Ceramic matrix composites bonding

In the second approach shown in Fig 3.12(b), a force is applied continuously using a Vickers microhardness indenter to compress the fiber into the specimen surface (Marshall, 1984). For ceramic matrix composites where the bonding at the interface is typically mechanical in nature, the interface shear stress, Tf, against the constant frictional sliding is calculated based on simple force balance (Marshall, 1984) ... 

However, some theoretical treatment considers only the special case of friction sliding of a single fiber along a mechanically bonded interface, particularly for some ceramic matrix composites, where the Coulomb friction law applies. See for example Zhou and Mai (1995) and Shetty (1988). Assuming a constant friction at the fiber-matrix interface and neglecting the Poisson effects, Shetty (1988) reported a simple force balance equation for the frictional shear strength, Tfr... 

Less-conventional processing techniques are also used to make ceramic matrix composites. Siliconized silicon carbide, for example, is made by liquid infiltration.16,17 A compact of SiC particles is formed and then presintered, or reaction bonded. Liquid silicon is then infiltrated into the structure. Many different microstructures of siliconized silicon carbide can be made in this manner. The volume fraction of SiC particles can be as high as 90vol.%. Bimodal structures have also been made by this technique. These materials are used for radiant heaters and heat exchangers.17,19... 

Osborne Reynolds was the first to show that tightly packed granular solids expand their volume when deformed.84 This phenomenon is called dilatancy. It is well understood and is discussed in some detail in the literature on soil mechanics.85-87 In vitreous-bonded structural materials such as silicon nitride, dilatancy has been suggested as a contributing factor in the formation of cavities,88 and may be an important factor in the cavitation of ceramic matrix composites.64 Dilatancy has also been suggested as an important factor in controlling the creep and creep relaxation of glass-ceramics.89... 

It seems unlikely that long-fiber ceramic matrix composites with strong bonds will find application because of their low temperature brittleness. However, for completeness, a model which applies to the creep of such materials can be stated. It is that due to Kelly and Street.21 It is possible also that the model applies to aligned whisker-reinforced composites since they may have strong bonds. In addition, the model has a wide currency since it is believed to apply to weakly bonded composites as well. However, the Mileiko18 model predicts a lower creep strength for weakly bonded or unbonded composites and therefore is considered to apply in that case. 

Chemically Bonded Phosphate Ceramic Matrix Composites... 

Chapter 14 Chemically Bonded Phosphate Ceramic Matrix Composites Fig. 14.7. ... 

The initial interest in small diameter oxide fibers as rivals to small diameter SiC fibers for use in ceramic matrix composites has been largely unfiilfilled. Although the oxide fibers do not suffer from oxidation, as do the SiC fibers, they are inherently less mechanically stable above 1000°C. Whereas the co-valent bonds in SiC resist creep the ionic bonds in... 

J.W. Lucek, G.A. Rossetti, Jr., and S.D. Haitline, Stability of Continuous Si-C (-0) Reinforcing Elements in Reaction-Bonded Silicon Nitride Process Environments, pp. 27-38 in Metal Matrix, Carbon, and Ceramic Matrix Composites 1985, NASA CP-2406, Edited by J.D. Buckley, NASA, Washington, B.C., 1985. 

Ceramic matrix composites require a fiber interface coating to prevent fiber-matrix bonding and to produce crack deflection and fibrous fracture in the composite. Work at the... 

---