| In this study, an experimental investigation has been performed to rationalize and to quantify the low cycle bending fatigue strength of steel bars under variable loading histories. To achieve this goal, eight groups of A36 steel square bars, totally 67 pieces, have been tested.; The test results show that under cyclic tests with constant displacement amplitudes, the fatigue life of specimens among different groups with different manufacturing processes are regular. However, under random loading, even though the displacement histories are the same, the fatigue life can vary significantly among different groups of specimens. Besides, using the conventional method to calculate the low cycle bending fatigue strength under random loadings will introduce large error.; By examining the microstructure of the tested specimens we find that the random low cycle bending fatigue life is highly dependent on the orientation angles of the material's grain. Based on this observation, a physical model is established to explain the various failure patterns of the test specimens.; By reviewing the failure mechanisms developed by previous researches and those determined in this study a more accurate formula to describe and quantify the low cycle bending fatigues strength of A36 steel bars under general loading histories is established. |
