Modeling to investigate the mechanical degradation of carbon fiber-reinforced polymer composites subjected to salt-fog and ultraviolet radiation synergistic environment

Mechanical degradation of carbon fiber-reinforced polymer composites (CFRP) under marine environment has become an increasing important concern due to its significance to reliable service. This paper aims to establish models to investigate the mechanical degradation of CFRP under marine environment, in which the evolution of component materials properties, initiation and growth of internal microcracks and delamination damage were considered. A representative volume element with randomly generated fibers was established to calculate the mechanical properties before and after environment aging. The microcracks induced by environment aging were described by a defect hypothesis, and a two-dimensional tensile model was developed to determine the numbers and size of the defects. Then the moisture absorption behavior and hygrothermal residual stress were investigated by three- and two-dimensional models. Finally, the evolution of interlayers properties was revealed by a specimen-sized interlaminar shear model according to the traction–separation cohesive law. The results show that the cracks inside the material can lead to nonlinear changes of mechanical properties. Moisture distribution in composite laminate is not affected by the ply orientation, while the hygrothermal stress is closely related to the layup sequence and significant stress concentration can be observed in the fiber–matrix interface. The evolution of interlaminar shear performance can be well explained by the degradation factors of interlaminar strength and fracture energy.