Characterization of high-strain rate mechanical behavior of AZ31 magnesium alloy using 3D digital image correlation

Characterization of the material mechanical behavior at sub-Hopkinson regime (0.1 to 1 000 s^-1) is very challenging due to instrumentation limitations and the complexity of data analysis involved in dynamic loading. In this study, AZ31 magnesium alloy sheet specimens are tested using a custom designed servo-hydraulic machine in tension at nominal strain rates up to 1 000 s^-1. In order to resolve strain measurement artifacts, the specimen displacement is measured using 3D Digital Image correlation instead from actuator motion. The total strain is measured up to ≈ 30%, which is far beyond the measurable range of electric resistance strain gages. Stresses are calculated based on the elastic strains in the tab of a standard dog-bone shaped specimen. Using this technique, the stresses measured for strain rates of 100 s^-1 and lower show little or no noise comparing to load cell signals. When the strain rates are higher than 250 s^-1, the noises and oscillations in the stress measurements are significantly decreased from ≈ 250 to 50 MPa. Overall, it is found that there are no significant differences in the elongation, although the material exhibits slight work hardening when the strain rate is increased from 1 to 100 s^-1.