Ceramic proof testing

FIGURE 17M Proof testing of a ceramic to be used in an application for lich ite properties are critical. The initial distribution of the measured property is given by the curve. After proof testing at a value of the pn rty sli itly above the value expected during use, the acceptable pieces correspond to those in the truncated distribution. 

Quality assurance is practiced at all steps of ceramic manufacture. All raw materials and process conditions are subject to scrutiny. Certification tests are also performed on the product. Proof testing assures that the ceramic part will give properties above those desired for a particular application. Proof testing is performed only when the ceramic part is used for a critical application. Finally, nondestructive investigations of ceramic materials were discussed in very general terms. 

Data from crack velocity experiments are used to Improve the reliability of ceramic materials. It is particularly useful for the application of proof-testing to structural ceramics, because it leads to an estimate of lifetime under load after the proof test has been used to weed out mechanically defective components. For this purpose, the data in the low crack growth velocity range are of prime importance, because it is, by and large, slow... 

Figure 3. Generalized design diagram used for structural ceramics showing minimum failure time os. applied structural load. Each curve represents a differed ratio of the proof test load to the service load.

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. 

Figure 9.8 Effect of proof testing on space shuttle tile materials. Compared to the initial strength distribution, the strength of the surviving specimens was found to be truncated close to the maximum proof stress. (From Green et al, 1982, reproduced courtesy of The American Ceramic Society, Westerville, OH.)...

This example, involving a heavy-duty diesel ceramic exhaust valve (Corum et al. ), was selected to contrast failure probability predictions for power law. Walker law and a proof test condition. The valves were made of NT-551 silicon nitride material. Table 1 contains a summary of the Weibull and SCG parameters obtained from four-point flexure bars at three different temperatures (Andrews et al. ). CARES/Life was used to obtain these parameters using the raw data listed in Andrews et al.. Data to obtain values for the Walker law parameters did not exist, so assumed values for Qv and A2/A1 were used. 

K. Ando, K. Furusawa, K. Takahashi and S. Sato, Crack-healing Ability of Structural Ceramics and A New Methodology to Guarantee the Structural Integrity Using the Ability and Proof-Test, J. Etir. Ceram Soc., 25, 549-58 (2005). 

K. Ando, M. C. Chu, M. Matsushita and S. Sato, Effect of Crack-healing and Proof-testing procedures on fatigue strength and reliability of SisN/SiC Components, / Eur. Ceram. Soc., 23, 977-84 (2003)... 

Ternary systems, containing three different chemical elements, demand suitable precursors with element ratios corresponding to the material of choice. Further, the stoichiometry control present in the molecular carrier should be preserved during the processing steps, which is not trivial given the ambiguity associated with the structure and composition of intermediate species. Nevertheless, various single precursors tested in the material synthesis provide the proof of principle for the application of molecules-to-materials approach in multi-component ceramics. 

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