Multiscale Numerical Damage and Fatigue Behavior of Polymer Composites Under Cryo‐Thermal Loading

ABSTRACT Polymer–matrix composites are increasingly used in multilayer cryogenic tanks for storing compressed gases in food, medical, nuclear, and aerospace applications. This study investigates damage evolution in these composites under cryo‐thermal fatigue at cryogenic temperatures using a multiscale numerical framework. A representative volume element (RVE)‐based micromechanical model is employed to compute effective material properties under coupled thermal and mechanical loading through homogenization, which are subsequently utilized to assess damage development in the inner shell of a liquid‐oxygen tank. Micromechanical analysis reveals that damage initiation under cryogenic thermo‐mechanical fatigue is mainly governed by interfacial debonding once a critical load is reached, followed by matrix cracking as the dominant damage mechanism. Comparison of microscale and macroscale predictions shows that macroscopic damage is about 5% higher than micromechanical estimates, while the microscale damage growth rate is roughly 50% higher than that from macroscale analysis. In addition, short‐term cryo‐thermal fatigue cycles exhibit a damage growth rate about 40% higher than under long‐term loading. The numerical results are consistent with trends reported in the literature and provide mechanistic insight into cryogenic fatigue damage, contributing to improved fatigue‐life assessment of composite structures operating under cryogenic environments.