Detection of the failure zone caused by cyclic loading

There is a simplified technique for detecting where the part of a structure undergoes failure due to cyclic loading; this technique appears to be of g reat practical value in its employment to prevent fracture. It is well known that when yield stress is applied to a law-carbon steel pl ate, Luders' lines become visible on its surface to the naked eye. It is a plausible hypothesis that the locations on the surface of the plate where t he Luders' lines appear are in a state of failure. The correlation of cycli c loading and Luders' lines should confirm whether or not Luders' lines rel iably indicate where failure results from fatigue loading. The Ra value of the surface roughness of the specimen before and after the appearance of Lu ders' lines is used to ascertain this correlation. The present paper takes up cyclic tensile loading with shoulder fillets as a concrete example of th e correlation of failure and stress.