Analyse oberflächennaher Eigenspannungszustände mittels komplementärer Beugungsverfahren

Manns, Thorsten

kassel university press, ISBN: 978-3-86219-042-3, 2011, 183 Pages
(Forschungsberichte aus dem Institut für Werkstofftechnik - Metallische Werkstoffe 11)

URN: urn:nbn:de:0002-30438

Zugl.: Kassel, Univ., Diss. 2010

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Content: The present work deals with the analyses of in depth residual stress gradients applying complementary diffraction methods. The main issue thereby is the development of a new procedure to determine stress gradients σ(z) in real space directly by special masks. Their slit design defines small gauge volumes which are located in different depth beneath the sample surface. For the practical implementation of the method appropriate samples are produced and characterised concerning their residual stress distributions by established diffraction techniques. To determine stresses accurately from the measured strains the diffraction elastic constants (DEC) are required. Therefore a computer program was developed within this work which calculates the DEC from single crystal coefficients.

To provide suitable residual stress states for the development of the real space procedure with highly absorbing beam limiting masks, steel (100Cr6) and ceramic samples (Al2O3) are produced and treated by deep grinding and shot peening respectively applying different process parameters. The resulting residuals stress distributions are analysed by means of LAPLACE and layer removal techniques (sin2ψ-method), yielding a well defined sample basis for comparisons with the real space method.

The progress in the development of the new procedure is described and discussed by different approaches. Applying a position sensitive CCD detector and fixed masks on the sample surface the principle function of the real space method is demonstrated for the first time, due to depth dependent diffraction signals from gauge volumes in the sample. Problems in the data analyses are caused by poor grain statistics due to the small dimensions of the gauge volumes which are 7-8 µm in height and 11 µm in width respectively. For continuative experiments a positioning stage was developed which enhances the quality of the diffraction images and the adjustment of the measurement depth. Furthermore negative influences from the surface topography of the sample can be eliminated. Experiments with Al2O3 bulk samples and a multilayer system demonstrate that the measured data for increasing depth correlate well with intensity distributions from simulations and moreover, that the residual stress analysis by the new real space procedure is generally possible. However further improvements of the procedure are necessary which involve the design and production of new masks with a thicker absorbing layer, a more accurate alignment and depth adjustment of the masks relative to the sample surface and an enhancement of the depth resolution of the gauge volumes.

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