Papers by Author: Jie Cai Han

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Authors: Bao Lin Wang, Jie Cai Han
Abstract: This paper investigates a moving crack in a nonhomogeneous piezoelectric material (NPM) plate. The mechanical and electrical properties of the plate are considered for a class of functional forms for which closed-form expressions for the moving crack tip electromechanical fields are obtained. Effect of material non-homogeneity and crack moving velocity on the crack tip fields are discussed. The crack moving velocity can increase or decrease the stress intensity factor. The cleavage stress, τθz, however, is always an increasing function of crack moving velocity.
Authors: Ming Fu Zhang, Huai Xin Guo, Hai Liang Zhang, Cheng Hai Xu, Ye Quan Zhao, Jie Cai Han
Abstract: In this study, a disk-shaped step-down piezoelectric transformer that consists of Mg:LN single crystals operating in the extensional vibration mode was proposed, and its characteristics wre investigated. This paper proposed the PT using ring/dot electrode which had an outer diameter of 22 mm, a narrow annular gap circle of 1.0 mm and a thickness of 1.0 mm. The transformer was poled along the thickness direction. The top surface was covered by two ring-shaped electrodes separated by a narrow annular gap, and the regions covered by the outer and inner ring electrodes serve as the output and input parts of the transformer, respectively. The bottom surface was fully covered with a gold electrode. Moreover, according to the physical equivalent circuit model of the latest invented vibration mode, PT of Mg:LN single crystals were fabricated and characterized. Finally, we investigated the gain under different load resistances and input voltage.
Authors: Jie Cai Han, Ping Hu, Xing Hong Zhang, Song He Meng
Abstract: The present study focuses on the dynamic oxidation resistance of five representative ZrB2-SiC based ultra-high temperature ceramics (UHTCs): ZrB2-SiC, ZrB2-SiC-Si3N4, ZrB2-SiC-TiB2, ZrB2-SiCHfB2 and ZrB2-SiC-ZrC using oxyacetylene torch and arc jet testing. The effects of second phase incorporation (Si3N4, TiB2, HfB2, ZrC) on oxidation resistance were compared and analyzed. The mechanism of oxidation based on experimental results and thermodynamic calculations were explored. Some approaches to improvement of oxidation resistance and future directions of UHTC are also presented.
Authors: Chang Qing Hong, Xing Hong Zhang, Jie Cai Han, Qiang Xu, Xiao Dong He
Abstract: TiB2 -Cu cermet with the relative density of 92% was produced from titanium, boron and copper powders by combustion synthesis and subsequently pseudo hot isostatic pressing. To improve its mechanical and thermal physical properties, the two-time hot pressing sintering test was carried out at 1050°, 1090° and 1150°C respectively. The deformation behavior and variation of micro- structure and mechanical properties were investigated in detail. The results showed that the relative density and the flexural strength increase remarkably after two-time hot pressing. The relative density reaches 605.5MPa and the flexural strength reaches 96% when the two-time pressing temperature is at 1090°C, and the values increase 12% and 6% compared to that before two-time pressing.
Authors: Shou Jiang Qu, Jie Cai Han, Song He Meng
Abstract: The compressive properties characterized as a function of the true stress-strain response of the ferritic oxide dispersion strengthened (ODS) alloys, fabricated by mechanical alloying, were examined at strain rates ranging from 0.01 to 0.5s-1. Based on the differential scanning calorimeter (DSC) analysis, the solidus temperature of the ferritic ODS alloys is 1446oC. Therefore, the compressive temperatures were chosen to be from 1050oC to 1300oC. Transmission electron microscopy (TEM) observation is indicative of the homogeneous distribution of the nano-yttria particles with the granularity of 100~200nm, which may exert a strong pinning effect on subgrains. The results indicate that flow stress of the ferritic ODS alloys enhances with decreasing compressive temperature and increasing strain rate. Investigation of the strain rate sensitivity exponent and apparent activation energy of the ferritic ODS alloys has been carried out in detail.
Authors: Li Xu, Jie Cai Han, Xing Hong Zhang
Abstract: The TiB2-40Cu-8Ni composite prepared by combustion synthesis is investigated. Both 2D digital radiography (DR) and 3D computed tomography (CT) are used to test the specimens nondestructively. The result shows that ceramic phase aggregation is the main defect. Then the mechanical properties of samples are assessed by means of three-point-bend test. It appears that mechanical properties are related with the distribution of TiB2 phase and Cu phase. The scanning electron microscope (SEM) is also used to observe the crack growth of the bending test sample.
Authors: Qiang Xu, Xing Hong Zhang, Jie Cai Han, Wei Pan
Abstract: TiB2 based cermets with different copper content were produced from titanium powder, boron powder and copper powder by Self-propagating High-temperature Synthesis under conditions of Pseudo Hot Isostatic Pressing (SHS/PHIP). In order to obtain the optimal copper content, the effect of copper content on the microstructures and properties of TiB2 based cermets was investigated. The size of the TiB2 particles in the products decreased with increasing amounts of copper. The hardness (HRA) and bend strength increased firstly, then decreased with copper increasing. Their maximum values appeared at 20 wt.% and 40 wt.% copper, respectively. The porosity of TiB2 based cermets decreased with the copper content increasing due to good fluidity of copper. With the addition of copper, the fracture toughness of TiB2 based cermets increased gradually. Crack-tip plastic blunting by a ductile metallic phase and crack deflection are the principal mechanisms of toughness improvement of TiB2 based cermets. The range of optimal copper content in the TiB2 based cermets is between 40 wt.% and 50 wt.%.
Authors: Yun Long Zhang, Yu Min Zhang, Jie Cai Han
Abstract: In this paper, micrometers long and 20–100nm diameter SiC nanowires had been synthesized in the Cw/SiC composites by annealing treatment. The present work demonstrated that it is possible to fabricate in-situ SiC nanowires toughening Cw/SiC composites. La2O3 had a significant effect on the morphology and distribution of the SiC nanowires in the Cw/SiC composites. The excess lanthanum resulted in the growth of SiC nanowires with an increasing growth rate in the longitudinal direction and a decreasing growth rate in radial direction. The addition of La2O3 would improve the mechanical properties in the room-temperature. The vapor–liquid-solid growth mechanism of the SiC nanowires along <111> direction was proposed. The combination of grain bridging, crack deflection, whisker debonding and SiC nanowires can improve fracture toughness.
Authors: Yue Feng Sun, Qiang Xu, Xing Hong Zhang, Jie Cai Han, Jin Huai Liu
Abstract: TiB2-Cu matrix composites from titanium, boron and copper powders were in-situ fabricated by exothermic reaction. The effect of the applied pressure on the mechanical properties of the composite was investigated. The results showed that when the applied pressure increasing, the relative density, bending strength, fracture toughness and hardness of the composites were on the increase due to the formation of fine microstructure and the improvement of densification with the pressure increasing. The high pressure is beneficial to the better mechanical properties.
Authors: Qiang Zhang, Ye Zhu, Jie Cai Han, Gao Hui Wu
Abstract: Two Al-Si alloys (Al-12Si and Al-20Si) and an industrial pure Al were reinforced with 70vol.% dual-sized SiC particles. The composites experienced annealing treatment, to investigate the effect of silicon addition and thermal history on the thermal expansion behavior of high SiC content aluminum matrix composites. The results showed that silicon additions led to a beneficial reduction in the coefficients of thermal expansion (CTEs) of the composites. In the temperature range between 20°C and 400°C, a continuous increase in CTEs with temperature was observed for SiCp/pure Al composite. However, the CTEs of SiCp/Al-12Si and SiCp/Al-20Si showed the maxima at 350°Cand 250°C respectively, then diminished at higher temperatures. This was related to the change of solid solubility of silicon in aluminum at elevated temperatures. The thermal expansion behavior of SiCp/Al composites was also influenced by thermal history. After annealing treatment, the CTEs were reduced when compared with those of as-cast composites. Annealing treatment reduced the original thermal residual stresses, and then altered thermal expansion behavior of the composites.
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