Fatigue damage stabilization and stiffness retention in core–shell rubber modified glass fiber composites under fully reversed loading

Abstract

This study investigates the fatigue behavior of glass fiber reinforced vinyl ester and unsaturated polyester composites modified with core–shell rubber particles (CSRP) under fully reversed tension–compression fatigue loading ( R = −1). A stiffness-based framework is adopted to characterize damage evolution and structural durability. Laminates containing 0, 2, 5, and 10 wt% CSRP were evaluated, with 5 wt% identified as the optimal modification level, preserving stiffness and strength while enhancing deformation capacity. Under cyclic loading at 40%–80% of the control compressive strength, CSRP-modified systems demonstrated fatigue life improvements of up to approximately 5.4×, particularly in the intermediate stress regime. A three-stage stiffness degradation model was developed to quantify damage progression, capturing early saturation, progressive degradation, and final failure. The modified systems exhibited reduced mid-life degradation rates (up to 52% in vinyl ester and 19%–23% in unsaturated polyester). Serviceability-based durability maps further showed improvement factors of 3–7 within the 50%–70% stress range. Fatigue stabilization is attributed to matrix-level toughening, where CSRP inclusions promote stress redistribution and delay crack coalescence. These results establish a direct link between matrix modification and improved fatigue durability in composite materials.