Exploiting spring-back differences for joining and pre-stressing sheet metal structures with tendons during forming - A mathematical-physical process model

Pre-stressing enables slender and high-strength structures in civil engineering. Previous studies have shown that it also offers a high potential for lightweight design of load-bearing sheet metal structures. Here, it is not only possible to join the sheet metal structures with the necessary tendons during a forming process, but also to prestress them at the same time. However, a targeted application of this technology requires a comprehensive understanding of the process mechanisms as well as calculation methods enabling an efficient structure and process design. To achieve this, the present article describes an analytical model of the underlying process mechanisms during the elastic-plastic forming process as well as the creation of the pre-stressing force acting between tendon and metal structure after spring-back. It is then transferred to two application-oriented processes. Numerical parameter studies serve the validation of these models and the further comprehension of additional process phenomena. It is shown that only a few geometrical, material and process related parameters are required to accurately calculate the pre-stressing force with a deviation of mostly less than 10 % from the numerical results.