Abstract
In this paper is presented a report of tests of constant strain low cycle torsional fatigue that were carried out on 0.81% C piano wires at room temperature and at elevated temperatures 270°C, 300°C and 400°C respectively, with a view to the investigation of the plastic fatigue phenomena. Three kinds of torsions were worked for the tests, completely reversed, fluctuating and pulsating, under the test speed of 1rpm. The main results obtained are as follows.
(1) There is larger effect of temperature on the fatigue life than that of the mean strain. Let the strain amplitude stand as it is, there is longer fatigue life at 270°C and shorter fatigue life at 400°C than room temperature, the former case being considered to be the annealing effect.
(2) The time-strength diagram shows linear decrease in strain amplitude γa against increase in the mean strain γm which the latter represents the number of cycles from the initiation of macrocrack N'=50 to its fracture N=200 or N=1000.
(3) The test result shows that there exists linear relationship between, the total plastic strain γp.total and N' or N, when they are plotted on a log-log scale. It is found also that the same relationship holds for the total hysteresis energy W, the not-total hysteresis w' and the strain amplitude γa. In the completely reversed tests, γp.total and W are defined as γp.total=4ΣNn=1γp+γmf and W=w·N, in which γp and γmf are the plastic strain amplitude and the mean strain just before fracture, respectively.
