Mapping pure plastic strains against locally applied stress: Revealing toughening plasticity

Abstract

The deformation of all materials can be separated into elastic and plastic parts. Measuring the purely plastic component is complex but crucial to fully characterize, understand, and engineer structural materials to “bend, not break.” Our approach has mapped this to answer the long-standing riddle in materials mechanics: The low toughness of body-centered cubic metals, where we advance an experimentally led mitigative theory. At a micromechanically loaded crack, we measured in situ the stress state applied locally on slip systems, and the dislocation content, and then correlatively compared with the occurrence—or not—of toughness-inducing local plasticity. We highlight limitations and potential misinterpretations of commonly used postmortem transmission electron imaging. This should enable better-informed design for beneficial plasticity and strength in crystalline and amorphous solids alike.

Automated identification of slip system activity fields from digital image correlation data

“…For instance, (quasi-)3D DIC, also know as Digital Height Correlation [29] , could be employed on nanoscale Atomic Force Microscopy (AFM) measurements, to access additional 3D displacement gradient tensor components, which can directly be included in the minimization function. Additionally, simultaneous in-situ EBSD (along DIC) [30] can yield local lattice rotations, and in particular their rotation axes, which might also contribute to the identification.…”

A Nanomechanical Testing Framework Yielding Front&Rear-Sided, High-Resolution, Microstructure-Correlated SEM-DIC Strain Fields

“…The main challenges in conducting these micro-testing techniques on polycrystalline and multiphase specimens, specifically when the focus lies on interface mechanics, include (i) the selection and extraction of specimens that contain (only) the most interesting feature (e.g. an individual interface) [36], (ii) measurement of the nanoscale deformation fields, with high-resolution SEM-DIC, during these micro-tests, which is currently only achieved by a small number of research groups [35,37,38] and (iii) attribution of deformations to microstructure features and subsequent identification of their character, which requires data collection of two (or more) sides of the specimen and careful data alignment.…”