Effect of tensile pre-strain on bending and unloading of automotive steels

In recent years, advanced high strength steels (AHSS) have been used in a wide range of automotive applications; they may have property variations through the thickness and the properties may also be dependent of prior processing including pre-straining. In order to model forming processes precisely using, for example, finite element analysis, it is important that material input data should adequately reflect these effects. It is known that shape defects in roll forming are related to small strains in material that has undergone prior deformation in a different strain path. Much research has already been performed on the change in the Young’s Modulus once a steel sheet has been plastically deformed,however many of these tests have only been conducted using tensile testing, and therefore may not take into account differences in compressive and tensile unloading. This research investigates the effect of tensile pre-straining on bending behaviour for various types of material;in bending, one half of the sheet will load and unload in compression and hence experience deformation under a reversed stress. Four different materials were pre-strained in tension with 1%, 3%, 7%, 11% and 25% elongation. Using a free bending test, moment curvature diagrams were obtained for bending and unloading. The results showed that the characteristics of the moment curvature diagram depended on the degree of pre-straining; more highly strained samples showed an earlier elastic-plastic transformation and a decreased Young\u27s Modulus during unloading. This was compared to previous literature results using only tensile tests. Our results could influence the modeling of springback in low tension sheet operations, such as roll forming

Effect of the microstructure on the unloading characteristics of DP steel

This study experimentally investigates the relationship between microstructure and unloading behaviour of dual phase steels. The findings of this work have improved the understanding of the springback mechanics in these steels and enables optimisation of future alloy design.<br /

Automated near-net-shape preforming of carbon fiber reinforced thermoplastics (CFRTP)

This paper aims to show, that the preforming process of parts made of Carbon Fiber Rei-forced Thermoplastics (CFRTP) can be improved, when using several technologies like near-net shape cut-piece generation with forming simulation, automated cut-piece detection, robotic gripping and lay-down of fabrics. Thereby the authors of this paper want to contribute to the increase of CFRTP appli-cations in modern aircrafts, which generally should lead to an increasing lightweight design of such aircrafts

The effect of microstructure on the decrease of the apparent Young\u27s Modulus in DP 780 steel

Currently, there is a significant effort into developing novel multiphase microstructures to further improve the strength/ductility combination of advanced high-strength steels. To achieve this, the effect of the microstructure on sheet formability needs to be further understood. In this study, the effect of the microstructure on the variation of the elastic modulus in loading and unloading of DP 780 steel has been investigated. Five microstructures with varying volume fractions of ferrite and martensite were generated using different heat treatment cycles. Tension tests were performed to different strain values and the Young&rsquo;s Modulus during loading and unloading was determined. The test results show that the reduction in unloading modulus with prestrain depends on the volume fraction and hardness of the martensitic phase

Automatisiertes endkonturnahes Preforming Carbonfaserverstärkter Thermoplaste mittels robotischer Halbzeugablage

Dieses Paper soll zeigen, dass der Preforming-Prozess für Luftfahrt-Strukturbauteile aus Carbonfaser-verstärkten Thermoplasten verbessert werden kann, wenn man verschiedene Methoden und Technologien wie Drapier- und Umformsimulationen, verschnittarme Nestings, autonome Zuschnittserkennung, Ultra-schallschweißen, Erstlagenfixierung sowie robotisches Greifen und Ablegen von Faserhalbzeugen geschickt miteinander kombiniert. Die Autoren dieses Beitrags möchten somit einen Beitrag zu mehr thermoplasti-schen CFK-Anwendungen im modernen Flugzeugbau bewirken, was in der Regel auch zu einer Verbesse-rung des Leichtbaupotentials solcher Flugzeuge führt

Dual Role of GdmH in Producer Immunity and Secretion of the Staphylococcal Lantibiotics Gallidermin and Epidermin

The biosynthetic gene clusters of the staphylococcal lantibiotics epidermin and gallidermin are distinguished by the presence of the unique genes epiH and gdmH, respectively. They encode accessory factors for the ATP-binding cassette transporters that mediate secretion of the antimicrobial peptides. Here, we show that gdmH also contributes to immunity to gallidermin but not to nisin. gdmH alone affected susceptibility to gallidermin only moderately, but it led to a multiplication of the immunity level mediated by the FEG immunity genes when cloned together with the gdmT gene, suggesting a synergistic activity of the H and FEG systems. gdmH-related genes were identified in the genomes of several bacteria, indicating an involvement in further cellular functions

Automated detection of yarn orientation in 3D-draped carbon fiber fabrics and preforms from eddy current data

Ensuring the correct fiber orientation in draped textiles and 3D preforms is one of the current challenges in the production of carbon-fiber reinforced plastics (CFRP), especially in resin transfer molding (RTM). Small deviations in fiber angle during preforming have a considerable effect on the mechanical properties of the final composite. Therefore, this paper presents an automated method for determining local yarn orientation in three-dimensionally draped, multi-layered fabrics. The draped fabric is scanned with a robot-guided high-frequency eddy current sensor to obtain an image of the sample's local conductivity and permittivity. From this image, the fiber orientation not only of the upper, but also of the lower, optically non-visible layers can be analyzed. A 2D Fast Fourier Transform is applied to local segments of the eddy current image to determine the local yarn orientation. Guidelines for processing the eddy current data, including phase rotation, filtering and evaluation segment size, are derived. For an intuitive visualization and analysis of the determined yarn orientation, reference yarn paths are reconstructed from the determined yarn angles. The developed process can be applied to quality inspection, process development and the validation of forming simulation results

Analysis of the 3D draping behavior of carbon fiber non-crimp fabrics with eddy current technique

Assessing and controlling the complex deformation behavior of textile reinforcements fabrics remains one of the major challenges in the production of fiber-reinforced plastics. In this paper, the draping of +45°/-45° biaxial non-crimp fabrics to a hemispherical shape is investigated with an eddy current imaging technique. After an automated draping process, the textiles are scanned with a robot-guided eddy current measurement system. From the resulting conductivity maps of the samples, the local yarn directions are extracted by image analysis and the paths of individual yarns are reconstructed for both the upper and the lower layer. Experiments are carried out for different forming speeds, blank holder forces and different non-crimp fabric parameters (stitch length, stitch type, stitch tension and yarn count). The influences of these parameters are compared and discussed, with the conclusion that blank holder forces have by far the most significant influence on the draping result. Sample experimental results are compared to results from an FEM draping simulation