Influence of repetitions of the high-pressure hydrogen gas exposure on the internal damage quantity of high-density polyethylene evaluated by transmitted light digital image

A quantitative evaluation of the bulk damage level after high-pressure hydrogen exposure for the hydrogen compatible polymeric materials are developed. The bulk damage level of the internal damage induced by high-density polyethylene (HDPE) after 90 MPa hydrogen exposure repetition were evaluated. Based on the light scattering by the internal damage, we established a quantitative damage index in terms of the light transmittance as brightness (B) of transmitted light digital image of the HDPE disk specimen; the relative extinction ratio of transmitted light intensity (β_r) as the brightness change ratio. β_r was obtained for each pixel of the image for whole specimen. According to the results of the specimen, β_r around the central region of specimen was higher than that of the edge region. Averaged β_r around the center of specimen (β_r¯) logarithmically increased with the increase in exposure number (N_ex). Judging from the results, the internal damage tends to generate at the center of specimen, and the internal damage amount increased with increase in N_ex.