Papers by Keyword: Fiber Eutectic

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: 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: The present work focuses on the failure mechanisms that occur in melt-growth composite ceramics mainly composed of fiber eutectics with random orientation. First, the stress field of the melt-growth composite ceramics under a tensile stress was obtained. It can be visualized that tensile force is transmitted between oxide fiber eutectics by means of shear stress that develop along the interfaces of oxide fiber eutectics. Consider fiber eutectics having lengths smaller than the critical length. During the composite ceramics fracture, fiber eutectics do not fracture. The average stress of a 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 ditrict βl. Finally, consider random orientation and length of the fiber eutectics. Composite ceramics failure by slip incompatibility. The strength model of the melt-growth composite ceramics is built. It is accordance with experiments.

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.

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.