Finite Element Analysis and Fatigue Life Prediction of an Aluminum Alloy Braze for High Temperature Thermoelectric Generator Package Assembly

Abstract

Thermoelectric generators (TEGs) are solid state devices that convert thermal energy into electrical energy using the Seebeck effect. They can be used for energy harvesting in trucks and passenger vehicles by taking advantage of the temperature difference between the exhaust pipes and ambient environment. The key issue with thermoelectric devices today is the demand for increased operating temperatures while maintaining adequate reliability and low cost. Since, TEGs are subjected to sub-critical thermal cyclic loading, ensuring satisfactory reliability is important for commercially viable products. TEGs used in passenger vehicles should be able to withstand extreme environmental conditions such as high temperature, shock and mechanical vibration [1]. Since the operating temperatures of TEGs can reach temperatures higher than 500 °C, aluminum brazes offer a good high temperature solution for die attach applications. The thermoelectric materials of TEGs are prone to oxidation and sublimation. A solution to minimize these phenomena is to enclose the TEG device in a hermetic package. This paper analyzes the reliability of aluminum alloy braze Al 718 (12% Si, 88% Al) used in TEG packages under fatigue loading. A power cycling temperature fluctuation method was employed to simulate the operating conditions of the TEGs for passenger vehicle. Low cycle fatigue simulations were performed using the direct cyclic approach embedded in the finite element software ABAQUS. Direct cyclic approach uses an extrapolation technique, which allows for efficient and computationally inexpensive simulations. The numerical model was validated using experimental test data. A validated damage model was used to analyze the cyclic damage evolution in the aluminum alloy braze for the hermetic TEG packages.