A Constant Incidence Angle Method to Estimate the Subsurface Distribution of Residual Stress by High-Energy X-Rays from Synchrotron Radiation Source

A new method is proposed to estimate nondestructively the distribution of the equibiaxial residual stress beneath the surface by using an Eulerian cradle type goniometer. By maintaining a constant value of the X-ray incident angle, the probing depth of X-rays is kept nearly constant, even though sin2ψ is changed. From the slope of the linear relation between the diffraction angle and sin2ψ, the stress value is calculated for a given probing depth. This new method is applied to estimate the residual stress of a shot-peened steel sample, whose compressive zone extended about 150μm below the surface. High energy X-rays of 72keV from synchrotron radiation source, SPring-8, was used for stress measurements. The residual stress distribution estimated by the new method agreed well with that determined by the conventional sin2ψ method with Cr-Kα radiation combined with the method of the successive removal of the surface layer by electropolishing.