The yielding behavior and plastic deformation of oxygen-free copper under biaxial quasi-static and dynamic loadings

This study investigated the yield behavior of oxygen-free copper under complex stress states and different loading rates. An optimized cruciform specimen and a novel electromagnetic biaxial split Hopkinson bar (EBSHB) were used to perform the dynamic biaxial tension tests at three different load ratios. The non-contact digital image correlation technique was adopted for strain measurement. Quasi-static and dynamic yield surfaces were obtained. Classical yield criteria, including the Tresca and von Mises yield criteria, were evaluated based on the experimental results. The von Mises criterion is found to provide better prediction of the yield surface under both quasi-static and dynamic loadings. The Johnson-Cook model from uniaxial test results provides a moderate prediction for experimental curves, while that from biaxial test results shows better prediction. Dynamic biaxial tests are proven necessary to acquire the constitutive models that can accurately describe the mechanical properties of copper under complex stress states.