STMS: Cross-scale tribological models of the frictional contact in tangential-impact tightened bolted joints

• Applicants: Professor Dr.-Ing. Albert Albers; Professor Dr.-Ing. Sven Matthiesen
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511570411

When tightening bolted joints, approx. 80 % of the tightening torque is required to overcome the friction. This means that even a small variation in the coefficient of friction results to a large variation in the resulting preload. This effect is particularly large in case of tangential impact wrenches, which are widely used in industry, because the scatter usually adds up over the number of impacts and deviations therefore accumulate. Despite the deviations in the preload, tangential impact wrenches are popular because, for example, they mechanically decouple the user. However, due to the strong scatter, bolted joints are often oversized, which increases the required resources for designs with bolted systems. Further weight-saving potential can be realized by adapting the bolted joints. This is particularly interesting in the field of lightweight construction. Tangential-impact tightening methods will continue to play an important role in assembly processes in the future. By analyzing and accurately modeling the friction mechanisms, assembly and bolting systems can be adapted by improving the predictability of the preload force. There is a lack of macro-level friction models, which can be used to describe the friction condition in the thread contact of bolted joints and to predict the preload in the tangential-impact tightening process. Therefore, the aim of the project is to investigate the tangential-impact tightening process by developing a cross-scale method for determining the coefficient of friction in through-bolt joints and taking it into account when tightening bolted joints.The investigation of the mechanisms requires a cross-scale approach, since parameters from both micro- and macro-level influence the tightening torque. Due to the large number of different bolted joints commonly used in designs, a scalable model for different bolt sizes is target-oriented. For this purpose, based on the real topographies of threaded surfaces, a micro-level friction model is created using the finite element (FE) analysis, which is integrated into a macro-level multibody simulation model. Both the FE simulation and the multibody simulation model of the entire bolted system are validated by physical experiments on the Bolt Tribology Test Bench (STP).

• DFG Programme: Research Grants