Vol.8 No.2 2015
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Research paper : Development of material testing equipment in high pressure gaseous hydrogen and international collaborative work of a testing method for a hydrogen society (T. IIJIMA et al.)−69−Synthesiology - English edition Vol.8 No.2 (2015) and the discussion should focus on the scenario and strategy.Comment 2: Pertaining to international standardization, while the technological comparison with USA is clearly presented in this paper, there is no description of the situation in Europe. Doesn’t the trend in Europe have effect on the international standardization in this field? Including the perspective of social demand of this technological field, I think the international standardization strategy will become clearer by considering and comparing Japan, USA, and Europe.Answer (Takashi Iijima)As you indicated in Comment 2, there was no description of the trend in Europe including that of ISO. Therefore, we described the trend on the standardization in Japan, USA, and Europe for on-board vessels and hydrogen station vessels in chapter 2. Then we discussed the R&D scenario toward international standardization and added the schematic diagram (Fig. 1) of the development model. Since we are not in the position to directly promote standardization, we used the expressions “approach” or “contribute” to the international standardization of the material testing method. Also, in terms of capturing the efforts in Japan, USA, and Europe, we added the global situations of the testing equipment for high-pressure gaseous hydrogen in chapter 3.Following Comment 1, we simplified the description on the technological details in chapter 4, and the data for SA-372 Grade J are referred to the paper published in July 2014.3 Comparison of the fracture toughness value in gaseous hydrogen evaluated by different methodsQuestion & Comment (Mamoru Nakamura)In the “direct comparison of Japanese and USA fracture toughness evaluation data” in this paper, the crack growth behaviors in gaseous hydrogen for SA-372 Grade J and SCM435 are quite different, and therefore, you describe that different evaluation methods were used for SA-372 Grade J, but the fracture toughness values obtained were almost the same. I felt it was rather unnatural that the fracture toughness values were almost the same, despite the greatly different crack growth behaviors. Do you mean to say that the obtained evaluation values of the fracture toughness were quite different by different evaluation methods, but in this case, you obtained the same values using different methods by “coincidence”?Answer (Takashi Iijima)As you can see from the experimental data, the fracture toughness values of SA-372 Grade J and SCM435 in 115 MPa gaseous hydrogen became very low, and although the detailed mechanisms are unknown, it is assumed that the behavior is somewhere between linear elastic fracture and elastic-plastic fracture. For this point, I think we have to do further, careful experiments. The ASTM E1820 describes the method for evaluating the fracture toughness of samples that show unstable crack extension and stable crack extension, where the fracture toughness values are derived using the J-R curve calculated from the unloading elastic compliance method. At the same time, in the case where the unstable crack extension is mainly seen, the method for calculating the fracture toughness value from the P-COD curve without unloading is mentioned in ASTM E1820 Annex A5. Therefore, the fracture toughness values of SA-372 Grade J and SCM435 turned out to be the same values not by “coincidence,” but we determined that they are comparable values obtained in the material test based on ASTM E1820. The details of the evaluation of fracture toughness value of SA-372 Grade J are described in Reference [20].

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