Vibration-induced fatigue behavior and damage mechanisms of polypropylene-argan nut shell composites

This study investigates vibration-induced fatigue of polypropylene (PP) reinforced with argan nut shell (ANS) particles. Specimens were designed by finite-element modal and harmonic analyses to target resonant frequency while limiting self-heating. Fatigue tests using a vibration shaker setup were used to evaluate fatigue performance based on S-N curves and the Basquin's equation. The results showed that the incorporation of ANS particles reduces fatigue resistance at high stress levels but improves it at low stress levels. Differential scanning calorimetry confirmed the nucleating effect of the particles through an increase in crystallinity, while dynamic mechanical analysis revealed a reduction in damping performance. These combined effects result in a stiffer material with reduced energy dissipation ability. Scanning electron microscopy (SEM) was used to observe crack initiation and propagation at the matrix-particle interface, revealing that the main fracture mechanisms were interfacial decohesion, void formation, and micro-shear bands. These findings emphasized the dual role of ANS particles: while they enhance stiffness and fatigue stability at low stress levels, they also make the material more brittle and cause local stress concentration.