Damage characterisation of short glass fibre reinforced polyamide with different fibre content by an interrupted in-situ X-Ray computed tomography test

Short glass fibre reinforced polymers (SGFR) are increasingly used in automotive industry for the replacement of metals since they provide a significant reduction of weight. Parts with anisotropic fibre orientation were produced during the injection moulding process. Local microstructure parameters such as fibre length and orientation are decisive for the damage behaviour of the injection moulded parts. Damage type and propagation investigation are necessary for better understanding of material behaviour under stress. X-ray computed tomography (XCT) is a suitable non-destructive method to characterise internal defects in SGFR specimens. With an interrupted in-situ XCT tensile test three dimensional damage propagation in SGFR can be observed. In this study an interrupted in-situ computed tomography technique was used to quantify the main damage mechanism in polyamide specimens with a glass fibre content (PAGF) of 15 and 30 wt%. Double notched adapted miniature tensile specimens were cut from a plate in two orientations, 0° and 90° relatively to the melt flow. Therefore the tensile force was applied parallel and perpendicular to the expected main fibre orientation (0° respectively 90°). After every force step, a XCT scan with a voxel size of (2 μm)3 was performed to detect the internal defects. Four different defect types were classified: matrix fractures, fibre pull-outs, fibre/matrix debondings and fibre fractures. Fibre pull-out was the dominating defect type. Defects were mainly induced in the shear region of the 0° specimens. The core region showed nearly no defects at the last load step before breakage. Summing up the results show that visualisation and quantification of the defect volume and mechanism at certain load steps was possible with this method. Clear differences between damage induction of the 0° and 90° specimens were observed.