SIGMA-XX(Z) AND SIGMA-YY(Z) STRESS-FIELDS CALCULATED FROM DIFFRACTION EXPERIMENTS PERFORMED WITH SYNCHROTRON RADIATION IN THE OMEGA-MODE AND PSI-MODE TECHNIQUES

The importance of synchrotron radiation for the evaluation of stress fields in polycrystalline specimens is outlined. As a special example we investigated residual stress-fields sigma-xx(z) and sigma-yy(z) which vary significantly below the surface of the polycrystalline specimens within the penetration depth tau of the X-rays. The individual crystals are elastically anisotropic. However on a macroscopic scale inside the irradiated volume the specimens are supposed to be isotropic and homogeneous. Special effects related to plastic deformations are neglected. It is shown how properly normalized strain curves epsilon-phi-psi are obtained from the diffraction experiments. From the epsilon-data a 'universal curve' is calculated which is independent of the reflecting lattice planes and the wavelength and which should be the same for experiments performed in the OMEGA- and in the PHI-mode. It was possible to demonstrate that strongly non-linear epsilon-(sin2-psi)-curves observed for the (531) reflection of a cold-rolled nickel plate are related to strong stress gradients. The experiments yield sigma-xx(tau) and sigma-yy(tau) which are closely related to the Laplace transforms of the corresponding curves in z-space.