Effect of temperature on the mixed-mode (I&II) fracture response of a rolled magnesium alloy

This work investigates the effect of temperature on the mixed-mode (I and II) fracture response of a rolled AZ31 Mg alloy by conducting experiments using asymmetric pre-cracked four-point bend specimens at room tem-perature and 100 degrees C. Digital image correlation analysis of in-situ optical images of the specimen is undertaken to map the strains and deformation on the surface. The deformation response has been further examined through microstructural characterization by optical microscopy, electron backscatter diffraction, and fractographic studies. The results show that the fracture toughness Jc enhances by a factor of about 3.5, irrespective of mode mixity over the above temperature range. A change in fracture mechanism from brittle cracking attributed to tensile twinning near the tip to ductile void growth and coalescence occurs over the above temperature range. Also, Jc drops by about 2.7 as fracture mode changes from mode I to II at both temperatures, notwithstanding the vast difference in fracture mechanism. The above trends are rationalized from the role of tensile twinning, which while critically influencing the fracture processes near the tip, can also contribute to Jc through substantial background plastic dissipation.