Three-point bending behavior of angle-ply GFRP laminates under static and LCF loading: Experimental and statistical analysis

Abstract

Deeper understanding of damage propagation in continuous fiber reinforced polymer composites is required to design safer composites. The process of sample preparation imparts sufficient damage to the free edges and can be easily considered as precursor to failure. This study examines the low-cycle fatigue (LCF) behavior and damage progression in woven angle-ply laminates under static and fatigue loading. Laminates with ply orientations of (0°/90°), ±15°, ±30°, and ±45° were tested with a load-controlled fatigue at 0.1 Hz and a stress ratio (R) of 0.1. Internal and free-edge damage were monitored using Transmitted Light Photography (TLP) and optical recording. Weibull statistics is used to generate S-N curve for reliability levels of 0.95, 0.99, 0.999, and 0.9999 and to find mean-time-to-failure (MTTF), standard deviations, and coefficient of variance (CV) in the fatigue life. TLP images showed delamination promoted by free-edge damage, while compressive face damage was caused by the loading cylinder. On-axis laminates developed fewer cracks, failing with a single through-thickness crack, while off-axis laminates exhibited multiple cracks that coalesced without a single fracture. Fiber orientation significantly influenced internal debonding, and damage from sample preparation could not be fully eliminated.