IntroductionSolid oxide fuel cells (SOFC) is a device that converts chemical energy into electrical energy. Compared with traditional power generation equipment, SOFC has the advantages of flexible fuel use, no noise, low emission and high conversion efficiency. SOFC operates at high temperatures (600-1000 ℃) for a long time, due to the mismatch of Coefficient of Thermal Expansion between anode-electrolyte-cathode electrode, metal connector and sealing material and the combined effect of temperature gradient. Even if the stress caused by mismatching is not enough to cause structural failure in a short time, the battery running under such stress for a long time at high temperature will cause large creep damage to each component, and the initiation of cracks will cause SOFC leakage.The porosity of porous electrode is closely related to its thermal expansion coefficient, elastic modulus, Poisson ratio, material diffusion, electrochemical reaction, effective conductivity, and other parameters, which is the main factor determining the performance of key SOFC components. When hydrogen is first supplied to the battery, the anode material will change, as well as the porosity of the anode layer, leading to variation on its physical and mechanical properties, which can affect its structural integrity and reliability under long-term high-temperature service conditions. Therefore, it is of great significance to study the effect of porous electrode porosity on the creep damage of SOFC at high temperature.MethodsBased on the previous modeling and research of SOFC multi-physical field, the SOFC model of gradient pore anode under multi-field coupling is established. Then, according to the Wen-Tu creep damage model, the effect of anode porosity on SOFC creep damage was analyzed.Considering that COMSOL Multiphysics has good multi-physics coupling ability and ABAQUS has strong nonlinear analysis and module development ability, the research method of COMSOL-ABAQUS is adopted. Firstly, the non-uniform temperature field calculated by COMSOL was applied to the node of the ABAQUS finite element model as a thermal load. Based on the creep model of ductile exhaustion theory and the damage mechanics model of continuum, the ABAQUS creep damage subroutine was written, and the USDFLD subroutine was embedded to simulate the creep damage and crack propagation law of single-channel SOFC. When ω = 0.99 is defined, the crack initiation unit of the sample is regarded as the failure unit. According to the method proposed by Saanouni et al., the elastic modulus of the Gaussian point of the failure element is reduced to 1/10⁶ of the initial elastic modulus, so that the subsequent stress of the point is approximately zero, indicating that the bearing capacity is lost here. By combining the high efficiency of COMSOL and the strong nonlinear convergence of ABAQUS, SOFC finite element model is established to analyze the creep damage and crack propagation law of a single planar SOFC element.Results and discussionCompared with the assumed uniform temperature field, the maximum equivalent stress of the upper connector, anode support, anode functional layer 2, anode functional layer 1, electrolyte, cathode and lower connector is 95%, 88%, 95%, 91%, 48%, 65% and 96% higher than that of the uniform temperature field, respectively. Therefore, the assumption of uniform temperature field is not accurate enough, and the real temperature distribution obtained under the coupling of multiple physical fields is needed to analyze the creep damage evolution of SOFC.The critical damage lifetime of SOFC connectors with gradient pore anodes is 31.4%, 26.4% and 17.9% longer than that of SOFC connectors with anode uniform porosity of 0.2, 0.3 and 0.4, respectively.Gradient pore anode design the upper connector of flat SOFC reaches the critical loss value at 64 kh, and the crack initiation, belonging to the surface crack, is located on the outer side of the 40 mm rib at the fuel outlet of the upper connector, and gradually expands to both sides. However, with the increase of time, the crack propagation rate gradually decreases, and the crack propagation almost stops at 80 kh. At this time, the crack length reaches a maximum of 32 mm, although it is a non-penetrating crack witch will not cause leakage, it is still a problem that cannot be ignored.ConclusionsThe main conclusions of this paper are summarized as follows: Compared with the assumed uniform temperature field, the maximum equivalent stress of each part of the flat plate SOFC under the coupling of multiple physical fields is higher than the predicted result under the uniform temperature field. The assumption that the uniform temperature field is not accurate enough requires the real temperature distribution obtained under the coupling of multiple physical fields to analyze the creep damage evolution of SOFC. At the same time, the critical damage life of SOFC connectors with gradient pore anodes is significantly longer than that of SOFC connectors with uniform anodes with different porosity. When the upper connector reaches the critical loss value, surface cracks are generated on the outer side of the fuel outlet rib of the upper connector and spread to both sides gradually, but with the increase of time, the crack propagation rate decreases gradually. Although it is a non-penetrating crack witch will not cause leakage, it is still a problem that cannot be ignored. This study shows that the gradient pore anode has potential advantages in long-term high temperature service and provides theoretical basis and data support for the structural integrity and reliability optimization design of SOFC structures.