Papers by Keyword: Bimodal Nanocrystalline Materials

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Authors: Song Feng Tian, Hong Jian Yu, Ying Guang Liu, Rong Yuan Ju, Xiao Dong Mi, Xiu Lei Peng
Abstract: Giving a bimodal grain size distribution in nanocrystalline materials can effectively achieve both high strength and high ductility. Here we propose a theoretical model to study the failure behavior of nc materials with bimodal grain size distribution. The dependence of failure properties on grain size distribution were calculated. Numerical results show the strength and ductility of bimodal nanocrystalline materials are sensitive to grain size and the volume fraction of coarse grains.
Authors: Hui Jun Li, Rong Yuan Ju, Ying Guang Liu, Xiao Dong Mi, Hong Jian Yu, Xiu Lei Peng
Abstract: A new theoretical model is proposed to describe the mechanical properties of bimodal nanocrystalline (BNC) materials.In this paper, we have studied the effect of grain size on the constitutive behavior and fracture of BNC materials. During the plastic deformation, dislocations emission from crack tips on the constitutive behavior of BNC materials are also analyzed, it is found that the nanocracks make a positive effect on the strain hardening instead of leading catastrophic failure. Numerical calculations have been carried out according to the model, the results show that the model can describe the enhanced strength and ductility of BNC materials successfully.
Authors: Ying Guang Liu, Xiao Dong Mi, Song Feng Tian
Abstract: To research the effect of grain size on the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials by considering a typical case where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, the cohesive zone size is assumed to be equal to the grain size d of the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It was found that the critical stress intensity factor increases with the increasing of grain size d of the NC matrix as well as the coarse grain size D. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size rather than that of NC matrix.
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