directions with respect to the vertical axis of the pillar (either in the same or opposite directions). Our simple analytic formulas can be applied to homogeneous and isotropic materials and crystals, requiring only standard data (displacement-force curve, aspect ratio, shear band angle and elastic strain limit) obtained from experimental results and eliminating the need for finite element computations. Our approach provides a more precise interpretation of experimental results and can serve as a valuable and simple tool in material design and characterization.