Thermal shock fracture of honeycomb-based porous thermoelectric materials with non-Fourier heat conduction

Compared with dense thermoelectric materials (TEMs), the auxetic honeycomb porous TEMs can enhance mechanical performance and energy conversion efficiency. The Fourier heat conduction law becomes unavailable due to the thermal wave speed in the porous TEMs is limited. Considering the non-Fourier law, this paper analyzes the thermal shock fracture characteristics of the porous TEMs bonded to an elastic substrate. A theoretical model for the effects of non-Fourier heat conduction, thickness of TME, shape and dimensions of honeycomb cell on strength failure and fracture failure is proposed. The analysis demonstrates that the maximum thermal stresses in the porous TEMs are underestimated without considering the non-Fourier heat conduction. The stress level in the auxetic honeycomb-based TEMs is much smaller than that in the traditional honeycomb TEMs with the positive Poisson's ratio architecture. It is found that a thicker TEM, a bigger relative density and a larger length ratio of the horizontal to the inclined strut can result in a smaller thermal stress. Based on the strength and fracture criterions, the envelope of safety angle between the horizontal and the inclined strut is identified. The simplified expressions of the safety angle envelope versus the applied thermal load are given.