Influence of grain boundaries on mechanical behavior at ultra-high strain rates and low temperatures

This project aims to investigate the influence of grain boundaries on mechanical behavior at ultra-high strain rates and low temperatures. For this micropillar compressions on copper bi-crystals containing different grain boundaries will be performed.

The strain rate sensitivity between single-crystalline and bi-crystalline micropillars of penetrable high angle grain boundaries was found to differ significantly at quasi static strain rates pointing to the need of rearranging of dislocations when passing a grain boundary of such type. This thermally activated process might be suppressed at high strain rates and low temperature which will be investigated within this project. Additionally, it is known that at higher strain rates the yield strength and deformation mechanism of materials changes significantly. So far, the influence of individual grain boundaries on the rate-dependent behavior of metals remains largely unexplored. Additionally, the influence of temperature on the grain boundary interaction with dislocations and its influence on the mechanical response of metals also remain open for investigation. New developments in micromechanical testing equipment now enable displacement-controlled micropillar compressions in the ultra-high strain rate regime (upto 10000/s), at low temperatures, and also combined high strain rate and cryogenic conditions.

Using such a novel small-scale mechanical testing device, this project aims to unravel the mysteries of grain boundary interactions at ultra-high strain rates and low temperatures using bi-crystal micropillar compression testing of copper. Additionally, the mechanical testing device will be adapted, so that it can perform high strain rate measurements at cryogenic conditions below liquid nitrogen temperatures.

Teaser image adapted from [1]