Instrumented anvil-on-rod tests for constitutive model validation and determination of strain-rate sensitivity of ultrafine-grained copper

Anvil-on-rod impact tests were performed on as-received (cold-rolled) OFHC copper rods and copper processed by 2- or 8-passes of equal channel angular pressing (ECAP). The average grain size ranged from ∼30 μm for the as-received sample to ∼440 nm for the 8-pass sample. The dynamic deformation states of the samples were captured by high-speed digital photography and velocity interferometry was used to record the sample back (free) surface velocity. Computer simulations utilizing AUTODYN-2D hydrocode with the Johnson–Cook constitutive model were used to generate free surface velocity traces and transient deformation profiles for comparison with the experimental data. The comparison of experimental results with AUTODYN simulations provided a means for extracting the strain-rate sensitivity of copper as a function of grain size. Strain-rate sensitivity was found to increase as grain size decreased.