Particulate reinforcing

Sohd rocket propellants represent a very special case of a particulate composite ia which inorganic propellant particles, about 75% by volume, are bound ia an organic matrix such as polyurethane. An essential requirement is that the composite be uniform to promote a steady burning reaction (1). Further examples of particulate composites are those with metal matrices and iaclude cermets, which consist of ceramic particles ia a metal matrix, and dispersion hardened alloys, ia which the particles may be metal oxides or intermetallic compounds with smaller diameters and lower volume fractions than those ia cermets (1). The general nature of particulate reinforcement is such that the resulting composite material is macroscopicaHy isotropic. 

Creep Resistsince. Studies on creep resistance of particulate reinforced composites seem to indicate that such composites are less creep resistant than are monolithic matrices. Silicon nitride reinforced with 40 vol % TiN has been found to have a higher creep rate and a reduced creep strength compared to that of unreinforced silicon nitride. Further reduction in properties have been observed with an increase in the volume fraction of particles and a decrease in the particle size (20). Similar results have been found for SiC particulate reinforced silicon nitride (64). Poor creep behavior has been attributed to the presence of glassy phases in the composite, and removal of these from the microstmcture may improve the high temperature mechanical properties (64). 

In contrast to the particulate-reinforced composites, all other reinforcement morphologies appear to provide enhanced creep resistance. The creep... 

Commercial grades of polymer may contain, in addition to glass fibre, fire retardants, impact modifiers and particulate reinforcing fillers. Carbon fibre may be used as an alternative to glass fibre. 

Particulate Reinforced Metals Via Pressure Infiltration" J. Mat. Sci., July, 1990. 

For particulate-reinforced composite materials, Paul derived upper and lower bounds on the composite modulus [3-4]. His approximate mechanics of materials solution agrees fairly well with experimental data for tungsten carbide particles in cobalt. 

B.Q. Han, K.C. Chan, T.M. Yue, and W.S. Lau, "A Theoretical Model for High-Strain-Rate Superplastic Behavior of Particulate Reinforced Metal Matrix Composites," Scr. Metall. Mater., 33 925 (1995). 

More recently, Stanicioiu, Chinta Hartner (1959) attempted to reinforce the cement with glass fibres, but this was not successful. The most serious study on the reinforcement of dental silicate cement was made by J. Aveston (in Wilson et al., 1972). Silicon carbide whiskers, carbon fibres and alumina powder were introduced into the cement mix. Unfortunately, the glass powder/liquid ratio had to be reduced, and the strength gained by reinforcement was thereby lost. It is clear that dental silicate cement cannot be strengthened by fibre or particulate reinforcement. 

Klier, E., Mortensen, A, Comic, J.A., and Flemings, M.C., "Fabrication of Cast Particulate Reinforced Metals Via Pressure Infiltration" J. Mat. Sci., July, 1990. 

Rothon RN (1994) Acicular particulate reinforcements. In Jones FR (ed) Handbook of polymer-fibre composites. Longman, Harlow, p4... 

Creep resistance -of particulate reinforced composites [COMPOSITE MATERIALS - CERAMIC MATRIX] (Vol7)... 

The particulate-reinforced MMCs are lightweight and demonstrate a significant increase in modulus and tensile strength at both ambient and elevated temperatures of the unreintorced material. The process was announced in late 1992 by Magnesium Elektron Ltd.. Manchester. U.K. 

Fibre-whisker- and particulate-reinforced ceramic composites... 

Taya, M., Hayashi, S., Kobayashi, A.S. and Yoon, H.S. Toughening of a particulate-reinforced ceramic-matrix composite by thermal residual stress , J. Am. Ceram. Soc. 73 (1990) 1382-1391. 

Turan, S. and Knowles, K.M., (1996a), a — (3 reverse phase transformation in silicon carbide in silicon nitride-particulate-reinforced-silicon carbide composites ,, /. Am. Ceram. Soc., 79 (11), 2892-2896. 

In the presentation of the elevated temperature mechanical behavior of ceramic matrix composites, some degree of separation has also been made between fiber-reinforced and whisker- or particulate-reinforced composites. This has been necessary because of the way the field has evolved. The continuous fiber-reinforced composites area in many ways has evolved as a field in its own right, driven by developments in fiber processing technology. 

Creep Deformation of Particulate-Reinforced Ceramic Matrix Composites... 

A typical tensile creep curve for a particulate reinforced ceramic matrix composite, siliconized silicon carbide (Si/SiC),28 is shown in Fig. 4.1. In comparison to the behavior of metals and metallic alloys, tertiary creep is suppressed in this material. There is only a slight upward curvature of the creep curve prior to failure. In many other ceramic matrix composites, tertiary... 

Improvement in the creep resistance of whisker-reinforced composites is modest compared to that obtained in particulate-reinforced composites. Creep... 

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