Under extreme loading conditions heat generation due to dynamic friction or thermomechanical instabilities leads to the development of highly localized thermal fields. Thermal localization occurs when the rate of heat generation by these dissipative mechanisms is much greater than the thermal diffusion effects. Predictions of thermomechanical modeling of dynamic deformation events need to be constrained by direct measurement of the associated temperature fields at high spatial and temporal resolutions.
At Brown we have recently designed and built a custom high-speed thermal imaging system with a 24×24 pixel HgCdTe focal plane array (FPA) (30 μm pixel pitch) capable of imaging at 5 million fps- a time resolution orders of magnitude faster than available commercially. The first part of our presentation covers system design and fabrication, including a custom read out integrated circuit (ROIC) and its hybridization with the FPA. The hybrid ROIC is cryogenically cooled to reduce the dark current and increase the quantum efficiency of the sensor while reducing leakage in the capacitive memory bank. Memory cell size is minimized by way of a dark current subtraction circuit, reducing the size of the ROIC. The voltage buffer design balances space constraints with the need to reduce charge sharing error. Sequential readout allows us to use cheaper ADCs and simplifies the wiring into the vacuum cryostat. Next we discuss an experiment demonstrating the instrument’s capability. A notched plate made of a model material is impacted to induce a propagating adiabatic shear localization. The temperature and deformation fields are measured simultaneously on either side of the specimen. Together, such measurements effectively constrain the predictions of thermomechanical simulations of the phenomenon. The experiments demonstrate the potential of the thermal imaging system to measure other dynamic dissipative events in materials and structures subjected to extreme loading conditions.
2025-04-09 09:00:00
