Mixed mode I/III fracture toughness in extruded magnesium alloys

Fracture toughness under mode I and mixed mode I/III loading were determined for magnesium (Mg) as well as binary Mg–Al and Mg–Zn alloys in as-extruded condition. It was found that in Mg and in Mg–1.25Zn alloy the fracture toughness under mixed mode I/III loading was higher than that under mode I loading whereas in binary Mg–1Al and Mg–3Al alloys it was lower than that under mode I loading. The results have been explained on the basis of the fracture mechanism and the nature of the stress fields ahead of the crack tip under mixed mode I/III loading.