Abstract

The strength assessment of welded structures is often conducted using FEA models with 3D continuum elements, especially when castings are involved. The accuracy of the corresponding displacement and stress fields is clearly superior to the one that can be obtained with shell element models. However, continuum element models exhibit a major disadvantage regarding the assessment of the stresses: The FE stress results at the weld root cannot be used directly for an assessment because they are strongly influenced by geometric singularities. The assessment of welds, on the other hand, relies primarily on equivalent linearized stresses across the weld section. Therefore, it is necessary to linearize the nonlinear FE stress fields. At a previous NAFEMS conference we have presented a first corresponding method, which is based on strain sensor elements. Unfortunately, the applicability of this method suffers from some geometric restrictions, and a more general solution is necessary. In this contribution, a fundamentally different and much more general postprocessing method is presented for calculating linearized stress fields in arbitrary sections of a continuum FE model. This method is based on the nodal forces of the FE elements adjacent to this section. From these forces an equivalent linearized stress field is calculated in a separate chain of bi-linear elements along the longitudinal direction of the section (weld). The corresponding algorithm was designed specifically for taking into account those nodal forces along the boundaries that arise from stress singularities. The problem is solved iteratively so that the linearized stress field equilibriates the FE element nodal forces. The calculated linearized stresses can be used directly for weld fatigue assessment (e.g., according to IIW). The proposed method has been implemented in the stress assessment software LIMIT along with an efficient workflow. The results are very encouraging and initiate further development of this method towards automated R1 notch stress assessment of welds.