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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.

During the pressure hull manufacturing, processes like cold bending and welding are often applied. These processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial preload in the structure, which accelerates the plastification process, decreasing pressure hull resistance. To quantify this reduction, a case study that considers residual stresses due to cold bending on hull plates and frame flanges had been performed using finite element models. The study encompasses hull diameters of 6, 8, and 10 m with hull plates and frame flange thickness from 20 to 30 mm, with HY100 steel. Finite element numerical analyses were done considering material and geometric nonlinearities. First, the cold bending residual stresses were determined using finite element models. Then, these cold bending residual stresses were introduced as initial stresses in the submarine pressure hulls' finite element models. In the end, it was possible to verify that the presence of cold bending residual stress reduces the submarine hull collapse pressure up to 4.3%.

During development of a spherical glass pressure hull made up of two hemispheres joined with a metallic joint ring, a problem of bearing edge cracking was encountered. A joint was developed through a series of model tests which placed the bearing edge in radial compression, thus eliminating the cracking. This joint was used to assemble a 56-in. spherical glass pressure hull which was proof-tested to 1610 psi (3650 ft) and cycled 100 times at 1000 psi (2250 ft). Three minor spalls occurred on the proof cycle. This spalling is attributed to either adhesion of the epoxy support material to the glass or support of surface irregularities by the epoxy. Testing was stopped at 100 cycles due to a failure in the epoxy seat-containing material. The joint concept appears workable to 4000 psi if the proper materials are used for the seat-containing material.

This study was initiated to: (1) perform an analytical structural analysis on an acrylic pressure hull, (2) compare the analytical results with all available experimental results, and (3) present an operating-depth curve. The design analyzed was a pressure hull incorporating twelve spherical pentagons of acrylic plastic bonded together to form a sphere with an outside diameter of 66 in. and a wall thickness of 2.5 in. Conical steel penetrations were located at the two poles. The experimental results were obtained from strain-gage data from two independent pressure tests to 500 psi on two acrylic hulls of the same design. The analysis on the structure was performed with a finite-element computer code with particular emphasis on the acrylic-steel boundary. The boundary conditions at the acrylic-steel interface were two extreme cases: perfectly fixed and perfectly free. A time-dependent yield-failure criterion for acrylic plastic was combined with the structural analysis to provide an operating-depth curve as a function of both time and temperature. Comparison of analytical and experimental results indicated excellent agreement. At a temperature of 70 deg F and a maximum of 50 hr load duration, the acrylic hull can operate to 1000 ft with a safety factor of 1.5 based on yield and a safety factor of 2.6 based on collapse.