Multi-material design as a method of lightweight construction enables the targeted use of materials in a component by utilizing the individual material properties. However, this advantage comes with additional challenges for the product developer, such as the increased effort involved in identifying the design. Multi-material topology optimization is a method that can support the product developer in creating initial weight-optimized component designs in multi-material design in early phases. In addition, several state-of-the-art studies show that the position of the interfaces between the materials has an influence on the strength of the optimization result. These investigations took place in 2D and developed optimization methods which largely use non-linear building blocks, such as cohesive behavior. The non-linear components lead to an increase in computational effort and a reduction in the robustness of the optimization. In this article, a method for the consideration of adhesive-bonded interfaces in multi-material topology optimization in 3D by means of an objective function is developed. For this purpose, requirements are derived based on an analysis of the different load cases of a bond and these are used to create the method. The method is then successfully validated by means of two numerical experiments. In addition, the influence of a newly introduced parameter on the optimization results is investigated by means of a parameter study.

Impact tightening is widely used in industrial assembly of bolted joints. Friction plays a decisive role in the impact tightening process of bolted joints, yet the dynamic frictional behavior during this process remains insufficiently understood. While previous studies have focused on single bolt sizes, this work expands the experimental investigation to M10, M16, and M20 bolted joints, revealing scale-dependent frictional mechanisms. The influences of bolt diameter, impact wrench power, socket length and preload level on the distribution of coefficients of thread and bearing friction are analyzed. Results show that both bolt diameter and impact wrench power significantly influence the dynamic coefficients of friction, with smaller bolted joints exhibiting higher coefficients and greater scatter. These transitions indicate changes in real contact conditions and stick–slip behavior under impulsive torque input. These insights advance the understanding of frictional dynamics in impact tightening and provide quantitative input for improving predictive models of impact tightening and preload estimation, supporting the development of more reliable industrial assembly processes.