Stress Distribution and Relaxation in Cellulose Nanocrystal- Enhanced GFRP Composites Under Sustained Loading

The viscoelastic nature of the polymer matrix in Glass Fiber Reinforced Polymer (GFRP) composites results in complex time-dependent stress redistribution under sustained loads, a critical factor for maintaining long-term structural integrity. This study presents a comprehensive experimental and numerical investigation into the creep behavior and stress relaxation mechanisms of GFRP composites, with a specific focus on the enhancement effects of cellulose nanocrystals (CNCs). The Norton-Bailey creep model was rigorously calibrated for a DGEBA epoxy matrix, demonstrating exceptional predictive accuracy (R² > 0.95) with a creep exponent of n ≈ 1.082. The Burgers model was employed to capture the time-dependent behavior of the fiber-matrix system. Micromechanical analysis via Finite Element Analysis (FEA) of high-fidelity Representative Volume Elements (RVEs) subjected to a sustained equivalent stress of 100 MPa for 7200 seconds revealed profound, orientation-dependent stress evolution. In 0° laminates, fiber stress decreased by 17% while matrix stress increased by 340%, signifying dramatic load transfer. Incorporation of 1.0 wt% CNCs was identified as optimal, reducing stress concentration factors by 17–36% and enhancing stress field homogeneity across all fiber orientations (0°, 45°, 90°) by improving interfacial bonding and matrix stiffness. This validated multi-scale framework provides critical insights and a reliable predictive tool for designing durable, high-performance composite structures in aerospace, automotive, and civil infrastructure applications.