Restoration of Ultimate Strength of Dented Hemispheres Under External Hydrostatic Pressure

This study aimed to restore the ultimate strength of dented stainless-steel hemispheres with a radius of 90 mm and a thickness of 0.86 mm. All of the hemispheres were subjected to external hydrostatic pressure. Small stainless-steel stiffened caps were used to eliminate the effect of indention on the ultimate strength. These caps had a radius of 36 mm, a thickness of 0.76 mm, and a height of 10.44 mm. Six hemispherical samples, including two intact hemispheres, two dented hemispheres without stiffening, and two dented hemispheres with stiffening, were prepared. Each hemisphere was geometrically measured for shape and thickness, hydrostatically tested for destruction, and numerically evaluated for comparison. The experimental and numerical data agreed well with each other. As a result, a spherical cap can effectively restore the ultimate strength of dented hemispheres under external hydrostatic pressure. The proposed restoration approach can be used to strengthen underwater pressure hulls with large local geometric imperfections.