P 1272 - Experimental and numerical investigation of the damping properties of bonded structures under dynamic loading

P 1271 - Application of the structural stress concept for steel structures subjected to fatigue loading This final report on the application of the structural stress concept to steel structures subjected to fatigue stress deals with structural stress-orientated evaluation approaches for the notch details of longitudinal stiffeners, transverse stiffeners and cross joints. The focus is particularly on the effects of manufacturing-related imperfections and thickness effects, which are investigated using suitable FE analyses and indirect stress increase factors. Extensive parameter studies on FE shell and solid models are carried out for this purpose. The numerical results are verified using our own experimental tests. For this purpose, static tensile and bending tests as well as experimental fatigue tests are carried out and analysed. On the one hand, the results can be used to verify the economic applicability of the structural stress concept compared to the nominal stress concept. On the other hand, specifications on the effects of imperfections and thickness effects can be determined, as some of the test series analysed are designed with intentional imperfections and different thicknesses. 3D laser scan measurements of all analysed test specimens enable a precise assessment of the imperfections present. In this way, stress concentration factors for the indirect determination of stress-increasing effects can be precisely determined and existing regulations can be verified. The results show that the structural stress concept for base plates with longitudinal stiffeners welded on both sides cannot be applied economically in many cases. It should be noted here that the evaluation of the static test series, using the normative notch cases of DIN EN 1993-1-9 [1], guidelines of the International Institute of Welding [2] and prEN 1993-1-9 [3], is subject to a wide scatter across regulations. With regard to transverse stiffeners and cross joints, the influence of imperfections on the decisive structural stress is more significant. Nevertheless, the structural stress concept, based on the currently valid normative notch classifications, can be used economically. However, the evaluation of the fatigue tests on cross joints tends towards an overestimated notch drop in the structural stress concept. It can also be established that straight pull effects lead to reduced stress ranges in fatigue tests. These effects have not yet been taken into account in the standards. Consequently, the general applicability of the structural stress concept must be critically scrutinised in some points. This research report sets out extended regulations for the professional application of the structural stress concept. The objective of the research project was thus achieved. Publication: June 2022 Authors: Sc. N. Rausch, Prof. Dr.-Ing. M. Mensinger

P 1273 - Development of an intelligent setup assistance system for straighteners to extend the process limits of processing high-strength wire materials The steel processing industry is characterised by 79% small and medium-sized companies with fewer than 100 employees. These companies generate a turnover of 79.8 billion euros, of which around 43 % is accounted for by preliminary products such as cold-rolled strip, drawn wire and sheet metal and forged parts [BMW15]. These preliminary products are usually supplied as strip material, wound onto coils. In a high-wage country such as Germany, efficient further processing is only possible with a high degree of automation in production. The material properties of the semi-finished product vary over the length of the coil. This affects the geometry, hardness, modulus of elasticity, pre-curvature and yield strength. These fluctuations are countered with the development of an intelligent, self-correcting levelling device. This can react to fluctuations in semi-finished products during the process. In order to be able to detect these fluctuations online during the process, investigations have been carried out into the sensor and actuator technology. In particular, the developed online measurement of the flat wire curvature enables a straightening strategy adapted to the fluctuations/changes in the semi-finished product. From this, a design system for the newly developed intelligent self-correcting straightener has been developed. Through fundamental experimental and numerical investigations, a validated numerical model was used to create a basis for identifying relevant process parameters. These process parameters could be investigated in isolation, whereby it was shown, for example, that the deformation capacity could be maximised for the subsequent process by applying a straightening strategy of the semi-finished product optimised with a few alternating bends, thus considerably strengthening the competitiveness of steel compared to non-ferrous metals due to the maximised remaining deformation capacity. Publication: 2021 Authors: Prof. Dr.-Ing. habil. A. Trächtler, Prof. Dr.-Ing. W. Homberg

P 1278 - Improvement of the application behaviour of hot forming tools by nitriding-appropriate selection of hot work tool steels In the project Improvement of the application behaviour of hot forming tools through nitriding-appropriate selection of hot work tool steels, the behaviour of materials was verified in various laboratory tests and application tests. Firstly, a selection of materials was made for the work. In static tempering tests, the materials were tempered at 780 °C for a period of 20 minutes in order to subsequently evaluate the oxidation and cracking behaviour as a result of the thermal load. For this purpose, microscopic images of the surfaces and cross-section preparations were made for evaluation. After the investigations, a material selection was qualified for the further dynamic annealing tests. In the test environment, a cyclic thermal load was exerted on the samples without any significant input of force. The test arrangement simulates the cyclic alternating load similar to hot moulding. The high thermal loads lead to an isolated thermal load situation, which results in cracking and oxidation behaviour of the surfaces. After evaluating the static and dynamic tempering results (cracking and oxidation behaviour as well as resistance of the nitriding zone), some steel materials were identified as potentially suitable and further investigated in fully automated series forging tests. The upper die was manufactured from the material to be analysed and nitrided accordingly. Cylindrical blanks (? 30 mm x 40 mm) made of the material 1.7225 (42CrMo4) were forged at 1,150 °C or 1,250 °C in continuous operation (500 or 1,000 forged parts per die under investigation). While the static and dynamic tempering tests, which tend to be more fundamentally orientated and load-isolated, have a low practical relevance, this is increased in the series forging tests. However, a complex load collective consisting of thermal, mechanical, chemical and tribological loads occurs, which no longer allows a purely isolated consideration. In the forging tests, industrial production processes can be simulated on a laboratory scale under reproducible conditions. Key production parameters such as cycle time or blank temperature can be specified individually. These series forging tests provided an initial impression of the material behaviour to be expected with different nitriding processes in real production processes. The series of tests in combination with the static tests made it possible to further narrow down the range of materials. Investigations into the residual stresses of the material 1.2343 were carried out in parallel in order to better understand the cracking behaviour on the surface caused by nitriding. It was previously known that residual compressive stresses are introduced in the edge zone by nitriding. This is not consistent with the observations of the increased tendency of nitrided materials to crack. Residual stress measurements were carried out on nitrided and non-nitrided samples as well as with and without tempering. The results show an influence of the treatment parameters on the materials. The detection of tensile stresses on the material surface, which subsequently leads to cracks, could not be conclusively answered. In industrial tests, selected plasma-nitrided materials were compared with the reference material 1.2367. The tests show a different wear behaviour to the reference material. The surface of the new materials investigated, 1.8550, 1.2362 and 1.2363, was well preserved compared to the reference material. However, there were isolated cases of die fractures that prevented further use. These could be avoided in future by adapting the die designs and fits. Publication: 2022 Authors: Prof. Dr G. Bräuer, Prof. Dr.-Ing. B.-A. Behrens, Prof. Dr K. Hiller

P 1279 - Design recommendations for the material-efficient use of high-strength steel tubes and profiles in agricultural soil tillage machinery The demands on the performance of modern agricultural machinery and equipment are constantly increasing and the associated development is facing enormous challenges. In view of these development trends, there is a conflict of objectives between the required performance, the permissible machine weights and the economically available cost framework. This problem is addressed in the project and investigated on the basis of agricultural soil tillage machines, which include, for example, rotary tillers, cultivators, harrows and ploughs. These tillage machines offer great potential for the lightweight-optimised and material-efficient use of high-strength steels, as they are profile-intensive constructions in which standard materials (e.g. S355) are traditionally used. The design is usually still based on experience without knowledge of the exact loads, which makes it difficult to optimise the design to suit the material. As part of the research project, an equivalent test collective for soil tillage equipment is being created. The basis for this is formed by realistic measurement runs with a soil tillage implement. The test collective forms the basis for the operational design of agricultural tillage equipment. Parallel to the determination of the load spectrum, fatigue strength tests are carried out on three design details that frequently occur in agricultural machinery, as well as on a sample component. Based on the experimental results, a notch case recommendation is developed for these details. Numerical parameter studies are used to vary key geometric parameters so that the results of the numerical analyses provide corresponding formulae that enable the stress concentration factors for the underlying construction details to be determined. Publication: 2021 Authors: Prof. Dr.-Ing. T. Ummenhofer, Prof. Dr.-Ing. Ch. Schäfers