Prediction of Residual Stress Distribution in Severe Surface Deformed Steel by Constant Penetration Depth Method

Abstract

The residual stress distribution below the specimen surface of a severe surface deformed medium carbon steel was investigated nondestructively by using high-energy X-rays from a synchrotron radiation source. The carbon steel plate was shot-peened with fine cast iron particles of the size of 50μm. By using the monochromatic X-ray beam with three energy levels of 10, 30 and 72keV, the stress values at the arbitrary depth were measured by the constant penetration depth method. The stress was calculated from the slope of the sin²ψ diagram. Measured stress corresponds to the weighted average associated with the attenuation of the X-rays in the material. The real stress distribution was estimated by using the optimization technique. The stress distribution was assumed by the polynomials with the order from the first to the third in the near surface layer and the second order polynomial in the deeper region. The coefficients of the polynomials were determined by the conjugate gradient iteration. The predicted stress distribution agreed very well with that measured by the conventional surface removal method.