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.)−66−Synthesiology - English edition Vol.8 No.2 (2015) experiment was KJIC,H = 63 MPa m1/2 in 115 MPa gaseous hydrogen. The fracture toughness value of SA-372 Grade J was KQ,H = 66 MPa m1/2 in 115 MPa gaseous hydrogen.[20] The fracture toughness values of SCM435 and SA-372 Grade J in 115 MPa gaseous hydrogen are shown in Table 2.Figure 7 shows the relationship between the material strength and fracture toughness values in high-pressure gaseous hydrogen (103 MPa) obtained by the constant displacement method (KTHa) and the continuously rising displacement method (KJH) at the Sandia National Laboratories,[18] and the fracture toughness value (KJIC,H) in high-pressure gaseous hydrogen (115 MPa) obtained by the rising displacement method using the unloading elastic compliance method. It can be seen that the fracture toughness value KJIC,H obtained by the unloading elastic compliance method, one of the rising displacement methods, showed almost equivalent values as KJH obtained by the continuously rising displacement method at the Sandia National Laboratories, and was lower than KTHa obtained by the constant displacement method.This indicates that although the detailed measurement conditions such as the displacement rate, load-unloading process, hydrogen purity, and pre-crack formations, as well as the form of the testing device and the measurement know-how such as hydrogen replacement procedures may be different, there is no major difference in the fracture toughness evaluation results by the rising displacement method, and that this method possesses universality as an evaluation method. Also, since the KJH and KJIC,H calculated by the rising displacement method were lower than the KTHa calculated by the constant displacement method, the fracture toughness value obtained by the rising displacement method is a conservative value, and it can be considered an effective method for quantitative evaluation of the metallic materials in high-pressure gaseous hydrogen conditions.5 SummaryTo establish a testing method of the hydrogen effect on the metallic materials used in high-pressure gaseous hydrogen, our research group developed a set of material testing devices that allows tensile tests, fracture toughness tests, and delayed fracture tests in high-pressure gaseous hydrogen up to normal operation pressure of 115 MPa. Using such testing devices we gathered data for materials in high-pressure gaseous hydrogen for general-use metallic materials to increase the choice of materials that can be used for the vessels and pipes of high-pressure gaseous hydrogen equipment. Particularly, with the cooperation of the Sandia National Laboratories, we conducted international comparison of the fracture toughness testing method for the standard material of Japan and USA for Cr-Mo low alloy steel that is expected to contribute to reducing the cost of high-pressure gaseous hydrogen equipment. As a result, it became clear that the fracture toughness test using the rising displacement method in high-pressure gaseous hydrogen was effective as a material testing method that allows quantitative evaluation of hydrogen embrittlement of general-use metallic materials. In the future, by accumulating data of the effects of various testing conditions, particularly of hydrogen gas pressure and displacement rate, we can review the effectiveness of the fracture toughness test by the rising displacement method in high-pressure gaseous hydrogen. We also plan to consider whether we can contribute to the international Fig. 6 P-COD curve of SCM435 by the unloading elastic compliance methodFig. 7 Relationship between yield stress and fracture toughness of Cr-Mo low-alloy steel[18][20]0.50.40.30.20.10.002468101214Load (kN)PCrack Opening Displacement (mm)CODSCM 435115 MPa in H2900800700600020406080100120140Yield stress (MPa)(MPa m1/2)KSA-372 Grade JSCM 435at AISTat SNLat SNLKJIC,HKJHKTHa762SA-372 Grade J63700SCM 435σys (MPa)115 MPa in H2Yield stressK (MPa m1/2)JIC,H66 ( )Q,HKTable 2. Fracture toughness of SCM435 and SA-372 Grade J[20]

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