Damage mechanisms of reinforced polyamide 6,6 have been studied in 3D through in situ X-ray tomography tensile tests. 3D pictures of the microstructure have been taken during tensile tests to catch damage evolution in the bulk of material. The effects of relative humidity and orientation sampling are particularly investigated in this paper. Main mechanisms have been identified such as fibre failure, debonding, damage at fibre ends and matrix damage (cavitation, fibrillation, damage growth). Qualitative observations reveal that the mechanisms are very sensitive to orientation sampling and relative humidity of the specimen. A specific procedure was developed to propose a quantitative analysis of the results. This analysis shows that identified mechanisms not only have different proportions but also have different kinetics according to relative humidity and orientation sampling of the specimen.
Cast aluminium alloys have a key position as structural materials for the automotive industry combining good mechanical performance, excellent castability and thermal conductivity, making them a suitable choice for engine parts such as cylinder heads. In this paper, the low-cycle fatigue behaviour of a cast aluminium alloys is investigated at ambient and elevated temperatures by the use of in situ optical surface crack monitoring, secondary electron microscopy and X-ray tomography which are combined to study the fatigue mechanisms. The observations highlight the effect of defect distribution and temperature on the crack propagation path and in particular the change of the role of eutectic regions as the temperature increases. In addition, based on the defects population analyses by tomography, a fatigue crack initiation model is proposed to consider both temperature and defect effects on the total low-cycle fatigue life and fatigue crack growth rates.
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