Modeling techniques for local stresses used in fatigue assessment based on multibody dynamic simulation

Fatigue assessment is essential in designing structural components subjected to cyclic loading in mobile machinery. Real-time-capable multibody dynamic simulations can provide operational stress histories, but current modeling constraints limit the incorporation of local geometric features, such as weld-toe notches which are critical for accurate fatigue evaluation. This study evaluates the accuracy and applicability of the Unit Load Model (ULM) and a mode-based submodeling approach for recovering local cyclic stresses required for fatigue assessment. A loading history from a structural component of a forestry crane laboratory demonstrator is used for experimental validation, employing a strain gauge placed in the region experiencing the highest nominal stresses. The comparison includes FE analysis, direct stress recovery (DSR) from the multibody simulation, and the ULM. The normalized mean square deviations relative to experimental measurements were 5.86 % for the FE model, 4.83 % for DSR, and 1.61 % for ULM. For the notch detail, ULM predicted a fatigue life 15.1 % higher than that obtained with mode-based submodeling. The results show that both methods are suitable for operational fatigue assessment in mobile machinery.