Improvement of fracture characterisation of high-strength steel sheet metals by means of coupling of optical strain analysis systems with acoustic emission techniques
Final Report Abstract
Strict regulations on emissions for new vehicles as well as high fuel prices have been leading to changes in vehicle concepts for years. In order to reduce the weight of their products, car manufacturers are increasingly relying on modern lightweight materials such as higherstrength 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 with the help of the equivalent plastic strain weighted on the stress state. As an example, the modified Mohr-Coulomb failure model can be mentioned here. To parameterise these failure models, characterisation tests are carried out with different specimens in a wide range of stress states. The equivalent plastic strain at material failure is determined by many testing laboratories by means of an optical measurement system on the specimen surface, when a macroscopic crack appeared. Acoustic emission analysis offers great potential for improving the accuracy of failure characterisation. Hereby, the improved or earlier detection of the crack initiation inside the specimen during the forming process is possible. By using the method with acoustic emission, a more accurate failure characterisation for the numerical design of forming processes with high-strength sheet materials can be achieved. The results in this research project have shown that the determination of the crack initiation time by means of acoustic emission analysis and the assumption of the crack location inside the specimen provide a significant influence on the failure models to be parameterised. An improved accuracy of the failure models by the new methodology with acoustic emission analysis could be confirmed by process simulations of a deep drawing process and subsequent comparison to experimental deep drawing tests. The investigations were carried out for the high-strength steels DP1000 and CP800.
Publications
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Evaluating material failure of AHSS using acoustic emission analysis. Materials Research Proceedings, 25, 379-386. Materials Research Forum LLC.
Stockburger, E.
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Failure Modelling of CP800 Using Acoustic Emission Analysis. Applied Sciences, 13(6), 4067.
Stockburger, Eugen; Wester, Hendrik & Behrens, Bernd-Arno
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Fracture Characterisation and Modelling of AHSS Using Acoustic Emission Analysis for Deep Drawing. Journal of Manufacturing and Materials Processing, 7(4), 127.
Stockburger, Eugen; Wester, Hendrik & Behrens, Bernd-Arno
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Optimised parametrisation of the MMC fracture model using AE and FE analysis. IOP Conference Series: Materials Science and Engineering, 1284(1), 012072.
Stockburger, E.; Wester, H. & Behrens, B.-A.
