Novel Capability for Microscale In-situ Imaging of Temperature and Deformation Fields under Dynamic Loading

To understand the mesoscale mechanisms responsible for the behavior of heterogeneous materials and to validate models, it is important to experimentally measure the deformation and temperature fields at the microstructure level. So far, there has been no methods that can yield such measurements simultaneously for dynamic experiments. Here, we report the development of a novel capability for simultaneous time- and space-resolved recording of both fields over the same microstructure area of a sample with micron-level spatial resolutions and microsecond time resolutions. Referred to as MINTED (Microscale In-situ Imaging of Dynamic Temperature and Deformation Fields), the system cohesively integrates a high-speed visible light (VL) camera and a state-of-the-art high-speed infrared (IR) camera via a custom-designed dichroic beam splitter-lens assembly. The combined VL and IR images allow the deformation fields to be obtained through digital image correlation (DIC) and the temperature fields over the same area to be obtained through pixel-level calibration of the differing emissivities of heterogeneous constituents in microstructures. Experiments are conducted on granular sucrose in a Kolsky bar [or split-Hopkinson pressure bar (SHPB)] environment, yielding both microstructure level fields along with overall material response. The strain and temperature fields provide detailed first-time insight into the processes of fracture, friction, shear localization, and hotspot development in the microstructures.