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Refractory materials generally refer to materials with a refractoriness not lower than 1580°C. Generally, materials and products composed of inorganic non-metallic materials, non-combustible and non-melting materials should generally belong to the broad sense. For example, in a high-temperature working environment of more than 1000 degrees, the components composed of bricks, tiles, mud, sand, etc. in the building are difficult to damage, and these materials can be called refractory materials.
It is mainly used in high-temperature containers in metallurgy, machinery, chemical industry, building materials and other industries. Its usage directly determines the service life of these important equipment, and ultimately affects the normal operation of the entire production process.
As the temperature changes, it will generate greater thermal stress, which will directly lead to its damage and functional failure. Thermal stress is often referred to as temperature stress. There are many reasons for thermal stress:
(1) Boundary constraints make the thermal expansion or contraction of structural members subject to external constraints;
(2) There is a temperature difference between the components of the structure;
(3) There is a temperature gradient between each part of each component of the structure;
(4) The component is composed of a variety of different materials, and different materials have different thermal expansion coefficients;
(5) There are inclusions inside the material;
(6) The material is anisotropic.
Thermal stress has the following main characteristics at the same time:
(1) The size of the thermal stress is directly related to the boundary constraints, and generally increases with the increase of the constraint degree. The thermal expansion coefficient, modulus and Poisson’s ratio of general materials will change with the temperature change, the temperature change will affect the size of the thermal stress, and the initial temperature will also have a certain degree of influence on its thermal stress;
(2) The thermal stress is balanced with the externally applied load, and thermal deformation occurs in all parts, but at the same time, it is limited by constraints. Generally, compression deformation occurs at high temperatures, and tensile deformation occurs at low temperatures;
(3) Thermal stress is self-limiting. Yield flow or high temperature creep will reduce thermal stress, and thermal stress will not cause component fracture of plastic materials, but alternating thermal stress will cause fatigue failure or plastic deformation accumulation of components. Over time, eventually a fracture occurs.
The research on the thermal stress of refractory materials is relatively complicated. Due to the rapid development of computers, the analysis of temperature field and thermal stress using finite elements has been gradually introduced into the research of refractory material structures at home and abroad since the early 1990s.