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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