Analysis of the impact of residual stress on instability and collapse of submarine pressure hulls

Abstract

Residual stresses and geometric imperfections are unavoidable consequences when manufacturing a submarine pressure hull. These effects can reduce collapse pressure by promoting earlier yielding, particularly in regions subjected to compressive stresses.

In this work, nonlinear finite element analyses were performed on ring stiffened segments of a pressure hull using Abaqus to investigate how residual stresses and geometric imperfections influence the collapse behavior. Residual stresses from welding and cold bending were implemented as initial stress fields using distributions from British Standard 7910:2019 and analytical cold bending formulations applied to pre-defined manufacturing-affected element sets. To investigate the effect of solely geometric imperfections, displacement fields obtained from relaxation of the residual stress state were imported as initial imperfections in separate analyses. Both the individual effect of residual stresses and the combined effect were studied.

The results show that cold bending, plating-web fillet welds and girth welds have the most significant influence on collapse pressure. Both residual stresses and geometric imperfections reduce the collapse pressure, but residual stresses have a stronger influence. Relative to the ideal, stress-free analysis of nominal geometry, residual stresses in combination with geometric imperfections reduce the collapse pressure by 10.5 – 14.6%, whereas the corresponding effect of solely geometric imperfections is 5.0 – 6.8% for the tested cases. This thesis improves the understanding of how different manufacturing-induced residual stress sources influence collapse behavior and shows that the governing mechanism is closely linked to the introduction of compressive stresses in vulnerable regions.

Popular Abstract

According to a new study at LTH together with Saab Naval, residual stresses from welding and manufacturing may reduce the collapse strength of submarine pressure hulls more than the imperfections from tolerances alone.

Submarine pressure hulls are designed to withstand extreme water pressures at great depths. However, manufacturing processes such as welding and rolling introduce residual stresses – stresses that remain inside the material after production. These processes can also deform the structure, creating geometric imperfections that affect collapse behavior.

The study investigated how residual stresses and geometric imperfections interact and influence the collapse pressure. The collapse pressure is the pressure at which the structure fails and collapses, similar to a soda can under external pressure. While both effects have been studied separately, their combined influence is less studied.

The work was carried out using the finite element method, a numerical simulation technique where the structure is divided into thousands of smaller elements. By analyzing how each element behaves under pressure, the collapse behavior of the entire hull can be predicted. A fictitious pressure hull was modelled to study the effects of residual stresses and geometric imperfections. However, the model was designed to resemble the design of real submarine structures in terms of both material and geometry, as found in the literature.

The results showed that a pressure hull containing both residual stresses and geometric imperfections collapses at lower pressures than a hull with imperfections alone. The location of welds was also found to be important. For instance, circumferential welds affected collapse pressure more severely than welds aligned along the submarine’s longitudinal direction.

Welding is unavoidable in submarine manufacturing and contributes heavily to reducing collapse pressure. In fact, the total length of welds in a submarine can correspond to the entire width of Skåne. Understanding how these welds influence structural integrity is therefore important when designing pressure hulls. Interestingly, residual stresses are not always harmful. In some cases, carefully designed welds can deform the structure in a way that counteracts the natural collapse path and improves stability.

These findings contribute to a new methodology for predictions of the structural response, potentially leading to more efficient and improved submarine designs.

• author: Garme, Greta and Olanders, Jesper
• supervisor: Martin Fisk
• organization: Solid Mechanics; Department of Construction Sciences
• alternative title: Analys av restspänningars inverkan på instabilitet och kollaps i ubåtstryckskrov
• course: FHLM01 20261
• year: 2026
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• publication/series: TFHF-5000
• report number: TFHF-5276
• language: English
• id: 9242539
• date added to LUP: 2026-06-25 13:35:44
• date last changed: 2026-06-25 13:35:44