Second harmonic passive thermography generated by cyclic loading in composites

Past analysis of the heat generated during cyclic loading of composites has been primarily focused on the thermal response that occurs at the same frequency as the cyclic load. However, it has been observed that a smaller amplitude signal occurs at twice the frequency of the cyclic load. A physics-based model is presented that describes how this signal is expected as a result of the heat generated by friction at a delamination. The second harmonic source is incorporated into a quadrupole two-dimensional simulation of heat diffusion, which allows for rapid simulation of a temperature profile at the surface from a friction source.