Analysis and assessment of residual stress components normal to the surface by X-ray diffraction techniques

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Due to the small penetration depth of the X-rays used, in case of diffraction residual stress analysis, in most cases a plane surface parallel residual stress state is assumed neglecting possibly existing stress components normal to the surface. This assumption, however, is often questionable and consequences are difficult to assess. In the present project using different types of diffraction residual stress analyses residual stress components normal to the sepecimens surface will be analysed for characteristic materials states and their depth distributions will be described. Investigations will focus on materials states after contact loading, which is very important in industrial practice, e. g. in drive technology or in interactions between workpiece and tools.Correlations between loading conditions, materials microstructures and residual stress components normal to the surface will systematically be studied. Different complementary diffraction techniques for stress analysis will be applied: conventional methods including electrolytical surface layer removal, special techniques to vary the information depths of the X-rays used including synchrotron radiation as well as measurements on specially prepared sections of the deformed materials volumes. Plain carbon steels with different microstructures will be investigated. Residual stress states will be produced by static and oscillating contact loading. In this way under well defined conditions the correlations between materials states, loading conditions and resulting residual stresses normal to the surface will be evaluated.