POLYCHROMATIC X-RAY-METHOD FOR RESIDUAL-STRESS MEASUREMENTS IN A SUBSURFACE LAYER

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