Ultrasonic Fatigue Tests on the Nafion Proton Exchange Membrane, Under the Modality of Three Points Bending

This work deals with the ultrasonic fatigue endurance under the modality of three points bending on the Nafion 115 proton exchange membrane used in fuel cells. All tests were carried out under the control of temperature and humidity in a patented ultrasonic fatigue machine, developed by first author (patent No. 323948, 2014 Mexico), using a program developed on the LabVIEW platform to control the testing starting, to count the number of cycles and to stopping the test when the specimen fails. Special attention was devoted to the applied planar stress on the membrane, the initial perpendicular load to the membrane surface, the amplitude of ultrasonic vibration, as well as the testing temperature and humidity. Numerical simulations were developed to generate the virtual model and to determine the stress distribution on the membrane under the combination of the applied loads. The fatigue endurance was obtained under the modality of three points bending and ultrasonic loading. Finally, the crack initiation and propagation were identified on the polymeric Nafion 115 membrane under the described loading conditions.