5.3.4.5 Creep
properties
Plastic deformation of metallic materials
under static loads is observed in long term experiments. Creep
phenomena are amplified at higher temperatures and limit the
application possibilities of metallic materials. Generally
speaking, the tendency of ceramic materials to creep at temperatures
below 1,000°C is very low. However, in contrast to metallic
materials, creep extensions of only a few per cent can lead
to failure of the material. As opposed to slow crack growth,
in which a single crack propagates, creep damage is understood
as the development of creep porosity and microcracks. This
causes a relatively homogeneous distribution of damage through
the entire volume of the material under stress. As a result,
the physical properties of the material are changed.
The creep behaviour in ceramic materials is influenced not
only by the stress but also the chemical bonding and microstructure
characteristics (grain size, grain shape, porosity, grain
boundary phases).
Test procedures for determining the parameters of creep deformation
in flexure at high temperatures are specified in DIN ENV 820-4
and EN 820-2.
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