Self-skinning polyurethane composites: Fatigue durability and thermomechanical degeneration mechanisms

Abstract

Modern trenchless rehabilitation requires advanced materials combining durability with structural adaptability. A novel self-skinning polyurethane composite (SSPUC) featuring a density-dependent skin-core gradient structure was developed for such applications. Through an integrated approach of macromechanical testing, microstructural SEM characterization, and real-time self-heating monitoring, the fatigue durability and thermomechanical degeneration mechanisms under cyclic compression were systematically elucidated. Key findings indicate that elevated stress levels, accelerated loading frequencies, and augmented material densities collectively compromised fatigue resistance, though density revealed a paradoxical dual role: simultaneously lowering fatigue threshold while enhancing fatigue strength. Microstructural variations manifested through density-dependent morphological transitions in skin-layer thickness, interface geometry, and cell core configuration. Fatigue self-heating showed spatial heterogeneity and three-stage evolution of max. temperature paralleling fatigue damage. Fatigue degradation mechanisms were identified as synergistic processes involving mechanical deterioration (surface delamination, cell structure collapse) coupled with thermally-induced damage (polymer matrix melting). Quantitative multi-dimensional analysis established structural hierarchy evolution and self-heating accumulation as fundamental determinants of fatigue performance trajectories. These findings provide fundamental insights for optimizing gradient polymer composites in infrastructure rehabilitation applications.