Experiment and numerical analysis of delamination mechanisms of CRFP composites under seawater hygrothermal environments

This study investigates the delamination failure mechanisms of T700/8911 carbon fiber reinforced polymer (CFRP) composites in seawater environments through combined experimental and numerical approaches. Three-point bending tests were conducted on specimens with [0° 16 //0° 16 ], [0°/90°] 4s //[0°/90°] 4s and [15°/-15°] 4s //[15°/-15°] 4s layup patterns under both ambient (25°C) and accelerated hygrothermal conditions (70°C temperature and 95% relative humidity). Experimental results revealed that moisture absorption caused a 23–37% reduction in interfacial bond strength. This reduction significantly altered failure modes from classical delamination to predominant interfacial debonding. The finite element model developed in ABAQUS incorporated humidity-dependent cohesive zone parameters and modified traction-separation laws, achieving excellent correlation with experimental data. Key findings demonstrate that hygrothermal exposure increases interlaminar fracture toughness while reducing in-plane modulus, leading to higher critical loads (28–35% increase) but lower stiffness in the linear elastic stage. The cohesive zone modeling approach successfully captured the three-phase delamination process: initial elastic deformation, critical crack initiation, and stable propagation. Analysis of mode mix ratios showed cohesive elements transition from shear-dominated to tensile-dominated damage as delamination progresses. The study establishes quantitative thresholds for interfacial stiffness reduction (15–20%) and provides a validated modeling framework for predicting performance degradation of marine composites, offering valuable insights for designing durable offshore structures in seawater environments.