P 835 - Hot-dip galvanising in steel and composite bridge construction

P 834 - Investigation of bolted connections in steel and composite construction for the creation of rules for the numerical design of structural fire protection in building construction In this research project, connections in steel and composite construction with high-strength bolts of strength class 10.9 are investigated in the event of fire. With the introduction of the component method, it is now possible to simulate entire structures at room temperature, taking into account the connection behaviour. This is not yet possible in the case of fire, as on the one hand there is no implementation of the component method or a comparable numerical model for the case of fire and on the other hand there are no validated material laws available for high-strength bolts in the case of fire. For this reason, material parameters for high-strength bolts of strength class 10.9 during and after a fire are initially developed on the basis of test series. This includes both the investigation of the pure bolt material by means of stationary and transient hot tensile tests and the investigation of bolt assemblies in tensile and shear tests. In the latter, not only the material but also the bolt geometry has a major influence on the behaviour. The tests show that the screws fail in the temperature range up to 420°C due to the usual thread stripping. In the temperature range from 420°C to 650°C, however, the screws fail due to a crack in the thread base. It can be shown that this crack is due to liquid metal induced stress corrosion cracking (LME). Above 650°C, the screws fail due to flank bending. As a result of the material investigations, validated material parameters will be available in future for modelling bolts within connection simulations, which take into account the various forms of failure at different temperatures. In addition, thermal and mechanical numerical models will be developed to describe the behaviour of head plate and flag plate connections in steel and composite construction. The models are validated by fire tests on two standard structural connections. Within the tests and the numerical models, a temperature field is taken into account, which is based on the unit temperature-time curve and a typical fire protection coating with an intumescent coating. A head plate connection in steel construction and a flag plate connection in composite construction are analysed. In the case of the flag plate connection, it is assumed that it is a hinged connection at room temperature. It is shown that a moment resistance can occur in the event of fire, provided that the premature failure of the continuous reinforcement is prevented. Finally, simplified spring models are developed for the two connection types on the basis of the component method, which can be used to determine the stiffness and load-bearing capacity of the connections in the event of fire. In summary, it will be possible in future to describe the behaviour of connections in the event of fire on the basis of validated bolt properties using finite element or spring models and to take this into account in structural calculations. The IGF project 16586 N of the Forschungsvereinigung Stahlanwendung e.V., Düsseldorf, was funded via the AiF within the framework of the programme for the promotion of 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 at the Gottfried Wilhelm Leibniz University of Hanover by the Institute of Steel Construction and at the Technical University of Darmstadt by the Institute of Steel Construction and Mechanics of Materials. Publication: July 2014

P 837 - Experimental investigation and simulation of the crash behaviour of mechanically joined joints Mechanical joining processes are increasingly being used in the realisation of innovative lightweight construction concepts to reduce fuel consumption and thus also CO2 emissions. Compared to thermal joining technology, mechanical joining technology offers the decisive advantage that it can also be used to realise mixed joints of different materials in a reliable process without reducing the positive material properties through thermal influence. Consequently, in addition to conventional joining methods such as resistance spot welding, a variety of mechanical joining techniques such as semi-tubular self-pierce riveting and direct bolting are used in automotive engineering. In recent years, the possible applications of these two mechanical joining techniques in automotive engineering have continued to develop. However, for the effective use of these joining techniques, especially in crash-relevant areas, there has so far been a lack of characteristic joint values that allow the load-bearing behaviour of these joints to be predicted. Mechanical joining processes are increasingly being used in the realisation of innovative lightweight construction concepts to reduce fuel consumption and therefore also CO2 emissions. Mechanical joining technology offers the decisive advantage over thermal joining technology that it can also be used to realise mixed joints of different materials in a reliable process without reducing the positive material properties through thermal influence [Hah94]. Consequently, in addition to conventional joining methods such as resistance spot welding, a variety of mechanical joining techniques such as semi-tubular self-pierce riveting and direct bolting are used in automotive engineering. In recent years, the possible applications of these two mechanical joining techniques in automotive engineering have continued to develop [Ban06]. However, for the effective use of these joining techniques, especially in crash-relevant areas, there has so far been a lack of characteristic joint values that allow the load-bearing behaviour of these joints to be predicted. In vehicle development, the crash simulation of entire vehicle structures plays an important role in the development process. The load-bearing behaviour of the entire vehicle structure is significantly influenced by its joints, whereby the joint areas must be taken into account in the crash simulation using simplified substitute models [Özd05]. Very detailed models of the joints cannot be used in the overall vehicle models that are used in the crash analysis, as these would lead to calculation times of several days or weeks and would not be realisable in the development schedule due to the large number of load cases and calculations for optimal structural design. As a result, simplified substitute models of the joints must be used, which reproduce the global deformation and failure behaviour under impact loading with sufficiently high accuracy but significantly less numerical effort. Against this background, corresponding calculation concepts have been developed in the past for resistance spot welding. These are based on experimentally determined force-deformation path curves, which have been determined on single-element samples as a function of the type of load (shear, head and peel tensile) [Özd05, See05, Som06]. Such a comprehensive characterisation of the crash behaviour of corresponding joints does not exist for mechanically joined joints. This is where the underlying research project comes in with its objective. Publication: 2010 Authors: Prof Hahn, Prof Gumbsch, Prof Iwainsky

P 832 - Solid self-pierce rivet coatings for use with high-strength steel materials The aim of this research project was to develop a rivet element coating that serves as corrosion protection and at the same time as a hydrogen barrier. The basis for this was the galvanic zinc-nickel system. However, the fact that the current yield in this electrolyte is only approx. 50% is problematic, as this means that only 50% of the electrical energy used contributes to the formation of hydrogen. Two riveting materials were analysed in this research project. These are the cold heading steel 1.5515 and the chromium steel 1.4035, which has a chromium content of 13% by weight. This high chromium content leads to passivation of the material, which makes galvanic coating more difficult. By modifying the pre-treatment of the rivet elements, it was possible to achieve a significant improvement in coating adhesion. However, after loading with hydrogen, the chrome steel rivet exhibited brittle fracture behaviour under quasi-static shear stress and the porosity of the coating was also demonstrated in the corrosion tests. Further optimisation is therefore required for an electroplating process in an aqueous electrolyte. PVD coating systems, which have shown good adhesion, are also conceivable. In addition, a modified rivet geometry was developed for the chrome steel rivet, which has proven to be good in terms of stability in the setting process and affinity to hydrogen embrittlement. The coating of the cold heading steel rivet did not show any problems. The modified pre-treatment of the rivet elements can also be used here. In addition to the zinc-nickel coating, the Almac ® and zinc-lamella coating systems are also available. All coatings can be applied without any problems. In addition, the 1.5515 rivet shows no signs of failure in combination with hydrogen, which is why it is preferable to the chrome steel rivet if there is a risk of hydrogen diffusion into the auxiliary joining part. Also with regard to their corrosion-inhibiting The coatings on the cold heading steel rivet also showed no abnormalities in terms of their corrosion-inhibiting effect and can be rated as suitable for preventing corrosion on the rivet element. The IGF project 16495 N of the Forschungsvereinigung Stahlanwendung e.V. - FOSTA, Düsseldorf, was funded via the AiF within the framework of the programme for the promotion of joint industrial research (IGF) by the Federal Ministry for Economic Affairs and Energy on the basis of a resolution of the German Bundestag. The research project was carried out at the Laboratory for Materials and Joining Technology at Paderborn University and the Institute for Materials Science at Leibniz Universität Hannover. Authors: G. Meschut, O. Hahn, M. Bergau, H. J. Maier, M. Nicolaus Publication: 2015

P 838 - Reliable and high-performance joining of high-strength fine-grain structural steels using a hybrid welding process with integrated preheating In the construction of wind turbines, ships, pipelines and mobile cranes, the aim is to reduce component weight while maintaining the same load-bearing strength and toughness. This makes it possible to reduce statically required sheet thicknesses and thus the dead weight of the structure and save material costs. High-strength fine-grain structural steels were developed for this purpose, which offer advantages in terms of load-bearing strength and toughness and are also suitable for welding. Parallel to steel development, a modification or development of suitable joining processes is required. Conventionally, fine-grain structural steels in the thick sheet range are joined using multi-layer arc welding processes at relatively low speeds. Both the consumption of additional materials and the production times required are high. production times are high. MIG laser hybrid welding represents a potential alternative here. It combines the advantages of MIG welding and laser beam welding and compensates for the disadvantages. These include, for example, the high welding speed, the high welding depth, the good gap-bridging capability and the relatively small heat-affected zone (HAZ). However, the high welding speed and the concentrated heat input compared to pure arc welding processes require a high cooling rate, which results in hardening of the HAZ and the weld metal. As part of these investigations, a combined welding process consisting of inductive preheating and a single-layer MSG laser hybrid welding process is being developed. In this process, high-strength fine-grain structural steels with a strength class of 460 to 690 MPa and sheet thicknesses of 10 to 20 mm are welded in a single operation. Induction preheating is used to influence the cooling time and therefore the microstructure and mechanical properties of the welded joint. Furthermore, inductive preheating can influence the formation of hot and cold cracks in the weld metal or in the heat-affected zone. In the course of the investigation, the weld seams were assessed using X-ray and visual inspections and classified in accordance with [DIN EN ISO 13919] and [DIN EN ISO 12932]. The welded joints confirmed the requirements of assessment group B of the above-mentioned standards. For further evaluation of the welded joints, cross-sections were taken, on which extensive hardness tests were carried out. Furthermore, tensile and notched bar impact tests as well as cyclic tests were carried out. Simulations of the preheating process and the welding process were carried out alongside the experimental investigations. A good correlation to the experimental measured values was established. The IGF project 16600 N of the Forschungsvereinigung Stahlanwendung e.V., Düsseldorf, was funded via the AiF within the framework of the programme for the promotion of 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 Laser Zentrum Hannover e.V., Institute of Electrical Process Engineering, Leibniz Universität Hannover and the Institute of Steel Construction, Leibniz Universität Hannover. Authors: D. Kracht, S. Kairele, A. Springer, O. Seffer, R. Lahdo, B. Nacke, H. Schülbe, J. Neumeyer, P. Schaumann, M. Collmann Publication: 2015