Progressive fatigue damage mechanisms and residual strength prediction of CFRP pressure shell under cyclic hydrostatic pressure

To meet the increasing demand for lightweight, high-strength, and fatigue-resistant deep-sea pressure structures, the fatigue behaviour of carbon fibre-reinforced polymer (CFRP) cylindrical pressure shells under cyclic hydrostatic pressure was investigated through a combined experimental and numerical approach. A progressive damage-based analysis framework was developed by incorporating fatigue failure criteria together with gradual and abrupt material property degradation, enabling the prediction of damage evolution and residual strength degradation. Cyclic hydrostatic pressure tests with 200 loading cycles were conducted, and the residual ultimate strengths of the three tested shells decreased to 91.48%, 92.96%, and 94.40% of their initial strengths, respectively. The numerical predictions showed good agreement with the test results, with deviations within 5%, demonstrating that the proposed model can effectively capture the structural performance degradation under cyclic loading. Furthermore, the numerical results revealed the fatigue damage evolution process from damage initiation to final structural failure in the pressure shell. The present study provides a theoretical basis and practical support for fatigue damage assessment and safe service evaluation of deep-sea composite pressure shells.