Improved Fracture Characterization of High Strength Steels due to a new Test Method for Shear Tension Specimen on uniaxial Tensile Testing Machines
Final Report Abstract
Strict legal regulations on emissions from new vehicles as well as high fuel prices have been leading to changes in vehicle concepts for years. Throughout the automotive industry, there is a clear trend towards lighter and more fuel-efficient vehicles. In order to reduce the weight of their products, car manufacturers are increasingly relying on modern lightweight materials such as higher-strength and high-strength steels. In order to optimally utilise the high potential of these steel materials for reducing vehicle weight, it is necessary to reliably design their forming capacity and the crash behaviour of the resulting sheet metal components by means of numerical simulation. This requires precise modelling of the material behaviour under process conditions. With regard to sheet metal forming, the flow condition, the hardening behaviour and the forming capacity must be characterised and modelled. To describe the forming capacity, failure models are often used that predict a crack by means of the equivalent plastic strain weighted on the stress state. The modified Mohr-Coulomb failure model is an example of this. To parameterise these failure models, characterisation tests are carried out with different specimen geometries in a wide range of stress states. The load paths are not constant for many specimen geometries and materials, so that the load path is often averaged for the parameterisation of failure models leading to inaccuracies. In order to improve the accuracy of failure characterisation and modelling, it is therefore of interest to develop a methodology with which the material can be tested under constant load paths. By characterising the failure of specimens under constant load paths, more accurate failure modelling can be achieved for the numerical design of forming processes with high-strength sheet materials. The results in this research project have shown that the new methodology of butterfly tests with loading angle correction have a significant influence on the equivalent plastic strain as well as the stress state and thus on the failure model. More constant load paths could be generated in the specimens and thus an improved accuracy of the failure models. The increased accuracy of the new methodology with loading angle correction was confirmed by process simulations of a deep drawing process and subsequent comparison of the experimental und numerical results. The investigations were carried out for the high-strength steels DP1000 and CP800.
Link to the final report
https://oa.tib.eu/renate/handle/123456789/18502
Publications
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Comparison of different testing approaches to describe the fracture behaviour of AHSS sheets using experimental and numerical investigations. IOP Conference Series: Materials Science and Engineering, 1157(1), 012059.
Behrens, B.-A.; Rosenbusch, D.; Wester, H. & Dykiert, M.
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Fracture Characterisation by Butterfly-Tests and Damage Modelling of Advanced High Strength Steels. Key Engineering Materials, 883, 294-302.
Behrens, Bernd-Arno; Brunotte, Kai; Wester, Hendrik & Dykiert, Matthäus
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Improved failure characterisation of high-strength steel using a butterfly test rig with rotation control. Materials Research Proceedings, 28, 737-746. Materials Research Forum LLC.
Stockburger, E.
