Papers by Author: Xie Quan Liu

Abstract: The eutectic composite ceramic is composed of parallel lamellar inclusions distributed in the matrix. First, the recessive expression for the effective stress and the flexibility increment tensor of eutectic composite ceramic are obtained according to the four-phase model. Second, the analytical formula which contains elastic constant is given by applying Taylor’s formula. The eutectic composite ceramic is transverse isotropy, so there are five elastic constants. Third, the effective elastic constants of composite ceramics are predicted.

Abstract: According to the interaction between lamellar inclusion and interphase, forth-phase model is suggested to determine the micro-stress-field distribution of three-phase cell in eutectic composite ceramic. On the basis of the volumetric average strain, the effective compliance tensor increment of eutectic composite ceramic is obtained. The remote stress boundary condition of the eutectic composite ceramic is accounted for getting the micro-stress-field of lamellar inclusion in eutectic composite ceramic. Analysis shows that the micro-stress-field of the lamellar inclusion in eutectic composite ceramic is associated with the stiffness and the volume fractions of each component in eutectic composite ceramic, the shape of interphase and lamellar inclusion. The-micro-stress field has apparent size effect: three direction stresses increase with the thickness of lamellar inclusion.

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: According to the microstructures in eutectic composite ceramic containing lamellae, the four phase model, which is composed of lamellae, eutectic interphase, matrix-atmosphere and effective medium, is put forward. Three phase cell that is composed of lamellae, eutectic interphase and matrix-atmosphere can be regarded as a composite inclusion. In view of Eshelby theory, the effective thermal expansion coefficients of eutectic composite ceramic containing the same orientation lamellae are determined. The eutectic composite ceramic is transverse isotropy and has two independent thermal expansion coefficients. The quantitative analysis shows that the effective thermal expansion coefficients have obvious size dependence.

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: 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: Ni base alloy composite coating containing spheroidal ceramic grains can be fabricated by a vacuum fusion sintering method. Composite coating was mainly composed of Ni base alloy and spheroidal ceramic grains with random orientation. The three-phase model is used to determine the thermal expansion coefficient of the composite coating. First, Eshebly-Mori-Tanaka method was used to determine thermal disturbance strain in two-phase cell aroused thermal inconsistency. Then, average thermal strain in the two-phase cell aroused by thermal inconsistency is gained by the means of volume equilibration. The two-phase cell is transverse isotropy and has two independent thermal expansion coefficients. Finely, based on mean strain of Ni base alloy ceramic composite coating containing spheroidal ceramic grains, the effective thermal expansion coefficient of the composite coating is obtained by considering random orientation of two-phase cells. Ni base alloy composite coating containing spheroidal ceramic grains is isotropy and has one independent thermal expansion coefficient.

Abstract: Fiber eutectics and transformation particles composite ceramic possessed good strengths and creep resistance. It is mainly composed of fiber eutectics with random orientation and transformation particles. First, on basis of the strong constraining effect of the microstructure in fiber eutectics, the micromechanical stress field in fiber eutectics is determined by shear stress that develop between the fiber- inclusion and matrix is obtained. Then, the stress concentration duo to the dislocation pileup on the fiber- matrix interphase is analysised, and the maximum stress in matrix is obtained. Letting maximum stress in matrix equaled to theoretical strength of matrix, the micro strength formation of fiber eutectics is gotten. Finally, considering random orientation and length of fiber eutectics, the macro mechanical strength model of fiber eutectics and transformation particles composite ceramic is built. Result indicates that the fracture strength of composite ceramic has obvious size dependence: the fracture strength of composite ceramic will increase as the diameter of the fiber inclusion in fiber eutectics decrease.

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.