Strain-based critical plane approach to predict the fatigue life of high frequency mechanical impact (HFMI)-treated welded joints depending on the material condition

After post-treatment with high frequency impact treatment (HFMI) of weld toes, a significant increase of fatigue strength or fatigue life can be achieved. Due to the lack of methods for the quantitative prediction of the HFMI benefits depending on the process and treated material, a widespread use of this process has not yet happened. One reason for that issue is that at the moment, no methods exist to predict the influence of the HFMI-treatment on welded components and structures at the moment in advance depending on the HFMI-treatment parameters. For this case, a strain-based approach based on the finite element (FE) simulation of the HFMI-process and the subsequent evaluation by critical plane approaches of the FE-post-processing was developed. This approach principally considers the beneficial effects of compressive residual stresses, notch effect reduction, and hardening of the HFMI-treated surface layer. Furthermore, residual stress relaxation during fatigue loading was taken into account. For numerical prediction of the influence of HFMI-treatment of welds, process parameters at the real device were measured and a suitable material hardening model was used from previous work to describe the conditions in the surface layer. After this, the process chain of welding, HFMI-treatment, and fatigue loading of butt joint specimen were simulated. The estimated fatigue life values were compared with the values of the fatigue tests for two different Treatment intensities and also a good agreement was reached.