When a mechanical structure subjected to a thermal load it can result in thermal expansion as the material in the structure expands (increases size and/or changes shape) when heat is applied. Different materials can have different coefficients of thermal expansion (CTE). Therefore, when a mechanical structure comprises components of more than one material, there is the possibility that one material expands more than another material. This can happen if the different components in the same mechanical structure are subjected to different thermal loading and/or are made of materials having different CTE. When two components in a mechanical structure are expanding by different amounts under thermal load, this can result in shear stress in the material at the interface between the two components. An example of this is the combination in a mechanical structure of ceramic materials or silicon with metal structures. Structures such as ihis should be designed to avoid failure of a connection between the different materials. One known way of reducing the likelihood of such a failure is to provide an appropriate interface material, allowing a large shear stress, between the two different materials/components. Another known way to avoid failure due to different levels of thermal expansion is to select materials for the mechanical structure with similar CTE. The structure can also be designed such that the temperature difference between the different materials in the structure is minimised by ensuring a limited thermal resistance between the components.
展开▼
