Characterisation of high rate plasticity in the uniaxial deformation of high purity copper at elevated temperatures

In uni-axial compression at strain rates above 104 s−1, FCC metals exhibit a rapid increase in strength. Mechanisms proposed to be responsible for this transition can be broadly split into two categories; that mobile dislocation velocities become limited by quasi-viscous scattering from phonons, or that some change occurs in the evolution of the materials dislocation structure. The relative contribution of each mechanism is difficult to identify, in part due to a scarcity of experimental measurements in varying deformation conditions. In this paper, we perform uni-axial compression experiments that reach rates between 104 and 105 s−1, at temperatures between 300 and 600 K. Analysis of the data at 0.1 strain shows both the absolute and relative levels of thermal softening increase with strain rate, an anomalous result in comparison to both existing models and measurements below the transition.