P 1064 - Economical production of weight- and property-optimised functional components by means of incremental sheet metal forming

P 1065 - Mould-integrated temperature measurement for press hardening If deviations from the designed mould hardening process are not reliably detected, this can lead to the processing of defective components in the further process chain. This can result in considerable follow-up costs. Sensors integrated into forming tools make it possible to detect any temperature irregularities and initiate countermeasures at an early stage. Furthermore, varying cooling rates during the production cycle, caused by fluctuations in the tool temperature, can be used as an input signal for active control of the holding time. Sensors based on thin-film technology offer the advantage of being in direct contact with the semi-finished product without reducing the component quality due to thermal interference. This means that the component can be monitored during the production process and manufactured without errors. Due to the increasing complexity of forming processes and production close to the process limit, these sensors offer great potential for reducing the number of rejects produced and cycle times. This enables the production process to be organised more economically and contributes to the resource-saving use of raw materials. The aim of this research project was to develop a tactile thin-film temperature sensor for direct use in forming tools. In order to ensure an economical service life of the sensors, investigations were first carried out to identify a suitable wear protection layer, with a layer of Al2O3 showing the best results. At the same time, processes for the production of thermoelectric and thermoresistive sensor coatings were developed. The sensor concepts were calibrated taking into account different forming tool temperatures. The thermoresistive sensor in particular showed good agreement in the temperature range up to 400 °C in comparative measurements. This allows the component to be monitored in the production process and ensures the further processing of a defect-free component. The IGF project 18338 N of FOSTA-Forschungsvereinigung Stahlanwendung e. V., Düsseldorf, was funded via the AiF as part of the programme to promote joint industrial research (IGF) by the Federal Ministry for Economic Affairs and Energy on the basis of a resolution of the German Bundestag. The project was carried out by the Institute of Forming Technology and Forming Machines and the Institute of Microproduction Technology, Gottfried Wilhelm Leibniz University of Hanover. Publication: January 2019 Authors: Prof. Dr.-Ing. B.-A. Behrens, Dipl.-Ing. Ch. Pfeffer, Dipl.-Ing. D. Yilkiran, Prof. Dr.-Ing. L. Rissing, F. Dencker M.Sc., Dipl.-Ing. M. Stompe

P 1062 - Load-bearing capacity of mixed connections of normal-strength and higher-strength steels in steel construction The requirement for filigree constructions with high stresses consequently leads to the use of higher-strength steels. In addition to questions of stability and fatigue, the connection and joining options are also decisive for their use. The procedure for mixed connections is open, i.e. when higher-strength S690 steels are connected to normal-strength S355 steels, for example. This is a situation that occurs as standard in practice because the choice of steel is usually adapted to the utilisation and there are always attachments with lower stresses. Current design concepts in EN 1993-1-8 for fillet welded joints do not take the strength of the weld metal into account. Also, mixed joints are currently to be designed according to the higher-strength steel with regard to the weld material, but may only be calculated with the values of the normal-strength base material. The aim of the research project is to check the applicability of the already adapted design model for fillet welds of the same base materials and to develop a realistic and comprehensible design model to determine the load-bearing capacity of hybrid welded joints with fillet welds made of normal-strength and higher-strength structural steels for use in steel construction and related areas (plant and crane construction). The aim is to improve the load-bearing capacity of fillet welds in hybrid joints in the current steel construction standards. Future consideration of the welding filler material in combination with the different base materials to be joined should enable a suitable selection of the optimum combination of load-bearing capacity, toughness and deformability. Component tests are carried out to characterise the load-bearing capacity and deformation of mixed joints and comprehensive material tests to determine the mechanical properties. Based on the correlation between component tests and mechanical properties, a detailed statistical analysis of the results was carried out. Based on the evaluation of the experimental test results and the results of the statistical analysis, the applicability of the adapted design model according to Rasche [7] was confirmed. The results were summarised in recommendations which, on the one hand, cover the design and welding of dissimilar joints for practical use and, on the other hand, provide design rules which can be forwarded to the CEN committees as a proposed standard via the German mirror committee. Publication date: April 2019 Authors: Prof. Dr.-Ing. U. Kuhlmann, J. Spiegler, M.Sc.

P 1067 - Determination of high toughness requirements for steel using hybrid damage mechanics methods In addition to the safety verification in the ultimate limit state, which is performed with the basic assumption of ductile material behaviour, the ultimate limit state verification for steel structures in Eurocode 3 also requires the selection of steel grades in accordance with DIN EN 1993-1-10 or DASt-RiLi 009 in order to avoid brittle fracture. The choice of steel grade, together with the requirements from the tensile test, is also regarded as a guarantee for ductile material behaviour. In Germany, the weld-on bending test (AUBI) in accordance with SEP 1390 for assessing the qualitative crack arresting capacity of the steel base material, which is currently generally required for welded steel structures for steel grades up to S355J2 with plate thicknesses greater than 30 mm, is another proof of toughness in the high position. However, in the course of harmonising European standards, the AUBI was not accepted by the other EU member states. Instead, a depth-oriented replacement criterion was introduced, utilising the better properties of fine-grained structural steels resulting from more modern production technology. In the past, investigations were carried out to correlate the AUBI with notched bar impact results; an endeavour that did not lead to satisfaction due to its strongly empirical character and left questions unanswered as a result. The unsatisfactory situation is that the AUBI is only used as a special substitute test for compliance with a special delivery condition, but is difficult to justify from a material-mechanical point of view as a high-strength criterion with regard to the safety requirements for load-bearing structures and can only be used to a limited extent. In any case, it was not designed for the increasingly required use of higher-strength steels and deviating geometric shapes. In the European product standards, toughness is tested in the notched bar impact test. There is therefore a desire to cover the remaining areas, for which the AUBI is still required in Germany, with formulations of minimum values from the notched bar impact test, especially for the high position. This applies to ranges up to S355J2 as well as to higher-strength steels and other product forms based on the nominal values of the materials. This is where the present research project comes in. Innovative scientific methods based on hybrid damage mechanics models are used, which allow the numerically supported simulation of the AUBI, taking into account both the cleavage fracture (low position) and toughening fracture (high position) failure modes. As a result, the correlation of the toughness high position of the notched bar impact test with the AUBI could be consistently demonstrated and numerically determined for all steel grades and thicknesses. This has created a general criterion that overcomes the material and product shape-related restrictions of the AUBI. Publication date: April 2019 Institute for Steel Construction, RWTH Aachen University Prof. Dr Markus Feldmann, Sandro Citarelli M.Sc. Institute of Ferrous Metallurgy, RWTH Aachen University Prof. Dr.-Ing. Sebastian Münstermann Markus Könemann M.Sc.