Determination of fracture toughness of AZ31 Mg alloy using the cohesive finite element method X. Guo a,b,⇑ , K. Chang c , L.Q. Chen c , M. Zhou d,⇑ a School of Mechanical Engineering, Tianjin University, Tianjin 300072, China b Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control, Tianjin 300072, China c Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA d The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405, USA article info Article history: Received 24 January 2012 Received in revised form 21 June 2012 Accepted 11 August 2012 Keywords: Fracture toughness Cohesive finite element method Microstructure Plasticity Mg alloy abstract The objective of this study is to develop a micromechanical approach for determining the fracture toughness. A phase-field model for grain growth is employed to generate micro- structures with varying attributes and the cohesive finite element method is employed to quantify the interaction between a propagating crack and microstructures of an AZ31 Mg alloy. Simulations show that fracture toughness increases as the average grain size decreases and that the local crack tip environment significantly affects the fracture behav- ior. Dramatically different dependences of fracture toughness on overall strain rate are seen when two different types of cohesive laws are employed. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Metallic alloys are microscopically-heterogeneous materials widely used in engineering. Among different metallic alloys, Mg alloys have been of recent interest due to increasing demand for light-weight materials in industry. The AZ31 Mg alloy has attractive mechanical properties, including high specific strength, good tensile properties [1], high machinability, and fatigue resistance [2]. Since AZ31 is not as tough as widely-used Al alloys, much effort has been devoted to investigating and improving its fracture resistance. Somekawa and Mukai [3,4] found that AZ31 Mg alloy samples with a pre-crack normal to the basal plane have a higher fracture toughness than those with a pre-crack parallel to the basal plane. Somekawa and Mukai [5] improved the fracture toughness of the AZ31 Mg alloy by refining grain structure in an equal-channel-angular- extrusion (ECAE) process. Designing microstructures for improving fracture resistance requires a detailed understanding of how an advancing crack interacts with the microstructures at multiple length scales [6]. Microscale failure can be analyzed by explicit micromechan- ical simulations. Through the consideration of representative samples of actual microstructures, effects of various fracture mechanisms can be delineated. The required features of the simulation framework should include (1) explicit accounting of real, arbitrary material microstructures, and (2) explicit modeling of fracture in a non-constrained manner so that arbi- trary crack paths or microcrack patterns are admitted. Among the multiple approaches for investigating fracture, the cohesive finite element method (CFEM) and the eXtended finite element method (XFEM) have shown their effectiveness. Song et al. [7] studied their performances for analyzing 0013-7944/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engfracmech.2012.08.014 ⇑ Corresponding authors. Address: School of Mechanical Engineering, Tianjin University, Tianjin 300072, China. Tel.: +86 22 2740 4934; fax: +86 22 8740 1979 (X. Guo), tel.: +1 404 894 3294; fax: +1 404 894 8336 (M. Zhou). E-mail addresses: [email protected] (X. Guo), [email protected] (M. Zhou). Engineering Fracture Mechanics 96 (2012) 401–415 Contents lists available at SciVerse ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech
Determination of fracture toughness of AZ31 Mg alloy using the cohesive finite element method
Jun 24, 2023
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