Polychromatic X-ray method for residual-stress measurements in a subsurface layer

The classical sin(2) psi method with characteristic X-rays is widely used to measure residual stress nondestructively in the steel members of a structure or a machine, With this method it is, however, difficult to measure the three-dimensional stress distribution with a steep gradient that occurs along the depth direction in a subsurface layer of the material after surface treatment such as grinding or cold rolling. This paper presents a new polychromatic X-ray method for residual-stress measurements in a subsurface layer, The relationship between the diffracted beam peak of the polychromatic X-ray and the strain along the depth direction in a subsurface layer was obtained by theoretical analysis. It was modeled by numerical simulation to obtain probable values of the parameters, and these were used along with experimental X-ray data to derive an experimental value for the stress gradient, This was compared with the values predicted from plate bending theory.