Experimental Residual Stress and Geometric Imperfections on Pressure Hull Instability Analysis

Residual stress produced by cold bending and welding processes contributes to the collapse pressure reduction of submarine hulls. Usually, the residual stress profiles used to quantify this reduction are obtained from analytical or numerical models. However, such models have limitations to take into account cold bending and welding in the same time. Hence, experimental analyses are necessary to better quantify the residual stress. Based on that, this paper presents residual stress experimental results obtained at six points on a pressure hull prototype using X-ray portable system. Based on these results, the residual stress profiles through the material thickness were estimated for each region on the frame by using a polynomial approximation. These profiles were introduced in a nonlinear finite element numerical model to study the collapse pressure reduction. Experimental results available on the literature were also used. Material and geometric nonlinearities were considered in the analysis. The results show that the residual stress reduces the collapse pressure as part of the frame web has stress level higher than the material yield. The preload introduced by the residual stress plays a less important role for the collapse pressure reduction at higher out-of-roundness and out-of-straightness defect amplitudes.