P 633 - Detailed solutions for fatigue issues and the use of high-strength steels in offshore wind turbines

P 632 - Manufacture of coil springs from tubular material Coil springs are essentially subjected to torsion. The material near the wire axis remains largely unutilised. By using tubular material, it is possible to reduce the spring mass by 20 - 40 % while retaining the same spring function. The prerequisite for this substitution is the availability of high-quality tubular material with similar strength properties to spring steel wire. A seamless tube made of 70Mn7 steel was used in the research project. To create the continuous transformation diagrams, the required cooling curves were determined, hardness measurements were carried out and microsections were made to determine the microstructure. The pipe material was available in different dimensions and treatment states. The exact dimensions, surface roughness and mechanical characteristics were determined in the tensile test. Metallographic analyses were also carried out. Based on the results of the wire tempering tests, the temperature range for pipe tempering was narrowed down to tempering temperatures between 350 and 500°C. It was determined that the tube should be formed into a spring in the soft state and then tempered to the desired strength. From the results of roughness measurements, it could be clearly concluded that only drawing with an internal mould leads to an internal surface that is suitable for the production of a dynamically loaded Bourdon tube. In addition, the inside of one part of the tube was peeled between two drawing stages. The final tube dimension was 10 x 2.0 mm. To test the springs, two geometries (w = 8 and w = 5) were produced using two forming technologies: coiling and winding. During coiling, a slight cross-sectional deformation of the tube was observed due to the pressure of the feed rollers and the bending of the tube on the circular arc. The subsequent treatment consisted of hardening the spring, tempering, shot peening and tempering again. The end coils of some of the springs were ground. The heat treatment was carried out in such a way that a strength of Rm approx. 1700 MPa was achieved. The spring test involved determining the characteristic curve, relaxation behaviour and fatigue strength. The latter was intended to show that springs made of tubular material are generally also suitable for use under oscillating loads (influence of the inner surface). The load change tests were carried out with a stroke stress (corrected) of 650 MPa (?ku = 300 MPa, ?ko = 950 MPa). The best test results were achieved with springs with non-ground end coils made of internally peeled tube. Load cycles of up to 14 million were achieved without breakage. The springs made of non-peeled tube showed failures under 100,000 load cycles. The cause of breakage was due to the inadequate quality of the inner surface. In the springs with ground end coils, the end coils broke. Further necessary and promising research directions were identified: ⇒ the use of higher-strength material (high-strength spring steel), ⇒ further reduction of the wall thickness of the tube and thus even greater material savings, ⇒ improving the economic efficiency of pipe production. Authors: G. Lehmann, F. Hoffmann, H. J. Schorcht, S. Lutz Publication: 2007

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