Influence of hygrothermal aging on the macroscopic mechanical properties of carbon fiber composites at the microscopic scale

Abstract This paper investigates the effects of hygrothermal aging (71°C, 85% RH) on the mechanical properties of carbon fiber/epoxy reinforced composites across micro- to macro-scales, establishing the relationship between the internal structure of the material, its mechanical properties, and structural mechanical behavior. This study introduces an equivalent temperature and establishes a mathematical model to simulate the hygrothermal diffusion in composites. The simulated diffusion rate results align with experimental observations, and the simulation of expansion forces reveals that stress concentration due to material heterogeneity is one of the causes of macroscopic failure. The finite element method (FEM) was applied to simulate the moisture absorption behavior of the composites over 45 days, yielding a simulated saturated moisture absorption rate of 0.9%, with an experimental error of 2.6%. The simulation time was significantly shorter than the experimental duration, demonstrating its practical utility. Through micro-scale hygrothermal simulation, the reasons for changes in macroscopic mechanical properties were further inferred. Comparisons between the simulated and experimental results under both dry and wet conditions showed errors within 7%. The simulation results provide a micro-scale explanation for macroscopic phenomena, elucidating the reasons for changes in mechanical properties and offering references for the application of other fiber orientations and different hygrothermal environments in the aerospace field.