Damage evolution in unfilled EPDM during various types of repeated hydrogen high-pressure cycles

The effect of repeated high-pressure hydrogen cycles on the decompression failure of unfilled EPDM was investigated from in-situ images of the damage field during decompression. The purpose was to characterize the relative influence of some parameters of the pressure cycle (decompression rate, residual pressure and time between two cycles) and to investigate damage cumulative features. Beyond that, the aim of this wide range of decompression conditions was to separately vary the external pressure and gas diffusion histories, in order to discuss them as driving force contributions to damage growth. Such extended decompression conditions confirmed coupled contributions of diffusion and mechanics. Exposure conditions allowing a significant part of gas diffusion promoted clustering and later macro-cracking, provided that the residual external pressure was low enough. A more heterogeneous spatial distribution of damage was also observed, within clusters and at the sample scale, with non-trivial re-opening of cavities from one cycle to another. More restrictive exposure conditions (i.e., limited diffusion times or residual external pressure) reduced or prevented the onset of cavities, clustering and transition to macro-cracking. More homogeneous damage fields were observed, along with more systematic re-appearing and growth of the same defects with cycling. Damage processes appeared more spatially confined.