Fatigue Characterisation and Monitoring in 3D Printed Short Fibres Reinforced Polyamide

3D printed composites are rapidly gaining a growing interest in several industrial sectors. However, for their widespread adoption, it is necessary to characterise their fatigue response. In this work, several 3D printed Onyx specimens were tested under tension-tension fatigue load with two main objectives. The first one was the assessment of different monitoring techniques for the fatigue damage evolution in the Onyx specimens. It was observed that the strain calculations from the machine crosshead displacement led to better results than strains from digital image correlation or extensometers. The second objective was the characterisation of the fatigue response of the Onyx specimens: SEM fractography was able to identify the fatigue damage initiation and propagation regions. Moreover, modulus and temperature trends were observed to assume a non-monotonic trend, which is unusual for composites. It was thus suggested that these quantities can be potential indicators of the fatigue damage in the specimens.