On the accuracy of monitoring inter-fibre fractures in composites using passive infrared thermography extended by microscopic analysis

This work deals with the accuracy of a non-destructive testing methodology to monitor the evolution of inter-fibre fractures in [903/02]s cross-ply carbon fibre-reinforced polymer laminates. Specimens are subjected to a continuous 3-point bending test. The locations of local energy releases corresponding to inter-fibre fractures are recorded during the experiment using passive infrared thermography. They are correlated to reference positions from an optical microscopic analysis in a post-processing step. The absolute difference between both positions is a measure for the accuracy of the passive infrared thermography. A correction function for the infrared data as well as criteria for the correlation and test execution are derived. The correlation allows the introduced methodology for low error localisation of inter-fibre fractures providing temporal and spatial information. The resulting temporal error is in the range of milliseconds, the spatial error in the range of microns.