Abstract
The purpose of this paper is to describe on the application of the electroplating method, which is first used by H. OKUBO on the experimental stress analysis, in the measurement of the repeated stress under which a machine element or a structural component has been operated.
The method is based on the fact that brownish flecks appear on the surface when a specimen is electroplated with copper and is subjected to repeated stress and that the relation between the stress amplitude and the number of repetitions at which the flecks appear is fairly defined if the plating conditions are appropriately chosen. Hence, the measurement is carried out as follows. First, the critical line which represents the above relation is determined on some reference specimen. Secondly, the elements or the components to be measured are electroplated under the same conditions as the reference specimen and then subjected to repeated loading until flecks appear, which indicate that the critical line is reached. Then we can decide the amplitude or the number of repetitions when one of them is known. The electroplating conditions should be so chosen as to give the critical line lying under the S-N curve of the material. By means of this method we can estimate the safety grade of machine elements or structural components.
In order to obtain informations about the critical line, some experiments were carried out. The results are summarized as follows:
1) The critical line under constant loading is similar in shape to S-N curve.
2) If the electroplated layer is coated with clear lacquer, it seems to be more stable to the atmosphere, the critical line showing little change with time.
3) In the case of two levels of stress, test results show similar tendencies to those of the endurance test of materials. For the practical purposes, therefore, it is permissible to estimate the safety grade of more complicated loading by the critical line and the S-N curve under constant loading.
