Thermal Diffusivity Characterization of Impacted Composites Using Evaporative Cryocooling Excitation and Inverse Physics-Informed Neural Networks

The thermal diffusivity measurement of impacted composites using pulsed methods presents an ill-posed inverse problem influenced by multiple factors such as sample thickness, cooling duration, and excitation energy. In this study, a novel excitation method - evaporative cryocooling - was introduced for measuring the thermal diffusivity of tested samples. Compared to conventional excitation modalities, evaporative cryocooling excitation is compact, portable, and low cost. However, evaporative cryocooling cannot be considered a pulsed method due to its prolonged excitation duration. In general, it is difficult to measure thermal diffusivity based on nonimpulsive pulsed excitation at times commensurate with the pulse duration, often due to ill-defined pulse shape and width and the subsequent potentially complicated thermal response, which may be subject to diffusive broadening. To address this challenge, inverse physics-informed neural networks (IPINNs) were introduced in this work and integrated with an evaporative cryocooling method. The Parker method combined with a photothermal method was employed as a reference. To improve the accuracy of both IPINNs and Parker methods, terahertz time-domain spectroscopy (THz-TDS) was employed for measuring the thickness of impacted composites. Simulations and experimental results demonstrated the feasibility and accuracy of the IPINN-based approach.