23. Mode Superposition Techniques for a Priori High Stress Detection and Fatigue Hotspot Identification

For the evaluation of a structure’s fatigue life, the knowledge of detailed stress histories plays a crucial role. In industrial application, the finite element method (FEM) has become the most widely applied tool for numerical stress- and subsequent fatigue analyses. While most computational cost is spent for the evaluation of time-dependent global stress fields, the areas that are relevant for durability analyses are limited to highly stressed local regions (hot spots). For the reduction of processed data, a subsequent fatigue analysis can be carried out using so-called hot spot filters, pointing out highly stressed elements. Available methods can be summarised as posteriori methods, as they root in the calculated stress histories or modal contributions. In this paper, a novel approach is developed, based on the a priori superposition of modal fields by means of appropriate prediction of maximum modal contributions. Main influences on modal contributions are identified and suitable parameters for superposition are summarised. As modal fields are scalable, special attention is paid to mode normalisation. Combining the developed approach with material data, appropriate threshold values for hot spot detection are presented. For validation, numerical fatigue analyses are carried out on a complex FE-model from automotive industry.