Grain size effects on dynamic fracture instability in polycrystalline graphene under tear loading
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Grain size effects on dynamic fracture instability in polycrystalline graphene under tear loading Yuxin Zhao1, Yunfei Xu2, Xiaoyi Liu2
, Jun Zhu3,a), Sheng-Nian Luo4,b)
1
College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064, People’s Republic of China; and The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People’s Republic of China 2 The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People’s Republic of China 3 College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064, People’s Republic of China 4 The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People’s Republic of China; and Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031, People’s Republic of China a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] Received: 30 November 2018; accepted: 13 February 2019
The stability of dynamic fracture is a fundamental and challenging problem in the field of materials science. The grain size effect on dynamic fracture instability in polycrystalline graphene under tear loading is explored via theoretical analysis and molecular dynamics simulations. The fracture stability phase diagram in terms of grain size and crack propagation velocity is obtained, and three regions of crack propagation are identified: stable, metastable, and unstable. For grain size above 2 nm, there exists a critical velocity beyond which fracture instability occurs, and this critical velocity depends linearly on grain size. Decreasing grain size leads to reduced characteristic time for correction of crack path deflection, which plays a dominant role in dynamic fracture instabilities. However, when grain size is below 2 nm, there does not exist a critical velocity for steady propagation of cracks due to discontinuous effects. Our results also provide a valuable insight into dynamic fracture of polycrystalline graphene as well as other 2D and quasi-2D materials.
Introduction Our understanding of dynamic fracture mechanisms is facilitated by nanomechanics at the beginning of this century [1, 2, 3]. It has been demonstrated that the propagation of a Griffith crack can be predicted by the Yoffe’s model in the case of harmonic and linear elastic materials [4, 5, 6] and by the Gao’s model in the case of hyperelastic materials [7, 8, 9]. In recent years, the interface effects on dynamic fracture have been of considerable interest. In 2017, Rezaei et al. constructed a mechanical model to predict fracture and damage in micro-/nanocoating systems by using the cohesive zone element technique implemented at grain boundaries as well as in the interface between the coating and the substrate [10]. Daniel et al. found that the fracture toughness of ceramic nanostructured materials can be improved more than 150% by a dedicated grain boundary orientation design with respect to the direction of the expected crack path without th
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