On stress concentration in nanotwinned metals

TL;DR

This paper reanalyzes experimental data on nanotwinned metals and shows that local stress concentration trends depend heavily on measurement methods, revealing a different relationship than previously reported.

Contribution

It demonstrates that stress concentration measurements in nanotwinned metals are highly sensitive to analysis parameters, challenging prior conclusions.

Findings

Stress concentration depends on averaging box size.

A reverse trend consistent with continuum mechanics is observed.

Measurement sensitivity affects interpretation of stress data.

Abstract

In their papers, Lu et al. analysed experimental data from in-situ transmission electron microscopy (TEM) and concluded that local stress concentration at grain boundary-twin boundary (GB-TB) intersections in nanotwinned (nt-) metals increases as the TB thicknesses is reduced (below ${\lambda}$ $\leq$ 18 nm). However, here, by analysing the raw experimental data in Lu et al. together with finite element simulations and dimensional analysis, we show that the measurement of local stress concentration in a nt-material is highly sensitive to the adopted averaging box size due to the high stress gradient near GB-TB intersections as well as to the TB location in the nt-grain. By careful analysis of the raw data, a completely reverse trend, which is consistent with well-established laws of continuum mechanics, can be captured.