Torispherical head buckling stability analysis and design improvement based on elastic-plastic theory

Torispherical heads are prone to buckling failure in the transition zone under internal pressure. Based on elastic-plastic theory, this study employs numerical analysis to investigate buckling instability, incorporating geometric nonlinearity, material nonlinearity, and initial geometric defects. The results show that the critical buckling load is highly sensitive to initial defects: a reduction in local shell thickness from 5 to 3 mm causes a 54.8% decrease in the critical buckling load. Over the studied thickness range, the critical buckling load increases approximately linearly with head thickness. To mitigate buckling, two improvement schemes were proposed and compared: longitudinal stiffening plates and a circumferential stiffening ring. The circumferential stiffening ring reduces the peak stress by 60.3%, whereas the longitudinal plates achieve only a 17.4% reduction. Thus, the ring significantly enhances the critical buckling load and effectively suppresses wrinkling in the transition zone. This study provides quantitative benchmarks for defect tolerance and design improvement of torispherical heads and similar thin-shell structures.