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Hideo NAKAJIMA, Kazuya HAMADA, Katsutoshi TAKANO, Yusuke KUDO, Kiyoshi ...
Article type: Article
Session ID: 638
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Japan Atomic Energy Research Institute (JAERI) has developed large superconducting magnets and cryogenic structural materials to construct the International Thermonuclear Experimental Reactor (ITER). Material rules in structural design code like ASME Boiler and Pressure Vessel Code is required to construct the ITER or commercial fusion facilities in rational way. From this point of view, it is important to predict the strength at cryogenic temperatures of nitrogen strengthened austenitic stainless steels based on the strength at room temperature. Tensile tests were performed at room temperature, in liquid nitrogen (77K), in liquid helium (4K), and in gaseous helium (about every 50 degrees between 7K and 227K). Empirical prediction quadratic curves in taking account of carbon and nitrogen (C+N) effect on strength were established for JJ1 and 316LN based on the test results. It is expected that cryogenic strength of commercial base materials can be predicted by using these curves.
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Arata NISHIMURA
Article type: Article
Session ID: 639
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The most important behavior of SUS316 in a cryogenic service is serrated deformation after yielding. So-called serration generally happens under stroke rate or cross head speed control during a tensile test. The serration is caused by the adiabatic deformation due to very low thermal conductivity at cryogenic temperature. The large superconducting magnet system in the fusion device requires stiff structure to support the huge electro-magnetic force, and SUS 316 is a common structural material for cryogenic support structure because of non-magnetism, high-toughness, and good machinability and weldability. Since the electro-magnetic force would not decrease so quickly, the serrated deformation has a potential to cause the continuous heat generation and crack propagation which leads to catastrophic failure of the structure. In this report, some key issues on application of SUS316 stainless steel to the cryogenic support structure of a large superconducting magnet system will be presented and pillar-wall structure for the support structure will be discussed conceptually.
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Katsumi HORIGUCHI, Yasuhide SHINDO, Yoko YAMAGUCHI
Article type: Article
Session ID: 640
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper examines the effect of magnetic field on the fracture properties of austenitic stainless steels at liquid helium temperature (4 K). Small punch tests were performed on cold-rolled 304 and 316 austenitic stainless steels. Previously proposed correlation for small punch and elastic-plastic fracture toughness test methods was applied to predict a small punch test-based fracture toughness from equivalent fracture strain.
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Tatsushi NAKAMOTO, Hirokatsu OHHATA, Toru OGITSU, Nobuhiro KIMURA, Yas ...
Article type: Article
Session ID: 641
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Radiation resistance with respect to mechanical properties of organic materials used in the superconducting magnets for the 50 GeV-750 kW proton beam line for the J-PARC neutrino experiment was studied. Specimens cooled at liquid nitrogen temperature of 77 K were irradiated by γ-rays from ^<60>Co up to 10 MGy. The flexural strength of glass-fiber reinforced plastics (GFRP) and the tear strength of polyimide films were evaluated. It was verified that the organic materials used in the superconducting magnet have a sufficient radiation resistance and degradation of the mechanical properties after 10 years operation was estimated to be negligible.
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Akira IDESAKI, Norio MORISHITA, Tomihiro KAMIYA, Tatsushi NAKAMOTO, To ...
Article type: Article
Session ID: 642
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Polyimide films and glass fiber reinforced plastics (GFRPs) are used as insulating material or structural material of superconducting magnets in a neutrino beam line of the Japan Proton Accelerator Research Complex (J-PARC). It is indispensable to evaluate radiation resistance of these materials, because they are irradiated at a high dose of 30kGy/year at low temperature of 4K. In this work, gas evolution from the polyimide films and GFRPs by γ-ray irradiation at 77K was investigated. It was found that the main component of the evolved gas is hydrogen. The amount of the hydrogen evlved from the superconducting magnet system used in the neutrino beam line was estimated to be 0.37mol/year (0.01L/year as the volume of liquid hydrogen).
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Makoto Teshigawara, Joeichi Kusano, Norio Morishita, Takashi Kato, Yuj ...
Article type: Article
Session ID: 643
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Japanese intense spallation neutron source (JSNS) driven by 3 GeV protons with power of 1 MW is constructed under joint project of Japan Atomic Energy Research Institute and High Energy Accelerator Research Organization. Super insulator is adopted to reduce heat load in hydrogen transfer line of JSNS. We performed irradiation test of super insulator (SI) using ^<60>Co gamma ray to evaluate the irradiation effect. Two kinds of super insulator (polyimide and polyester) coated both side by aluminum with thickness of 5×10^<-8>m were irradiated. After gamma ray irradiation, we performed tensile test and gas analysis of super insulator. Polyester based SI became brittle at about 10 MGy, on the other hand, polyimide based SI did not loss ductility even over 60 MGy. Polyester based SI generated about 30 times higher gas yield than that of polyimide based SI. However, it was very small amount of gas yield even polyester based SI. Gas analysis method by Q-mass was very effective to identify the unknown gas (i.e. H_2O) to compare with gas chromatography.
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Toshio NOGUCHI, Tsutomu EZUMI
Article type: Article
Session ID: 644
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The polycarbonate of the polymeric material was assumed to be test material in this research, and a dynamic three-point bending was done under the low temperature environment. The low temperature environment used and reproduced the liquid nitrogen. The crack of notch was inserted in the test specimen, and it experimented. The experiment used the simple high speed photography and the caustics method. The analytical result is used. It took a picture of the caustics image and the dynamic stress intensity factor was calculated. And this experiment was evaluated from the requested dynamic stress intensity factor. As a result, the dynamic fracture behavior of the polycarbonate with the low temperature environment effect in the dynamic load was examined. As a result, some tendencies were obtained in this experiment.
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Akihiro INAMOTO, Yasuhide SHINDO, Susumu KUMAGAI
Article type: Article
Session ID: 645
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper describes an experimental and analytical study on the cryogenic fatigue behavior of GFRP (glass fiber reinforced polymer) woven laminates under Mode I loading. Fatigue crack growth rate tests were performed using CT(compact tension) specimens at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). The fracture surfaces were also examined by SEM(scanning electron microscopy) to correlate with the fatigue properties. A finite element method coupled with fatigue damage was adopted for the extensional analysis. The effects of temperature and loading condition on the fatigue crack growth rates are examined.
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Yutaka YAMADA, Kazumune KATAGIRI, Akifumu IWAMOTO, Hiroaki KUMAKURA, K ...
Article type: Article
Session ID: 646
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Effect of metal powder addition on the transport current and strain performance of ex-situ processed MgB_2 tapes with Ni sheath has been studied. The addition of low melting point metal powder, e.g. In and Sn, produces an appreciable increase in the Jc of MgB_2 core. The 10vol% In addition enhances Jc by a factor of 6-7 after the combination of the rolling and the annealing at 200℃. The 10vol% Sn addition enhances Jc by a factor of 〜3. Both of In and Sn metal impregnate into gaps among MgB_2 grains improving the linkage of the grains. The current may transfer through the impregnated metal by the proximity effect. Furthermore, the In and Sn addition improves appreciably the strain tolerance of the MgB_2 tapes.
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Kazuya TAKAHATA, Hitoshi TAMURA
Article type: Article
Session ID: 647
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Temperature rise in a quenching cable-in-conduit conductor is strongly affected by thermal contact conductance between the cable and conduit. To evaluate this temperature rise, contact conductance is directly measured under compressive pressure at room temperature by using a small copper bock with heaters. The results show that the contact conductance is affected by surface pressure and the conductivity of ambient gas. Therefore, to evaluate temperature rise in a quenching conductor, it is necessary to take into account conductance under a surface pressure equivalent to an electromagnetic force. In addition, the conductivity of ambient gas must be considered when a surface pressure is low.
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Kenji UMEKAWA, Toru ITO, Yuta FUKASAWA, Tomoaki TAKAO, Hideki TANAKA, ...
Article type: Article
Session ID: 648
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Recently, high field superconducting magnet is being desired with improving superconducting wires. On the other hand, a large electromagnetic force is applied to the winding when the magnet is operated, and the characteristic degradation caused by the mechanical stress of the winding cannot be disregarded. In this study, we have investigated the degradation and the reversibility of critical currents (I_c) due to transversal compressive stress at 4.2 K and 14 T. Few works on degradation of superconducting wires against transversal compressive stress have been reported. Ta-reinforced Nb_3Sn superconducoing wire was used as a sample. According to the experimental results, a large recovery of I_c appeared clearly by removing its load after the I_c degradation due to the transversal-compressive force was noticed, and the reversibility was seen.
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Hitoshi TAMURA, Toshiyuki MITO, Yutaka YAMADA
Article type: Article
Session ID: 649
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Current leads using HTS material have been developed rapidly for large scale superconducting magnet systems. NIFS and Tokai University have been investigating characteristics of Bi2212 tubular bulk which was prepared by a diffusion process. 8 kA of the maximum transfer current was achieved at 4 K with the bulk size of 38 mm/30 mm in outer/inner diameters and 200 mm in length, respectively. HTS bulk should be reinforced so that a mechanical strength was improved. Alumina fiber with epoxy resin seemed to be good for the reinforcement for the Bi2212 HTS. Bi2212 HTS prepared by diffusion process has a potential for flexible design since superconducting layer can be reacted on the surface of any shapes of substrate. In this paper, a design of a current lead using this type of Bi2212 tubular bulk was studied with conventional heat exchanger part and low-Tc superconducting bus line considering a shape of HTS part.
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Takashi HIGUCHI, Naoki SEKINE, Satoshi TADA, Yuta FURUMURA, Tomoaki TA ...
Article type: Article
Session ID: 650
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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ZFRP's bobbins that consist of particular fiber's winding tension expand to the direction of the circumference at the time of cooling. The superconducting coils' operation temperature is cryogenic temperature. Consequently, when ZFRP's bobbins are used of superconducting coil's bobbins, those bobbins expand to the direction of the circumference. Because the expansion constrains superconducting wire's mechanical disturbance by electromagnetic force, the quench current of superconducting coil's wire is stabilized, In this paper, we measured the quench current of superconducting coil using ZFRP's bobbins and GFRP's bobbins which were the general material used for cryogenic temperature. And the effect of improvement of superconducting coil's stability by ZFRP's bobbins was investigated by weighing those measurement results of each coil's quench current.
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Atsuhiko YAMANAKA, Hiroshi HIRAHATA, Kenji HOSOYAMA
Article type: Article
Session ID: 651
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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High field superconducting solenoid magnets sometimes quench by wire motion by electro-magnetic force. High strength polyethylene fiber reinforced plastic (DFRP) has a negative thermal expansivity, low frictional coefficients, high thermal conductivity, and high electric resistance. In the case of a superconducting coil fabricated with a DFRP bobbin, it is expected that wire motions in high field are decreased by expansion of the coil bobbin and that training becomes effective by low frictional coefficients on the surface of the bobbin. In this work, tap voltage between both ends of the coils fabricated with DFRP bobbin and stainless steel (SUS) bobbin were measured with increasing current. The coil using SUS bobbin showed many sharp peaks in tap voltage induced by quick wire motions and those using DFRP bobbin showed only a few small peaks. By the repetition of excitation of coil using SUS bobbin, some peaks vanish. In the case of DFRP bobbin, all peaks or zigzag curves vanish at 2^<nd> excitation. It is considered that conductor moved to stable positions at the 1^<st> excitation.
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Masayuki AKITA, Keiro TOKAJI
Article type: Article
Session ID: 701
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper describes the notch fatigue behaviour of a 316 stainless steel hardened by carburizing. Fatigue tests were performed using cantilever-type rotary bending fatigue testing machines in laboratory air at ambient temperature. Notched specimens with three different stress concentration factors (α=2.08, 3.55 and 6.50) were evaluated. All carburized notched specimens showed higher fatigue strength than the untreated ones and the increase in fatigue strength decreased with increasing stress concentration factor. Fatigue cracks initiated at the surface of the notch root at higher applied stresses, while subsurface at lower applied stresses in the carburized notched specimens with α=2.08 and 3.55, but surface regardless of stress level in the carburized notched specimens with α=6.50. Both untreated and carburized materials indicated a significantly low notch sensitivity, but the notch sensitivity was enhanced slightly by carburizing.
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Hidetaka NISHIDA
Article type: Article
Session ID: 702
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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We developed The Total Residual Life Assessment Method, which can use coarse HAZ, Coarse Weld Metal, Fine HAZ and Fine Weld Metal at Welding Joints. Its constructed by Damage Mechanism at Welding joints that I inks between Voids at last stage destruction. Using at Thermal Power Stations this method, We can use their for long time, and contribute to the reduction of maintenance costs.
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Chihiro MATSUSHIMA, Mitsuo NOTOMI, Haruo Shimosaka, Hirokazu SHIMODA, ...
Article type: Article
Session ID: 703
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The low cycle fatigue of rubber material for the component of laminating rubber of seismic isolation is studied using cylinder specimen. The specimen is laminated cylinder shape and the rubber disk was bonded to the metal disk at both circular planes by vulcanization. It is applies shear loads during earthquake, however, when the rubber is applied tensile load in tall structure which aspect ratio is large, void nucleation may have occurred inside rubber. It is possible affect shear properties due to void. Low cycle fatigue examination to rubber disk with voids is performed. From the experiments, the rate of reduction of the maximum load of each cycle of rubber without void is larger than that of with void.
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Hiroshi KUGIMARU, Noriyuki HISAMORI, Kenichi TAKAI, Yukito HAGIHARA
Article type: Article
Session ID: 704
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Compact tension specimen of hydroxyapatite ceramics (HAp) was prepared and cyclic fatigue test was performed in air, deionized water and simulated body fluid (SBF) to investigate the fatigue property of HAp. The environment where fatigue limit stress (N_f=10^7) was the lowest was deionized water environment. Subsequently was SBF environment, air environment. Fatigue fracture was observed with scanning electron microscope (SEM) to clarify this mechanism. As a result, as for the fatigue fracture configuration, fracture in transgranular was observed with high stress condition. On the other hand, intergranular fracture was observed with low stress condition. That is to say, it was stress dependence type with a short life time of case, and it was environment dependence type with a long life time of case. In addition, two fatigue fracture configuration was observed to SBF environment when soak was done for a long time. The fracture surface which intergranular fracture and apatite precipitated surface was observed. By the time that apatite precipitated, improvement of fracture stress was shown in a S-N curve. Therefore, it was shown that fatigue limit stress had higher on SBF environment than deionized water environment.
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Kazuhiro ODA, Dai-heng CHEN, Nao-Aki NODA, Masanao HASHIMOTO
Article type: Article
Session ID: 705
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In this study, the inverse problem of the three-dimensional semi-elliptical surface crack in a finite plate is treated. The unknown parameters, crack location, crack dimensions and loading stress, are determined by the gradient search based on the strain information around the crack. In order to get the solution with short CPU time, the direct analysis of strain is performed by using the cracked model of semi-infinite body instead of the finite plate model. In this approximate calculation, the crack location and loading stress are obtained accurately when the plate sizes are widely changed. To obtain the accurate crack size, the effective position of measuring point for strain is investigated.
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Hiroyoshi Takeda, Takao Inukai
Article type: Article
Session ID: 706
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The rotor and casing parts of steam turbines exposed high temperature and high stress for extensive periods are deteriorated by correlation between creep and fatigue. Microcrack initiates and coalesce with the main crack under creep condition. In order to apply to steam turbine components for creep crack propagation evaluation, the most suitable parameter must be selected for creep crack propagation evaluations of degrade CrMoV. Therefore, in this study, the experimental characteristics of the creep crack propagation behaviour has been investigated by both FEM analysis and creep burst test of cylinder model for the aged CrMoV rotor steel. As a result, comparisons of predicted the crack length to crack propagation time being used by parameter J* and Q* with experimental results show good agreement. In the study, though parameter K is too conservative, both parameters J* and Q* are available to predict of the creep crack propagation behaviour for aged CrMoV steel for practical use.
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Kazuhiro ODA
Article type: Article
Session ID: 707
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The proportional method, based on the stress or displacement near the crack tip, is one of the most useful methods to easily obtain the accurate value of stress or displacement near the crack tip, is one of the most useful methods to easily obtain the accurate value of stress intensity factor. In this study, the method is applied to the analysis of stress intensity factor for an interface crack in bonded materials. In the interface crack problem, ratio of stress intensity between the treated problem and reference problem is not constant because of oscillatory stress singularity. However, relation between energy release rate K_i and distance r from crack tip becomes constant within the wide range of r/a. Then, the energy release rate can be easily calculated by using the proportional method.
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Mitsuhiro MUTO, Masamitsu NONAKA, Kyoji HOMMA, Sayuri MURAKAMI, Takuji ...
Article type: Article
Session ID: 708
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper describes non-destructive evaluation by means of the ultrasonic inspection of the frictional welding in cast iron using a neural network. Specimens altering the frictional welding condition were carried out to the inspection. Feature extracted waveforms in terms of the reflected echo from frictional welding location were learned and classified by the neural network. It was concluded that discriminations of frictional welding condition were possible by the proposed approach.
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Tohru TAKAMATSU, Yoshio MIYOSHI, Hirotaka TANABE, Muneyoshi SEGAWA
Article type: Article
Session ID: 709
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The purpose of this study is to confirm the validity for evaluation of fracture toughness on the surface layer of ceramics by the sphere indentation test. The sphere indentation tests using HIP sintered Si_3N_4 specimens were carried out to obtain the ring crack initiation load for various indentation diameters 2R. On the assumption that a ring crack is induced from microcracks on the surface layer, the crack length c_i of microcracks were estimated from the experimental results in terms of a stress intensity factor K_I for a surface crack under the sphere-plate contact loading condition. The ring crack initiation condition was assumed as K_I.>K_<th> where K_<th> is the threshold fracture toughness and was assumed as 5.3 MPa・m^<1/2>. The mean value of c_i ws 8-9 μm and was almost independent of 2R in the case of large 2R.
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Makoto OHASHI
Article type: Article
Session ID: 710
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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A statistical analysis of ductile fracture surface was performed on JIS FCD400 spheroidal graphite cast iron with feritic matrix. Both the notched specimens with different notch acuity and the unnotched specimens were employed to obtain a wide range of stress triaxiality. All specimens were loaded to break under tensile loading at room temperature. The maximum nominal stress to break the specimen increased slightly with stress triaxiality, compared with structural steels. However, the extreme value probability of the maximum dimple size in a given unit area showed a clear dependence on the maximum nominal stress. In addition, the lateral growth factor of the maximum dimple against the graphite size increased due to an increased level of transverse stress with stress triaxiality. Thus, the extreme value analysis of the maximum dimple size and the lateral growth factor of the maximum dimple should be expected for providing a positive and quantitative information regarding the fracture behavior of the ductile cast iron.
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Hiroyuki AKEBONO, Hidehiko MAKIDA, Masahiro FUKUMOTO, Masao SHIMIZU
Article type: Article
Session ID: 711
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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To investigate the effects of the surface roughness of substrate on fatigue properties of a thermally sprayed specimen, three types of substrates with different surface roughness were prepared. After thermal spraying, two types of post heat treatments (fusing) were performed by an induction heating system and a vacuum furnace: Then rotational bending fatigue tests were carried out. Two types of fatigue fracture mechanisms were observed; in the former was an interface delamination mode and in the latter was a coating fracture mode. In the case of the interface delamination mode, substrate roughness strongly affected the fatigue strength of the sprayed specimen; the rougher the substrate surface, the higher the fatigue strength. This is because rougher substrate leads to higher adhesive strength between the coatings and the substrate. In the case of the specimen failure in the coating fracture mode, the surface roughness of the substrate had no remarkable effect on the fatigue strength of the sprayed specimen.
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Hisanori NISHIMORI, Hiroyuki AKEBONO, Masao SHIMIZU
Article type: Article
Session ID: 712
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to clarify the effects of the defect on the fatigue properties of thermally sprayed steel with special focus on the defect size, rotating bending fatigue tests and measurements of the defect size were performed of specimens with the long heating period and short one in the fusing process by using a vacuum furnace. The fatigue strength and the defect size of long heating period specimens were lower and smaller than that of short one. Additionally with the long heating period specimens, rotating bending fatigue tests and measurements of the defect size were carried out about three types of coating thickness. The defect size strongly affects the fatigue properties; the thinner the coating, the smaller the defect size and the higher the fatigue strength. It can be considered that the defect size in coating is one of the most important factors which affect the fatigue properties of the thermally sprayed steel.
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Nobumitsu MASUDA, Hiroyuki AKEBONO, Masao SHIMIZU
Article type: Article
Session ID: 713
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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To clarify the relationship between fatigue properties and fusing methods, using vacuum furnace and induction heating system, rotational bending fatigue tests were performed on a medium carbon-steel(S35G) coated with thermally sprayed Ni-based self-fluxing alloy, under the condition of a fixed fusing temperature of 1010℃. As a result of these fatigue tests, the specimens fused by vacuum furnace (fusing time:30minutes to 10hours) did not show any delamination under cyclic loading. And a gradual reduction in fatigue strength was observed with the increase of fusing time. This is caused by the formation of inhomogenety in the coating layer with the increase of fusing time. On the contrary, the specimens fused by induction heating system(fusing time:200 seconds to 4hours)showed nearly the same fatigue strength as substrate did, because every specimen of these series showed delamination between substrate and coating layer. But formation of inhomogenety in the coating layer did not observed as specimens fused by vacuum furnace.
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Yoshiko SHINHARA, Taro TOKUDA, Rongguang WANG, Mtuo KIDO
Article type: Article
Session ID: 714
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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To examine the relation between the surface distribution and delamination of thermal sprayed materials, the deformation behavior of SUS304 under increasing load was investigated using the ESPI method. Nect, alumina thermal sprayed SUS304 steel material was investigated by the same method. Then, the results were compared. It is thought that not only the generation of delamination but also the strain hardening of substrate is included in the surface strain when the delamination is found in coating interface. The delamination at the interface between substrate and coating was caused by smaller strain at high temperatures compared with low temperatures, under repeated stress, the surface strain of thermally sprayed coating at the delamination was generated hardly changed, compared with it of substrate.
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Kouji MUKAI, Tetsuya HIRANO, Toshikazu HATAKENAKA, Yoshio HARADA, Mits ...
Article type: Article
Session ID: 715
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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WC thermally sprayed coating is widely used in industry for its high wear resistance properties. Unfortunately, WC-Co coatings are plagued by low corrosion resistance in aqueous solutions. In this study, first, two kinds of coatings (WC-12Co & WC-10Co-4Cr) were deposited on SS400 steel by high-velocity flame spraying. Second, fracture behavior was investigated through corrosion fatigue testing in a Na_2SO_4 aqueous solution (R=0∫=14Hz). Improvement of corrosion fatigue was also examined. COrrosion fatigue fractures were found to associated with corrosion pits formed at the interface between the coating and the substrate. Thermal spraying of Al-Zn as an undercoat between the WC thermally sprayed coatings and the substrate appears to be an efective method for improving corrosion fatigue strength.
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Takashi NAKAMURA, Toru NOGUCHI, Noritaka HORIKAWA, Yukiko OGIUCHI
Article type: Article
Session ID: 716
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Compressive fatigue tests and static compression tests were carried out ontwo types of giant magnetostrictive materials with different porosities. The observation of crack initiations and the classification of fragments after fractures clarified a mechanism of fatigue failure. As a result, the following were obtained: (1) Both the static and fatigue strengths showed a clear dependence on porosity. (2) The static strength σ_c was well expressed by an equation "σ_c=σ_0exp(-4_p)" with the porosity p and the strength of a pore-free material σ_0. (3) The S-N plots standardized by σ_c of the former equation distributed in a narrow band regardless of different porosities. This means that the compressive fatigue strength can be evaluated by using the porosity. (4) Many small intergranular cracks initiated from pores were observed in the fatigued test peice. The fatigue fracture results from the chain coalescence of these cracks.
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Katsuaki FURUKAWA, Yasuo OCHI
Article type: Article
Session ID: 717
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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It is well known that the initial crack growth rate is very high, when notched specimen is loaded by cyclic compressive stress. This reason is estiamted to be a occurrence of crack opening by the existence of a remained tensile stress. Therefore the influence of compressive stress for the crack opening phenomena and for the non-propagating crack was investigated. Used material was Alminum alloy and specimen figure was CT specimen. On the condition of three kinds of stress ratio R (R=0, R=1 and only compressive stress) crack propagation tests were performed. Even when absolute maximum values are same and crack dose not propagate by only tensile stress, there exists non-propagating crack on the condition of R=-1 and only compressive stress. Therefore it is found that non-propagating crack has a close relation to compressive stress.
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Hiroshi MATSUNO, Yoshihiko MUKAI
Article type: Article
Session ID: 718
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Based on an equivalent stress ratio R_<EQ> which was previously proposed as a parameter for correspondence between the cyclic stress conditions of notched and unnotched specimens, the fatigue strength concerning axial, bending, torsional and their combination loading is rearranged on the diagram where the abscissa indicates R_<EQ> and the ordinate indicates the notch-root-concentrated stress range (Δσ_<NR.w1>). As a result, it is found that the diagram is consistent in spite of differences of stress concentration factors and loading types. Moreover, the notch sensitivity of material is discussed on the basis of the diagrams.
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Kenta YAMAGIWA, Masahiro TAKANASHI, Satoshi IZUMI, Shinsuke SAKAI
Article type: Article
Session ID: 719
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Fractal analysis has been widely used to characterize the fracture surface. It has been recognized that the local Hurst exponent, which is based on the concept of self-affine fractal, is useful to detect the transition point of fracture surface. For the calculation of the local Hurst exponent, a high resolution profile is needed. To measure the profile, however, much time and effort are needed. Therefore, it is difficult to calculate all profiles of fracture surface and evaluate the feature of fracture surface in detail. In this study, a new method to calculate the two-dimensional local Hurst exponent is proposed. It is realized to evaluate the feature of fracture surface by using the local Hurst exponent. To investigate the validity of the two-dimensional local Hurst exponent, the calculation was applied to the gray-scaled images in which the stretched zone was observed and the width of stretched zone(SZW_c) was measured. Consequently, SZW_c calculated by the two-dimensional local Hurst exponent and detected by the human observation have the good agreement. Therefore, it was found that the two-dimensional local Hurst exponent is useful to detect the transition point of fracture surface.
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Mitsutoshi KAMAKURA, Keiro TOKAJI, Hideaki SIBATA, Norikatsu BEKKU
Article type: Article
Session ID: 720
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Extrusion was applied to AZ61A and AZ31B magnesium alloy billets with three different controlled conditions. As a result, it was found that the control of extrusion condition was one of the most effective approaches to attain grain refinement, because grain refinement took place in both alloys, where grain size decreased with decreasing outlet temperature, particularly remarkable in AZ31B for which the average grain size of approximately 2μm was obtained. Subsequently, roatating bending fatigue tests were performed using smooth specimens of the extruded materials in laboratory air at ambient temperature. In AZ61A, fatigue strength was not affected significantly by extrusion condition, while in AZ31B, it increased with decreasing outlet temeprature, i.e. grain size. The grain size dependence of fatigue strength could be described with the Hall-Petch relation in AZ31B, but not in AZ61A.
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Kiyotaka MASAKI, Yasuo OCHI, Takashi MATUMURA, Mitsushi WADASAKO, Tuyo ...
Article type: Article
Session ID: 721
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to investigate the high cycle fatigue property at elevated temperature on alumina short fiber reinforced AZ91D magnesium alloy composites (Mg-MMCs), rotating bending fatigue tests were carried out in the air at room temperature (R.T.) and 200℃. AZ91D magnesium alloy and the two kinds of Mg-MMCs with 10% and 18% volume fraction of alumina short fiber which made high pressure casting process were prepared. The fatigue strength at 10^7 cycles of both Mg-MMCs at 200℃ condition decreased by about 20MPa compared with each fatigue strength at 10^7 cycles at R.T.. The fatigue property of Mg-18MMC at 200℃ was the same as the fatigue property of alumina short fiber reinforced A6061 aluminum alloy composites (Al-MMC: Vf25%) at 200℃.
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Youhei KUMAGAI, Kiyotaka MASAKI, Yasuo OCHI, Takashi MATSUMURA, Tatsuh ...
Article type: Article
Session ID: 722
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Degassed processing (DG) is very excellent method for improvement of fatigue property on casting alluminum alloy. In this study, with the aim of more fatigue property improvement of the casting alumium alloy AC4CH, the short peening treatment was applied, and rotating bending fatigue tests with the shot peened DG AC4CH, were carried out. As the results of fatigue tests, fatigue life property of shot peened DG AC4CH is more improved. To investigate the cause of the fatigue life improvement, hardness distributions of near the surface layer was measured and fracture surface of all specimens were observed with SEM.
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Hideyuki Hirata, Daisuke Inoue, Yutaka Mihara, Katsuhiko Murakami
Article type: Article
Session ID: 723
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The metal hollow sphere (MHS) is expected as a super-light weight metal for lightening the vehicle. The strength properties of sintered MHS were evaluated through the tensile test and tensile fatigue test. The small ball connected area and unconnected area were clearly observed in the fracture surface observation. The number of the connected ball and the number of the unconnected ball were counted in the fracture surface of all the test pieces. Then, a small ball connected rate was decided from the number. It was known that the strength of the test piece having high small ball connected rate was higher. And, the stress analysis of the part which smalll balls connect was done. It was shown that the strength of the sintered MHS could be explained from local stress concentration.
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Masanobu KUBOTA, Hitoshi SATO, Chu SAKAE, Yoshiyuki KONDO
Article type: Article
Session ID: 724
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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To prevent fatigue failure and improve fatigue strength of fine cupper wire used in electronic equipment, evaluation method of fatigue strength has been developed. The fatigue specimen was consisted of a 50μm diameter wire, film and adhesive which bonds wire to film. Since very thin wire is used, the value of stress in wire was greatly influenced by the property of the adhesive. Six type of specimen, which shape of wiring, sort of adhesive and wire fixation were different, were used in this study. Fatigue strength of these specimens was expressed in a line by the results of elasto-plastic finite element stress analyses.
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Nobuo KINO, Takeshi YAMAMOTO, Keizo OTANI, Noriko UCHIYAMA
Article type: Article
Session ID: 725
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Bearings used for automotive powertrains sometimes suffer flaking damage that unexpectedly shortens their life due to peculiar microstructural changes at their subsurface. The results of our previous studies have indicated that this type of flaking is a kind of hydrogen embrittlement caused by the diffusion of hydrogen into the steel due to the decomposition of the lubricant by tribochemical reactions during rolling contact. In this study, the influence of micro-slip that occurs in the contact area was investigated as one of the factors influencing the amount of hydrogen diffusion and accelerating the flaking induced by hydrogen embrittlement.
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Satoshi OHYANAGI, Kazutomo YANAGIHARA, Masanobu KUBOTA, Chu SAKAE, Yos ...
Article type: Article
Session ID: 726
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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To crarify the effect of hydrogen on the fatigue sterngth of low-alloy high strength steel SCM440H, fatigue tests were done in hydrogen chrage environment. Vaccuum quenching was appllied to the material so that the effect of hydrogen is appeared clearly. Three kinds of fatigue tests, which are unchraged, hydrogen charged before fatigue test and charged continuously during fatigue test, were done. Hydrogen chrage was done using cathodic chrage method. Internal fatigue fracture was caused in all specimens regardless of chraged or uncraged. Fatigue life of hydrogen charged material decreased comapred with that of uncharged one. in case drastically decrease of fatigue life was whosn, relatively large inclusion was observed at the crack origin. In case of small decrease of fatigue life was shown, no inclusion was observed at the crack origin.
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Norio Kawagoishi, Takashi Yamakita, Kazuhiro Morino, Kazunori Fukada, ...
Article type: Article
Session ID: 727
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Rotating bending fatigue tests were carried out for radical nitrided SNCM439 steels in order to investigate the influence of nitriding time on the fatigue strength. The hardend layer was increased with increase in nitriding time. However, there was not or little influence of nitriding time on the fatigue strength, though the fatigue strength was increased by nitriding. Fracture at low stress levels occurred from internal inclusions near the boundary between hardened and non-hardened layers. By removing the compound layer, the origin of fracture was changed from subsurface to surface and fatigue strength was decreased.
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Takashi MATSUMURA, Ryo TANAKA, Yasuo OCHI, Kiyotaka MASAKI
Article type: Article
Session ID: 728
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to investigate the fatigue properties of high strength steels in the very long-life range (N〓1×10^7), the cantilever type rotating bending fatigue tests were carried out for high strength steel SNCM439. We conducted the statistical analysis to high-cycle fatigue properties using the fatigue life date of 15 institutions. As a result, from the P-S-N curve using the fatigue life data of 15 institutions, it was found that the dispersion of the fatigue life data of slope part in 'surface crack origin type' area is smaller than the dispersion of the fatigue life data of slope part in 'internal crack origin type' area. The fatigue life data of 'surface crack origin type' over σa=1300MPa follow the 2-parameter Weibull distribution and but those below σa=1300MPa don't follow the 2-parameter Weibull distribution and nearly follow the mixed Weibull distribution or the composite Weibull distribution. The fatigue life data of 'internal crack origin type' almost follow the 2-parameter Weibull distribution. The dispersion of the fatigue life data of 'internal crack origin type' is almost larger than that of 'surface crack origin type'.
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Hidehiko KIMURA, Yoshiaki AKINIWA, Keisuke TANAKA, Yutaka HATTORI, Tad ...
Article type: Article
Session ID: 729
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The smooth specimens of ultrafine-grained steel with the average grain size of less than 2 μm were fatigued under cyclic axial tension compression at room temperature and the crack initiation and early propagation behaviors were investigated by crystallographic orientation analysis based on the electron backscatter patterns (EBSP). Two types of slip lines were observed. One is cross slip that initiates a fatigue crack as previously reported. The other is simple slip which does not initiate a fatigue crack and observed on the specimens with coarser grains as well. The crystallographic orientation analysis revealed that only one slip system was activated at the early stage of fatigue cycles, while the cross slip introduces several active slip systems resulting in the crack initiation at the grain boundary.
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Atsushi SUGETA, Yoshihiko UEMATSU, Eiichi KURONAGA, Masahiro JONO
Article type: Article
Session ID: 730
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Akhmad A. Korda, Y. Miyashita, Y. Mutoh, T. Sadasue
Article type: Article
Session ID: 731
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Fatigue crack growth test and in-situ SEM observation of ferritic/pearlitic and ferritic/bainitic steel plates were performed. Study was conducted to investigate the effect of microstructure on fatigue crack initiation and propagation behavior. The ferritic/pearlitic steel shows slightly higher FCG rate at region II and ΔK_<th> compared to the ferritic/bainitic steel. In-situ observation of the crack tip position at the ΔK_<th> showed that the crack was arrested in ferrite grains slightly below the pearlite phase band for the ferritic/pearlitic steel. In case of the ferritic/bainitic steel, the crack was arrested at the bainite phase of the sheaves oriented closely perpendicular to the crack growth direction. In the ferritic/pearlitic steel, crack generally passed through the ferrite grains and followed the interface of ferrite/pearlite when the crack faced the pearlite phases. The fracture path in the ferritic/bainitic steel was observed to: (1) follow the interface of bainite and ferrite (2) follow the bainite sheaves (3) pass through the bainite sheaves.
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Masato YAMAMOTO, Akito NITTA, Takayuki KITAMURA
Article type: Article
Session ID: 732
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to clarify the effect of the local stress distribution on the fatigue crack propagation rate of directionally solidified superalloy, elastic stress analysis was carried out with simulating grain configuration of a test specimen. Local stress along loading direction showed higher value near grain boundaries, which attained about 1.5 times as the average stress. The crack propagation rate obtained by the crack propagation test was accerelated at intermittent regions, which was coinside with the stress concentrating regions in the stress analysis. It was suggested that the local stress distribution may affect the crack propagation rate.
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Yuka KOJIMA, Satoshi MASUDA, Noboru EGAMI, Hirohisa KIMACHI, Hiroyuki ...
Article type: Article
Session ID: 733
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Tension test, S-N fatigue test and fatigue crack growth test for Ti-55.3mass%Ni alloy with shape memory effect were conducted at room temperature. As the result of tension tests, Young's modulus E_A in the austenite phase is 28.5 GPa, E_M in the martensite phase is 13.4 GPa, the transformation stress σ_r is 69.2 MPa and breaking strain δ is 18.9%. S-N diagram obtained by the S-N fatigue tests was divided into three regions; Region I, II and III. In Region I where the applied stress was above 200MPa, the fatigue life was the low cycles less than 6.0×10^4 cycles. Then, main crystal structure was martensite phase. In Region II from the fatigue limit(about 153MPa) to 200MPa, fatigue life was varied by the rate of austenite and martensite phase. Region III is bellow the fatigue limit. In this region, the austenite phase mainly occupies. Fatigue crack growth test was conducted under three kinds of maximum stresses, 80, 90 and 110MPa with the constant stress ratio. For each maximum stress, the linear relation was obtained when the crack growth rate daldN was plotted against effective intensity factor ΔK_<eff> on double logarithmic plot. After the crack initiation, crack growth rate was constant or decreases. After the fatigue tests, fractgraphy was conducted by SEM. The striations were observed in fracture surfaces of fatigue crack growth test. There space was equal to the crack growth rate.
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Nobuhito MIWA, Yoshihito KUROSHIMA, Syoji HARADA
Article type: Article
Session ID: 734
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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As for initial fatigue crack, quantitative evaluation was onsidered to e difficulty for reasons of both sides of metal-lurgical factor and mechanics factor influence behavior and crack growth mode change. In this study, paid its attention to initial fatigue crack growth to a depth direction, and examined Stage I fatigue crack behavior. To examine a mechanics condition governing stage I fatigue crack growth, fully reversed uniaxial push-pull high cycle fatigue tests were carried out on a low carbon steel. As a result behavior of Stage I fatigue crack became clear.
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Tasuku GOTOH, Hirofumi ARII, Yoshihito KUROSIMA, Syoji HARADA
Article type: Article
Session ID: 735
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In the extremely low cycle fatigue, a transition of the fracture mode occurs from the surface to internal fracture with an increase in the plastic strain range. Such a transition is caused by an increase in the paerlite cracking inside the material. The pearlite cracking is greatly dependent on the own direction of lamellael. However, Work Hardening seldom affects an increase in the paearlite cracking.
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Congling Zhou, Shin-ichi Nishida, Nobusuke Hattori
Article type: Article
Session ID: 737
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In the present study, torsional fatigue properties of tensile pre-strained structural carbon steels have been investigated in view-point of fatigue strength, crack initiation and propagation behavior, hardness and so on. According to the experimental results, tensile pre-strain improves the torsional fatigue strength, increases the surface hardness and affects the crack initiation and propagation characteristics.
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