Bow-free tri-component assembly for aerospace optoelectronics applications: Predicted thermal stresses

There is an obvious incentive for using bow-free (temperature change insensitive) assemblies in aerospace optoelectronics: elevated bow might lead to the reduction or even to the total loss in the coupling efficiency. A bi-material bi-component assembly cannot be made bow-free: the total bending moment is never zero in such an assembly. To become bow-free, an assembly comprised of dissimilar materials should contain at least three components in order to produce forces that would lead to a zero resultant bending moment. The induced stresses in a bow-free assembly could be, however, high and, if appreciable inelastic stresses occur, the bow-free condition might be compromised. Accordingly, the objective of the present analysis is to obtain a bow-free condition for a tricomponent tri-material assembly and to develop analytical predictive stress models for the evaluation of the interfacial shearing and peeling stresses, as well as for the normal stresses acting in the cross-sections of the assembly components. Analytical (mathematical) modeling enables one to better understand the physics of possible failures and to design a reliable product. The carried out numerical examples have indicated that all the three stress categories could be rather high and on the same order of magnitude. The developed models could be of help in the analysis and design of bow-free opto-electronics assemblies for aerospace applications. The models could be employed in other areas of applied science and engineering, when there is an incentive for using bow-free assemblies and to quantify the induced stresses. The future work should include thorough accelerated testing to establish the allowable level of the induced stresses.