In this work, we apply the finite element (FE) method to simulate an approximate low velocity impact induced model. One important characteristic of low velocity impact damage is the presence of multiple defects located at different depths, creating overshadowing among each other, affecting the thermal diffusion and therefore the blind frequency and temperature distribution on the surface, understanding this phenomenon is paramount in order to quantify the magnitude of under-the-surface damages. In this paper, we create a representative geometry of a defect using the meshing code CUBIT and solve the finite element model in ARIA thermal code in order to simulate the phase component of reflected thermal waves. The phase and thermal data collected from the FE solution on the surface above each defect is post processed and linearly correlated, in conjunction with a two-point strategy to provide information about the defect below the surface of interest. We also present a comparison with a single defect representation of the defect, proving that single model defect is not accurate to represent damage created by low velocity impact.
In this work we apply the finite element (FE) method to simulate the results of pulsed phase thermography experiments on laminated composite plates. Specifically, the goal is to simulate the phase component of reflected thermal waves and therefore verify the calculation of defect depth through the identification of the defect blind frequency. The calculation of phase components requires a higher spatial and temporal resolution than that of the calculation of the reflected temperature. An FE modeling strategy is presented, including the estimation of the defect thermal properties, which in this case is represented as a foam insert impregnated with epoxy resin. A comparison of meshing strategies using tetrahedral and hexahedral elements reveals that temperature errors in the tetrahedral results are amplified in the calculation of phase images and blind frequencies; we investigate the linearity of the measured diffusion length (based on the blind frequency) as a function of defect depth. The simulations demonstrate a nonlinear relationship between the defect depth and diffusion length, calculated from the blind frequency, consistent with previous experimental observations. And finally a two-point strategy is presented to better estimate the defect depth and thickness.
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