Standardisation of flexure testing of engineering ceramics
With the increase in usage of engineering ceramics, a new industrial standard is required in order to evaluate its properties and to perform a fair and just trade. The thesis investigates the faults and omissions of existing work and judges today's requirements thereby constructing a framework with which today's and future standards in flexure testing can be based. The draft standard presented in this thesis covers the three major testing methods for determining the biaxial flexural strength (modulus of rupture) of engineering ceramics. The ring-on-ring, ball-on-ring, and 4-Ball test fixtures were all adopted as standard, since it is known that each of these systems is suited for a particular application and each has different advantages and disadvantages. The three major biaxial test methods prescribed in this draft standard have been devised so that more consistent and accurate test results can be obtained. However, the uncertainty of measurement in flexure testing always exists and needs to be estimated. The estimation of uncertainty in flexure testing in this study is based on the methodology provided in the ISO Guide to the expression of uncertainty in measurement. The results of the estimation showed that the uncertainty in measurement for the biaxial flexure test standard proposed in this thesis is very low compared to the inherent variability of the strength of ceramic materials. It was also found that the applied load, thickness of the disc plate, and random effects are the three major components contributing to the overall uncertainty. The total uncertainty of measurement in biaxial flexure testing can be significantly minimised by the reduction of the uncertainty contributed from these components, especially from random effects.