P 1158 - New evaluation options for the toughness and damage tolerance of thin-walled structures

P 1152 - Approach for the numerical determination of hardness evolution in the mould surface layer due to thermal loads during mould hardening Tailored tempering, based on mould hardening, is a process for the production of components with tailored properties. By using partially preheated tools (approx. 500 °C), the critical cooling rate of the 22MnB5 blank material is deliberately undercut locally, thereby suppressing martensite formation in the component. The increased tool temperature and the press forces that occur lead to a high thermal load on the tool engraving and ultimately to signs of wear, which are dependent on the hardness evolution and tempering effects that occur. This affects the dimensional accuracy of the components and the tools have to be reworked or even replaced, which is costly and time-consuming. More precise knowledge of the processes in the tool surface and their consideration in the numerical process design contribute to a significant increase in process understanding. In this context, the heat transfer between the workpiece and the tool is another important aspect that is required to calculate the prevailing surface temperatures of the tool. Precise calculation of the surface temperatures allows changes in properties such as decreases in hardness due to tempering effects in the tool surface layer to be predicted, which are important for estimating the service life of the tool as a whole. By knowing the influences on the wear properties of the tool materials, measures can be taken to realise significant cost savings for SMEs. The scope for costly tool repairs can be reduced and tool life improved. The aim of the research project is to consider the hardness evolution of the tool material as a function of the number of thermal cycles in the wear calculation and thus increase the quality of the results of the simulative prediction. For this purpose, the hardness development was determined metallographically using the determined temperature curves in the tool surface during a model test. Based on this data, an analytical approach was developed and implemented in a commercial FE programme that enables the local tool hardness to be calculated as a function of the forming cycles and the existing tool temperature. Finally, a validation was carried out as part of a self-designed and constructed model test for the production of components with locally controlled hardness distribution. With the implementation developed in the project, the decrease in hardness in the tool could be predicted realistically, thus achieving the objective of the research project. Publication: 2021 Authors: Prof. Dr.-Ing. B.-A. Behrens

P 1151 - Testing of the laser beam submerged arc hybrid welding process for industrial applications in the area of large sheet thicknesses The previous series of tests on laser beam-submerged arc hybrid welding have clearly demonstrated the fundamental usability of the newly developed process variant. The weld seam qualities achieved in position-counterposition joint welds using both types of laser beam (CO2 and solid-state) are more than satisfactory within the scope of the investigations carried out. Sheet thicknesses of up to 50 mm could be reproducibly joined with low porosity. The aim of the current project was to optimise and homogenise the mechanical-technological characteristics of joint welds using the position-versus-position technique over the seam depth, based on the testing of suitable wire-powder combinations. A solid-state laser was used as the laser beam source, which provided a spot diameter of 0.4 mm with the applied optical components. In the same step, the increase in process stability against slag running into the laser foot spot was investigated by testing correspondingly tough and current-carrying welding flux variants. Furthermore, in addition to a sensor system for recording and automatically controlling the laser beam-induced welding depth, a sensor system for detecting precipitating submerged arc welding powder and advancing slag/melt was determined and tested. Publication: May 2020 Authors: Professor Dr Ing. U. Reisgen, Dr.-Ing. S. Olschok, O. Engels M.Sc.

P 1150 - Usability of weathering-resistant structural steel in bridge construction Weather-resistant structural steel is protected from corrosive attack by a weather-resistant barrier layer, the patina. Special alloying elements such as chromium, copper, nickel and phosphorus lead to the formation of the patina. The patina results in less corrosive erosion than with unalloyed structural steel, making an additional corrosion protection system superfluous. This leads to demonstrable economic and ecological benefits for structures used over the long term, such as bridges. In addition, weathering-resistant structural steel has largely the same mechanical properties as unalloyed structural steels, which allows it to be used without restriction in accordance with Eurocode 3. However, in order to utilise these material advantages, a design adapted to the corrosion behaviour is required, which in the past has led to a limited use of weathering-resistant structural steel in bridge construction. For this reason, the present FOSTA short study was carried out to investigate the corrosive behaviour, the build-up of the protective patina of the steel under current atmospheric conditions and the load-bearing capacity of this material in slip-resistant prestressed connections. The aim was to demonstrate the current efficiency of weathering-resistant structural steel for bridge construction. The results provide an initial statement on corrosion behaviour, which demonstrates the possible applications of weathering-resistant structural steel under current atmospheric conditions. It was also possible to show that it is advantageous to use pre-stressed, non-slip connections made of weathering-resistant structural steel that are weathered and without a non-slip coating. It has also been shown that the requirements for the load-bearing capacity of these connections are met despite weathering. Publication: 2016 Authors: D. Ungermann, D. Rademacher, A. Peters, S. Friedrich, P. Lebelt