Extracting information from noisy data: strain mapping during dynamic in situ SEM experiments

Micromechanical testing techniques can reveal a variety of characteristics in materials that are otherwise impossible to address. However, unlike to macroscopic testing, these miniaturized experiments are more challenging to realize and analyze, as loading and boundary conditions can often not be controlled to the same extent as in standardized macroscopic tests. Hence, exploiting all possible information from such an experiment seems utmost desirable. In the present work, we utilize dynamic in situ microtensile testing of a nanocrystalline equiatomic CoCrFeMnNi high entropy alloy in conjunction with initial feature tracking to obtain a continuous two-dimensional strain field. This enables an evaluation of true stress-strain data as well as of the Poisson's ratio and allows to study localization of plastic deformation for the specimen. We demonstrate that the presented image correlation method allows for an additional gain of information in these sophisticated experiments over commercial tools and can serve as a starting point to study deformation states exhibiting more complex strain fields.

Automated summary

Micromechanical testing techniques can reveal characteristics in materials that are otherwise impossible to address, but they pose more challenges compared to macroscopic testing. In this study, dynamic in situ microtensile testing and feature tracking were used to obtain continuous strain fields and evaluate stress-strain data, Poisson's ratio, and localization of plastic deformation. The presented image correlation method provides additional information in these experiments over commercial tools, serving as a starting point for studying deformation states with complex strain fields.