Threshold Identification for Micro-Tomographic Damage Characterisation in a Short-Fibre-Reinforced Polymer

The micro-tomographic technique represents an important tool for the analysis of the internal structure in short-fibre-reinforced polymers samples. For the investigation of damage mechanisms, detection of the micro-voids within the matrix can be facilitated by applying a tensile load in-situ during the scan. The investigations here described started from two micro-CT acquisitions, at different strain levels, of the same PA6.6GF10 sample. An original procedure for micro-voids identification is proposed, based on the statistical elaboration of the matrix grey-tone range. In order to validate the suggested procedure beyond visual inspection, an independent method based on an optimisation approach, which puts to use the two available micro-tomographic sets, was developed and applied. The effect of the tensile load, which can induce a progression of the damage within the specimen, was investigated, and the relations among strain, fibre distribution and micro-voids volumetric fraction were studied. Our findings point out that the mechanisms of damage progression, even under static loading as in this case, appear to be more complex than those related to the fibre-density-induced stress concentrations alone and require further investigation.