Strength of Planar Cells for SOFC Application

The mechanical behaviour of SOFC cells with different anode thickness and proprietary microstructural differences is analysed. Bending tests are performed with the surface of the anode either in tension or in compression. Thicker cells are tested using a four-point bending set up, whereas thinner cells are tested using a ring-on-ring loading device. Calculations of the residual stresses within the layers at room temperature show a large compressive stress in the electrolyte. Thus even when a tensile stress is applied to the electrolyte the crack initiates in the anode near the interface with the electrolyte. Hence the modulus of rupture of the anode is determined as the characteristic parameter from the bending tests. Consideration is given also to the effect of the flexural rigidity of the multilayered composite and the distance of the failure origin from the neutral axis. The influence of residual stresses and the effect of the microstructure on the fracture stress are discussed.