Abstract
Mode I, static fracture experiments and uniaxial tension/compression tests are conducted at three temperatures in the range from 25 to 100∘C using fatigue pre-cracked four-point bend and micro-tensile/compression specimens machined from a rolled AZ31 Mg alloy plate. Digital image correlation technique along with in-situ optical imaging is employed to analyse the specimen surface deformation. It is found that the fracture mechanism which is operative near the tip changes from quasi-brittle cracking caused by tensile twins to ductile void growth and coalescence as temperature is raised above 65∘C. This corroborates with reduction in tensile twin development near the crack tip with enhancement in temperature. On the other hand, at higher temperature, more profuse twinning and pronounced texture changes are perceived in the far-edge of the ligament, where compressive normal stress prevails. Simplified analyses are performed to show that the evolution rate of tensile twin volume fraction with energy release rate J near the tip will diminish strongly, while micro-void growth rate will enhance between 25 and 100∘C, thereby triggering the observed brittle-ductile transition. The fracture toughness rises dramatically above 65∘C and is also accompanied by significant notch blunting. This is rationalized from the transition in fracture mechanism and large plastic dissipation in the ligament far-edge due to twinning.
Original language | English |
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Pages (from-to) | 89-114 |
Number of pages | 26 |
Journal | International Journal of Fracture |
Volume | 238 |
Issue number | 2 |
DOIs | |
State | Published - Dec 2022 |
Externally published | Yes |
Keywords
- Basal texture
- Fracture mechanism
- Fracture toughness
- Mg alloys
- Temperature dependence
- Tensile twinning