Multiscale Thermomechanical Simulation and Experimental Validation of Cryogenic Flexural Failure Mechanism in Carbon/Epoxy Laminates

ABSTRACT This study investigates cryogenic flexural failure mechanisms of carbon fiber/epoxy composites using an experimentally validated multiscale simulation framework. A novel approach based on temperature‐dependent stress amplification factors (SAFs) is developed to bridge the micro‐ and macro‐mechanical behaviors under three‐point bending from room temperature down to −183°C. The framework, derived from a three‐phase unit‐cell model, enables bidirectional stress transfer and dynamic stiffness degradation. Excellent agreement is achieved between simulated and experimental force‐displacement responses for both unidirectional and cross‐ply laminates. Results demonstrate a significant cryogenic strengthening effect, with flexural strength increases significantly at cryogenic temperatures: unidirectional laminates gain 29.37% (−55°C) and 62.24% (−183°C), whereas cross‐ply laminates show improvements of 17.07% and 29.27%, relative to room temperature. Simulations identify regions with minimal fiber‐spacing as damage‐sensitive zones, where SAFs intensifies at low temperatures. Microscopic damage initiates at the fiber/matrix interface, with cryogenic conditions delaying its onset. Both architectures undergo progressive failure: interfacial debonding, matrix damage, and finally fiber fracture. Macroscopically, cooling shifts unidirectional laminates from ductile to brittle fiber‐dominated failure, whereas cross‐ply laminates transition from a pseudo‐ductile response driven by interlaminar stiffness mismatch, to brittle interlaminar failure. These insights provide a reliable foundation for the design of cryogenic composite components.