Papers by Author: Jian Feng Wan

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Authors: Jian Feng Wan, Yan Qiong Fei, Jian Nong Wang
Abstract: ab-initio calculations on the interaction between the single-walled carbon nanotube (SWCN) and the Mg (0001) surface have been reported. It was found that the charge transfer from metal surfaces to the nanotubes takes place depending on both the electronic structures of the nanotubes and the work functions of the metal surfaces. The stable geometries for the nanotube between two consecutive objectives with C-Mg chemical bonds formed. The interaction energy in the most stable geometry is found to be CNT’s structural dependence. Concerning the electronic properties, the most stable structure showed a decrease in the density of states near the Fermi level due to the formation of C-Mg bonds enhancing the metallic character of the nanotube by the contact with the surface. The nature of the nanotube-interface interaction for nanotubes of larger diameters has been also discussed based on the calculated bond order.
Authors: Jian Feng Wan, Shipu Chen, T.Y. Hsu
Authors: Jian Feng Wan, J.H. Zhang, Y.H. Rong
Abstract: The kinetics of martensitic variant reorientation as well as the evolutional pathway under the continuous tensile stress in NiMnGa alloys has been investigated by using Phase field method. The simulated results revealed that the final structures and the pathway of evolutioncan be determined by the different external stress and there existed a critical stress to obtain the single variant. The related kinetics and the mechanism of the structural conversion were proposed to explain the inner physical nature. The pseudo-elasticity related to the structural conversion was also investigated. The mechanism of the motion for interfacial step associated with the nucleation and growth of one variant in another variant at the twin boundary was discussed.
Authors: Yan Guang Cui, Jian Feng Wan, J. Man, Z.H. Guo, J.H. Zhang, Y.H. Rong
Abstract: A twin boundary model was established to describe the multi-variant interface in the martensitic materials. The modified semi-implicit Fourier-spectral method was proposed to solve the 3-D phase-field equation. Self-accommodation plays an important role in the micro-structural evolution during the loading and unloading. The external compressive stress can cause the rearrangement of martensites from three variants to one variant. After releasing the loading, another variant can nucleate and grow in one variant at the twin boundary. Cyclic stress may lead to the redistribution of martensite variants besides the rearrangement.
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