| The history of the application of engineering ceramics is littered with examples where copycat designs based on the performance of metals have resulted in spectacular failures of ceramic components. Ceramic engineering design requires consideration of materials properties, operating environment and the fabrication process used. Limiting factors in ceramic designs include cost, component geometry, dimensional tolerances, reliability and risk of premature failure. The Design to manufacture Process for Ceramic Components The design to manufacture phase of a ceramic component may be illustrated by the following flowchart: | 
| | Figure 1. Flowchart showing the processing going from the design to manufacture of a ceramic component. | Application Requirements A clear and prioritised specification of the requirements of the application is a prerequisite of any ceramic engineering design. What function is the component expected to perform and what conditions will it be subjected to? For most engineering applications this will invlove consideration of the following: · The load to which the component will be subjected and more importantly the stress distribution which arises · The temperature of operation including transients · The chemistry associated with the operating environment · The potential for impact and abrasion · Other external environmental factors such as high electrical or magnetic fields and ionizing radiation Property Limitations The first stage of selecting a ceramic material for a given application is accomplished by comparing the application conditions to the appropriate properties of the material. This apparently simple task is often complicated by lack of property data particularly data measured under the appropriate conditions. The usual sources for property data for ceramics are reference works that are often limited in scope and refer to classes of materials, or suppliers’ data sheets that give typical values or ranges of properties achieved by specific materials. Given the scarcity of relevant data the designer should be prepared for the need to measure the properties of the materials himself. Prediction of Performance The next stage in the material selection process involves a prediction of performance of the ceramic in the application. This will involve a consideration not only of the relationship between different properties but also component specific aspects such as shape and size, and also the interfacing of the component with neighbouring components in the design. Finite element and other mathematical modelling techniques are of great value in prediction of the behaviour of ceramic components particularly in complex stress situations or where transient thermal and mechanical conditions prevail. In many instances there are well-documented performance predictions which draw on material properties. In other instances the simplest and cheapest route is to make the component and evaluate its performance directly in the application. Fabrication and Manufacturing Issues The fabrication route chosen for the component is influenced by the shape and size, and also the economics of manufacture which itself is strongly driven by the manufacturing rate. The fabrication route also determines the type and population of process related flaws which themselves limit the properties and reliability which can be achieved. For instance, identical components which are manufactured by slip casting and pressing and firing will, in spite of having the same density, exhibit different shape and size microscopic defects (e.g. bubbles in the slip cast item, and small cracks in the pressed item). These will lead to differences in strength and toughness, which could make the component made by one route unsuitable for the application. One of the most important features which is affected by the fabrication route is the reliability of the measured properties. The statistical scatter of test results arising from a batch of ceramic test specimens can be used to predict the probability of failure of a component under given operation conditions. Consequently components can be designed (over-engineered) to meet an acceptable failure rate. What constitutes an acceptable failure rate will depend on the criticality of the application - with applications where life is at risk being the most demanding. Once the fabrication route is chosen the designer must review his property data and determine that it remains relevant, and that any mathematical modelling which has been done is still valid. | 
CERAM
