Accelerateci life assessment methods for thermoelectric modules with mechanical stress tests

Abstract

During the operation of a Thermoelectric (TE) module, one side of it has thermal expansion and the other side has cooling shrinkage. The corresponding resulted tensile and compressive stresses at the interfaces of its constituent materials will often cause the fatigue failure, especially during the repeated operations of the module. However, knowing the life of TE Modules is often required no matter for designers or end users. Thus, this study investigated some alternatives of the quick life assessment methods by applying mechanical stresses through bend and shear tests respectively. Generally, the reliability tests of the TE module is time consuming and usually take thousands of hours to get a result. It can't fit the requirement in the development of TE products. Based on the concept of accelerated life test, this study developed the mechanical bend test to simulate the deformation of the TE Modules during operations. A special fixture was designed in the tests that can load the TE module to generate similar deformation as that in the real world applications. Considering shear stresses are also the dominate factor in causing the TE modules' failure, a shear test was also developed for testing the TE modules. The results from these two tests are compared and discussed. Regarding the bend test, various descending displacements and speeds are used for shortening the test time. The results and failure modes are also examined. Besides, finite element analysis was used for the parametric analyses of different geometrical dimensions of TE Modules for checking the optimum design of it operational life. Also, the normal and shear stresses on the TE Modules with those tests are also compared with each other. The test results showed that it takes longer time for failure to occur with the bend test than that with the shear test. It was concluded that TE modules are more vulnerable to shear loadings. Based on the experimental and analytical investigations, the mathematical models to predict the service life are presented, and even the design improvement for TE modules is also proposed. It is believed that the studied results will be beneficial to the related applications of thermoelectric modules.