Papers by Author: Xin Hua Ni

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Authors: Bao Feng Li, Jian Zheng, Xin Hua Ni, Yan Mei Qu, Xiao Wen Li, Shu Zeng Zhao
Abstract: The resistance pressure was the key to solve these problems that long rod projectiles penetrated ceramic targets at high velocity. Based on the twin shear united strength theory and the A-T model, the penetration depth were calculated. But the calculation result didn’t agree with experiment data. So the tension-compression ratio was redefined to apply to the dynamics problems according to the experiment data. And satisfied results were obtained.
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Authors: Xin Hua Ni, Xie Quan Liu, Bao Hong Han, Guo Hui Zhong, Tao Sun
Abstract: Based on the microstructure of fiber eutectics and transformation particles composite ceramic, the bridging stress of the fiber eutectic is determined. The bridging load that makes crack closure to reduce the stress concentration of crack tip is calculated. The energy dissipative value of the bridging load is obtained by considering the random orientation of the fiber eutectic. Finally, according to the relationship of the fracture toughness and energy dissipation, the bridging toughening mechanism is established. Analysis shows that the bridging toughening value is enhanced with the increasing of volume fraction and fracture strength of fiber eutectic, and enhanced with the decreasing of interface bonding strength and length-diameter ratio.
178
Authors: Xie Quan Liu, Xin Hua Ni, Shu Qin Zhang, Zhao Gang Cheng, Lei Zhao
Abstract: This paper presents on the cracking mechanisms of fiber-eutectics and transformation particles composite ceramic. First, supposing that the tensile stress among fiber eutectics is transmitted by means of shear stress along the interfaces of fiber eutectics, based on fiber eutectics having lengths smaller than the critical length, the force acting along the fiber eutectic can be determined by the shear stress. Then, the probability of ending fiber eutectics and bridging fiber eutectics can be gotten by defining a critical district. Finally, according to the random orientations and the lengths of the fiber eutectics, composite ceramics will crack by slip incompatibility among bridging fiber eutectics. The cracking stress of the composite ceramics is built.
170
Authors: Xin Hua Ni, Zhan Jun Yao, Xie Quan Liu, Jun Ying Wang
Abstract: Recent experiment showed that nano-fibers composite ceramics, fabricated through SHS process, could acquire high toughening and strengthening. Composite ceramics are mainly composed of fiber eutectic with random orientation, in which nanometer sized zirconia fibers are dispersed within the alumina matrix. First, it can be visualized that tensile force is transmitted from the matrix to the nano-fiber by means of shear stress that develop along the fiber- matrix interface. Then the shear stress on the surface of the fiber eutectic is obtained. It related to the volume fraction and slenderness ratio of the nano-fibers, and external strain of the fiber eutectic. The maximum shear stress is at the ends of the fiber eutectic perpendicular to applied tensile stress. As maximum shear stress on the surface of the fiber eutectic is equal to the critical shear stress, the composite ceramics would crack. So the applied tensile stress on composite ceramics arousing the surface crack of the fiber eutectic is gotten.
2432
Authors: Jing Xin Kang, Xin Hua Ni, Jian Zheng, Yong Ling Zhao
Abstract: Based on experiments, micro-mechanics and finite element theory, nanocomposite ceramics is simplified as representative volume cell in the paper, and in order to study the interaction of the particles, each cell concludes two nano-ceramic particles. We use ANSYS program to construct the cell model and simulate the stress field. The stress distribution and the material properties are obtained. The results show that the stress is uneven in the cell and the elements near the nano-ceramic particle with high stiffness will damage first. Finely, the stress change and damage evolution route are simulated by using the element birth and death technology. The computational results are accordance with experiments and theories.
1657
Authors: Jian Zheng, Xin Hua Ni, Jing Xin Kang
Abstract: For Ceramic particle Ni base alloy composite, experiments and damage evolution finite element analysis shows that arc-microcracks happen only at the interfaces between the particles and matrix, and then extend to the matrix. Composite strength is coincident with matrix failure. First, the three-phases model is used to determine the external strains of two-phases element. Then micromechanical stress field in the matrix is obtained. Based on the generalized thermodynamic force in damage process, the damage equivalent stress can be computed. As the damage equivalent stress is equal to the ultimate stress of the matrix, the failure stress of matrix in composites is given.
1654
Authors: Bao Feng Li, Jian Zheng, Xin Hua Ni, Ying Chen Ma, Jing Zhang
Abstract: The composite ceramics is composed of fiber-eutectics, transformation particles and matrix particles. First, the recessive expression between the effective stress in fiber-eutectic and the flexibility increment tensor is obtained according to the four-phase model. Second, the analytical formula which contains elastic constant of the fiber-eutectic is obtained applying Taylor’s formula. The eutectic is transverse isotropy, so there are five elastic constants. Third, the effective elastic constants of composite ceramics are predicted. The result shows that the elastic modulus of composite ceramic is reduced with the increase of fibers fraction and fibers diameter.
182
Authors: Xiao Bo Lu, Xie Quan Liu, Xin Hua Ni, Shu Qin Zhang
Abstract: The composite ceramics that contains nano-fibers and transformation particles, fabricated through SHS process, is performed with high fracture toughness and high plasticity. The matrix of composite ceramics was mainly composed of fiber eutectics with nano-fibers. The transformation particles were distributed along boundaries of the fiber eutectic structures. First, Mori-Tanaka method was used to predict the stiffness of the fiber eutectic. The fiber eutectic is transverse isotropy and has five independent elastic constants. Then considering random orientation of the fiber eutectic, the Young’s modulus and Poisson’s ratio of the matrix is determined by even strain. The matrix is isotropy. Finely, assuming the transformation particles as spheres distributed in the matrix, the effective stiffness for composite ceramics was computed. When the volume fraction of fibers and particles increase, the Young’s modulus of composite ceramics decrease and are little smaller than the volume average value, the Poisson’s ratio of composite ceramics decrease and are little bigger than the volume average value.
2528
Authors: Yun Ting Liu, Xie Quan Liu, Xin Hua Ni, Shu Qin Zhang
Abstract: The pressure sensitive transformation criterion is used to determine the constitutive relation of transformation toughened ceramics. By the use of the strain energy release rate criterion and the method of weight function, the fracture enhancement of mixed-mode I-II crack in transformation toughened ceramics is predicated. The theoretical expressions of the toughening effect for both the stationary and steady-state growing crack are given respectively. The result show there is no toughening effect for the stationary crack and the toughening effect for the steady-state growing crack is associated with the modulus of elasticity, the width of transformation and its volume fraction.
2444
Authors: Xie Quan Liu, Xin Hua Ni, Yun Ting Liu, Bao Hong Han
Abstract: Recent experiment showed that nano-fibers composite ceramics, fabricated through SHS process, can acquire high toughening and strengthening. Composite ceramics are mainly composed of fiber eutectic structures with random orientation, in which nanometer sized zirconia fibers are dispersed within the alumina matrix. First, it can be visualized that tensile force is transmitted from the matrix to the nano-fiber by means of shear stress that develop along the fiber- matrix interface. Then the mesomechanical strength model of the fiber eutectic structure is built. The longitudinal tensile stress of the fiber eutectic structure and shear stress on the surface of the fiber eutectic structure are obtained. They related to the volume fraction and slenderness ratio of the nano-fibers, and external strain of the fiber eutectic structure. Then considering random orientation of the fiber eutectic structure, as composite ceramics is subjected to tensile stress, external strain of the fiber eutectic structure can be determined. Finally, theoretical expression for the strength prediction of composite ceramics is gotten.
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