In this paper, the change in the magnetic property of steel subjected to repeated tension and compression is studied as an aid to the analysis of the fatigue of mild steel. A specimen of annealed 0.3% C-steel is fitted to the Heigh's Fatigue Tester, and the prescribed tensile and compressive stresses of six grades within the range of 12-38kg/mm2 are applied a definite number of times, that is, more than 104 times. Then, after the threaded parts of both ends of the specimen are cut off, the parallel part is finished and the hysteresis curve is obtained by means of the method of easy and continuous search for the hysteresis loop of the specimen utilizing the magnetometer and the nomograph such as were reported in 1953. The change in the magnetic property due to fatigue was observed by varying the number of repetition and applying various repeated tensile and compressive stresses.
Some of the results are summarized as follows: under the experimental conditions, the residual magnetism andthe coercive force are almost constant for the various stresses regardless of the number of repetition: the hysteresis loss scarecely changes when the stress is under a certain value regardless of the number of repetition but tends to decrease as the number of repetition increases when the repeated stress goes beyond a certain limit (which agrees with the fatigue limit), and this fact is consistent with that achieved by the method of rotating bending or repeated stress: and the susceptibility and other several magnetic properties seem generally to have the mean value of the values of the annealed steel and the cold worked one, and decrease gradually within the range of these two values with the increase of the number of repetition.
