T700 Carbon Fiber/Epoxy Resin Composite Material Hygrothermal Aging Model

The hygrothermal aging model, based on Fick's second law of diffusion, characterizes the degradation of engineering constants in T700 carbon fiber/epoxy resin composites. It focuses on changes in the tensile modulus, shear modulus, and transverse Poisson's ratio due to moisture absorption and temperature variations. The model validates through mass change observations before and after seawater immersion, along with surface morphology assessments and tensile experiments. The results reveal that the saturated moisture absorption rate for single-layer laminates in seawater immersion is 0.35%. Short-term seawater immersion at room temperature (≤60 days) does not induce cracks or defects (≥10 μm) on the composite's surface. The composite's modulus decreases as moisture absorption increases, with the longitudinal tensile modulus dropping by an order of 10^-5%, while the other engineering constants decrease by an order of 10^-3%. The modulus also decreases with rising temperature; the closer the temperature is to the matrix's glass transition, the faster the modulus declines, with the longitudinal tensile modulus decreasing by 0.84%, and the other engineering constants decreasing by 100%. This research provides valuable insights for the engineering applications of composite materials in marine environments.