In with this numerical tool. A bending

In industrial
vessels, refractories were mainly used to conserve the steel construction from
high process temperatures. These vessels are widespread, for example in
metallurgical industry, glass industry, and chemical as well as in the building
materials industry. Refractory materials reach temperatures of more than 1500°C
based on their application. Due to the thermal expansion and the mechanical
constraints mechanical stresses appear in the lining. These loads facilitate
mechanical failure and can accelerate the wear rate of the refractory material
and necessitate a premature replacement of the refractory product. The behavior
of the lining can be improved with adequate selection of the materials,
optimization of geometry or adaptation of process parameters. To clarify
failure mechanisms it is necessary to allow for nonlinear material behavior
especially in the course of crack formation. It is possible to analyze for example
the loads in the bottom wall transition zone of a LD-converter in which
carbon-rich hot metal is converted into steel with this numerical tool. A bending
moment in the bricks of the transition zone is usually induced by the thermal
expansion of the lining in the bottom and the wall. The stresses in radial
direction are shown in a contour plot at the right side of the figure. Zones
with tensile stresses are red and zones with compressive loads are colored
yellow. These bending stresses lead to crack formation parallel to the hot
face, which can cause spalling of brick parts. The strength and fracture
behavior of ceramics are considered with particular reference to oxides.
Ceramics fracture in a brittle manner and the strength of most materials is
about two orders of magnitude less than the theoretical strength. The basic
requirements are reliability and long service life when materials are
introduced into their operational life. A suitable combination of physical,
chemical and mechanical properties is needed to achieve successful performances.
In the case of ceramic materials under mechanical and thermal loads the situation
is complicated due to their low fracture resistance. However there are
applications where exclusively such materials can be used. The typical example
are refractory materials that are used broadly in many industrial branches. In
this case thermal stability and acceptable thermal shock resistance together
with satisfactory mechanical properties are the key requirements on the material.
Composite materials are developed to meet these demands. The design of
ceramic-based composite materials leads to the development of multi-component
systems where each constituent has a specific function in the material. Tensile
tests of brittle ceramics are usually not performed. It is difficult to shape
these materials into the proper test structure, difficult to grab the brittle
material without breaking it, and it is difficult to align the test samples to
avoid bending stresses which can destroy the sample. For brittle ceramics, a
three-point bending apparatus is used determine the stress-strain behavior, and
the measurement results are used to calculate an equivalent elastic modulus.