P 1418 - Profile straightening by partial rolling during roll forming

P 1416 - Extension of the areas of application of hot-dip galvanised steel components in combination with beam welding processes The aim of the project was to extend the range of applications for hot-dip galvanised components and to increase the cost-effectiveness of infrastructure projects through the advantages of laser beam welding in a vacuum (LaVa). The aim of this study was to determine the extent to which laser beam welding is suitable for joining large hot-dip galvanised components. The key point here was to first galvanise and then weld the components by modifying the process, which is only possible with laser beam welding in a vacuum. The motivation of the project was therefore to model the welding and galvanising process as precisely as possible and to validate the numerical models. It was found that the combination in the new process sequence produces favourable residual stress states. A further objective was to optimise the welding process, including the prevention of contamination of the coupling window of the vacuum chamber and the development of integrated corrosion protection. This serves as an alternative to thermal spraying. Subsequently, welds and tests were carried out on components from different process chains in order to investigate the occurrence and influence of residual stresses. The results of the welding investigation show that the joining of galvanised sheets up to 20 mm sheet thickness with zinc up to 200µm in the joining gap is only possible to a limited extent, whereas solid welded joints can be produced in accordance with the standard up to sheet thicknesses of 40 mm when welding without zinc in the joining gap, only on the surface with up to 400µm. The limited weldability is shown by the fact that the weld seam has a pronounced seam collapse, as there is no material in the joint gap due to the evaporating zinc. A model was developed and validated from experimental tests and their numerical calculations. This allowed the stress and strain states after galvanising, laser welding and their combination to be investigated. It was found that the thermal process does not leave any noticeable restrictions in the component after the production steps. Due to the restrictions imposed by the joining process on butt joints, only these can be considered validated for the time being. Fillet welds and other welded joints should therefore be considered in future investigations. The aim of the research project was achieved. Publication: June 2024 Authors: R. Kühne, Dr.-Ing. H. Bartsch, Ch. Frey, Dr.-Ing. S. Olschok

P 1415 - Innovative load capacity analysis of welded steel components using damage mechanics In this project, the load-bearing behaviour of welded joints, in particular with high-strength steels, was investigated experimentally and using damage mechanics simulations. To this end, a methodology was first developed that allows damage mechanics parameters to be derived for the heat-affected zone and the weld metal. An approach was developed to take into account the mesh size dependency, prepared for application and implemented in commercial FE software. The numerical models were validated in laboratory and component tests. In addition, numerical studies on geometric and material influences on the load-bearing behaviour were carried out. The result of the experimental and numerical investigation is that the influence of soft zones (softening) in the heat-affected zone and also of undermatching in welded joints on the bearing loads is significantly lower than the differences in strength would suggest. The soft zones (softening zones) are forced into softening by high strains, which changes the load-bearing effect. The design rules for welded joints were also scrutinised. This revealed potential for optimisation. Using the findings on the minor influence of softening zones on the load-bearing capacity, a weighted approach to the tensile strength of weld metal and base material for undermatching joints was derived, which means an improvement in the design rules. The results will promote the use of high-strength steels in the future, which will benefit in particular the planning companies, e.g. engineering offices, as well as manufacturers, which predominantly come from the SME sector. In addition, Germany will be strengthened as a business location, as qualifications in the production of welded joints of high-strength steels are available here. The results enable more economical steel constructions, which reduces the consumption of resources and promotes the use of steel as a material. The objective of the research project was achieved. Publication: October 2023 Authors: M. Sc. F. Eyben, M. Sc. H. Bartsch, Dr.-Ing. S. Schaffrath, Univ.-Prof. Dr.-Ing. M. Feldmann, Ch. Häffner, M. Sc., M. Sc. D. Lenz, Dr.-Ing. M. Könemann, Univ.-Prof. Dr.-Ing. S. Münstermann

P 1413 - Shape optimisation of welded-on lamellae under fatigue loading A weight-optimised design to avoid an unnecessarily increased consumption of resources is becoming more and more important in terms of economic efficiency and especially against the background of significantly increased procurement prices. Localised reinforcement measures, so-called reinforcement lamellas, are used for this purpose in the construction industry and also in other steel processing sectors. These locally increase the cross-section to match the external stress. In the case of alternating stresses, such as those caused by traffic passing over steel bridges, these structures must be designed to withstand fatigue failure. Here, the very notch-sharp end of the lamella leads to a poor notch case classification, which represents the resistance side in the fatigue analysis. The aim of the research project was therefore to make the end of the lamella significantly less notchy by optimising its shape and production. To this end, various disc shapes and designs were analysed numerically in a first step as part of the preliminary investigations. Experimental investigations were then carried out on selected variants. By varying the disc shape and different designs with, for example, tapered weld seams, the two most promising shapes and designs were then selected for the main tests as part of the preliminary investigations. Influencing factors such as the material quality, the design and the installation situation were analysed experimentally as part of the investigations. In addition, the transferability of the small component tests to larger dimensions was checked by means of large component tests. The design of the tapered lamellae with tapered weld seams proved to be very notch resistant and led to a significant increase in fatigue strength in both the untreated and post-treated states compared to conventional standard moulds. In addition, the parameter range of the experimental tests was extended by a comprehensive numerical parameter study and the design of the lamella shapes was additionally optimised by accompanying numerical models. As part of the project, a design recommendation for tapered weld seams with tapered lamellae was developed on the basis of the nominal and notch stress concept. In order to enable applicability in practice, additional design recommendations were developed that contain quality requirements with regard to the design. The aim of the research project was achieved. Publication: February 2024 Authors: A. Dürr, J. Roth, M. Mensinger, N. Rausch, M. Wilnhammer

P 1423 - Qualification of numerical simulations for the characterisation and evaluation of the boundary layer condition of free thermal cut surfaces As part of the research project "Qualification of numerical simulations for the characterisation and evaluation of the surface layer condition of free thermal cut surfaces", thermal cutting tests were carried out, the characteristic quality features were determined experimentally and compared with the results from the numerical investigations. For this purpose, the laser cutting process was selected as the main method and tests were carried out on a structural steel S355NC and a high-strength steel S1100M. It can be seen that the hardness integrity value of DIN EN 1090 is clearly exceeded with S1100M and that the maximum hardness of around 570 HV1 is not directly at the cutting edge. It drops to around 480 HV1 to 520 HV1 up to the surface. A decreasing carbon content at the cutting edge could be one reason for this. In comparison to the numerical investigations, the following points can be determined: The dimensions of the heat-affected zone can be determined via the numerical calculations and are in good agreement with the micrographs. The phase fractions at the low cooling rates indicate a complete transformation into martensite at the surface layer. The maximum hardness of the HAZ agrees with the experimental results. The hardness distribution over depth in relation to the HAZ is in good agreement. Deviations in the width of the HAZ are very small. The results show that the cutting process can be modelled by numerical simulation and that the surface layer condition can be evaluated after the cutting process. The microstructure, the maximum temperatures and the hardness distribution can be determined and thus offers the possibility of saving time and costs when determining the quality of thermal cutting edges. The effort required to create the numerical models must be put into perspective here and the method must be accepted in quality testing. The aim of the research project was achieved. Publication: December 2022 Authors: M. Sc. P. Diekhoff, Dr.-Ing. J. Sun, Dr.-Ing. T. Nitschke-Pagel, Prof. Dr.-Ing. K. Dilger