Numerical Simulation Of Fatigue Crack Growth Of Proton Exchange Membrane For Hydrogen Fuel Cells

As a clean energy technology with high energy efficiency,proton exchange membrane fuel cells have attracted wide attention.As a key component,the durability of proton exchange membrane is of great significance for the lifetime of fuel cells.In this dissertation,the fatigue crack growth behavior of the membrane under different loading conditions and humidity cycles is studied numerically.A relation between damage evolution of the cohesive elements and Paris law is employed to simulate the biaxial fatigue crack growth.The effects of transverse stress,loading waveform,overload,and loading history on the fatigue crack growth are investigated.It is found that the predicted biaxial fatigue crack evolution is in a good agreement with various experimental results.Both the transverse stress and the tensile overload can retard the fatigue crack growth.It is also found that the fatigue crack growth associated with a shorter pre-crack depends more on the load waveform.Moreover,fatigue crack growth is faster under the low-high loading history than the high-low one,indicating that the membrane is more vulnerable to damage during the start/stop or the acceleration/deceleration process.In the study of fatigue crack growth of proton exchange membrane under humidity cycling,the effects of clamping displacement,channel shape and location,and crack location in the membrane are considered.The results show that the clamping displacement has two competing effects on the crack growth.On the one hand,it squezzes the membrane in the direction perpendicular to the crack growth and thus retards the crack growth,but on the other hand,it bends the membrane in the direction of crack growth and thus accelerates the crack growth.When the humidity amplitude is large,the fatigue crack growth rate can be significantly reduced by changing the channel shape and channel loacation.The fatigue crack growth rate in different regions of the membrane is related to the in-plane stress state of the region under the humidity cycle.Compared with the region where the in-plane stress alternates between the tensile state and the compressive state,the fatigue crack growth rate in the region where the in-plane stress keeps the compressive state is significantly reduced.The results in this dissertation are helpful to understand the fatigue crack growth of the membrane under service conditions,and provide insights into improving the durability of the membrane.