Anisotropic plastic flow of low/medium carbon steel plates in different loading conditions: Characterization of the r-value

The reproduction of materials’ plastic flow behavior is a critical component of the constitutive modeling in sheet metal forming. As an important material property indicator reflecting the anisotropy of plastic deformation, the r-value is closely correlated with the plastic flow. This paper focuses on the r-value of the low/medium carbon steel plates in different loading conditions. Some general rules of the r-value asymmetry and evolution are concluded among these materials. In uniaxial loading, the r-value continually decreases with strain, while in uniaxial compression, the r-value continually increases with strain. The viscoplastic self-consistent (VPSC) simulation indicates this phenomenon is related to the evolution of the grain shape and the texture. In some cases of the nonproportional loading, a remarkable instantaneous evolution of the r-value occurs right after the loading path changes, which exhibits the tension-compression asymmetry as well. The aforementioned behaviors are characterized through the digital image correlation (DIC) strain measurement method. The procedure to characterize the r-value in uniaxial tension is clarified and an online method to characterize the r-value in uniaxial compression is newly proposed and verified. The proposed method provides a reliable evaluation of the compressive r-value since it can continuously record the r-value during the compression process and reduce the impact of the friction on the testing results.