Fatigue tests on the proton exchange membrane Nafion 115 (perfluorosulfonic acid) of fuel cells, under the biaxial modality: Tension and torsion

Abstract

Fatigue tests have been carried out under biaxial modality: tension and torsion, on the membrane material Nafion 115 (perfluorosulfonic acid, PFSA). This polymeric material is used in fuel cells as proton exchange membrane, frequently undergoing mechanical loading of tension and torsion during its industrial life. A self-designed machine has been constructed to obtain the fatigue endurance of this polymeric material under the following testing conditions: from 0 to 50 degrees of torsion, 0–60 MPa of initial tensile stresses, from room temperature (22–25 °C) to 80 °C, and two values for relative humidity: environmental and saturated relative humidity. All fatigue tests were carried out at the frequency of 1.2 Hz. The first results concerning this paper have been obtained under the following conditions: constant torsion angle of 50 degrees, 5 initial tensile stress of 60, 55, 50, 45 and 40 MPa, room temperature (22–25 °C) and environmental humidity (50–55%). According to the experimental results, fatigue endurance decreases sensibly when the tensile stress increases. Finally, the fracture surfaces of testing specimens were analyzed by SEM in order to investigate the principal trends of crack initiation and propagation, under this modality of biaxial fatigue loading.