CFRP materials are progressively used in areas where the weight as well as the strength of materials matter. Since they are used in safety relevant environments, like aircrafts and cars, an assessment of the components for defects is mandatory. Flash thermography [1] has proven to be a valuable tool to resolve defects. However, a quantitative evaluation of the defect extent and depth within the specimen is extremely challenging, since the commonly used analytical models [2,3] do not incorporate lateral heat flow around the defect areas. Hence a reconstruction of the samples by numerical simulations is a path to improve the results. This finally enables pass and fail tests for specimens based on quantitative results.
The properties of the anisotropic CFRP materials vary dependent on the matrix and fibre chosen. In addition, the fabrication processes are distinct, hence it is strongly desirable to measure the properties of a sound sample in a fast and reliable way. The knowledge of diffusivity and heat capacity in three dimensions enables a more accurate simulation. This allows to derive the geometry of the specimen in an iterative process.
The in-plane diffusivity is determined by heating the sample with a laser line (a flat top profile focused in one dimension) and monitoring the transient temperature at the front surface of the sample. This method is compared to measurements of the diffusivity using a Gaussian laser spot [4,5]. The results are compared with the data obtained by flash thermography in transmission. In addition, the heating process of the sample on its surface as well the heat conduction is monitored using an IR-microscopic objective. Hence the transparency of the sample as well as the temperature conduction of the two components in microscopic scale can be studied. Finally the results are applied to provide precise parameters in the simulation of defects in a CFRP sample [6]
