Using short-time creep relaxation effect to decrease the residual stress in the bonded compliant seal of planar solid oxide fuel cell - A finite element simulation

Bonded compliant seal is a new sealing design for planar solid oxide fuel cell. During brazing, large residual stresses are generated which have a great effect on failure of the brazing connection. Therefore, how to decrease the residual stresses is a critical issue for structure integrity. This paper presents a study on decreasing residual stresses by using short-time creep relaxation effect. A sequential-coupled calculation model is developed based on finite element method. The brazing temperature field is firstly obtained by simulating the convection and radiation heating, and then the residual stress is calculated by a thermal-elasto-plastic-creep model. The calculated results are verified by neutron diffraction measurements. During cooling, a short holding time at 600 degrees C is designed to relax the residual stress by creep effect. The results show that this effect has a remarkable impact on decreasing the residual stress. The stresses in cell, Ag-CuO and foil have been reduced by about 26.9%, 13.6% and 22.1%, respectively, as the holding time increases up to 40 h. When the holding time exceeds 40 h, the residual stresses remain almost unchanged. It is thus suggested that the holding time should be reasonably determined to allow sufficient stress relaxation. (C) 2013 Elsevier B.V. All rights reserved.