Estimation of delamination contact resistance in composites

A key composite delamination characteristic that determines thermographic detectability is the extent to which it blocks the flow of heat from one ply to an adjacent ply. A measure of this heat flow barrier is the contact resistance which is proportional to gap spacing between the two plies. From thermographic data acquired on a composite with delaminations and a three-dimensional simulation of the heat flow in a delaminated composite based on computed tomography characterization of the delaminations, a delamination contact resistance map is estimated. The contact resistance values are smaller than expected based on the gap spacing estimated from computed tomography data. A model is presented that assumes there are small variations in the gap spacing which are not captured by the computed tomography. This model indicates if there is sufficient variation in the gap spacing, the contact resistance is significantly smaller than a value obtained from the average gap spacing. The contact resistances calculated from different amplitudes of the variations are compared to the estimates of contact resistance from experimental data.