Quantitative prediction and degradation mechanism of CFRP-TC4 adhesive joints under hygrothermal aging

Adhesive joints between carbon fiber reinforced polymer (CFRP) and titanium alloy (TC4) are widely used in aerospace and rail transit structures.They offer excellent specific strength and lightweight advantages.However, their long-term performance is often threatened by hygrothermal coupling environments.This study systematically investigates the mechanical degradation of CFRP-TC4 single-lap adhesive joints under varying temperature (40, 60, and 80 °C), humidity (95% RH and immersion), and aging time (0-720 h).The novelty of this work lies in quantitatively identifying humidity as the dominant factor affecting joint strength through response surface modeling, supported by experimental validation.Results show that both failure strength and stiffness decrease with aging, with a strength loss of over 40% after 720 h at 80 °C/100% RH.Fracture morphology evolves from interfacial or matrix failure to cohesive failure, while SEM and FTIR analyses reveal that moisture ingress and epoxy hydrolysis induce adhesive plasticization and functional group transformation.These findings provide a scientific basis for durability design and service life prediction of CFRP-metal bonded structures in humid and high-temperature applications.