Notch sensitivity of combined mode I–II fracture behaviour of a rolled magnesium alloy

ABSTRACT

Fatigue pre-cracked four-point bend specimens of a rolled AZ31 Mg alloy are loaded asymmetrically and their mixed-mode (I and II) fracture behaviour is contrasted with pre-notched samples. In-situ mapping of displacement and strain fields is performed through optical imaging coupled with digital image correlation analysis. The fracture surface morphology and the deformed microstructure are also studied. The fracture toughness J_c for both types of specimens is highest for mode I and drops steeply with increase in mode II component. Furthermore, at the same level of mode-mixity, J_c for the notched samples is between two to three times the value pertaining to pre-cracked specimens. This is primarily attributed to quasi-brittle failure, irrespective of mode-mixity, for the latter, whereas the former display a combination of ductile and brittle fracture surface features. At the crack-initiation stage, more profuse tensile twinning is perceived at the far-edge of the ligament in the notched specimens, which also contributes to the observed toughness enhancement.

KEYWORDS:

• Mixed-mode fracture
• notch sensitivity
• magnesium alloy
• tensile twinning
• fracture toughness

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Here, the fracture toughness is taken to be the critical value of energy release rate, J_c, corresponding to the stage where a crack has initiated from the deformed notch/pre-crack tip under the application of mixed-mode loading.

Additional information

Funding

This work was supported by Indian Institute of Science under the Institute of Eminence.

Notes on contributors

Dhrubjyoti Baruah

Dhrubjyoti Baruah is currently pursuing his Ph.D. in Mechanical Engineering at Indian Institute of Science, Bangalore. He received his B. Tech. degree in Mechanical Engineering from Tezpur University in 2013 and M. Tech. in Automobile Engineering from NIT, Warangal in 2016. His research work involves experimental and numerical studies on mixed-mode fracture behavior of magnesium alloys.

K. V. Vaishakh

K.V. Vaishakh is a postdoctoral researcher at Brown University. He completed his B. Tech. in Mechanical Engineering from College of Engineering, Trivandrum, M. Tech. in Applied Mechanics from IIT Delhi, and Ph.D. in Mechanical Engineering Department at Indian Institute of Science, Bangalore. His current research interests include fracture behavior of engineering materials and damage mechanics.

S. Arjun Sreedhar

S. Arjun Sreedhar is currently pursuing his Ph.D. in Mechanical Engineering at Indian Institute of Science, Bangalore. He received his B. Tech. degree in Mechanical Engineering from Government Engineering College, Thrissur in 2012 and M. Tech. in Machine Design from NIT, Calicut in 2017. His research work involves experimental and numerical studies on high strain rate and temperature effects on mode I fracture behavior of magnesium alloys.

Saurabh Kumar Gupta

Saurabh Kumar Gupta is a Ph.D. scholar in the Department of Materials Engineering at Indian Institute of Science, Bangalore. He has completed his B. Tech. in Mechanical Engineering from Abdul Kalam Technical University and M. Tech. in Materials Science from IIT, Kanpur. He joined Indian Institute of Science, Bangalore in 2018, as Ph.D. student under the supervision of Prof. Satyam Suwas and Dr. Kaushik Chatterjee. His research work focuses on additive manufacturing of titanium implants for orthopedic applications.

Satyam Suwas

Prof. Satyam Suwas received his Ph.D. from Indian Institute of Technology, Kanpur in 1999. He is currently a professor in Materials Engineering at Indian Institute of Science, Bangalore. His research interests are Processing-texture Relationship, Deformation and Thermo-mechanical Processing, and Microstructure-mechanical Property Correlation.

R. Narasimhan

Prof. R. Narasimhan received his Ph.D. in Applied Mechanics from California Institute of Technology in 1986. He is currently a professor in Mechanical Engineering at Indian Institute of Science, Bangalore. His research interests are Solid Mechanics, Fracture Mechanics, and Mechanical Behavior of Materials.