Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Influence of production-related gaps on strength properties and deformation behavior of spot welded TRIP Steel HCT690T
    ( 2012)
    Brauser, S.
    ;
    Pepke, L.-A.
    ;
    Weber, G.
    ;
    Rethmeier, M.
    In this study, the influence of production-related gaps on the shear tension strength and fatigue performance was investigated for resistance spot welded TRIP steel HCT690. Furthermore, the local strain distribution in shear tension test was calculated by the digital image correlation technique (DIC). The static shear tension strength was found to be almost independent of gaps up to 3 mm. The maximum local strain in the spot weld region however decreases depending on which sample side (deformed or undeformed) is considered. In addition, it has been ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap-free shear tension samples. This fact could be attributed to decreased stiffness, higher transverse vibration and higher rotation (?) between the sheets as well as increased local stress calculated by 2 dimensional FE simulation.
  • Publication
    Potential of optical strain field measurement for the characterisation of the properties of resistance-spot-welded joints
    ( 2011)
    Rethmeier, M.
    ;
    Brauser, S.
    ;
    Weber, G.
    For the designing of safety-relevant components particularly by means of finite element calculations, great significance is attached to the determination of local material parameters in the welding region. Conventional test methods can merely provide global parameters which, however, are frequently not sufficient precisely for the calculation of resistance-spot-welded components since these are characterised by the existence of joining zones with tight local limitations. In contrast, modern test methods such as optical strain field measurement permit the determination of the characteristic material data for concrete locations and times. In order to establish the potential of optical strain field measurements for the characterisation of the local material behaviour of spotwelded joints, tensile shear tests as well as tensile tests were carried out on resistance-spot-welded high-strength steels. The results show the high potential of this procedure not only for the quanti fication of the local strain behaviour in the joining region but also for the determination of local characteristic material data.
  • Publication
    Methods to obtain weld discontinuities in spot-welded joints made of advanced high-strength steels
    ( 2011)
    Gaul, H.
    ;
    Brauser, S.
    ;
    Weber, G.
    ;
    Rethmeier, M.
    Resistance spot welding is the major joining technique in mass car production. This applies in particular to high-strength steel and advanced high-strength steel (AHSS) joining of thin sheet steel components for lightweight body shell structures. Joining of AHSS in mass production might lead to weld discontinuities under certain circumstances. Those discontinuities in form of cracks might be an initial start of cracking in the spot-welded joints regarding fatigue loads. It is of great interest to figure out, if, in comparison to specimens without weld discontinuities, the crack initiating point changes and if the fatigue resistance might be reduced by the discontinuities. In this contribution, an overview of potential discontinuities is given. Their possible causes are discussed and means for their detection are highlighted. Among the possible causes of weld discontinuities, two major groups are distinguished: the welding parameters as primary influences in the welding process, and the production-specific influences as secondary ones. With emphasis on major cracks penetrating the weld nugget, these influences are analysed. Finally, a combination of extreme welding parameters with production-specific influences is chosen in order to establish a method which enables the preparation of fatigue test specimens with reproducible major cracks in different locations of the spot-welded joints. This method is than applied in order to prepare spot weld specimens for fatigue tests.