Papers by Keyword: Fracture Strength

Abstract: Fracture strength is one of the key mechanics performances for engineering ceramics products, greatly influenced by the microscopic topography and residual stress field of ground surface. In this work, several testing equipments, such as the metallurgical microscope, surface profiler and X ray residual stress tester were introduced to investigate the relationships between microscopic topography, surface roughness, residual stress and fracture strength of ground ceramics, after the surface grinding and mechanical polishing. The experimental results show that a smoother machined surface with low roughness and residual stress is obtained through polishing with absolute alcohol for 20 minutes; the fracture strength of Si₃N₄SiC and Al₂O₃ are increased by 6.64%8.18% and 6.58% respectively, comparing to the ceramics without polishing; the surface stress concentration and residual tensile stress of polished ceramics are both reduced after an appropriate time of polishing process, which causes a certain improvement of ground fracture strength.

Abstract: Wheat protein composite fiber is a kind of new regenerated cellulose fiber containing protein utilization of wheat bran prepared. The fundamental characteristics of wheat protein composite fiber were studied. The results show that the dry fracture strength is 2.03 cN/dtex and it is lower than that of viscose fiber. It has high moisture regain and low fracture strength and the moisture regain of the fiber is 12.23%. The whiteness of wheat protein composite fiber is lower than viscose fiber. The combustion performance of wheat protein composite fiber is similar to viscose fiber. Compared with wool, the combustion performance is easy. Dyeing properties of the fiber with reactive dyes is excellent and the goods have bright color and good color fastness. The dyeing percentage of direct dyes reached to 90%. The wheat protein composite fiber product is deeply liked by people with its good wearing property, and extensively applied to wear base material with its fine affinity.

Abstract: Engineering ceramic are special hard and brittle materials, their surface properties are very sensitive to the state of the surface stress, the compressive residual stress can be improved part strength and surface properties in a certain extent, especially can increase breaking strength, tensile residual stress in the opposite role. The choice of grinding parameters and grinding temperature have great influence on the residual stress. improving grinding conditions can improve the surface properties, within a certain range, increasing grinding depth and reducing grinding temperature are advantageous to produce the beneficial compressive residual stresses on the surface properties.

Abstract: The use of ceramic processes inducing a microstructural organization at the grain scale favors the improvement of strength and toughness. With layered structures, it is possible to design the microstructural characteristics of materials, leading to increased threshold strength. Layered structures can be arranged to control the local residual stresses causing elastic mismatches between dissimilar materials and crack deflection at interfaces. In this way, multilayer composites from kaolinite and alumina or mullite fibers were shaped by tape casting and staked by thermo-compression, or by centrifugation. During sintering, they show at strong anisotropic behavior, which is in correlation with different activation energy for sintering. Mullite growth is also anisotropic, inducing the formation of an organized micro composite microstructure. The mechanical and elastic properties are correlated with the organization degree of mullite crystals, due to the formation of an interconnected mullite network in the microstructure. It is also shown that variations of mechanical and elastic properties are correlated with the texture index obtained by Quantitative Texture Analysis from X-ray data. The anisotropy of the elastic properties is evidenced by different values of Young’s modulus in directions parallel and perpendicular to the casting direction. Beside, the crack growth resistance is governed by discontinuities along layer boundaries and fiber interfaces.

Abstract: The multi-component AlxCoCrFeNiTi0.5 (x=0, 0.2, 0.5, 0.8, 1.0) high-entropy alloys were prepared by vacuum arc melting. The microstructure and mechanical properties were studied. It was found that the structure transformed from FCC into FCC + BCC + Laves, and finally into BCC with the increase of Al content. The compress test results showed that with the addition of aluminium from 0 to 1.0, the fraction strength increased while plasticity reduced. In the stain rates of 5×10^-3/s and 1×10^-3/s, when x=0.8 the fraction strength achieved maximum and x=0 the plastic was best, the strength of 2879MPa and 2433MPa, the strain of 0.21 and 0.22, respectively. The hardness increased obviously (from Hv479.1 to Hv692.7) when Bcc phase and Laves phase appeared. The analysis revealed that the strengthen mechanism was mainly composed of solid solution strengthening and precipitation strengthening.

Abstract: As an emerging brand new type of engineering material for a variety of important high technology applications, the deep understanding of the mechanical behavior of freestanding diamond films has become an emergent task of vital importance. Unfortunately the mechanical behavior of this brand new material is not fully understood. Effects that affect the fracture strength are still not very clear except that the fracture strength of freestanding diamond films is only depended on the grain size (film thickness), and is insensitive to the microscopic defects, and the strength is considerably higher when the nucleation side is in tension than that when the growth side is in tension. However, this is not the full story. Based on the experimental date accumulated in USTB (University of Science and Technology Beijing) for high power dc arcjet diamond films, other factors that may affect the fracture strength of freestanding diamond films are discussed in detail. Effects of the quality of the diamond films, impurities (nitrogen, hydrogen, non-diamond carbon etc.), film morphology and texture, on fracture strength are discussed. Effects of the deposition parameters are explained. Advantages for small amount of nitrogen addition, and for the use of higher substrate temperatures in the increase in fracture strength are demonstrated, which have already been applied in the mass production of tool grade freestanding diamond films. It is hoped that the present paper will be helpful for those who wish to understand and use this brand new type of engineering material

Abstract: The paper starts with the fiber strength which is one of the most important factors that could influence the fiber spinnability. By discussing the relationship between fiber strength and its four chemical compositions and analyzing the relevance between them with the method of grey correlation, this research come to a conclusion that the content of cellulose influence most on the fiber strength, and the second is lignin. Then set up four grey models between the fiber strength and pectin, hemicellulose, cellulose and lignin, and carry on error analysis at last. This paper makes a contribution to provide the theoretical basis to the research and development of the hemp fiber.

Abstract: With Ag-loading MWNTs antibacterial agent as functional material, the antibacterial functional PET fibers were prepared by melt blending spinning-draft one-step method. The crystallinity and the orientation of specimens were characterized by differential scanning calorimetry, polarization microscope and sound velocimeter. Moreover, the mechanical properties and antibacterial properties were measured. The results showed that the antibacterial PET fibers had good spinnability when the content of Ag-loading MWNTs less than 1.0 % (wt); compared with pure PET fibers, the degree of crystallinity, the degree of orientation and the fracture strength were improved, but the elongation was decreased; the antibacterial PET fibers exhibited excellent antibacterial properties against E.coli by the method of flask shaking.

Abstract: Alumina ceramics with inter-connected pores were fabricated by freeze casting method. The open porosity and fracture strength were controlled by the concentration of Al₂O₃ slurry and sintering temperature. Sintered at 1600°C, the open porosity and fracture strength of Al2O3 ceramics fabricated by the slurry with concentration of 70wt% are 46.4% and 23.8 MPa, respectively.

Abstract: The mechanical stability of nanostructures depends on the surrounding medium. Their stability was probed by lateral force microscopy in liquid media. Previously reported data on water and isopropanol showed an increase in the fracture strength for the latter. Further tests with other alcohols (ethanol, 1-butanol) also showed an increasing strength. The interface between the liquid and the surface is the decisive factor for the influence of the media. When altering the interface with a cationic surfactant or a self-assembled monolayer, an increase of the fracture force by 100 % compared to de-ionized water could be measured.