Fracture mechanism and toughness of a rolled magnesium alloy under dynamic loading

Static and dynamic fracture experiments are performed using fatigue pre-cracked three-point bend specimens of a rolled AZ31 Mg alloy on a servo-hydraulic universal testing machine and a Hopkinson bar setup, respectively. The results are interpreted using in-situ optical imaging along with digital image correlation analysis. Microstructural analysis reveals that the fracture mechanism changes from twin-induced quasi-brittle cracking for static loading to micro-void growth and coalescence under dynamic loading accompanied by decrease in tensile twinning near the tip with loading rate. By contrast, the density of twins near the far-edge of the ligament and associated texture change enhance strongly with loading rate. The fracture toughness increases dramatically at high loading rates which is attributed to enhanced work of separation and dissipation in the background plastic zone.