Key Engineering Materials Vols. 326-328

Abstract: Mechanical tests have been conducted to understand compressive behavior of a plain weave C/SiC composite, especially to investigate the failure mechanism. The stress-strain curves of this composite show linear feature in compression. The specimens fail along a flat plane 13°~15° to the weave plane, running across four typical regions in the bulk: weft bundle, warp/weft interface, warp bundle, and inter-ply. According to the observed fracture route, four basic failure modes are schematically presented. Cracks form and develop in these areas along fiber/matrix interphase or within matrix, depending on the strength competition between interphase and matrix. The fracture mechanism reveals dependence of compress strength on matrix abundance between and within bundles. Based on the failure modes new method for compress strength prediction can be further investigated.

Abstract: SiC particulates reinforced with Al matrix composites were fabricated using a thermal spray process. In addition, the dry sliding wear behavior was investigated using various sliding speeds and applied loads. Premixed Al and SiC powder was sprayed onto an Al6061 substrate by flame spraying, and dry sliding wear tests were performed under varying sliding speed and applied load conditions. Wear behavior of the composites were studied using a scanning electron microscope(SEM), X-ray diffraction(XRD) and a surface roughness tester.

Abstract: A highly concentrated solution of polystyrene (PS) in N,N-dimethyl formamide (DMF) was electrospun and the surface morphology of the electrospun PS fibers was investigated. Unlike the porous morphology observed on the surface of the fibers electrospun from the PS solution in a volatile solvent, e.g. tetrahydrofuran, a regular protuberance morphology was found on the surface of the fibers electrospun from the PS solution in the non-volatile solvent, DMF. This unique surface morphology was formed due to the presence of residual DMF solvent inside the electrospun PS fiber. Due to the large diameter of the PS fibers (~5 to ~10 μm) formed from the highly viscous PS solution, the DMF could not evaporate completely from inside them during the electrospinning process. Therefore, the extrusive force of the residual solvent inside the fiber induced the formation of a unique surface morphology. We believe that this unique surface morphology increases the surface area of the electrospun fibers, thus making it possible to control their wetting or adsorption behavior.

Abstract: This paper dealt with the fabricating process of liquid phase sintered (LPS) SiC ceramics containing the oxide additives of Al2O3 and Y2O3, in conjunction with the evaluation of their mechanical properties. LPS-SiC ceramics was sintered at the temperature of 1820 oC under an applied pressure of 20 MPa and a pressure holding time of 2 hour. A commercial SiC powder with an average size of about 0.3 μm was used as a starting powder. LPS-SiC ceramics with additive composition ratios of 1.5 and 2.3 (Al2O3/Y2O3) represented an excellent density of about 3.2 Mg/m3. LPS-SiC ceramics had a flexural strength of about 800 MPa and a fracture toughness of about 8.0 MPa⋅m0.5 at an additive composition ratio (Al2O3/Y2O3) of 1.5.

Abstract: The Al2O3-TiC/Al composites were prepared by injecting CO2 gas into Ti contained Al-Si alloy melts. The microstructure of the composites was examined by XRD, SEM and TEM. It was indicated that both Al2O3 and TiC particles can be formed by the in situ reaction of CO2 with Ti and Al in the melten alloys. The Al2O3 and TiC particles in size of 0.3~1.5μm distributed uniformly in the matrix. The volume fraction of the particles is mainly depend upon the time of CO2 injection.The tensile strength at room temperature of the composites can reach 346.08MPa and the hardness is 149.6MPa HBS, repectively, which are higher than those of the matrix alloy.

Abstract: This paper proposes a new accelerated life test method of hydraulic pump used in vehicles, which have multiple alternating loads. For determination of life time of hydraulic pump for given field conditions with respect to duty cycle, the equivalent load and speed of this unit has to be determined. Equivalent load and speed can be calculated from the given duty cycle using the predominant theory for cumulative fatigue damage. Finally, we can perform accelerated life test on hydraulic pump by determination of test pressure and speed from calculated equivalent cumulative damage per working cycle and weighted average speed.

Abstract: In this study, we proposed a process of an accelerated life testing method of 5-speed manual transmissions used in vehicles, which loads are consisted of multiple alternating loads. The entire process of an 5-speed manual transmission’s accelerated life testing method where no failures are allowed, is a process that requires an abundance of assumptions, and other factors that are estimates such as the shape parameter, beta(
) and the fatigue damage exponent (x). And the process is consisted of 7-step process. From the 1-setp, which is the deriving the service(use) torque and speed(rpm) profile of the transmission, to the 7-step, we could determine the accelerated life time, the accelerated torque and the accelerated speed(rpm), which are the equivalent cumulative fatigue damage. Also, we have performed accelerated life test on 5-speed manual transmission by using the following 7-step process.