An experimental investigation of fatigue performance and damage distribution mechanism in Bi-Directional GFRP composites

Abstract

This study presents an experimental investigation of the fatigue performance and damage distribution mechanism of bi-directional GFRP composites. Uniaxial fatigue tests have been conducted under load-control, at stress ratios, R = 0.1, 0.5 and critical stress ratio (χ=-0.9). The influence of gauge length and surface roughness on fatigue life has been examined for R = 0.1. An infrared (IR) camera is employed to monitor temperature evolution and capture thermal images during the fatigue experiments. Fatigue stiffness degradation, energy dissipated per cycle, and severity of damage progression have been analyzed to elucidate the effects of stress levels and mean stress on fatigue performance. At higher stress levels, the damage is intense and localized, resulting in relatively shorter life due to fiber-breakage accompanied by rapid fatigue stiffness degradation. At lower stress levels, the damage is uniformly distributed and less severe, primarily involves stress concentration, resulting in longer fatigue lives. The study highlights the contrasting damage progression mechanisms for tension–tension and tension–compression fatigue. Under tension–tension fatigue, an oval-shaped damage zone forms perpendicular to the loading direction indicating transverse crack propagation, while under tension–compression fatigue, the damage zone aligns parallel to the loading direction indicating longitudinal crack propagation due to compressive loading.