Experimental Study On Mechanical Behavior Of Proton Exchange Membranes Under In-plane Biaxial Cyclic Loading

Proton exchange membrane(PEM) plays an important role in transporting proton while at the same time preventing the crossover of reactant gases in fuel cells. Whereas, PEM is expected to be under biaxial cyclic stresses in work conditions, since the membrane is clamped along the lands and seal gasket of fuel cells and constrained by the catalyst and gas diffusion layers. In order to improve the stability and integrity, the biaxial cyclic mechanical responses of PEM should be researched.In this study, a tailored testing system has been developed to study the mechanical behavior of PEM under in-plane biaxial cyclic loading. The center of the specimen can be kept motionless during loading since the grips were driven by right-and-left ball screw, which can guarantee the movement identical and symmetric in each direction. The Non-contact Displacement Detecting System(NDDS) was developed to perform two-dimensional strain measurements accurately without contacting the specimen. This testing system has been proved feasible, reliable and effective, thus, the requirements of tests are met.The shape of cruciform specimen are analyzed using finite element software. This paper researches five common shape by comparing the uniformity of strain, the value of shear strains, and the stress concentrations outside the test zone, finally choosing cruciform specimen with expanded fillet and slotted arms as the sample’s shape. Then a further analysis is made about the dimension of fillet.Six stress-controlled cyclic paths, including circular path, rhombic path, square path, proportional path, constant stress path, and uniaxial path, are designed in order to study the biaxial cyclic mechanical responses of PEM. According to these in-plane experiments, the strain-stress relationship, the biaxial ratcheting behavior, strain energy density evolution and the effects of loading history have been discussed.