Uniaxial ratcheting under tension and compression

The simulation and experimental results are presented graphically in Figure 3. The strains and stresses are computed by averaging the values in the elements lying at the center of the specimen. The experimental curve shows three distinct regions: a linear elastic region, an elastic-plastic transition zone, and an almost linear response region at large strain values. The model with two backstresses captures this response very well. One of the backstresses has a large value of the parameter $\gamma$, which captures the shape of the transition zone correctly, while the second backstress with a relatively small value of $\gamma$ captures the nearly linear response at large strains correctly. The parameter $\gamma$ in the model with one backstress has a relatively large value, which results in large discrepancies between the experimental and predicted responses at large strains.

The simulation results obtained for the model with one backstress and the model with two backstresses, together with the experimental results, are depicted in Figure 4. The strains were computed by averaging the strains in the elements lying at the center of the specimen. The figure shows that both simulation models are capable of predicting ratcheting. It also shows that the results obtained using the model with two backstresses correlate better with the experimental results.