P 1396 - Analysis of the failure behaviour of bonded steel joints during material-conserving debonding in car body repair

P 1395 - Design of building envelopes in lightweight metal construction for German and European earthquake zones, taking into account load-bearing properties and damage minimisation Building envelopes in lightweight metal construction, such as sandwich elements or multi-shell constructions with trapezoidal profiles, primarily only have a space-enclosing function. For use in industrial and commercial construction, the building envelope is designed for loads resulting from the effects of wind, snow and temperature. This research project investigated the extent to which the wall and roof elements also assume a stiffening and co-supporting function in relation to the main load-bearing structure in the event of an earthquake. Roof and wall elements and their connections with the substructure are analysed experimentally and numerically with regard to their cyclic behaviour, energy dissipation capacity and functionality after seismic events. Firstly, individual connections were tested monotonically and cyclically in the fastener tests. Cut-outs of sandwich elements and trapezoidal profiles were used as test specimens. The parameters sheet thickness of the trapezoidal profiles, sheet thickness of the substructure, component thickness of the sandwich elements and the contact pressure of the screws were varied. In the next step, the load-bearing effect of the sandwich elements and trapezoidal profiles as a wall or roof panel was determined experimentally in the form of shear panel tests. The focus was on analysing the load-bearing behaviour under load at component level. The parameters sheet thickness and component height were varied for the trapezoidal profiles, while the component thickness and core material were varied for the sandwich elements. The numerical model of the reference structure (industrial hall) was used to analyse the contribution of the building envelope to the load transfer of the supporting structure based on the test results. In addition to non-linear push-over analyses, time step analyses were carried out for earthquake loads of different intensities. The experimentally determined monotonic and cyclic behaviour of the elements was also recalculated using analytical approaches. Here, the resulting load-bearing capacity and stiffness of a wall of an industrial hall was determined on the basis of the load-bearing properties of individual fasteners and compared with the test results for wall elements. In addition, building physics tests were carried out on sandwich elements to assess the extent to which sandwich elements would continue to fulfil their function of sealing off rooms after an earthquake event. In particular, the airtightness of the building envelope was analysed. The research results were discussed within the European standardisation committee during the project and used for the new version of EN 1993-7, Annex D. The objective of the research project was achieved. Publication: December 2024 Authors: Prof. Dr.-Ing. Hoffmeister, L. Bittner, Univ.-Prov. Dr.-Ing. T. Ummenhofer, A. Wallner, Univ.-Prof. Dr.-Ing. M. Kuhnhenne, M. Lüdecke

P 1397 - Model-based life cycle engineering for the development of eco-efficient components and structural parts for vehicle applications This final report describes the work carried out and project results of the research unit Institute for Machine Tools and Production Engineering (IWF) of the Technical University of Braunschweig in the IGF research project "Model-based life cycle engineering for the development of eco-efficient components and structural parts for vehicle applications (MBLCE)" for the period from 01 October 2021 to 30 September 2023. The MBLCE project focussed on the development of a methodology for conducting a life cycle analysis of automotive parts/components and the transfer of the methodology into a suitable tool. As a web application, this tool developed in the project supports users in carrying out life cycle assessments for individual components, determining the break-even point for alternative materials and evaluating the effects of the material and process efficiency of various production processes on life cycle emissions. In addition, the tool facilitates scenario analyses by enabling users to change the electricity mix in the production and use phase and also to understand the emissions from raw material extraction to the recycling of a component. For decision-making purposes, the tool can assist in selecting the most suitable material or an alternative component design made from the same material. This approach enables users to both minimise environmental impact and maximise process efficiency. These objectives of the research project were achieved. Publication: April 2024 Authors: J. Haupt, St. Blömeke, Prof. Dr.-Ing. Ch. Herrmann

P 1398 - Forecast models for the service life and continued operation of wind turbines The energy transition is a global challenge. Energy generation with renewable energies, and wind energy in particular, plays a key role here. For an economical design of tubular steel towers of wind turbines, the proof of operational stability is relevant and often decisive. Local concepts enable an improved proof of fatigue strength and a realistic prediction of the service life for typical construction details of wind turbines, such as the horizontal butt weld. They also allow the decisive influencing variables to be explicitly taken into account and contribute to reliable decisions regarding the extended continued operation of existing turbines. In this research project, the existing experimental investigations in the literature were initially analysed in a targeted manner and the need for additions was determined. Compared to structural engineering structures, wind turbines differ from them in key aspects with regard to the type and extent of stress. These include the total number of cycles during the service life (~108 to ~109) and the specifics of the sequence of stresses, which is difficult to predict. At present, the nominal stress concept, the structural stress concept and the notch stress concept are usually used, which essentially differ in terms of the effort required and the mapping of the notch geometry. On the basis of the investigated input variables, e.g. material behaviour and geometry of the weld seam, the two-phase model was extended to construction details typical for wind turbines in order to explicitly and accurately capture the crack initiation phase and crack propagation. The two-phase model makes it possible to take into account a large number of input variables, which were determined as part of the research project by means of experimental investigations, FE calculations and analytical approaches and whose influence on the fatigue strength was analysed as part of sensitivity investigations. The experimental investigations include material characterisation, notch detail and component tests. The existing database in the VHCF range (up to 108 cycles) was expanded using notch detail tests with a sheet thickness of 10 mm. In addition, notch detail tests were carried out with a thickness of 20 mm and 35 mm in order to be able to record any influence of the sheet thickness. The findings of the notch detail tests were confirmed by three component tests with pipes with an outer diameter of 610 mm and a wall thickness of 14.3 mm. The input variables determined from the experimental investigations, FE calculations and analytical approaches served as the basis for a probabilistic prediction model and Monte Carlo simulations. Simplified models for engineering practice were derived on the basis of the nominal stress concept using our own tests and the Monte Carlo simulations. With the help of the methodology described above, a basis for a resource-saving and targeted fatigue strength verification of horizontal butt welds was created for engineering practice. The objective of the research project was achieved. Publication: August 2023 Authors: Prof. Dr sc. techn. habil. M. Knobloch, H. Bissing, Prof. Dr.-Ing. M. Rauch

P 1399 - Development of a method for the evaluation of a steel-intensive mixed construction bonded joint of a battery housing against mechanical and medial load under consideration of the interphase structure One of the main requirements for the adhesive bond of battery housing structures is to ensure tightness and corrosion resistance in the wet area of the vehicle. These requirements can be transferred to other sectors that are strongly characterised by SMEs, such as plant and container construction. There is a great deal of uncertainty on the market as to what a reliable design method based on experimental tests of a corresponding steel bonded joint, as well as its verification and quality assurance, can look like. Complex tests on real components are difficult to realise, especially for SMEs, due to the high financial outlay involved. For this reason, the research institutes have developed an application-oriented and fundamentally scientifically validated method to predict the long-term behaviour of the steel adhesive bond under the given requirements. To this end, material-adhesive combinations relevant for use in battery housings were first selected. Subsequently, operationally relevant corrosive loads for bonded joints and requirements for the tightness of bonded joints were determined. The long-term resistance of the adhesive system to the defined rapid ageing tests was then determined using adhesive substance samples. Subsequently, the influence of the load on steel-intensive mixed joints was identified and a test rig was developed that enables a leak test under superimposed mechanical load. The results of the leak test were correlated with the structure of the adhesive/metal interphase and its load-dependent degradation behaviour. The findings were used to develop a model of the damage mechanism and a test methodology for determining resistance. These findings are primarily used by SMEs for the long-term design of bonded joints. To validate the method, a component-like sample geometry was developed, which was used to verify the transferability of the test method to more complex components. Publication date: September 2022 Authors: T. Schmolke, Prof. Dr.-Ing. G. Meschut, P. Vieth, Dr. D. Meinderink, Prof. Dr.-Ing. G. Grundmeier