A Fast Method for Ratchetting Strain Prediction
A time efficient method for predicting ratchetting strain is proposed. By finding the ratchetting rate, at only a few cycles, the ratchetting strain of any cycle can be determined. It is shown that a trajectory of the origin of stress may be defined in the deviatoric stress space as the ratchetting progresses. The method for obtaining this trajectory from a standard uniaxial asymmetric cyclic loading is presented. At the beginning, this trajectory coincides with the initial stress origin and approaches the mean stress, displaying a power law relationship with the number of loading cycles. This path defines a moving frame of reference for stress tensor calculations. Ratchetting rates for different cyclic loading are calculated with the knowledge of this frame of reference and through utilizing a constitutive cyclic plasticity model which incorporates deviatoric stresses and back stresses that are measured with respect to this moving frame. The proposed model is used to predict ratchetting strain of 1070 steel under single step constant amplitude and multi-step loading. The method is also applied to non-proportional loading. Results obtained agree with the available experimental measurements.