Study on the ultimate strength of stiffened plates under combined effects of residual stress relaxation and plastic damage accumulation

Objectives To accurately assess the in-service safety of ship structures, it is essential to clarify the effects of welding-induced residual stress relaxation and cumulative plastic damage on their load-carrying characteristics and to develop a rapid method for predicting ultimate strength. Methods Finite element models of stiffened plates incorporating initial imperfections were established using the general-purpose finite element software ABAQUS. The ultimate strength and failure mechanisms of stiffened plates under cyclic loading were systematically investigated, and a physics-informed neural network model incorporating the evolution laws of load-carrying capacity was developed. Results The results indicate that, under low-amplitude cyclic loading, the relaxation of welding-induced residual stresses can increase the ultimate strength by up to approximately 10%. By contrast, under high-amplitude cyclic loading, progressive accumulation of plastic damage leads to a maximum reduction in the ultimate strength exceeding 70%. Strain amplitude and the number of loading cycles make the largest contributions to ultimate strength degradation, accounting for 26.1% and 17.9%, respectively. Approximately 93% of the database samples have absolute relative errors below 5%, while the coefficient of determination for the predictions on the independent dataset is R2 = 0.984, indicating that the proposed neural network model has good predictive accuracy and generalization capability. Conclusions Residual stress relaxation and cumulative plastic damage exert significant effects on the ultimate strength of stiffened plates subjected to cyclic loading. The proposed prediction model provides a reference for the strength assessment of ship structures.