Thermomechanical coupling effects in small volumes under high loading rates

Adiabatic Shear Bands (ASB) provide an additional plastic flow mechanism under high loading rates. This localized deformation behavior has been already well established. Generally, substantial efforts are currently invested into the understanding of small volume mechanical properties. As such the present study objective is the search for critical experiments regarding ASB initiation and propagation aided by nanomechanical testing. Materials, which included a glassy polymer (PMMA), polycrystalline metallic bulk surfaces (4340 steel and Pb-Sn alloy) and a 1 μm thin film of Ti on silicon, were investigated using nanoindentation and microscratch tests. The study revealed thermomechanical coupling effects associated with localized deformation and damage evolution. The lauer was typical to the PMMA while dynamic recrystallization occurred in the Pb-Sn alloy. For the Ti thin film, the intensive cracking was attributed to the high propensity to form ASB particularly at high scratch velocity. This was a different mode as compared to low velocity scratches. The current experimental/theoretical study suggested the following conclusions: first, small volume characterization requires comprehensive consideration, which include thermo-mechanical effects. Second, nanotesting might advance the current understanding regarding dynamic response. As such, it can assist in establishing a better fundamental basis in terms of models and simulations by following nanotesting methodologies. In this context, considerations regarding penetrator performance is illustrated and discussed as a realistic application.