Thermal Diffusivity Mapping of Carbon/Carbon Composites

In order to develop new capabilities to simultaneously nondestructively determine discontinuities and measure thermal diffusivity in carbon/carbon (C/C) composites, a study was conducted of NDT methods for identifying subsurface discontinuities in C/C composites by thermal diffusivity measurements using a step-heating technique. Since traditional NDT methods are effective for thin carbon/epoxy composites, but are not very effective in detecting discontinuities in thick C/C composites, there is substantial industrial demand for nondestructive, rapid, online testing of the thermal diffusivity of an entire C/C composite part's surface. Therefore, this paper applied a step-heating infrared thermography technique to conduct through-thickness thermal diffusivity measurements and NDT for whole-field C/C disk brakes. In this work, a brief description of the theory behind the step-heating technique and a sample application are given. Finite element analysis (FEA) was also used for comparison with the experimental results and it was found that they were in good agreement with one another. The results established that this technique is capable of evaluating discontinuities in C/C composite materials. With more research, it is believed that this technique will be found to be efficient, economically feasible, easy to implement, and capable of providing rapid assessment of discontinuities in C/C composite materials that will be able to be incorporated into a manufacturing process quality control system.