Axial Fatigue on Carbon Steel in the Plastic Range

Abstract

The following is the report of axial fatigue tests carried out in the plastic range on smoothed specimens with uneven cross section of 0.29% carbon steel. In the completely reversed and pulsating straining tests and the completely reversed stressing tests, we made investigations of the fatigue lives and the variations of stress-strain hysteresis curves during the fatigue tests. Measuring the diametral changes on the minimum cross sectional portion of the specimens, we dealt with the results of the experiment in true stress and true strain. Since the smoothed specimens with uneven cross section did not present buckling even under high compression strain, it was possible to make tests over the wide range of strain amplitude. For the sake of comparison completely reversed straining tests were made on smoothed specimens with uniform cross section.The main results of the experiment are as follows.(1) The relations between the true strain amplitude and the number of cycles to fracture are expressed in the following formulas.(a) For the completely reversed and pulsating straining tests on smoothed specimens with uneven cross section, etaN0.51=0.41(b) For the completely reversed straining tests on smoothed specimens with uniform cross section, etaN0.41=0.16(2) The fatigue life of smoothed specimens with uneven cross section is longer than that with uniform cross section in the completely reversed straining tests. The larger the strain amplitude is, the greater the difference of the lives is.(3) Two types of fractures were observed in the completely reversed stressing tests, contracted fracture in tests with the fatigue life of less than about 100 cycles and fatigue fracture in tests with the fatigue life of above as many cycles.