Fatigue Behaviour and Damage Mechanisms of Short Glass Fibre-Reinforced Recycled Polypropylene Produced by Pellet-based Polymer Material Extrusion Under Different Load Ratios

This study investigated the fatigue behaviour of short glass fibre-reinforced polypropylene with a recycled matrix produced via Additive Manufacturing through Pellet-Based Polymer Material Extrusion (AM), and injection moulding (IM). In particular, the focus is on the influence of load ratios (R = -1 and R = 0.05) and infill patterns (0°, 45°, and 90°) on the fatigue performance of materials processed via these two manufacturing processes. Approximately 70 fatigue tests were carried out on AM and IM specimens, with the latter process also testing the material with a virgin matrix for comparison purposes. The fibre distribution was analysed via computed tomography, and macro- and microscopic damage analyses were conducted after fatigue failure. The main experimental outcome is that the fatigue strength for each R, both for the AM and IM specimens, is proportional to the tensile strength. Normalized Walker’s equation has been calibrated on all data results providing a fatigue curve unifying all the processes and parameters considered for the analysed materials.