Residual Stresses Measurements on a Valve Camshaft

The well known influence of residual stresses (RSs) on contact fatigue is the main reason to specify a minimum value of the RSs, after heat treatment, at certain positions on the cam of a valve camshaft. The influence of the RSs in this case depends on their distribution along the depth of the component rather than on a particular value at the surface. This paper compares the values of RSs at the surface with the distribution of circumferential and radial RSs along the depth, measured on a transverse section of the cam, by X-ray diffraction and 'blind hole' techniques. The results are compared in terms of the specified values and limitations of each technique. (The camshaft used was machined from a rolled bar of steel, type SAE 8660.)