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 (βr) as the brightness change ratio. βr was obtained for each pixel of the image for whole specimen. According to the results of the specimen, βr around the central region of specimen was higher than that of the edge region. Averaged βr around the center of specimen (βr¯) logarithmically increased with the increase in exposure number (Nex). Judging from the results, the internal damage tends to generate at the center of specimen, and the internal damage amount increased with increase in Nex.
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