Experimental study on the cyclic deformation and plastic flow of U71Mn rail steel

The strain cyclic characteristics and ratcheting behaviour of U71Mn rail steel were experimentally investigated under uniaxial cyclic loading at room temperature. The effects of cyclic strain amplitude, mean strain, strain rate and their histories on strain cyclic characteristics were studied. The effects of stress amplitude, mean stress and their histories on the ratcheting under asymmetrical stress cycling were also analysed. Then, the interaction between strain cycling and stress cycling was discussed, too. Based on the experimental stress–strain data, the plastic flow properties of U71Mn rail steel under cyclic loading were analysed. Plastic modulus and its evolution rule were calculated from experimental data and were discussed under strain and stress cycling, respectively. It is shown that both the strain cyclic characteristics and ratcheting depend not only on current loading state, but also greatly on previous loading history. Under asymmetrical stress cycling, the evolution rule of plastic modulus is different from that under strain cycling. The strain cyclic characteristics and ratcheting behaviour of the material can be described essentially by the evolution of plastic flow.