Key Engineering Materials Vols. 368-372

Abstract: Ceramic column and metal sleeve are often used together by interference fit. The stress distribution in brittle ceramics is different from that in metal. Two important factors for their connection strength such as interference value and the length of envelope surface are discussed in this paper. The results showed that interference value is the decisional factor for the strength of interference fit between ceramic column and metal sleeve, while the length of envelope surface impacts it slightly.

Abstract: SrZrO3@SiO2 composite materials, in which perovskite polycrystalline SrZrO3 was wrapped by amorphous SiO2, were prepared. The corrosion behavior of the samples was studied under hydrothermal conditions in 40% NaOH solution. The composite materials were easily corroded in the sodium hydroxide solution by reason of the presence of a continuous amorphous SiO2 phase. The corrosion rate increased with the increasing of the porosity because the pores provided channels, via which corrosion solution could enter into the sample, and increased the contact area between corrosion solution and the sample. There was a nonlinear relation between the corrosion and time.

Abstract: LaPO4-ZrO2 composites were prepared by slip casting and pressureless-sintered in air. The effects of LaPO4 addition on microstructure and thermal shock resistance were addressed. The thermal shock resistance of the composites was evaluated by air quenching and a subsequent three-point bending test to determine the strength degradation. Comparisons were made with results from parallel experiments conducted using a ZrO2 ceramic without LaPO4 additions. The reference ZrO2 ceramic showed the expected substantial strength losses when thermally quenched from 470oC above room temperature. By contrast, the LaPO4-ZrO2 ceramics, while displaying reduced strength relative to the reference ZrO2 ceramics, exhibited minimal strength degradation under severe thermal shock conditions.

Abstract: SiO2 coated and SiO2/Al2O3 coated nano-ZnO were synthesized by chemical liquid deposition method. The surface properties and dispersion stability of the coated and uncoated ZnO nanoparticles were characterized. The results showed that a SiO2 or SiO2/Al2O3 amorphous layer was coated on the ZnO nanoparticles. The adsorbed hydroxyl content of ZnO was found to increase accompanied by the decrease of UV-shielding ability by surface modification; moreover, the isoelectric point of ZnO slurry was changed, and the stability of nano-ZnO in water was also improved effectively.

Abstract: In this paper, effect of heat treatment on the SSA of Si-C-O fibers was investigated and morphologies of the treated fibers were studied using SEM. The results revealed that weight loss was proportional to the treatment time at 1573K and the specific surface area (SSA) increased sharply when the weight loss reached above 6wt%. A rough and porous ceramic fiber with SSA of 23.76m2/g could be obtained at the weight loss of 9.1wt%, as a result of the treatment at 1573K for 32h.

Abstract: Artificial neural networks have been successfully used in classification, formulation optimization, defect diagnosis and performance prediction in ceramic industry. However, an artificial neural network based on the traditional backpropagation (BP) algorithm showed some disadvantages in mapping the nonlinear relationship between the composition and contents of the ceramic materials and their properties. In this paper, a new PSO-Grain (Particle Swarm Optimization Gain) BP algorithm was introduced, and an improved artificial neural network model was employed to predict the properties of an alumina green body. The training performance of the neural network using the PSO-Gain BP algorithm was analyzed and it was indicated the POS-Gain BP based neural network could reduce convergence to local minima and was more efficient than the traditional BP based network. The prediction accuracy of the properties such as linear shrinkage and bending strength using the PSO-Gain BP based neural network was higher than that of the BP based neural network.

Abstract: Improved genetic algorithm, combined with artificial neural network, is present for the optimal design of 2.5D braided composite. Dispersal simulation data, including maximal stresses and elastics properties, are adopted by artificial neural network for the calculation of strength property. Based on calculation method of strength mentioned above and other calculation models for other mechanical properties, genetic algorithm is employed for the design of structure parameters of 2.5D braided composite, such as wrap fiber density, fill fiber density and interface strength. These structure optimal parameters are finally optimized for practical application.

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: As a typical biological material, bone possesses high fracture strength and fracture toughness, which are closely related to its exquisite microstructure. SEM observation of a cannon bone shows that the bone is a kind of layered bioceramic composite consisting of hydroxyapatite sheets and collagen matrix. The hydroxyapatite sheets are of long and thin shape, distributing in parallel. The fracture toughness of the bone is analyzed with the representative model of the hydroxyapatite sheets and the concept of maximum pullout energy. It is shown that the lathy shape as well as the parallel distribution of the hydroxyapatite sheets increases the pullout energy and endows the bone with high fracture toughness.

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.