Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Nishimura Shin Last modified date:2018.04.06

Professor / Advanced Hydrogen Materials / Department of Mechanical Engineering / Faculty of Engineering

1. Keiko Ohyama, Hirotada Fujiwara, Shin Nishimura, Inhomogeneity in acrylonitrile butadiene rubber during hydrogen elimination investigated by small-angle X-ray scattering, International Journal of Hydrogen Energy, 43, 2, 1012-1024, 2018.01.
2. Sylvie Castagnet, Hiroaki Ono, Guillaume Benoit, Hirotada Fujiwara, Shin Nishimura, Swelling measurement during sorption and decompression in a NBR exposed to high-pressure hydrogen, International Journal of Hydrogen Energy, 42, 30, 19359-19366, 2017.07, Unlike for other gases, the volume change of the rubber materials due to the sorption of hydrogen is very low and hence difficult to measure. Conversely, the volume change occurring during decompression is significantly more than that occurring during sorption equilibrium. The aim of the present experiment is to measure the significantly different volume changes due to hydrogen content during the two stages of a high-pressure exposure cycle at room temperature simultaneously. Spherical samples of unfilled NBR were tracked by two high and low-resolution devices, with a good connection of measurements series in both conditions. The effect of thermal expansion (Joule-Thomson effect) and the compressibility contributions were removed to measure the term due to hydrogen sorption precisely..
3. Takefumi Okumura, Shin Nishimura, ポリエチレンカーボネート系ポリマー電解質への可塑剤添加効果, 高分子論文集, 74, 2, 139-143, 2017.02, Properties of polymer solid electrolytes composed of poly(ethylene carbonate) [PEC], lithium bis(trifluoromethane sulfonimide) [LiTFSI, LiN(CF3SO2)2] and propylene carbonate [PC] as plasticizer have been analyzed using Raman spectroscopy and ac impedance spectroscopy. Including 14 wt% of PC in the PEC based polymer electrolyte with LiTFSI concentration of 0.2 mol per polymer repeat unit, made it possible to increase the ionic conductivity (σ) by one order of magnitude to a practical-use level of 1.3 mS cm−1 at 20°C. The correlation between σ and temperature fits well the Williams-Landel-Ferry equation, so it is considered that ionic conductivity depends on thermal activation of the polymer chains. From the correlation between σ and temperature, it is concluded that PC (with greater mobility than the polymer chains) partly solvates with lithium ions, and σ is improved by lowering its activation energy..
4. Shin Nishimura, Shuji Kawamoto, Hirotada Fujiwara, Hydrogen characteristics and ordered structure of mono-mesogen type liquid-crystalline epoxy polymer, International Journal of Hydrogen Energy, 41, 18, 7500-7510, 2016.05, Fuel cell systems, such as those used in electric vehicles require lightweight hydrogen fuel storage. Polymer composites are candidate materials for storage vessels requiring high fracture resistance for high pressure cycling, as well as high thermal conductivity. Here, we investigate 4,4′-diglycidyloxybiphenyl (DGOBP) epoxy for such applications, and clarified the relationship between the hydrogen penetration properties and the ordered structure of the epoxy. We controlled the ordered structure of the DGOBP polymer by adjusting the curing temperature of a 4,4′-diaminodiphenyl methane (DDM) curing system. We obtained a series of cured DGOBP with DDM samples with crystallinity values of 19%, 27%, 32%, and 36%, corresponding to curing temperatures of 130, 120, 110, and 100 °C, respectively. The thermal conductivities of these samples were 0.26–0.31 Wm−1 K−1. Cured DGOBP showed hydrogen contents of 403–1271 ppm (25–75% smaller than that of conventional epoxies). Liquid crystalline epoxy polymers can be a candidate material for hydrogen storage systems requiring well-controlled hydrogen penetration properties..
5. Masahiro Kasai, Dohi Hideyuki, Shin Nishimura, 5-V plateau observed for Li-rich Li1 + xMn2 − xO4 stoichiometric spinels containing low-temperature-grown Li2MnO3 as an impurity phase, Elsevier, 289, 77-86, 2016.06, The redox reaction of tetravalent Mn4 + ions has attracted much interest since it is considered that this reaction is closely related to the generation of high capacity in layered cathodes with excess lithium.
We considered that to investigate materials, which include tetravalent Mn4 + ions and have a different crystal structure from Li2MnO3, is valuable for understanding the reaction mechanism. The result will reveal whether Mn4 + ion in the Li2MnO3 structure is essential or only existence of Mn4 + ion is sufficient for appearance of the high capacity. In this work, we investigated Li-rich Li1 + xMn2 − xO4 (x = 0.20, 0.25, 0.30, 0.33) stoichiometric spinels. For a Li content of x = 0.33, a capacity of 50 mAh g− 1 was observed in 5-V region. It is possible that the Li-rich spinel includes a small amount of Li 2MnO 3 impurity, which exhibits the 5-V plateau. No significant changes in lattice constants are observed from x = 0.25 to 0.33, which indicates generation of Li 2MnO 3. We estimated the amount as 9.2 wt.% for x = 0.33 by standard addition analysis, and true Li concentration of the spinel component as 0.23. However, the observed 5-V capacity cannot be attributed to only the impurity phase of Li 2MnO 3, because the specific capacity must exceed 540 mAh g − 1 to explain it. It is considered that the observed 5-V capacity is caused by two components of the Li-rich spinel and the other phase like a composite material of Li 2MnO 3/Li-rich spinel. The 5-V capacity for the pure spinel component estimated by extrapolating the 5-V capacity vs. impurity-concentration plot is 7.9 mAh g − 1..
6. Takefumi Okumura, Shin Nishimura, Lithium ion conductive properties of aliphatic polycarbonate, Elsevier, 267, 66-73, 2014.12, Properties of polymer electrolytes composed of poly(ethylene carbonate) [PEC] and lithium bis(trifluoromethane sulfonimide) [LiTFSI, LiN(CF3SO2)2] have been analyzed using Raman spectroscopy, dynamic mechanical analysis (DMA) measurements, and ac impedance spectroscopy. The lithium ion transference number of a PEC based polymer electrolyte is 0.4, which is 4 times higher than that of a poly(ethylene oxide)[PEO] based polymer electrolyte. The glass transition temperature of a PEC based polymer electrolyte decreases with the increase of LiTFSI concentration above 0.2 molar ratio of LiTFSI to repeat unit of the carbonate in PEC. Raman spectra show that the abundance ratio of undissociated LiTFSI increases at LiTFSI concentration above 0.2 molar ratio. Moreover, ionic conductivity of a PEC based polymer electrolyte increases with the increase of LiTFSI concentration above 0.2 molar ratio. The highest ionic conductivity is 0.47 mS cm− 1 at 20 °C..
7. Masahiro Kasai, Shin Nishimura, Akira Gunji, Hiroaki Konishi, Xiaoilang Feng, Sho Furutsuki, Shin Takahashi, Electrochemical study on xLi2MnO3-(1-x)LiNi1/3Co1/3Mn1/3O2 (x=0.5) layered complex cathode showing voltage hysteresis, Elsevier, 146, 79-88, 2014.11, The layered complex cathode has attracted much interest recently due to its high capacity, which exceeds 250 mAhg−1. On the other hand, it also shows large voltage hysteresis which causes energy loss when applied as a practical battery material. It has been reported that the hysteresis is an intrinsic bulk property, and the phenomenological model due to the migration of transition metal has been also proposed. Then, it is considered that to study the hysteresis for various compositions of transition metal is valuable to clarify the phenomenon. In this work, the layered complex cathode of 0.5Li2MnO3-0.5LiNi1/3Co1/3Mn1/3O2 was investigated. The results are discussed in comparison with the previous reports for 0.5Li2MnO3-0.5LiMn0.5Ni0.5O2. Investigating dQ/dV profilesrevealed that redox peaks at around 3.75 V showed small dependency on composition of transition metal, while it seemed that a reduction peak at 3.26 V was independent on the composition. Precise measurement of open circuit potential vs. capacity characteristics demonstrated that the energy dissipation during a cycle was abut 26 kJmol−1..
8. Atsushi Koga, Tadahisa Yamabe, Hiroyuki Sato, Kenichi Uchida, Junichi Nakayama, Junichiro Yamabe, Shin Nishimura, A Visualizing Study of Blister Initiation Behavior by Gas Decompression, 8, 1, 68-75, 2013.01, This study presents the effects of the type of polymer and gas on blister fracture in terms of visualizing O-ring behavior under high-pressure gas. To visualize blisters (internal cracks) by optical microscopy, transparent EPDM and VMQ O-rings were molded, and a special viewable high-pressure vessel with a glass viewport was developed. The O-ring specimens were exposed to high-pressure hydrogen, helium, and nitrogen gases at 10 MPa under room temperature, 25°C, after which these gases were rapidly decompressed for 0.3 seconds. The blister fracture occurred in EPDM but not in VMQ even though the two materials had the same Young's modulus. It is presumed by AFM observation that the difference in microstructure at sub-micrometer level between EPDM and VMQ influenced their blister initiation. The blister damage of the transparent EPDM O-ring in nitrogen gas was the most serious, while that in the helium gas was the slightest. The reason why the blister damage of the O-ring in the helium gas was the slightest is considered to be because solute helium gas diffused out from the O-ring after decompression faster than the other gases..
9. Junichiro Yamabe, Shin Nishimura, Tensile Properties and Swelling Behavior of Sealing Rubber Materials Exposed to High-Pressure Hydrogen Gas, 日本機械学会, 6, 6, 466-477, 2012.06, Rubber O-rings exposed to high-pressure hydrogen gas swell, and the volume increase induced by swelling influences tensile properties of the O-rings. Samples of nonfilled (NF), carbon black-filled (CB), and silica-filled (SC) sulfur-vulcanized acrylonitrile-butadiene rubber were exposed to hydrogen at 30 °C and pressures of up to 100 MPa, and the effect of hydrogen exposure on the volume increase, hydrogen content, and tensile properties was investigated. The residual hydrogen content, measured 35 minutes after decompression, increased with increasing hydrogen pressure in the range 0.7-100 MPa for all three samples. In contrast, the volumes of NF, CB, and SC barely changed at pressures below 10 MPa, whereas they increased at pressures above 10 MPa. This nonlinear volume increase is probably related to the free volume of the rubber structure. The volume increase of the CB and SC samples was smaller than that of the NF samples, possibly because of the superior tensile properties of CB and SC. As the volumes of the NF, CB, and SC samples increased, their tensile elastic moduli decreased as a result of a decrease in crosslink density and elongation by volume increase. Although the true fracture stress of NF was barely dependent on the volume of the specimen, those of CB and SC clearly decreased as the volume increased. The decrease in the true fracture stress of CB and SC was related to the volume increase by swelling, showing that the boundary structure between the filler and the rubber matrix was changed by the volume increase..
10. Hirotada Fujiwara, Shin Nishimura, Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance, 高分子学会, 44, 832-837, 2012.06, Hydrogen molecules dissolved in rubber due to high-pressure hydrogen gas exposure have been analyzed using 1H nuclear magnetic resonance (NMR) with solution and solid-state probes. To analyze the characteristics of dissolved hydrogen in rubber materials and to compare them with gaseous phase hydrogen, we measured the NMR spectra of gaseous phase hydrogen and evaluated the chemical shifts and pressure dependency. Measurement using a sealed tube and liquid phase probes enabled the simultaneous analysis of dissolved hydrogen in rubber and gaseous phase hydrogen eliminated from the rubber. Two peaks at 4.3 and 4.8 p.p.m. were observed in the 1H MAS NMR of the rubber samples after high-pressure hydrogen exposure. Using information from the chemical shift of the free hydrogen gas and the time dependency of hydrogen quantification in the rubber, both of these peaks were confirmed to be attributable to dissolved hydrogen. Their differences in relaxation time confirmed that their mobilities were different. In conclusion, the hydrogen dissolved in acrylonitrile butadiene rubber exists in two different forms with different mobilities. The ratio of those two hydrogens differs and is affected by the exposure pressure and elimination process time..
11. Junichiro Yamabe, Shin Nishimura, Influence of carbon black on decompression failure and hydrogen permeation properties of filled ethylene-propylene–diene–methylene rubbers exposed to high-pressure hydrogen gas, Wiley, 122, 5, 3172-3187, 2011.12, Eight carbon black (CB)-filled ethylene–propylene–diene–methylene linkage (EPDM) rubbers were manufactured by varying the content and type of CB. Then, the relationship among crack damage caused by high-pressure hydrogen decompression, the hydrogen permeation properties, and the mechanical properties of the rubbers was investigated. The hydrogen gas permeability of the rubbers decreased with an increase in the CB content and depended little on primary particle size. In contrast, the hydrogen gas diffusivity and solubility depended on both the CB content and primary particle size, that is, the hydrogen gas diffusivity decreased with an increase in the CB content and a decrease in the primary particle size, and the hydrogen gas solubility increased with an increase in the CB content and a decrease in the primary particle size. As for the mechanical properties, the CB-filled rubbers were more strongly reinforced by an increase in the CB content and a decrease in the primary particle size. The crack damage by high-pressure hydrogen decompression became larger as the ratio of the hydrogen gas solubility to estimated internal pressure at crack initiation relating to the mechanical properties became larger. As a smaller CB particle increases the hydrogen gas solubility of EPDM rubbers, while at the same time it reinforces the rubbers, the crack damage in the CB-filled rubbers was not influenced by the primary particle size..
12. Junichiro Yamabe, Hirotada Fujiwara, Shin Nishimura, Fracture Analysis of Rubber Sealing Material for High Pressure Hydrogen Vessel, 日本機械学会, 6, 1, 53-68, 2011.01, In order to clarify the influence of high pressure hydrogen gas on mechanical damage in a rubber O-ring, the fracture analysis of the O-ring used for a sealing material of a pressure hydrogen vessel was conducted. The O-ring was exposed twenty cycles to hydrogen gas at 100 MPa. All the cracks observed in this study emanated from the interior, which can be classified into two types, type 1 and type 2, from the viewpoint of the location of crack initiation and the direction of crack growth. The type-1 cracks started from the center of the O-ring, while the type-2 cracks started from the sites near the surface of the O-ring. It is implied that tensile stress by compression influenced crack initiation and growth of the type-1 cracks. The mechanical damage by the type-1 cracks was more serious than that by the type-2 cracks. Stress analysis was conducted by the nonlinear FEM; then fatigue crack initiation of the O-ring was evaluated in terms of the maximum principal strain criterion, which has been widely employed for the evaluation of fatigue strength of rubber materials. The strain generated by compression was considerably smaller than fatigue fracture strain although the increase in the strain due to swelling was considered. It is considered that the type-1 cracks initiated and grew due to strain concentration caused by bubbles which were formed from supersaturated hydrogen molecules after decompression in addition to the strain due to compression and swelling..
13. Hirotada Fujiwara, Hiroaki Ono, Shin Nishimura, Degradation behavior of acrylonitrile butadiene rubber after cyclic high-pressure hydrogen exposure, Elsevier, 40, 4, 2025-2034, 2015.01, The deterioration of rubber composites filled with different types of fillers was analyzed to determine the influence of cyclic high-pressure hydrogen exposure. The mechanical properties of acrylonitrile butadiene rubber (NBR) unfilled and filled with carbon black or silica were evaluated. The storage modulus of the silica-filled NBR decreased in the rubbery state as the number of exposures increased, while those of the unfilled and carbon black-filled NBR did not change. Changes in the chemical structure such as hydrogenation or chain scission were not detected in the solid state NMR spectra of the exposed composites. However, deterioration of the filler–gel structure formed at the interface of the filler and polymer was observed in the silica-filled NBR. Fracture of this filler–gel structure occurred due to fatigue in the silica-filled NBR resulting from a reduction of the elastic storage modulus caused by cyclic high-pressure hydrogen exposure..
14. Junichiro Yamabe, Shin Nishimura, Crack Growth Behavior of Sealing Rubber under Static Strain in High-Pressure Hydrogen Gas, 日本機械学会, 5, 12, 690-701, 2011.12, In order to enable hydrogen society in the near future, it is necessary to clarify the influence of hydrogen on the mechanical, physical and chemical properties of the materials used for hydrogen energy systems. In the case of rubbers, there is a particular danger of mechanical damage resulting from internal fracture, which occurs when high-pressure hydrogen gas is suddenly decompressed. Although our previous studies focused on fracture and deformation caused by high-pressure hydrogen decompression, the fracture and deformation of rubber materials under pressurization have not been studied. From this viewpoint, static crack growth tests of an unfilled sulfur-crosslinked ethylene-propylene-diene monomer (EPDM) rubber were conducted in hydrogen gas at 10 MPa and room temperature (around 25°C) by using a high-pressure hydrogen vessel with glass viewing ports. Deformation of the rubber during pressurization was hardly seen at ≤ 10 MPa, although hydrostatic pressure was applied and hydrogen gas penetrated into the rubber. The static crack growth rate for hydrogen gas at 10 MPa was consistent with that in air (0.1 MPa). A lot of facets with about 100 µm in size caused by the initiation and successive coalescence of secondary cracks ahead of the main crack were observed on the fracture surface of the specimens tested in air and hydrogen gas at 10 MPa, and these fracture surfaces showed a similar aspect. From these results, it was clarified that a hydrogen environment at ≤ 10 MPa did not influence the static crack growth characteristic of the rubber..
15. Hiroaki Ono, Hirotada Fujiwara, Shin Nishimura, Nanoscale heterogeneous structure of polyacrylonitrile-co-butadiene with different molecular mobilities analyzed by spin–spin relaxation time, 高分子学会, 45, 1027-1032, 2013.04, To identify components with different spin–spin relaxation times, T2, in the solid-echo pulse proton nuclear magnetic resonance (1H-NMR) spectra of crude acrylonitrile (AN)–butadiene rubbers (NBRs) with five different AN contents, we tried to understand the inhomogeneity in the crude NBRs in terms of their microstructures and molecular mobilities. The results of small-angle X-ray scattering, differential scanning calorimetry and dynamic mechanical analysis showed that crude NBRs have a single-phase and homogeneous morphology on the nanoscale. The microstructure of the crude NBRs shows alternately copolymerized AN–butadiene (BU) and BU block sequences, as indicated by 1H-NMR spectra. The T2 of the crude NBRs revealed three components with different molecular mobilities, even in homogeneous samples. The content of the highest-mobility component with T2l is negligible. Judging from the AN content dependence of the 1H ratio of these components, the low-mobility component with T2s and high-mobility component with T2m were assigned to the alternately copolymerized AN–BU sequences and BU block sequences, respectively..
16. Shin Nishimura, Hirotada Fujiwara, Detection of hydrogen dissolved in acrylonitrile butadiene rubber by 1H nuclear magnetic resonance, Elsevier, 522, 43-45, 2012.01, Rubber materials, which are used for hydrogen gas seal, can dissolve hydrogen during exposure in high-pressure hydrogen gas. Dissolved hydrogen molecules were detected by solid state 1H NMR of the unfilled vulcanized acrylonitrile butadiene rubber. Two signals were observed at 4.5 ppm and 4.8 ppm, which were assignable to dissolved hydrogen, in the 1H NMR spectrum of NBR after being exposed 100 MPa hydrogen gas for 24 h at room temperature. These signals were shifted from that of gaseous hydrogen molecules. Assignment of the signals was confirmed by quantitative estimation of dissolved hydrogen and peak area of the signals..
17. Hirotada Fujiwara, Junichiro Yamabe, Shin Nishimura, Evaluation of the change in chemical structure of acrylonitrile butadiene rubber after high-pressure hydrogen exposure, Elsevier, 37, 10, 8729-8733, 2013.05, The influence of high-pressure hydrogen on the chemical structure of organic materials is essential for designing suitable materials for the safe and efficient use of hydrogen. In this paper, we clarify the cause and mechanism of “explosive failure by decompression” (XDF) in rubber used under high-pressure hydrogen circumstances, and the chemical structure of acrylonitrile butadiene rubber (NBR), which is commonly used for O-rings, was analyzed after exposure to hydrogen at 100 MPa. Solid-state nuclear magnetic resonance (NMR) and liquid-phase NMR for 1H and 13C, as well as infrared and Raman spectroscopy, were employed for the evaluation. The results show no evidence of structural changes in NBR such as hydrogenation of the olefinic bonds in butadiene or of the cyano groups in acrylonitrile..
18. Atsushi Koga, Kenichi Uchida, Junichiro Yamabe, Shin Nishimura, Evaluation on High-Pressure Hydrogen Decompression Failure of Rubber O-ring Using Design of Experiments, 2, 4, 123-129, 2011.04, The rubber O-rings used in high-pressure hydrogen environment sometimes suffer from the decrease in durability due to decompression failure. A high-pressure durability tester, which enables rubber O-rings to expose repeatedly high-pressure hydrogen gas at arbitrary test conditions, was employed, and then sensitive factors for the durability of the O-rings were evaluated by using a L18 orthogonal array. Of lower-limit pressure, upper-limit pressure, material, temperature, O-ring filling ratio, holding time at lower limit, holding time at upper limit, and decompression time, it was clarified that the material, temperature, O-ring filling ratio, and decompression time were sensitive factors..
19. Junichiro Yamabe, Atsushi Koga, Shin Nishimura, Failure behavior of rubber O-ring under cyclic exposure to high-pressure hydrogen gas, Elsevier, 35, 193-205, 2013.12, This paper presents the effects of hydrogen pressure, ambient temperature and pressure cycle pattern on fracture behavior of O-rings moulded from a peroxide-crosslinked EPDM rubber with white reinforcing filler under cyclic exposure to high-pressure hydrogen gas. By using a developed durability tester which enables the O-rings to expose cyclically high-pressure hydrogen gas, pressure cycle tests were performed at hydrogen pressures ranging from 10 to 70 MPa and ambient temperatures ranging from 30 to 100 °C under two pressure cycle patterns (test frequencies). The cyclic hydrogen exposure caused cracks in the O-rings, and their crack damage became more serious with an increase in the hydrogen pressure and the ambient temperature. The serious crack damage under high temperature is believed to be due to degradation of mechanical properties with increasing ambient temperature. At a hydrogen pressure of 10 MPa, cracks (blisters) caused by bubbles formed from supersaturated hydrogen molecules after decompression were observed. At a hydrogen pressure of 35 MPa or more, a large volume increase of the O-rings was observed by swelling; then, its volume increase induced extrusion fracture of the O-rings in addition to blister fracture. The crack damage also became more serious with a decrease in test frequency. The effect of the test frequency on the crack damage of the O-rings is presumed to be attributed to time-dependent crack growth behavior of the EPDM rubber..
20. Shin Nishimura, Hirotada Fujiwara, Junichiro Yamabe, Determination of chemical shift of gas-phase hydrogen molecules by 1H nuclear magnetic resonance, 498, 1-3, 42-44, 2010.01, The precise and detailed chemical shift of gas-phase hydrogen molecules was successfully determined by 1H nuclear magnetic resonance (NMR), avoiding the intervention of neighboring molecules such as in hydrogen occluding materials (free hydrogen). The measurement was conducted with double walled NMR sample tube taking into consideration the change of hydrogen pressure. The inner tube was filled with standard substance (DHO in D2O at 4.8 ppm). The chemical shift of free hydrogen molecules was determined to be 7.40 ± 0.01 ppm at 0.18 MPa, 25 °C, which is different from previously reported chemical shifts of hydrogen gas with intervention of neighboring molecules..
21. Junichiro Yamabe, Takashi Matsumoto, Shin Nishimura, Application of acoustic emission method to detection of internal fracture of sealing rubber material by high-pressure hydrogen decompression, Elsevier, 30, 1, 76-85, 2011.01, An acoustic emission (AE) method was used to detect internal fracture of sealing rubber material by high pressure hydrogen decompression. According to preliminary results, AE signals were hardly detected during the tensile test in air, but many signals were detected during the static crack growth test in air. AE measurement of hydrogen exposed specimens was also conducted. With the increase in number and size of internal cracks generated due to high pressure hydrogen decompression, the AE event count and amplitude also increased. In addition, AE signals were generated from the specimen exposed to hydrogen gas at 0.7 MPa, although no cracks were initiated. It is inferred that these AE signals were generated due to bubbles, which are mechanically reversible cavities formed by dissolved hydrogen molecules after decompression..
22. Shin Nishimura, Junichiro Yamabe, Nanoscale fracture analysis by atomic force microscopy of EPDM rubber due to high-pressure hydrogen decompression, Springer, 46, 7, 2300-2307, 2010.11, The relationship between internal fracture due to high-pressure hydrogen decompression and microstructure of ethylene–propylene–diene–methylene linkage (EPDM) rubber was investigated by atomic force microscopy (AFM). Nanoscale line-like structures were observed in an unexposed specimen, and their number and length increased with hydrogen exposure. This result implies that the structure of the unfilled EPDM rubber is inhomogeneous at a nanoscale level, and nanoscale fracture caused by the bubbles that are formed from dissolved hydrogen molecules after decompression occurs even though no cracks are observed by optical microscopy. Since this nanoscale fracture occurred at a threshold tearing energy lower than that obtained from static crack growth tests of macroscopic cracks (Ts,th), it is supposed that nanoscale structures that fractured at a lower threshold tearing energy (Tnano,th) than Ts,th existed in the rubber matrix, and these low-strength structures were the origin of the nanoscale fracture. From these results, it is inferred that the fracture of the EPDM rubber by high-pressure hydrogen decompression consists of two fracture processes that differ in terms of size scale, i.e., bubble formation at a submicrometer level and crack initiation at a micrometer level. The hydrogen pressures at bubble formation and crack initiation were also estimated by assuming two threshold tearing energies, Tnano,th for the bubble formation and Ts,th for the crack initiation, in terms of fracture mechanics. As a result, the experimental hydrogen pressures were successfully estimated..
23. Fracture Analysis of Rubber Sealing Meterial for High Pressure Hydrogen Vessel .
24. Fracture Analysis of Rubber Sealing Meterial for High Pressure Hydrogen Vessel .
25. Atsushi Koga, Junichi Nakayama, and Hideyuki Tokumitsu, Masaya Otsuka, Junichiro Yamabe, and Shin Nishimura, A Study on Blister Damages of Rubber O-ring by High Pressure Hydrogen Durability Tester, Proceedings of the 2008 International Hydrogen Conference, 2009, pp. 307-404, 2009.08.
26. Junichiro Yamabe, Masatoshi Nakao, Hirotada Fujiwara, Shin Nishimura, Blister Fracture of Rubbers for O-ring Exposed to High Pressure Hydrogen Gas Effects of Hydrogen on Materials, Proceedings of the 2008 International Hydrogen Conference, 2009, pp. 389–396, 2009.08.
27. Structural Analysis of Vulcanized NBR Using Swollen State, Solution State and Solid State 1H, 13C NMR Spectroscopy .
28. Estimation of Hydrogen Pressure at Blister Initiation of EPDM Composite Exposed to High Pressure Hydrogen Gas.
29. Junichiro Yamabe, Shin Nishimura, and Atsushi Koga, A Study on Sealing Behavior of Rubber O-ring in High Pressure Hydrogen Gas, SAE paper, 2009–01–0999, 2009.04.
30. Junichiro Yamabe and Shin Nishimura, Influence of fillers on hydrogen penetration properties and blister fracture of rubber composites for O-ring exposed to high-pressure hydrogen gas, International Journal of Hydrogen Energy, 34(4) 1977-1989, 2009.01.