Papers by Author: Xin Hua Ni

Abstract: Based on micro-mechanics and finite element theory, the stress field of fiber-eutectic was researched by using the ANSYS program. First, in order to study the interaction of fiber and interphase, fiber- eutectic can be simplified as representative volume cell. Then we use ANSYS program to construct the cell model and simulate the tensile stress field. The results show that the stress is uneven in the cell and the elements near the interphase with high stiffness will damage first. At last the stress change and damage evolution route are simulated by using the element birth and death technology.

Abstract: On basis of the residual-stress-field of the composite ceramic, the frictional force on the boundary of the lamellae can be computed. Then the frictional work is determined. The pull-out toughening mechanism is gotten. The result shows that the toughening value is dependent on the size of lamellae: the pull-out toughening value will increase as the thickness of the lamellae increase.

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.

Abstract: Based on the interaction between nano-fiber and eutectic interphase, forth-phase mode is used to get the mechanical stress field of matrix in eutectic composite ceramics. The effective flexibility increment tensor of eutectic ceramic composite is obtained by the volumetric average strain. The remote stress boundary condition of the eutectic composite ceramis is accounted for getting the mechanical stress field in matrix. The results show the mechanical stress field of the matrix is associated with the stiffness and the volume fractions of each component in eutectic composite ceramic , the shape of interphase and nano-fiber. The stresses in matrix will decrease due to the strong constraining effects of the eutectic interphase. The eutectic interphase make the eutectic composite ceramics strengthen.

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.

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.

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.

Abstract: Considering the interaction between fiber-inclusion and strong constraining interphase, forth-phase model is suggested to determine the local stress field distribution of three-phase element in eutectic ceramic rod. On the basis of the volumetric average strain, the effective compliance tensor increment of eutectic ceramic rod is obtained. The remote stress boundary condition of the eutectic ceramic rod is accounted for getting the micro stress field of fibers in eutectic ceramic rod. The results show the micro stress field of the fiber-inclusion in eutectic ceramic rod is associated with the stiffness and the volume fractions of each component in eutectic ceramic rod, the shape of interphase and fiber. The micro stress field has apparent size effect: three direction stresses increase with the diameter of fiber- inclusion.

Abstract: Many material have different stress-strain relation in tension and compression, generally the relation is nonlinear. In this paper, we use two exponential functions to approximately represent the stress-strain relation of nonlinearly elastic material and analyze strength-difference structure of bars jointed to Rigid-body of fixed-point motion. The displacement method is used to derive the universal expression of calculating stress and strain. The nonlinear equations for computing angular displacement of the rigid-body has been given and general computing program has been worked out. They can be accurately and conveniently calculated. This problem has been solved satisfactorily.

Abstract: Rod-shaped oxide eutectic ceramics fabricated through SHS process can acquire outstanding mechanical properties. First, Four-phase model method was used to study effective disturbance strain of rod-shaped oxide eutectic ceramics produced by nano fibers with inter-phases, then average strain of rod-shaped oxide eutectic ceramics aroused thermal inconsistency is obtained. The effective thermal expansion longitudinal strain and transverse strain of rod-shaped oxide eutectic ceramics are determined by the average strain. Rod-shaped oxide eutectic ceramics is transverse isotropy and has two independent thermal expansion coefficients. The results show that the thermal expansion coefficients of rod shaped oxide eutectic ceramics are dependent on the diameter of nano-fiber. The thermal expansion coefficients will decrease when the diameter of nano-fiber decrease.