Papers by Author: Yan Jun Zheng

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Authors: Jun Tao Li, Yan Jun Zheng, Li Shan Cui
Abstract: The recovery strain in the near-equiatomic, severely cold-deformed NiTi, has been investigated through the study of thermal expansion by employing dilatometer (DL). By designing the shape of the original surface curve, macroscopic domains with different dislocation density were introduced into the NiTi alloys and materials possessing the characteristics of composites were obtained. Results show that in-situ composites of NiTi alloys rendered a distinct recovery strain of shape memory compared to directly cold-deformed NiTi alloys. We presume that the interactions between the dislocation texture and martensite variants are introduced when the NiTi martensite is cold rolled at room temperature might be responsible to the phenomena, which are discussed and compared with the differential scanning calorimeter (DSC) analysis in this paper. All the phenomena above show it is feasible to the method for controlling the thermal properties of a material by a proper design of the dislocation texture.
Authors: Yan Jun Zheng, Li Shan Cui, Jan Schrooten
Abstract: There are only limited ways to improve the interface bond strength of SMA wire reinforced composites. In this paper, the effect of the additional reinforcing fibers on the interface debond temperature of a TiNiCu wire reinforced epoxy matrix composite was studied. It was shown that the Kevlar fiber composite had a better interface between the TiNiCu wire and the epoxy matrix than that in the glass fiber composite. The negative thermal expansion coefficient of the Kevlar fibers were thought to be beneficial for relieving the thermal stresses at the SMA/epoxy interface. From this angle of view, the Kevlar fiber composites are better candidates as the matrix of the SMA composites than the glass fiber composites.
Authors: Limin Huai, Li Shan Cui, Lai Bin Zhang, Yan Jun Zheng
Abstract: The effects of bias springs with different coefficient on the actuation and transformation behaviors of TiNi wires were studied. Results showed that the maximum output stress increases with increasing spring coefficient. The reverse martensitic transformation starting temperature of the TiNi wires does not change with spring coefficient, but the reverse transformation finishing temperature increases with increasing spring coefficient.
Authors: Ren Bo Xu, Li Shan Cui, Yan Jun Zheng
Abstract: The mechanical behaviors of bare and carburized NiTiCu specimens under dynamic impact loading were investigated using a home-built impact testing system. The contact force was measured with piezoelectric force sensor and digital signal processing system in real time during impact process. Predicted instantaneous velocity and displacement formula were presented. The results show that the maximum deformation depth of carburized specimens was less than that of bare specimens, and the carburization process can increase absorbed energy and cushion effect to impact of specimens during impact process. The decrease of deformation depth and increase of absorbed energy can reduce the contact force and materials damage of specimens during impact process.
Authors: Ting Yong Xing, Yan Jun Zheng, Li Shan Cui
Abstract: The objective of present work is to investigate the internal friction behavior of TiNi shape memory alloy fiber/Ni matrix composite. The TiNi fiber/Ni matrix composite was fabricated by an electroplating method using TiNi alloy fiber as the cathode and Ni plate as the anode. The internal friction as functions of temperature and strain amplitude was measured respectively. The results showed that the internal friction peaks of the TiNi/Ni matrix composites, which due to the martensitic reverse transformation of the TiNi fiber, broadened with increasing prestrain level. There was a sharp internal friction increment at the high temperature, which due to thermal expansion mismatch between the TiNi fiber and Ni matrix and recovery stress generated. Contrast to the pure TiNi alloys, the internal friction background of the TiNi/Ni composites increased with increasing temperature. Furthermore, the internal friction of the TiNi/Ni composites decreased with increasing strain amplitude measured.
Authors: Li Shan Cui, Yan Jun Zheng
Abstract: In a constrained martensitic transformation of shape memory alloys, a fraction of martensite is always retained in the materials. Experimental results showed that the remaining martensite could be plastically deformed by the generated recovery stresses. The self-tension process elevated the reverse transformation temperatures of the remaining martensite, and the external constraint conditions had no significant effect on the self-tension process of the remaining martensite.
Authors: Rui Song Yang, Li Shan Cui, Yan Jun Zheng, Jin Long Zhao
Abstract: . NiTi particles were prepared by the reaction between Ti and Ni powders in high temperature molten salts. Results of differential scanning calorimetry (DSC) confirmed the martensitic transformation of the prepared NiTi particles. Backscatter electron image of scanning electron microscopy (SEM) showed that the synthesized NiTi particles were captured by the molten salts, which revealed the mechanism of the chemical synthesis method in molten salts.
Authors: Ren Bo Xu, Li Shan Cui, Yan Jun Zheng
Abstract: The contact force during impact of a NiTi alloy was studied in this paper. The contact force and contact time during impact between a spherical impactor and the specimen at different impact velocity and temperature were measured in real time. The maximum contact force and contact time of the NiTi alloy in the martensite state increased and decreased respectively with increasing temperature. The maximum contact force of the NiTi alloy in the parent phase state showed a plateau with increasing impact velocity of the impactor.
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