Abstract
The high-strain rate response of ultra-fine grained (UFG) copper processed by
Equal Channel Angular Pressing (ECAP) was characterized by reverse Taylor impact and Hopkinson-bar experiments. Two types of copper samples are tested using Hopkinson bar: (a) cylindrical samples to investigate the response at high strain-rates,(b) hat shaped samples to compare the shear band characteristics in UFG copper with the ones that have been studied in coarse grained samples. This can be attributed to the high strain-rate sensitivity of the fine grained FCC metals. Upon impact, the samples were found to undergo heat induced static recrystallization at a calculated temperature of 360K, indicating that the UFG copper is thermally unstable. Reverse Taylor tests were conducted on as-received OFHC Cu rod and ECAP specimens with sequential ECAP passes (2 and 8). The dynamic deformations of the samples are modeled using AUTODYN-2D and a modified Johnson-Cook constitutive equation was found to capture the dynamic response. Similar to the compression test results, the impacted front of the samples were found to recrystallize extensively and preferentially.