ESTIMATION OF CRITICAL PRESSURE OF DECOMPRESSION FAILURE OF EPDM COMPOSITES FOR SEALING UNDER HIGH-PRESSURE HYDROGEN GAS

摘要

To clarify the relationship between the decompression failure behaviours of EPDM and the nature of their reinforcement fillers, EPDM composites were exposed to hydrogen gas at 30 °C and up to 10 MPa. Optical microscopic studies of the interiors of composites showed that cracks initiated as a result of stress concentrations from micrometre-sized bubbles formed by supersaturated hydrogen after decompression. The critical pressure (p_F) at which no cracks initiated after decompression was determined. Each bubble was regarded as a disc-like cavity with an internal pressure, and its tearing energy (T) was calculated by the finite-element method. The critical inner pressure (∏_F) was then calculated on the basis of the criterion that T ≥ T_(s,th) (the threshold tearing energy for a static crack). The critical hydrogen pressures of unfilled and silica-filled EPDM could be successfully estimated because p_F ≈ ∏_F. However, for the carbon black-filled composite (CBP), the value of nF was about twice that of p_F. It is considered that the internal pressure of bubbles (n) became higher than the applied pressure of hydrogen (p) in terms of absorbed hydrogen on carbon black in CBP, unlike unfilled or silica-filled composites.