What general design criteria apply to ceramic joints?

The following principles should be kept in mind when designing with glasses and ceramics:

• Operating conditions and requirements on the component must be specified as closely as possible. It is necessary to know the external loading and temperature regime: forces (dead weight, centrifugal force, etc), thermal shock (thermal stresses in particular can cause severe problems) and whether conditions are cyclic or static, etc.
• The design must take into account the specific properties of the glass or ceramic:
  
  
  1. High brittleness (lack of ductility) compared with other structural materials;
  2. High strength in compression but lower in tension, bending and torsion;
  3. Susceptibility to impact load and point load: high contact stresses, particularly at points of support or load transfer, are very dangerous in glass or ceramic because the associated stress cannot be accommodated by plastic deformation. Thin, ductile metal interlayers are sometimes inserted to distribute this stress more uniformly;
  4. Most glasses and ceramics have low thermal conductivity and increased susceptibility to thermal shock: components subjected to temperature fluctuations should have simple and symmetrical form as well as thin walls. For example, a cylindrical rod will resist sudden changes of temperature better than a rod with square cross-section;
  5. Sensitivity to stress concentrators: abrupt changes in shape or thickness, notches and corners, etc - which increase the stress - should be avoided or rounded to a suitable radius;
  6. Ceramics and glasses contain flaws, especially at the surface: cracks and other faults are mostly produced during manufacture; sometimes they form during use, e.g. through contact stresses or thermal shocks. The probability of larger flaws increases with increasing body dimensions.

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