Coupled Diffusion-Deformation-Damage Model for Polymers Used in Hydrogen Infrastructure

The soft materials used in the infrastructure of hydrogen storage and distribution systems are vulnerable because exposure to high-pressure hydrogen can lead to mechanical damage and property degradation. Polymers are one of the widely used classes of soft materials within hydrogen infrastructure. Many small cavities exist within the polymer material due to their long molecular chains. When exposed to high-pressure hydrogen gas, the gas diffuses through the polymer material and occupies these cavities. When outside hydrogen pressure reduces suddenly, the hydrogen gas inside the cavities does not get enough time to diffuse out as diffusion is a much slower process. Instead, this trapped gas causes blistering or in extreme cases rapture of polymer material. This phenomenon is also known as rapid decompression failure. In this study, a continuum mechanics-based fully coupled diffusion-deformation model with damage is developed to predict the stress distribution and damage propagation while the polymer undergoes rapid decompression failure. The hyperelastic material model, along with the maximum principal strain failure theory, was chosen for this study as it represents the nonlinear material response with sudden failure observed in uniaxial tensile tests perfectly. EPDM polymer was chosen for this study because of its commercial availability and common use in hydrogen storage and distribution system. It has superior mechanical properties, high and low-temperature resistance, and certain compounds work well in hydrogen gas. Stress concentration was observed on the periphery of the cavity at the point closest to the outside surface which lead to damage initiation at the same location. Also, this work showed that the coefficient of diffusion plays an important role in damage initiation. As the value of the coefficient of diffusion increases, the amount of damage decreases due to the higher coefficient of diffusion ensures a safe passage for trapped hydrogen to escape to the atmosphere. This work is useful for design engineers to alter the parameters while manufacturing polymer composites to increase their performance in a high-pressure hydrogen environment.