Critical hydrogen pressure at crack initiation of silica-filled EDPM composite in high pressure hydrogen gas

A silica-filled EPDM composite (SCT) was exposed to hydrogen gas at P _H ≤ 10 MPa, and the critical hydrogen pressure at crack initiation P_H,cr was evaluated. From observations of cracks by an optical microscope, P_H.cr ranged from 4 to 5 MPa. It was inferred that these cracks initiated due to the stress concentration of the micrometer-sized bubbles caused by supersaturated hydrogen molecules after decompression. Furthermore, tearing energy of these bubbles, T, was calculated by FEM and theoretically. In this calculation, the SCT was regarded as a hyperelastic material, and so its strain energy density was approximated by a polynominal Mooney-Rivlin model which can express the strain energy density of practical sealing materials more exactly than the Neo-Hookean model. Parallel to the calculation, static crack growth tests were conducted using single edge crack specimens in air and in 0.7 MPa hydrogen gas at room temperature. Since the hydrogen gas did not influence the T_s,th value, an inner pressure at T ≥ T _s,thΠ_F, was estimated using the T_s,th value in air. As a result, the critical hydrogen pressure at crack initiation of the SCT was successfully estimated, i.e., P_H,crΦ_F as well as that of an unfilled composite.