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texture in these layers. The stresses in the Nb5Si3 laminates were quantified using an isotropic elastic analysis that accounts for both residual stresses and bending stresses.
doi:10.1016/S0026-2714(98)00155-3 
Copyright © 1998 Published by Elsevier Science Ltd. All rights reserved
Research Note
Application of a ‘surrogate’ layer for lower bending stress in a vulnerable material of a tri-material body
Received 22 December 1997;
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Abstract
Low strength materials in multi-layer (multi-body) structures subjected to temperature change often fail because of the high curvatures and bending stresses caused by the elevated thermal expansion (contraction) mismatch of the constituent materials. In some cases, an introduction of an additional, ‘surrogate’, layer (not needed from the standpoint of the normal operation of the system) of a high expansion (contraction) and/or high modulus material can be an effective means to flatten the composite structure, thereby reducing the bending stress in the vulnerable material. We consider an epoxy molding compound on a thin ceramic substrate, and suggest that a ‘surrogate’ layer of a high coefficient of thermal expansion (CTE) and high modulus polymeric material be applied onto the outer side of the substrate to flatten the structure. Clearly, the ‘surrogate’ material should be able to withstand high tensile stresses. We suggest also that this material be processed concurrently with the basic molding operation. A simple formula is obtained for choosing the appropriate thickness of the ‘surrogate’ layer for the given material(s) in the package, including the ‘surrogate’ material itself.
