This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

For industrial applications fatigue analysis is established as an important addition to strength analysis with finite elements. Based on stress results design decisions are made to improve the performance of parts and assemblies. Damage, the result of the fatigue analysis, significantly extends the knowledge about structural behavior under loads compared to pure stresses. In lightweight construction, this knowledge advantage is crucial. The industrial standard so far is to run fatigue analysis in a separate software from stress analysis software. This error-prone, difficult and time-consuming process slows down the development process. A fundamental change is necessary to improve the process significantly. This necessary breakthrough can only be achieved by a new approach in which fatigue analysis is integrated into the FEM solver. This offers two principal advantages for industrial application. The access is simplified, and the efficiency is raised drastically. The new integration approach makes it effortless for the user to add fatigue analyses to their stress analyses. The integration of the fatigue analysis in the FEM solver enables simplified access. Damage can be calculated and exported as an additional secondary result during stress calculation. Already calculated matrices, the stresses at element gaussian points with the knowledge of element shape function, and stresses at the interior of the structure for accurate stress gradient functions are used directly. The additional effort for material fatigue input is small and can then be reused. Material input is significantly simplified by a SN-curve generator based on the FKM guideline. The SN-curve generator determines the material SN-curve automatically from the inputs, one of the 23 FKM material group numbers, the failure strength and the yield stress. Since not only nodes but also the full element and surface information are available, the local SN-curves can then be calculated internally with the considering influence factors such as the surface finish, roughness factor or boundary layer factor, without any additional user effort. The damage results are determined directly by the general FEM software, the standard industrial process is reduced to starting one single software. Data management of huge stress files is no longer necessary. This speeds up product development, makes it simpler and improves its quality at the same time. The second major advantage of integration are the drastically reduced run time and disc space requirements. The solver data structure is optimized for HPC, a uniform database is used, interfaces are eliminated, and unnecessary or duplicate data storage is completely avoided. The hard disc limit that previously existed for large, finely meshed models is eliminated by automatic 'œon the fly' stress calculation, which means that only just required stresses are calculated at that moment and not stored. This allows significantly larger industrial models and the run time for fatigue analysis is drastically reduced. The fast run time and the simple input enables fatigue analysis as a standard application for FEM analyses. The improvements and simplification of handling are clearly shown using a practical example of an analysis process and the SN-curve determination. The fast computing-times and low storage space consumption are illustrated using an industrial example of a truck chassis. The integration of fatigue analysis is done in the commercial FEM solver software PERMAS.