Showing papers by "Jens Gibmeier published in 2006"

Determination of Real Space Residual Stress Distributions σij(z) of Surface Treated Materials with Diffraction Methods Part I: Angle-Dispersive Approach

Abstract: A measuring and evaluation strategy for the determination of residual stress depth distributions σ ij (z) in real space within different depths beneath the samples surface is introduced. The proposed method allows the analysis of residual stresses within a specific gauge volume using the well-known sin 2 ψ-method. Hence it allows a real 'stress scanning' in real space and will be applicable to laboratory X-ray sources as well as middle and high energy synchrotron radiation, consequently holding for different information depths. In contrast to the hitherto applied strain scanning methods the basic idea of the herein proposed procedure considers the use of fixed beam limiting apertures being inserted in the primary and the secondary beam path. In the project, which is a cooperation between the Institute for Materials Engineering (University of Kassel) and the Hahn-Meitner-Institute Berlin, it is distinguished between an angle-dispersive and an energy-dispersive approach. For the angle-dispersive approach (soft X-rays) the gauge element is defined by using beam limiting masks coupled to the samples surface. The geometries of the masks are tailored with respect to the X-ray wavelength and the samples tilt relative to the beam path. For the energy dispersive approach, the gauge, volume is defined by a pair of slits, coupled with the sample. Its geometry depends on the ψ tilt of the sample and the alignment allows a translation relative to the sample in order to realize the depth scan (see also Part II [1]). In part I of the contribution an outline of the entire scope of the project is given. In addition detailed information on the handling of the angle-dispersive approach will be presented.

In Situ X-Ray Stress Analysis for the Highly Textured Mg-Base Wrought Alloy AZ31

Abstract: The deformation behaviour of the highly textured Mg-base wrought alloy AZ31 subjected to tensile and compressive elasto-plastic loading was characterized by means of synchrotron radiation. In former publications it was shown that there exists an asymmetry in the deformation behaviour of the investigated alloy, which can be related to the deformation mechanism of the hexagonal structure due to the crystallographic texture relative to the loading direction. A local X-ray stress analysis was carried out on highly textured metal sheets for different {hkil}- planes of the hexagonal crystal structure. The load transfer was investigated within in-situ loading experiments in order to account for suitable XEC´s, thus ensuring accurate stress evaluations. An X-ray imaging method was applied in order to provide bending stress distributions with a high local resolution using synchrotron radiation (beamline G3, Hasylab (DESY)). Stress analyses were carried out on the side face of a bending bar being subjected to elasto-plastic bending up to total strains in the outer layers of approximately 2%. It is distinguished between loading stress distributions measured in in-situ loading experiments as well as residual stress distributions monitored after unloading of elasto-plastically bended bars. Furthermore the loading direction was alternated, in order to investigate the effect of the twin formation as well as the reversibility of the twinning on the results of X-ray stress analysis.