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Modeling of Failure in Aluminum Alloy Braze for a High Temperature Thermoelectric Assembly
Keywords: aluminum alloy braze, high temperature, thermoelectric assembly
The objective of this work is to design a commercially viable TEG assembly that can be used in passenger vehicles and can withstand extreme environmental conditions. Nowadays, thermoelectric generators (TEGs), solid state devices utilizing the Seebeck effect converting thermal energy to electrical energy, are considered for energy harvesting in trucks and passenger vehicles by taking advantage of the temperature difference between the exhaust pipes and the ambient environment. The operating temperatures of the proposed TEGs can reach levels in excess of 500 C. Among materials used in a TEG assembly, aluminum braze alloys offer a good high temperature solution. The wide temperature variations are the primary factor that causes the stress generated at the braze-ceramic interfaces and braze-semiconductor interfaces due to the coefficient of thermal expansion (CTE) mismatch. The interface stresses usually cause significant damage and failure of the TEG device. The evolution of fatigue damage in the aluminum braze must be understood in order to ensure acceptable reliability of the TEG. Since the design, fabrication, and testing of TEG assemblies are complex and expensive processes, finite element modeling was performed to understand the fatigue damage evolution and to predict the reliability of the TEG packages. The finite element model based on a continuum damage mechanics approach was used to model the failure in the aluminum braze alloy (12% Si, 88% Al). Both the ductile and shear damage were considered simultaneously due to the presence of a complex stress-strain state. Experimental shear tests were conducted and finite element simulations were used for validation of the numerical model. A full scale three-dimensional finite element model of a prototype TEG assembly was constructed and cyclic behavior was evaluated. The reliability of the TEG package is discussed based primary on the numerical analyses conducted.
Aicha Elshabini, Distinguished Professor
University of Idaho
Moscow, ID

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