Estimation of hydrogen pressure at blister initiation of EPDM composite exposed to high pressure hydrogen gas

Transparent EPDM composite crosslinked by peroxide with no fillers was exposed to hydrogen gas at a maximum pressure of 10 MPa, and then the behavior of blister initiation and growth in the composite after decompression was observed by an optical microscope. The critical pressure where no blisters initiated P_H.cr was 1-2 MPa, while micrometer-sized blisters initiated in the composite at PH > 1-2 MPa. It is considered that these blisters initiated due to stress concentration of micrometer-sized bubbles under an inner pressure Π formed by supersaturated hydrogen molecules after decompression ; then the energy release rate-tearing energy, T-of these bubbles was calculated theoretically or by FEM. Parallel to the calculation, static crack growth tests were conducted, and the threshold tearing energy for the static crack T_s.th was experimentally obtained. From the criterion expressed by T> Ts.th, the inner pressure at blister initiation πF was estimated and then was compared with P_H.cr. Consequently, πF≈PH.CT, i.e., the critical pressure where no blisters initiated was successfully estimated in terms of fracture mechanics.