P 632 - Manufacture of coil springs from tubular material

P 633 - Detailed solutions for fatigue issues and the use of high-strength steels in offshore wind turbines The promotion of renewable energies by the German government is causing an enormous upswing, particularly in the wind energy sector. In order to meet the ever-increasing demand, the construction of offshore wind farms is planned in the North Sea, the Baltic Sea and the Irish Sea, as large areas with a higher and more even wind supply are available offshore than on land. However, the conditions here are more difficult due to the great water depths, the large tower and hub heights required as a result and varying site conditions. The aim of this research project was to identify the particular difficulties that arise in terms of stability and durability and to develop new solutions. This includes the selection of the steel grade, the connection technology, in particular questions regarding cylindrical or conical connections, the estimation of the remaining service life and the consideration of problems with corrosion. The design of wind turbines is largely determined by the fatigue strength of critical notch details, especially weld seams. The fatigue strength and thus the service life of these notch details can be significantly increased through the targeted application of suitable weld post-treatment processes. Shot peening, ultrasonic peening (UP) and ultrasonic impact treatment (UIT) were investigated in detail as part of the research project. By combining geometric and mechanical effects, the UP and UIT processes significantly increase the fatigue strength of welded joint details. The results from tensile swelling tests confirm this for welded ring flange segments, butt welds and welded transverse stiffeners with sheet thicknesses of 8 to 30 mm. The ultrasonic methods were also analysed for the possibility of upgrading existing components. The results show that when the method is applied to samples that have been pre-damaged up to the end of their calculated service life, it is possible to increase the residual fatigue strength to the level of components treated immediately after production. For water depths of over 30 metres, the trend for the foundation structures of offshore wind turbines is towards dissolved structures. For this reason, the tripod structure was analysed more closely within this research project. In detail, this concerned the design of the upper central node, which is the most critical detail for the fatigue design of the tripod. Conventional cylindrical tubes and tubes with conical expansion were considered for the design of the upper central node, which represents the connection between the tower and the base struts. In crane construction, such connections are designed with an internal stiffening ring. Inspired by this, a new node design was developed and investigated, whereby the upper central node was designed with a stiffening ring. In the field of corrosion protection, the special aspects of corrosion protection for offshore wind turbines using high-strength steels were discussed. The questions regarding the interaction of coatings with the cathodic corrosion protection, the rust surcharge, the corrosion behaviour in encapsulated systems and the formation of cracks in the steel under the coatings were dealt with in depth. High-strength steel is not a new material for use in offshore support structures and can be used in exactly the same way as the structural steel previously used. Authors: R. Puthli, S. Herion, J. Hrabowski, T. Ummenhofer, I. Weich, T. Faber, M. Lossin, H. Huhn, J. Uecker Publication: 2008

P 630 - Production of lightweight composite containers with extremely thin-walled stainless steel core containers for pressurised storage of hydrogen and oxygen gases The aim of the research project was to develop very lightweight composite containers with high storage efficiency for the mobile storage and transport of pressurised gases. The preferred field of application for such containers is the temporary storage of the energy gases natural gas, methane and hydrogen to supply combustion engines and fuel cells, but they can also be used for other industrial and speciality gases, such as the distribution of oxygen in medical technology. A particular task in this research project was to use stainless steel grades as the material for the metallic core container (the so-called liner), as these have some significant advantages over conventional container materials. There are numerous tried and tested production technologies for processing them. They have an excellent surface quality, are corrosion-resistant and, in the case of metastable, austenitic stainless steels, have a high hardening potential. The overall project consisted of two sub-projects in which liners made of two different steel grades were developed and analysed. The aim of the first sub-project was to create a container with the shape and contents of a 6 litre breathing gas cylinder. ThyssenKrupp Nirosta GmbH (TKN) recommended the steel 1.4318 for the manufacture of the liner and provided sheet material with a wall thickness of 0.76 mm. Cylindrical pipe sections and corresponding hemispherical bases were produced from this material by laser welding and deep drawing. The thin-walled individual parts were welded together to form containers at the Schweißtechnische Lehr- und Versuchsanstalt Duisburg (SLV) using oscillating laser welding, and the raw containers produced in this way were then hydraulically expanded in a mould tube by 10 or 20% in a controlled manner in order to achieve a higher material strength, and then work-hardened accordingly. However, during this production step, which was decisive for the intended liner concept, a large number of the test containers failed due to numerous defects in the laser-welded longitudinal seam, so that this sub-project could not be continued in the originally planned form, but had to be completed with the investigation of the mechanical properties and chemical resistance of the work-hardened liner material. For the second sub-project, conventionally manufactured containers made of the metastable, austenitic CrNi steel 1.4301 were used by UCON. These three-part welded containers are usually used in large numbers in the beverage industry at low operating pressures. In this project, the containers were used as liners for the production of composite containers. For this purpose, it was necessary to first subject the containers to a controlled cryo-moulding process in order to achieve high material strength. The containers were stretched by internal pressure in a mould tube at 77 K using liquid nitrogen. The resulting plastic deformation of 15% led to an increase in the yield strength of the container material by a factor of 4. Composite containers were manufactured from the high-strength stainless steel liners qualified in this way using a corresponding carbon fibre laminate structure and tested for their suitability and approvability in accordance with the regulations applicable to natural gas vehicle tanks. As the test results summarised below show, the tanks designed for an operating pressure of 200 bar fulfilled the most important requirements with regard to their burst and load cycle safety. As part of the research project, proof was thus provided that the manufacturing concept pursued can be used to produce composite tanks that are not inferior to the tanks with aluminium alloy liners or those with plastic liners currently on the market in terms of their storage efficiency, or even significantly exceed them.1 Introduction Publication: 2008 Authors: Dr.-Ing. M. Kesten

P 636 - COMBRI - Competitive Steel and Composite Bridges by Improved Steel Plated Structures Publication: 2006

P 638 - Roll and gap profiling - Assessment of the product and market potential of the new target product As part of current endeavours to advance the development and application of lightweight construction strategies, the main objective is to achieve increasingly higher component strengths with decreasing material volumes and to be able to cover critical component areas with weight-reducing materials in the future. In addition to the development of high-strength and ultra-high-strength materials as part of lightweight material construction, efforts are also being made in lightweight mould construction to reduce the sheet thickness while maintaining the same component properties. However, one problem with weight reduction is component failure due to buckling or buckling caused by instabilities. An effective design element for shifting this instability limit towards higher loads is the introduction of bifurcations. With the help of the gap profiling process, a forming process has been developed that allows branches to be realised on the strip edge of sheet metal, which was previously only possible by doubling material within die bending or roll forming processes. In addition to the effect of increased profile rigidity, it is possible to utilise branches for new, load-adapted joining strategies. Furthermore, the downstream processing of branched profiles opens up a wide range of new functional profile applications. As part of the activities of the "Roll and gap profiling" working group, the process development of gap profiling was advanced through the realisation of a new type of tool concept. A hydrostatic compressive stress state is induced in the workpiece through a targeted arrangement of nip and auxiliary rollers, which increases the material's ability to change shape and leads to the formation of branches, so-called flanges, on the edge of the sheet metal strip. The results obtained during development were presented using the example of two micro-alloyed fine-grained steels. It was possible to produce branches with a span of approx. 30 mm. The splitting profiles have a macroscopically crack-free surface as well as a significant hardening gradient, starting from the surface facing the splitting rollers. Based on this, it is possible to further process the slit profiles using forming technology. Die bending and roll forming processes can be used to create functional multi-chamber profiles which, in addition to increased rigidity, buckling and buckling stability, also offer the possibility of functional integration. As part of the working group's activities, the roll forming of gap profiles into a single-chamber profile was investigated in particular. Conventional tools for designing roll forming processes cannot be used due to the fact that branches cannot be modelled. Instead, the process was modelled and analysed using FE systems. Furthermore, aspects of tool design and layout were investigated that arise when profiling branched semi-finished products due to the occurrence of undercuts. The single-chamber profile realised as part of the working group demonstrates the possibilities opened up by a process chain consisting of gap and roll forming: The process limits of slit profiling allow the geometry of the semi-finished product slit profile for subsequent forming to be varied over a wide range, enabling the production of thin-walled, integrally branched multi-chamber profiles of variable geometry with free flanges. Prospective opportunities therefore lie in particular in the realisation of innovative, multifunctional products with advantages that affect both their properties and the production possibilities and costs. The activities of the Rolling and Gap Profiling Working Group are being continued as part of the transfer project "Control of tolerance fields in gap and roll profiling" within the framework of the SFB 666. The main objectives of this project are to analyse accuracy and tolerances in order to derive industrially feasible product classes and, based on this, appropriate strategies for the process-reliable design of a continuous process chain for slitting and roll forming. Authors: P. Groche, D. Vucic, P. Beiter, R. Salomon Publication: 2011