P 967 - Reinforcement elements for composite bridges

P 1014 - Development of a concept to evaluate the brittle fracture tendency of high-strength bolts of large dimensions when used at low temperatures High-strength HV system bolt assemblies are increasingly being used as prestressed assemblies in large dimensions up to M72 in highly stressed steel structures. In addition to static and cyclical stresses, the connections are also exposed to low temperatures. It is known that the risk of brittle fracture increases with increasing thickness of steel components at low temperatures - in principle, this also applies to larger bolt diameters. In this research project, systematic investigations were carried out into the brittle fracture tendency of high-strength bolts of large dimensions in the diameter range from M24 to M64 at low temperatures. First, the mechanical properties were characterised and the fracture toughness behaviour was described in the form of notched bar impact tests and fracture mechanics tests. The transition temperatures from the notched bar impact test and fracture mechanics test could be correlated with each other using existing correlation approaches. By analysing finite element calculations, it was possible to identify the stress state in the first load-bearing thread as decisive with regard to brittle fracture. In component tests at low temperatures, in which the screws were pre-damaged from a mechanically introduced notch under a fatigue load, it was clearly demonstrated that the screw steels currently used are not at risk of brittle fracture when used at temperatures down to -50 °C. Based on the test results, fracture and damage mechanics calculation models were created in order to define minimum requirements for the material properties to prevent brittle fracture. The damage mechanics model showed very conservative results here, so that it is currently not possible to derive minimum requirements without further development. The fracture mechanics model was able to reproduce the test results, but also delivered conservative results in the derivation of minimum requirements. The fracture mechanics model must be further verified on the basis of a broader database. In the present research project, however, a fundamental evaluation of the brittle fracture tendency of high-strength bolts of large dimensions at low temperatures was carried out. It was shown that the bolt steels currently used are not susceptible to brittle fracture when used at low temperatures. Publication date: April 2019 Authors: Prof. Dr.-Ing. habil. N. Stranghöner, Ch. Lorenz, M.Sc., Prof. Dr.-Ing. M. Feldmann, S. Citarelli, M.Sc., Prof. Dr.-Ing. W. Bleck, Prof. Dr.-Ing. S. Münstermann, Dr.-Ing. Brinnel

P 1016 - Self-pierce riveting of high-strength steel materials in mixed structures using self-clinching self-pierce riveting elements The statutory regulations to reduce greenhouse gas emissions are prompting the automotive industry to implement consistent lightweight construction. The reduction of CO2 emissions to an average of 95g CO2/km in passenger car traffic by 2020 has been decided. The vehicle body, which accounts for over 30% of the total weight, offers the greatest potential for implementing lightweight construction, which can be achieved by using high-strength steels and other lightweight materials such as aluminium. In particular, the mixed construction of press-hardened steel and aluminium in combination with adhesive bonding leads to economical lightweight construction solutions. One suitable technology for joining this combination of materials is full-punch rivet bonding. However, full-punch rivet bonded joints lead to gaps between the parts to be joined and thus to poor adhesive bonding, especially when using particularly thin materials for the parts to be joined. The aim of the research project is to develop a modified self-pierce riveting technology for joining high-strength sheet materials with aluminium alloys. This is achieved by modifying the solid self-pierce riveting process so that it works without an embossing ring on the die-side tool. The embossing contour is positioned directly under the setting head of the rivet. Joints produced using the innovative self-clinching self-pierce riveting process should then be characterised by low joining process-related deformations and good adhesive bonding. As part of the research project, geometry optimisations were carried out using simulation, which were validated by experimental investigations. The flexibility of the newly developed process was then determined on the basis of a process analysis. In addition, the joining properties of the process in combination with adhesives were optimised and the property profile recorded as part of investigations into hybrid joining. A joining process was developed with which it is possible to produce efficient and economical joints from 22MnB5 sheets and aluminium sheets in the thin sheet range. Publication: 2017 Authors: Prof. Dr.-Ing. G. Meschut