Experimental and numerical analysis of strength degradation in CFRP-repaired pipes under fatigue loading

Carbon Fiber Reinforced Polymer (CFRP) repair of defective pipes offers high strength-to-weight ratio and corrosion resistance. However, when CFRP-repaired pipes operate in marine environments, they are often subjected to cyclic loading, such as vortex-induced vibrations due to pipeline spanning. Such cyclic loads cause progressive strength degradation, which necessitates investigation of their long-term performance and durability. This paper presents an experimental investigation of ultimate bending strength, fatigue life, and residual strength degradation of CFRP-repaired pipes under cyclic loading. A fatigue cohesive zone model is proposed for interface strength degradation under fatigue loads. Considering degradation of both interface and steel pipe, a numerical model is established to analyze residual strength. The numerical model is validated by experiments, with a maximum discrepancy of 4.13%. Through combined experimental and numerical analysis, degradation characteristics are examined, providing a reference for durability assessment of CFRP-repaired structures under cyclic loads.