Lifetime calculation model for sheet metal in the area of frictional connections

• Applicant: Dr. Robert Szlosarek
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525498704

The proposal deals with fatigue cracks in sheet metal near frictional connections. This can be observed for bolt joints. Due to the fatigue crack the lifetime respectively operating life will be limited. One typical example is the fatigue crack initiation in the area of the bolt joint between hub and rim of utility vehicles. In own publications and references of other authors it is stated that the cycles to fatigue crack initiation depend strongly on the pretension of the bolt. Regarding the position of the crack initiation it is stated that for low pretension the crack arises at the clearance hole and for high pretensions in the contact zone between the bolt and sheet metall. This observation results in the conclusion that the fatigue crack is initiated by mechanical stresses in combination with tribological loading due to the contact pressure and relative slip between the bolt and sheet metal. The aim of the research proposal is to find a general model for this type of loading in order to enable a prediction of the location of the crack initiation and the cycles to crack. To achieve these objectives the following steps will be done. Firstly, the fatigue properties of a representative sheet metal and different bolt joints will be observed by experiments. Secondly, tribological experiments will investigate the fatigue crack initiation due to different friction coefficient, contact pressure and relative slip amplitude. Therefore, the contact pressure between the bolt and the sheet metal will be measured by a pressure measurement film and compared to numerical models. The model for the combined mechanical and tribological loading will be based on the stress analysis by using the finite element method. For that reason, existing models for the fatigue crack initiation induced by mechanical stresses will be implemented. In particular, it is planned to improve the critical plane approach by using the Newton’s method. The fatigue damage model for the tribological loading will be based on the experimental results. Finally, the models for the mechanical and tribological fatigue analysis will be combined and validated by the experimental results. The developed damage model will be applied and validated also by other frictional connections like tapered interference fit. Within the research project it is planned to combine the fields of fatigue and tribology research of the institute and to strengthen the research for the combined mechanical and tribological induced fatigue crack initiation.

• DFG Programme: Research Grants