Breviary Technical Ceramics






7.2.1 Influence of Material Properties

Due to the complete lack of plastic deformation, ceramics fail suddenly at low and medium temperatures on reaching the local material strength in the region of critical microstructural inhomogeneities. High stresses occur particularly in the region of small radii, sharp edges, steps, offsets and holes, as well as in areas where forces are applied at points or along lines. Under certain circumstances stresses will be generated that reach the limit of the material strength much earlier than would be expected on the basis of the part's external loading, due to notch effects associated with these geometrical features, effects that can be considerable.

For this reason, notch-like geometries (stress concentrations) should be avoided in the design of a ceramic part, or at least only implemented in a softened or optimised form. The particular advantage of ceramic materials is the ability to withstand high compressive loading. One of the primary goals of design for ceramics should therefore be to make use of this property as much as possible, and to keep the number of areas where the part will experience tensile or bending stress as low as possible. High stress concentrations should particularly be avoided in regions subjected tensile stress.

These basic principles are often not sufficiently considered by some users. Instead, the desire is often expressed to obtain a direct copy of a component that was originally designed "metallically", in ceramic material but having the same shape. This can, however, not only increase the manufacturing costs, but can even put the feasibility of the product in question.


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