Ceramic matrix composite

About: Ceramic matrix composite is a research topic. Over the lifetime, 7807 publications have been published within this topic receiving 117020 citations.

Effects of tool vibration on fiber fracture in rotary ultrasonic machining of C/SiC ceramic matrix composites

Abstract: The carbon fibers fracture mechanism depending on fiber orientation significantly affects the machined surface quality of C/SiC composites. The rotary ultrasonic machining (RUM) has been proved to be a beneficial method for C/SiC composites drilling with minor tearing defects at the hole exits. In contrast, the effects of tool vibration on surface topography in RUM of C/SiC composites considering fiber orientation have not been reported. In order for a unique evaluation of surface generating mechanism in RUM of C/SiC composites, several RUM experiments were conducted on 2D-C/SiC composites. The micro structural characteristics of the hole surfaces under various fiber directions, ultrasonic amplitudes and spindle speeds were analyzed. The fiber fracture mechanism in RUM of C/SiC was discovered through theoretical analysis. The results displayed that both fiber cutting direction and cutting speeds significantly affect the surface topography in RUM and CG of C/SiC composites. The tool ultrasonic vibration could contribute to the hole surface quality improvement in RUM of C/SiC composites by the fiber fracture mechanism alteration. With the ultrasonic vibration contribution, the fiber cutting direction tended towards 90° and the cutting speeds were increased. In contrast, due to the non-monotonic effect of the cutting speed on the surface roughness, only when the spindle speeds were relatively low, the higher ultrasonic amplitude apparently contributed to the hole surface quality further improvement.

Fabrication and characterization of reaction bonded silicon carbide/carbon nanotube composites

Abstract: Carbon nanotubes have generated considerable excitement in the scientific and engineering communities because of their exceptional mechanical and physical properties observed at the nanoscale. Carbon nanotubes possess exceptionally high stiffness and strength combined with high electrical and thermal conductivities. These novel material properties have stimulated considerable research in the development of nanotube-reinforced composites (Thostenson et al 2001 Compos. Sci. Technol. 61 1899, Thostenson et al 2005 Compos. Sci. Technol. 65 491). In this research, novel reaction bonded silicon carbide nanocomposites were fabricated using melt infiltration of silicon. A series of multi-walled carbon nanotube-reinforced ceramic matrix composites (NT-CMCs) were fabricated and the structure and properties were characterized. Here we show that carbon nanotubes are present in the as-fabricated NT-CMCs after reaction bonding at temperatures above 1400 °C. Characterization results reveal that a very small volume content of carbon nanotubes, as low as 0.3 volume %, results in a 75% reduction in electrical resistivity of the ceramic composites. A 96% decrease in electrical resistivity was observed for the ceramics with the highest nanotube volume fraction of 2.1%.

Micromechanical stresses in SiC-reinforced Al2O3 composites

Abstract: Applying an Eshelby (1957) approach, the internal micromechanical stresses within an SiC-inclusion-reinforced (platelet to whisker geometries) polycrystalline alumina matrix composite were calculated. The results are compared to the experimental residual stress measurements of a SiC-whisker-reinforced Al2O3 by Predecki, et al. (in press) and found to be in excellent agreement. The calculations are then extended to SiC-reinforced composites with polycrystalline mullite, silicon nitride, and cordierite matrices. It is concluded that the internal stresses are significantly influenced by the inclusion geometry as well as the thermoelastic differences between the inclusion and the matrix and also the volume fraction.