Designing with ceramics

Other approaches being taken to increase the reliability of ceramics are nondestructive testing and proof testing. The latter approach is briefly discussed in Sec. 11.5.2. 

One can describe the strength distribution of a ceramic in a variety of formalisms. The one most widely used today is the Weibull distribution This two-parameter semiempirical distribution is given by 

Since one is dealing with a strength distribution, the random variable is defined as o/oq, where t is the failure stress and oq is a normalizing parameter, required to render. r dimensionless and whose physical significance will be discussed shortly. 

Rewriting Eq. (11.23) as 1/5 = exp(cr/cro) and taking the natural log of both sides twice yields 

Multiplying both sides of Eq. (11.24) by —1 and plotting — lnln(l/5) versus In a yield a straight line with slope — w. The physical significance of (7q is now also obvious It is the stress level at which the survival probability is equal to 1/e, or 0.37. Once m and cto are determined from the set of experimental results, the survival probability at any stress can be easily calculated from Eq. (11.23) (see Worked Example 11.2). 

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This enormous hardness is exploited in grinding wheels which are made from small particles of a high-performance engineering ceramic (Table 15.3) bonded with an adhesive or a cement. In design with ceramics it is never necessary to consider plastic collapse of the component fracture always intervenes first. The reasons for this are as follows. 

Designing with ceramics ice forces on offshore structures... 

Materials Selection in Designing with Ceramics and Glasses... 

High, Si steel fabrication issues Coated materials (Pt) cost issue Ceramics promising, but have fabrication and joining issues Dry wall boiler design with ceramics may be option Data needed with iodine contamination Incoloy 800HT may address intergranular corrosion C—SiC composites should be examined... 

A further and very important consequence of the Weibull distribution is the size effect, i.e. the mean strength decreases with increasing specimen size. This is the most important consequence of fracture statistics for designing with ceramics. 

R. Hopkins, R. J. Price, Fusion reactor design with ceramics, Nucl. Eng. Des. Fusion, 2 (1985) 111-143. 

As the anodes of the cathode-grounded tubes are cooled through the ceramic insulator, narrower insulators should lead to more heat transferable. For lower voltages, tube designs with twice the actual anode load are feasible. 

Ceramics, without exception, are hard, brittle solids. When designing with metals, failure by plastic collapse and by fatigue are the primary considerations. For ceramics, plastic collapse and fatigue are seldom problems it is brittle failure, caused by direct loading or by thermal stresses, that is the overriding consideration. 

And we are still learning how best to fabricate and use them. As emphasised in the last chapter, the mechanical properties of polymers differ in certain fundamental ways from those of metals and ceramics, and the methods used to design with them (Chapter 27) differ accordingly. Their special properties also need special methods of fabrication. This chapter outlines how polymers are fabricated and joined. To understand this, we must first look, in slightly more detail, at their synthesis. 

D. Designing with metals, ceramics, polymers and composites... 

Figure 9-15B. Typical metal hold-down plate for use with ceramic or carbon packing. Note It rests directly on top of the packing bed-limiters are similar in design in metal or plastic, bolted to column wall above packing. Used by permission Norton Chemical Process Products Corp., Bull. TA-80.

The Rockwell hardness tester is designed for measurement of fine- and medium-grained rocks and ceramic products of moderate hardness. In engineering, excluding metallurgy, it has wide uses in the hardness testing of files and grinding wheels with ceramic binder, as well as soft materials (scale Hrd and others). 

It is somewhat more difficult to relate dynamic abrasion methods to diamond indenter methods. Since the Scott tower is designed for abrasiveness tests with ceramic glazes, it is obvious that the attempts to correlate abrasiveness derived by this method with hardness, relied on test results for glazes. The hardness of glazes is similar to that of typical glasses, and... 

As a consequence of the large diversity of microstructures which can adjusted by microstructural design, Si3N4 ceramics are a whole class of materials with an inherent large variety of properties and therefore a large variety of potential applications (Sect. 10). Different qualities depend on amount and distribution of the microstructural features (Sect. 6.1.4). Often small variations have severe... 

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