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Numerical and analytical methods for calculating thermal stresses and deformations in a flat plate connected to a cooled wall with an intermediate layer of solder or adhesive are proposed. In the numerical method, the nonisothermal flow theory for layer material was used. In the analytical method, the layer material was elastic if shear stresses were less than yield limit and ideal-plastic if they exceeded it. The plate and the wall were elastic in both methods. Specific computations were performed for the ferrite plate soldered to the metal wall of a high-power waveguide. Results showed the length of the plastic zone in the layer could be large not only in operation (when heat in the plate was releasing), but also after cooling in a plate-to-wall connecting process. The less accurate but simple analytical method can be useful for estimations of thermal stress and cooling rate, which can provide the necessary temperature and strength of both the plate and the layer. To calculate a deflection of the plate due to the thermal gradient in its cross section, the Bubnov's-Galyorkin's approximate method was used. It was shown that the deflection is small if a layer is made of solder and could be significant if the layer is adhesive.
thermal stress, plastic deformations, electronic devices, waveguides, ferrites, plates, elastic base, solders, adhesives
Senior researcher, American Combustion, Inc., Norcross, GA