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258 Nuclear Reactors and Fuel Cycle | Progress Report

Residual Stress Assessment
Applied to Finite Element Pressure
Hull Instability Analysis

Residual stress produced by cold bending and
welding processes contributes to collapse pres-
sure reduction on submarine hulls. Usually,
the residual stress profiles used to quantity
this reduction is obtained from analytical or
numerical models.

However, such models have limitations to take Figure 15. Residual stress profile.
into account in the same time cold bending
and welding. Hence, experimental analyses are
necessary to better quantify the residual stress.

Based on that, experimental residual stress
profiles through the material thickness were
approximated for each region on the normal
frame (see Figure 15). These profiles were intro-
duced 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 Figure 16. Nonlinear buckling failure mode with re-
sidual stress, displacements in mm.
considered on the analysis in a pressure hull
geometry defined based on open source doc-
uments. In the end, it was verified that the
residual stress reduces the collapse pressure as
a large 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 collapse pres-
sure reduction at higher out-of-roundness and
out-of-straightness defect amplitudes. (see
Figure 17. Depth x radial displacement curves for 0.3%R out-of-
Figures 16 and 17). roundness defect amplitude and no out-of-straightness defect.

Instituto de Pesquisas Energéticas e Nucleares