AN INVESTIGATION ON SOFTENING IN CONSTITUTIVE RELATIONSHIP OF METALS AT HIGH STRAIN LEVEL

摘要

To study the constitutive relationship of metals at high strain levels, equal channel angular pressing (ECAP) was used to impose high strain into the pure copper and ultra-low carbon steel samples, and tensile testing was used to estimate the yield stress. It is found that the stress -strain (accumulated through ECAP) constitutive relationship shows softening at high strain levels. This softening behavior could not be described by the existing constitutive relationship models of the Hollomon power-law relationship at low strains, or the Voce exponential relationship at high strains. A new constitutive equation was deduced to describe this softening behavior. The softening behavior could be explained by the occurrence concurrent recrystallization, which was confirmed by the abnormal relationship between stored energy from ECAP and subsequent recrystallinzation temperature after ECAP.