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    Volume 7, Issue 4 (June 2018)

    Special Issue Paper

    Reliable Residual Stress Analysis for Thin Metal Sheets by Incremental Hole Drilling

    (Received 19 July 2017; accepted 24 January 2018)

    Published Online: 14 June 2018

    CODEN: MPCACD

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    Abstract

    Sheet metal–forming processes induce characteristic residual stress-depth gradients into technical components. Regarding thin metal sheets with thicknesses of only a few millimeters, or those in the sub-mm range, surface finishing processes, e.g., machining processes like grinding, polishing, lapping, or mechanical post–surface treatments, might cause significant distortions. These may result from intentionally induced one-sided residual stress distributions or residual stress redistributions through one-sided materials removal. For process assessment and control, accurate residual stress analysis is indispensable. However, in sheet metal formation, the residual stress state is often accompanied by pronounced crystallographic textures, which usually cause failure of the standard laboratory procedures. As an example, X-ray residual stress analysis according to the standard sin2ψ-method is not feasible for markedly textured material states because of curved 2θ-sin2ψ distributions. On the contrary, we have already shown that the incremental hole drilling method that uses case-specific calibration data and considers specimen thickness and crystallographic texture provides reliable stress evaluation. Hereby, for thin metal sheets, the appropriate support condition is very important since improper support can lead to significant restraints, i.e., the specimen fixture hinders the strain relaxation on the specimen’s surface during the hole drilling process, and, for nonflat sheets, even assembling stresses can be superimposed. Consequently, stress calculation based on the measured strain relaxation data leads to erroneous residual stress results in application of the incremental hole drilling method. This work is derived from the necessity of measuring residual stress-depth gradients in thin molybdenum sheets. Thereby, an appropriate specimen support strategy for hole drilling application on thin metal sheets is proposed based on a systematic parametric study using 3-D finite element modeling that considers different sheet thicknesses. Based on the simulation results, a support ring with an adequate inner diameter is proposed as the most suitable specimen support. The numerical findings were verified by experimental residual stress analyses with the use of two different specimen supports.

    Author Information:

    Simon, Nicola
    Karlsruhe Institute of Technology, Institute of Applied Materials, Karlsruhe,

    Mrotzek, Tobias
    Plansee SE, Reutte,

    Gibmeier, Jens
    Karlsruhe Institute of Technology, Institute of Applied Materials, Karlsruhe,


    Stock #: MPC20170111

    ISSN:2379-1365

    DOI: 10.1520/MPC20170111

    Author
    Title Reliable Residual Stress Analysis for Thin Metal Sheets by Incremental Hole Drilling
    Symposium ,
    Committee E08