Keywords: structural weld simulation, local fatigue assessment, post-weld treatment, high frequency mechanical impact, Noch stress or strain approach.

By the permanently increasing requirements to save energy resources and thereby reduce noxious emissions, the design of lightweight and endurable welded structures is fundamental. In the case of high-strength steel welded joints, post-treatment methods enable the opportunity to enhance the fatigue behaviour significantly. One common technique in industrial applications is the high frequency mechanical impact (HFMI) treatment. Gained local benefits increasing fatigue strength are a compressive residual stress state, a reduced notch effect at the weld toe, and additionally local work hardening of the material. To optimize the treatment time and subsequently reduce the total costs a fatigue assessment based on numerical simulation of the whole manufacturing process is of uppermost interest. This paper presents the set-up of a simulation loop including structural weld simulation, numerical computation of the HFMI-process, and finally, a numerical estimation of the local fatigue life.

A thermo-mechanical coupled weld process simulation using Sysweld is built-up to assess the course of residual stress and strain conditions arising from welding. The resulting local microstructural dependent material behaviour and residual stresses are transferred as mechanical cards thereby invoking the solver Abaqus for the subsequent numerical simulation of the HFMI-process. Hence, major influences such as different material hardening models, friction conditions and special process characteristics are considered. Finally, a numerical estimation of the local fatigue behaviour by the local stress and strain approach is performed using the postprocessor fatigue packages Femfat and nCode. A comparison of the numerical simulation with experimental fatigue test results proved their basic applicability, as well as advantages in local fatigue life assessment but also numerical limitations of the simulation tools presented. The major benefit of the established simulation chain is the opportunity to study different weld process and HFMI-treatment parameters with regard to fatigue without the need of comparably expensive fatigue tests.

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