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Kohji MINOSHIMA, Yoshitaka OIE, Kenjiro KOMAI
Article type: Article
Pages
295-296
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In this investigation, an analysis system that enables the nanoscopic in situ imaging the environmentally induced damage such as a stress corrosion crack under a dynamic loading condition has been developed. The system consists of an atomic force microscope (AFM), a dynamic loading system, an x-y-x positioning stage, an environmental chamber, and their controllers. To reduce disturbing vibrations, the system is equipped with an environmental chamber, and their controllers. To reduce disturbing vibrations, the system is equipped with an isolator. A dynamic load can be applied to a sample by using an electromagnetic actuator, with various loading wave forms including sinusoidal, triangular, and other programmable ones, and with a maximum load capacity of ±100N. The nanoscopic in situ AFM observation can be done in a controlled gaseous environment or in an aqueous solution. By using the developed system, in situ nanoscopic AFM observation of a fatigue crack in dry air and an environmentally-induced crack under a sustained load (static stress corrosion crack), under a sustained load with a high-frequency varying load (cyclic stress corrosion cracking), was successfully performed in a high-strength stainless steel : the nanoscopic crack tips can be clearly visualized. The crack tips of the environmentally induced or stress corrosion cracks are sharp compared with a fatigue crack in dry air, with a larger scatter band. This resulted from structure sensitive crack growth of a stress corrosion crack and what the growth is sensitive to the hydrogen content at the crack tip.
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Haengsik JOO, Kunihiro YAMADA
Article type: Article
Pages
297-298
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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A study on the delayed fracture behavior of high strength steel induced by hydrogen was carried out using thin plate specimens. of which stress state would be plane stress condition, to compare them with solid round bar specimens that were subjected to plane strain condition. The specimens were cathordically charged with hydrogen under sustained load conditions. The delayed fracture time of thin plate specimens lasts longer than the solid bar specimens. As the thickness of the plate specimens became thin, the delayed fracture time showed the tendency that became long.
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Yoshio ARAI, Eiichiro TSUCHIDA, Ming Zhang
Article type: Article
Pages
299-300
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The effects of thermal cycling on the fracture toughness of SiC particulate reinforced cast aluminum alloy have been studied. The results were discussed in terms of a microstructure controlled mechanism which is void growth, coalescence and debonding of SiC particle/matrix interface for fracture. The fracture toughness of thermally cycled material is twice larger than that of as received material. The measurements of 3D shape of fracture surfaces show that the crack blunting occured in front of the SiC particle clusters in the material with thermal cycling. The micro-mechanism of fracture is void coalescence and debonding of the SiC particle/matrix interface in this case. The behavior is basically consistent with void/inclusion models. A new formulation is proposed and its validity is demonstrated.
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Takashi USUI, Masao KIKUCHI, Ikuo UCHINO, Yuuji HIROTA
Article type: Article
Pages
301-302
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The failure analysis on the drive shaft is reported. Mechanism of the internally initiated failure was discussed in terms of fractgraphy and internal residual stress distribution. The crack was initiated at the existed casting defect. This internal defect caused a brittle crack propagation and the crack stopped still inside the shaft. The area of this brittle failure inside the shaft corresponds to the area where the tensile residual stress distributed. The estimation of brittle failure stress using fracture mechanics showed that the measured tensile residual stress of 400MPa near the center of the shaft was almost enough to start the brittle crack propagation from the internal defect. It was concluded that the crack initiated near the center of the shaft propagated by the residual tensile stress to the certain size, then finally failed by fatigue caused by the external operating force applied on to the shaft.
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Kunio Fukuyama, Shigeki Takeuchi, Toshihiro Fuwa
Article type: Article
Pages
303-304
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order that we do the cause survey of failure accident precisely, we need to accumulate the knowledge regarding the detailed fracture information in the failure accident that occurred in the past time. Last year. two accidents occurred in a railroad. One was the damage of two truck bolts. The other was the damage of a brake shoe. As a result of the fractography, the cause of the truck bolt's damage was fretting fatigue destruction. Also, it understood the cause of the brake shoe's damage that is a heat crack the fatigue destruction as an origin. In this paper, we described the fracture structure that was observed with those fracture analyses.
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Takashi HONDA, Etsuji YOSHIHISA, Tetsuya SASAKI, Yutaka MAEDA
Article type: Article
Pages
305-306
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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This paper presents two types of resent occupational accident caused by damage of materials used in machinery. One case is that a hoist link chain used in a factory mainly recycling cathode-ray tubes failed during the cleaning process of cullet. Consequently, the worker working this process was burnt with the high-temperature cleaning solvent since the load fell in the cleaning tank. In this case, link chains were subjected to over load repeatedly due to removing the coil spring above the hock. The other case is that the molten metal leaked from the die of a centrifugal casting machine due to failure of screw threads cramping the upper die with the inner die . Four workers fell sacrifices to this accident.
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[in Japanese], [in Japanese], [in Japanese]
Article type: Article
Pages
307-308
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Shoji KAMIYA, Hideaki NAGASAWA, Hiroyuki HANYU, Masumi SAKA, Hiroyuki ...
Article type: Article
Pages
309-310
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Fracture behavior and mechanical integrity of a thin film deposited on substrate should be influenced by basically four parameters, which are strength of the film, strength of the interface, Young's modulus of the film and residual stress in the film, provided that properties of the substrate are given. These parameters were evaluated and compared in this study among the cases of CVD diamond, PVD TiAlN and TiN coatings deposited on cutting tools. Toughness of adhesion was not so much different while toughness of the film was drastically lower for the case of PVD, which resulted in clearly different fracture behavior observed for these coatings.
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Kaoru IKENAGA
Article type: Article
Pages
311-312
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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As for the surface modification processing of the ferrous material, a more highly developed technology is demanded of a social environment at the present age. Especially, making to the energy saving and making to oilless are paid to attention for a social environment in the machine industry which centers on the car. The Diamond-Like-Carbon (DLC) film with high hardness and low coefficient of friction is paid to attention as new surface modification processing in that situation. The research investigated the adhesion of DLC film with such a characteristic.
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Fumitaka TSUCHIYA
Article type: Article
Pages
313-314
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Recently, the thinning of the plastic product is advanced. However it causes many molding problems such as distortion, crack and remaining in the cavity. Surface modification technology based on the metallic material is one of the solution. It is possible to improve the resin adhesive strength and friction force using the mold surface modification.
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Jeongseok OH, Masashi NAKAMURA, Tadao HARAGUCHI, Hideto SUZUKI
Article type: Article
Pages
315-316
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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It has been investigated that the cause of failure of forming roller for clutch-pulley of automotive air conditioner and the reason of its short life. Fracture surface analysis, and vibration measurement with laser displacement gage were carried out in order to find the cause of failure and its remedy. Especially, the cause of failure was examined comparing L series with the short life, and S series with the long life of the forming roller. From fracture surface analysis, it is clarified that the fracture mode of forming roller is fatigue fracture. The fatigue fracture produced the cause due to which the life of the forming roller became short during the forming process, owing to vibration (cyclic vibration) of the roller at the top part. As a result of measuring width-side vibration of the roller in forming process, it was found that maximum vibration of the roller was 408μm with the laser displacement gage, and there is a correlation between the vibration and the life of the roller. Therefore, it is necessary to select a material having large fatigue-resistance.
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Masashi NAKAMURA, Jeongseok OH, Hideto SUZUKI
Article type: Article
Pages
317-318
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The improvement of the fatigue brittle fracture characteristics on DLC coated Al-Si sintered alloy was examined. Especially, healed effect of the damage by DLC coated was investigated in detail. The fatigue strength of DLC coated Al-Si sintering alloy has improved about 10%, and also in a fatigue brittle fracture region, the fatigue life was improved about 3 times compared to that of virgin material. From fracture surface analysis, the crack generating and crack progress mechanism in DLC coated differed from virgin material clearly. The crack of extraordinary length was observed on the surface. This crack was propagated along the surface of material in DLC coated. The meso-cracks of the length of about 1∿5μm were generated, and distributed in virgin material. The main crack was propagated in the direction of the inside of material. The causes of the healed effect by DLC coating were as follows; (1) The defect of the delamination between Si particles and Al matrix were covered with DLC. (2) The compressive residual stress existing in DLC coated suppressed generating of delamination between Si particles and Al matrix. (3) Since the crack was initiated by the delamination on the interface between Si particles and Al matrix in DLC coated, it can be regarded as an internal crack.. Therefore, a stress intensity factor becomes small as compared with virgin material.
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Hideto SUZUKI, Kosuke OTAKI, Masashi NAKAMURA, Makoto ISHIDA, Ying JIN ...
Article type: Article
Pages
319-320
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Railway wheel is carried out film coating for prevention of "climbing derailment". Properties of DLC (Diamond Like Carbon) film are low friction and high hardness. DLC film showed good film properties in the test piece level. Then, model wheel coated with DLC film by UBMS (UnBalanced Magnetron Sputtering) was evaluated friction and wear properties on Twin-Disc Rolling Contact Testing Machine. Model wheel coated with DLC-Nitriding layer kept low traction in three kinds of environments respectively. In addition, the contact stress was diffused by the hardness inclination that the nitriding layer brought about, the delamination was not confirmed between the substrate and this film.
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Hideto SUZUKI, Masashi NAKAMURA, Takeshi KASUYA
Article type: Article
Pages
321-322
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Influence of diamond like carbon (DLC) and MoS_2 coating on the fatigue reliability of bismuth machining steel was investigated with the aim of the fatigue fracture mechanism analysis. The main results were as follows. (1) In comparison with the virgin material, fatigue strength of bismuth free machining steel which conducted DLC is the 15% lowering. And bismuth free machining steel which conducted micro poral layer and MoS_2 improved 12%. (2) In the DLC material, the initial crack is held to 79.0% of the fatigue life ratio by surface restraining force of the carbide membrane. This crack becomes a trigger, and the rapid fracture has been caused. It is the factor in which a rapid hardness inclination from the surface causes the rapid fracture of this material. (3) In the MoS_2 material, micro poral layer which exists on the surface suppresses the sliding, and the initial crack has been delayed. The compressive residual stress added on the surface suppresses the progress, even if the crack is generated. It is the factor in which the fatigue strength of the MoS_2 material is improved by the control of generation and progress of the crack.
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Hirorou NOMURA
Article type: Article
Pages
323-324
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The surface reforming layer where a lubricant thin film was compound and processed to an excellent hard coating in abrasion resistance was examined and a mechanical characteristic of the film was examined by investigating the sliding characteristic and the wear-out characteristic with the ball on disk type friction wear-out examination machine. As a result, it has been understood that frictional properties of initial and the regular wear-out region can be greatly decreased by making it to the compound film and the aggressiveness to the other party material is also small.
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M. Okazaki, H. Yamano, M. Arai
Article type: Article
Pages
325-326
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Propagation of naturally initiated debonding crack in the themal barrier coating (TBC) which consitsted of Ni-base superalloy substrate, CoNiCrAlY bond coat, and 8% yttria stabilized zirconia, was investigated at room and high temperatures, when it was subjected to cyclic loading. Special foucus was put on the understanding of the crack initiation and propagation mechanisms.
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Shoji KAMIYA, Hideaki NAGASAWA, Kiichiro YAMANOBE, Masumi SAKA, Hiroyu ...
Article type: Article
Pages
327-328
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Mechanical strength of a thin film deposited on a substrate should be characterized by basically four parameters, which are strength of the film, strength of the interface, Young's modulus of the film and residual stress in the film, provided that properties of the substrate are given. A systematic method of measurement for these parameters has recently been developed by the authors. In this study, variations of this method are newly developed in order to evaluate those parameters even in the case of brittle thin films with tough interface and large residual strain which the original method could not manage. The new technique is successfully applied to the case of wear resistant PVD coatings on cutting tools.
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Lihe QIAN, Shijie ZHU, Yutaka KAGAWA, Takahiro KUBO
Article type: Article
Pages
329-330
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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A plasma spraying method was applied to deposit the coating materials. A NiCoCrAlY alloy was used as the bond coat, a ZrO_2 ceramic partially stabilized with Y_2O_3 as the top coat, and a stainless steel selected as the substrate. In-situ optical microscope combined with SEM observation was made, and load-displacement curves were recorded synchronically. Cracking and fracture behavior in the as-deposited coating system were evaluated using a sandwiched uni-axial tensile testing method. It was found that initial cracking was followed by multiple cracking transversely propagating in the coatings. After the saturation of the multiple cracks, decohesion occurred at the bond coat/substrate interface. Finally, a model was proposed to describe the fracture processes.
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Takahiro KUBO, Takehisa HINO, Tsuneji KAMEDA, Yoshiyasu ITOH
Article type: Article
Pages
331-332
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Burner heat type thermal cycle testing machine under axial loading was newly developed in order to evaluate the life of thermal barrier coating (TBC). This test machine is able to load both mechanical stress and thermal stress independently. The outer surface of hollow shape specimen is heated by ring shape gas burner, while inner surface is cooled by the air. When the surface temperature was elevated at 1100℃, the temperature differnce between TBC surface and inner surface was about 200℃. Thermal stress could be loaded by this temperature gradient, which is equivalent to the actual blade with TBC and cooling hole. This testing machine is also able to load axial tensile and axial compression stress that simulates mechanical stress of TBC components. It is concluded that this testing machine is able to simulate the operation conditions, which is high temperature, thermal stress by temperature gradient, and mechanical stress like centrifugal force.
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Makoto TANAKA, Shijie ZHU, Yutaka KAGAWA
Article type: Article
Pages
333-334
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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To improve the thermal efficiency of a gas turbine, thermal barrier coatings (TBC) have been developed to protect superalloy components. The damage in TBC is often caused by mechanical and thermal residual stress in TBC. Therefore, it is very important to evaluate residual stress distribution in TBC coating system. In this study, the residual stress of TBC has been measured by Raman spectroscopy. The testing material is a plasma-sprayed TBC containing 8% Y_2O_3 on a stainless steel. To understand the residual stress near interface, the TBC dissolved from the substrate has also been used to measure residual stress. The sharp raman peak exists at a frequency of 640 (cm)^<-1> for the tetragonal zirconia. It has been found that compressive stress in TBC system can be released in the TBC without substrate. However, this occurs with a thickness up to 100 μm.
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Izuru NISHIKAWA, Keiji OGURA, Yoshitomo YABUUCHI
Article type: Article
Pages
335-336
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Near threshold fatigue crack growth (FCG) behavior under cyclic loading in TiAl intermetallic and Ti-6Al-4V alloy was investigated at elevated temperature. Crack opening displacement (COD) was measured by using the Laser speckle strain/displacement gage (SSDG) during the fatigue tests. It was found that the FCG rate in TiAl intermetallic at 800℃ was controlled by the effective stress intensity factor range ΔK_<eff>, while the FCG rate in Ti-6Al-4V alloy above 500℃ was controlled by the maximum stress intensity factor K_<max> as well as ΔK_<eff>. It was also found that the fatigue threshold ΔK_<eff, th> in TiAl intermetallic at 800C was higher than that in Ti-6Al-4V alloy above 500℃.
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Suguru YAMAGUCHI, Misao ITOH, Tamotsu MAJIMA
Article type: Article
Pages
337-338
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Low cycle fatigue tests were performed to investigate the effect of notch shape for an aluminum alloy A6061-T6. The normal notched cylindrical specimen and the one with protuberances were employed. The total strain range from 0.007 to 0.03,which includes the strain levels for the extremely low cycle fatigue, was applied at the net section. The fracture ductility of the material employed is a main factor dominating the fatigue life. The fatigue life depends strongly on the total strain range at the notch root. The stress triaxiality at the net section has a strong effect on the fatigue life when a total stress range is applied.
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Masao KINEFUCHI, Keisuke TANAKA
Article type: Article
Pages
339-340
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The reliability of fatigue strength is one of the most important properties on the light-weight car components using high tensile steels. In this study, the effect of mean stress on fatigue strength of hot-rolled sheet steel under two surface conditions was discussed. As a result, Haigh diagram used actual rupture stress was well predicted fatigue limit under the conditions of that maximum stress was not beyond yield stress. When Haigh diagrams will be used a design of components, it is important to select adequate line for prediction of fatigue limit.
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Satoru ODAHARA, Yukitaka MURAKAMI, Masahiro INOUE, Atsuo SUEOKA
Article type: Article
Pages
341-342
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The method of fatigue life prediction is presented for structures under flow-induced vibration. A small wind tunnel was made and used to reproduce fatigue failure by flow-induced vibration. A medium carbon steel specimen attached to a larger styrofoam cylinder was fixed to the experimental equipment. A small artificial hole was introduced onto the specimen surface. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) developed in another project of the authers' team was used to acquire the service strain histogram at a critical point of the specimen. Fatigue damage D defined by the Modified Miner Rule was calculated by using the strain histogram at the initial stage of the test. The values of D were all smaller than 1.0 and ranged approximately from 0.2 to 0.8. The effect of initial defect size on the values of D was clarified by focusing the relationship between small crack growth behaviour and strain histogram.
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Qiang YU, Masaki SHIRATORI, DoSeop KIM, Yasuhiro TAKAHASHI, JaeChul JI ...
Article type: Article
Pages
343-344
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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As the Sn-8Zn-3Bi solder is hard and difficult to deform, the stress concentration which occurs in solder joints is high. And it is thought that the stress concentration is the reason why the brittle fracture occurs in and along the intermetallic compound layer. However, failure mechanism and fatigue strength in solder joints where different two solder materials were used are not yet known. In this study, failure mechanism in the composite construction solder joints was examined using the two-layer structure solder joints of Sn-3Ag-0.5Cu and Sn-8Zn-3Bi.
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Kazuyoshi OHISHI, Takashi SUMIGAWA, Takayuki KITAMURA
Article type: Article
Pages
345-346
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to evaluate slip behavior inside a crystalline material, a stress calculation by finite element method (FEM) and a high cycle fatigue test in a multicrystalline copper specimen were carried out. 17PSBs are observed near grain boundaries on the surfaces and the FEM result shows that the PSBs are generated where maximum resolved shear stress, τ_<mrss> is high. It suggests slip behavior inside materials is depicted with distribution of τ_<mrss>. The region of τ_<mrss> concentration is within 50μm from the surface and the maximum magnitude of τ_<mrss> on the surfaces is larger than that inside the specimen. This implies initial slips occur at surface near grain boundaries.
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Soichi HITOMI
Article type: Article
Pages
347-348
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Kouji YAMADA, Susumu MIYAKAWA
Article type: Article
Pages
349-350
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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To investigate the extra-long fatigue properties of aluminum die casting materials, fatigue tests were conducted on two type of aluminum die casting materials. One type is Al-Si-Cu die casting alloys (ADC10-T5) and the other is Al-Si-Mg die casting alloys (AC4C-T6). In the case of AC4C-T6,the fatigue fractures were caused by shear type crack and fatigue strength decreased along with the increased along with the increase of the number of cycles. In the case of ADC10-T5,the fatigue fractures did not occur, that is, fatigue strength did not decrease along with the increase of the number of cycles.
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Takahiro SHIINA, Takashi NAKAMURA, Toru NOGUCHI
Article type: Article
Pages
351-352
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to clarify properties of the surface-originating fracture in high vacuum environments, uniaxial tension fatigue tests were carried out in air and high vacuum using pieces made of Ti-6Al-4V alloy with micro-defects by drilling. As a result, the following were obtained : (1) Compared with in air, fatigue lives in high vacuum strongly depended on stress. (2) Interior-originating fractures in high vacuum occurred from higher stress level than those in air. Therefore, we must pay attention to the effect of the interior-originating fracture in case of using this material in vacuum environment like space. (3) There was the possibility that the effect of the dependence of the &K_<th> on crack size in high vacuum is stronger than that in air.
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Yoshio ARAI, Eiichiro TSUCHIDA, Yasunobu KIMURA
Article type: Article
Pages
353-354
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Fractographic examinations were performed on crack initiation sites for 10%SiC particulate reinforced aluminum cast alloy. Rotating-bending fatigue test were conducted in air and RT. Stereo imaging technique was applied to examine 3D shape of the fatigue crack initiation sites. Based on the observation results a mechanism of fatigue crack initiation for this material was constructed and a model to predict fatigue life of 10%SiC particulate reinforced aluminum cast alloy was proposed using linear fracture mechanics.
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Shijie ZHU, Fumin XU, Fugang WANG
Article type: Article
Pages
355-356
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. Fatigue crack growth was in direction of from 5% to 30%SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching at interfaces were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the lavers shielded crack tip driving force, i.e., decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread across the interface from the weaker material into the stronger material.
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Takashi NAKAMURA, Takahiro SHIINA, Toru NOGUCHI
Article type: Article
Pages
357-358
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to clarify how compression load affects interior-originating fatigue fracture surfaces of high strength steel, uniaxial tension fatigue tests were carried out under different stress rations (R=0.3,0 and -1). The results were as follows; Interior-originating fractures under R=-1 occurred in shorter fatigue lives than those under R=0.3. Optically Dark Area (ODA) was formed even in short fatigue life of (10)^5 cycles. The morphology of ODA was closely related to the stress ratio, especially compression stress. Even though the fracture origin of the specimen was not inclusion, ODA was formed on the fracture surface.
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Haeng Nam KO, Hisatake ITOGA, Keiro TOKAJI, Masaki NAKAJIMA
Article type: Article
Pages
359-360
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to study the effect of inclusion on the step-wise S-N characteristics of high strength steel, cantilever-type rotary bending fatigue tests were performed at room temperature on two kinds of high carbon chromium steels with different cleanliness. It was found that the transition stress, transferring the fatigue fracture initiation from the specimen surface to the subsurface, did not depend on the cleanliness, but on the size of inclusions. In subsurface fracture region, fatigue life became shorter in steel with smaller inclusions, but the features of fish-eyes were almost the same.
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Takashi MATSUMURA, Shinya YOSHIDA, Yasuo OCHI, Kiyotaka MASAKI
Article type: Article
Pages
361-362
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to investigate the effect of tempering temperature on the fatigue properties of high strength steels and surface hardened steels in the super-long life range (N≥1×(10)^7), cantilever type rotating bending fatigue tests were carried out for SNCM439 specimens which tempered by the tempering temperature of four kind of 160℃, 300℃, 500℃ and 620℃. As a result of fatigue tests, all specimens tempered at 500℃ and 620℃ were "surface crack origin type". For the case of tempering temperature of 300℃, one specimen was "internal crack origin type" and other specimens were "surface crack origin type". For the case of tempering temperature of 300℃, 500℃ and 620℃, the tendency in which the S-N curves decreased again in the very long life regime over (10)^7 cycles could not be observed.
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Nobusuke HATTORI, Shinichi NISHIDA, Ryu SASAKI
Article type: Article
Pages
363-364
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to clarify the influence factor on high-cycle fatigue of High strength steel SUJ2,the fatigue test have been carried out up to (10)^8 cycles under rotating bending at room temperature. According to the experimental results, in the case of failure under the conventional stress condition, there is only one crack initiation point. On the other hand, in the case of two-step stress condition there are plural crack initiation points. Furthermore, when the fatigue damage under the two-step stress condition is evaluated by Modified Miner's low, it should be added with S-N curve by surface failure and that by internal one respectively.
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Syuji KUBO, Takasi YOSIMURA, Yoshihito KOROSIMA, Syoji HARADA
Article type: Article
Pages
365-366
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The fatigue life prediction law of internal fatigue failure referred to as fish eye was not made. Therefore this study paid attention to the internal crack growth properties and calculated fatigue life based on the crack growth properties which put next two internal crack growth properties together. (1) the small crack growth properties of the internal interposition thing circumference and (2) the surface crack growth properties in vacuum which simulates the environment of internal fatigue. The results showed that the fatigue life that was calculated was equal almost the real life under some stress.
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Shigeo OMATA, Hisao MATSUSHITA, Hideo KOBAYASHI
Article type: Article
Pages
367-368
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Fatigue tests of forged low-alloy steel, KSFA110 (NK standards, σ_B=1,080MPa class), with various surface conditions were carried out to clarify fatigue property in the ultra-high-cycle regime over (10)^8 cycles of repeated stress. Two-fold S-N curves were observed and they were remarkably affected by the existence of residual stresses. Fatigue crack propagation life was calculated assuming that the crack propagation life is predominant in the fatigue life. Calculated parameters of fatigue crack propagation low for interior fracture were m=7.1 and C=7.87×(10)^<-19>. Threshold stress intensity factor range of propagation depended on the initial crack size.
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Junji NAGATA, Yukitaka MURAKAMI
Article type: Article
Pages
369-370
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Recent studies have provided a warning that fatigue failure can occur in the life regime exceeding N=(10)^7 and at stresses lower than the conventional fatigue limit. In the present study, the mechanism of fatigue failure in extremely high cycle regime was studied on bearing steels, SAE 52100. Specimens having a longer fatigue life had a particular morphology beside the inclusion at fracture origin. The particular morphology looked optically dark when observed by an optical microscope and it was named the optically dark area, ODA. The ODA looks a rough area when observed by SEM and AFM. The condition for the critical size of ODA for the start of conventional fatigue crack growth mechanism was analyzed by fracture mechanics. The critical stress intensity factor range △K_<ODA> can be correlated with the threshold stress intensity factor range △K_<th> for small cracks expressed by the √<area> parameter model.
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Tohru UEDA, Yukitaka MURAKAMI
Article type: Article
Pages
371-372
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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ODA (Optically Dark Area) in the vicinity of inclusions at fracture origin has a crucial importance in the mechanism of ultralong life fatigue failure. From the authors' previous studies, it has been presumed that ODA is formed by the fatigue due to cyclic stress coupled with hydrogen which is trapped by the inclusion at fracture origin. The ODA observed by a SEM with low resolution revealed a granular morphology. However, a high resolution SEM images obtained by tilting the fracture surface identified that the true morphology of ODA was not granular but was very sharp and irregularly rough. In order to reveal the effect of hydrogen on the formation of ODA, the microstructure around the inclusions at fracture origin was investigated. The hardness in the vicinity of inclusions in Specimens QT which contained 0.7-0.9 ppm hydrogen was much lower than that for Specimens VQ which contained ∿0.01ppm hydrogen.
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Mitsuhiro TAKEDA, Tatsuo SAKAI, Noriyasu OGUMA
Article type: Article
Pages
373-374
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In order to clarify the effect of strength level on the fatigue prorerty in a wide life region, fatigue tests in the life region of N=0.5∿(10)^9 were performed for high strength steels of SUJ2,SUCM439 and the carbon steel of S35C with low strength. S-N characteristics of respective steels were compared with each other and the fatigue mechanisms were discussed from a view point of fractography. Thus, it was found that S-N property for high strength steels of SUJ2 and SNCM439 have duplex S-N characteristics, respectively. However, the S-N property for the low strength steel of S35C does not have such an aspect, but it has the simple S-N characteristics.
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Noriyasu OGUMA, Hisashi HARADA, Tatsuo SAKAI
Article type: Article
Pages
375-376
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Mechanism of interior inclusion induced fracture of bearing steel in long life region was experimentally examined under rotating bending, and discussed from a viewpoint of electron microscope observation. Fish-eye was formed on the fracture surface in the interior inclusion induced fracture, and rough surface area was necessarily observed near the inclusion. Based on TEM observation of longitudinal section of fracture surface, it was found that structural changes were caused around the inclusion. Fine grains caused around the inclusion have the sizes within 40nm. It seems that the rough surface area around the inclusion is the boundary of this fine grain region and matrix.
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Tatsuo SAKAI, Nobuaki TANAKA, Kenji OKADA, Miyuki YAMAMOTO, Kanji FUJI ...
Article type: Article
Pages
377-378
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Ultra-long life fatigue properties of SCM435were experimentally examined in rotating bending. High cycle fatigue data of the same kind of steel were extracted from the DATABASE ON FATIGUE STRENGTH OF METALLIC MATERIALS published by JSMS. These results were put altogether and the statistical fatigue properties of this steel were analyzed as P-S-N characteristics.
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Shinichi NISHIDA, Nobusuke HATTORI, Akihiro UCHISAKO
Article type: Article
Pages
379-380
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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As more than 90% of failure cases are initiated from stress concentrated portion and more than 90% are due to fatigue, it is practically very important to improve the fatigue strength of notched portion. Some of the authors have been investigating to improve the fatigue strength of to improve the fatigue strength of notched portion applying plastic deformation method. In this study, the torsional fatigue test about roller-worked specimen had been performed. The material was carbon steels (JIS standards S25C). The main results obtained were as follows; When the plastic deformation value is 1mm, the torsional fatigue strength of notched specimen by roller-working increases 68MPa than that of the notched specimen by non roller-working. The photographs of surface condition roller-worked before failure showed many blocks like cracks, which were not observed in the case of non roller-worked specimen.
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Hirohito ETO, Katsuyuki MATSUI, Kotoji ANDO
Article type: Article
Pages
381-382
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The authors investigated their characteristics and the strength of NH materials treated by Double Shot Peening (DSP). The results obtained are summarized as follows : (1) Increased diffusion layer hardness between the surface and depth of 400μm by DSP (2) Remarkably high residual stresses of surface residual stress with -701MPa and maximum compressive residual stress with -733MPa of the NH+DSP material (3) Considerably increased fatigue limit of the NH+DSP material. 33% (stress ratio R≧0) and 28% (R=-1) higher fatigue limit than the NH materials, respectively.
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Yasuo Ochi, Takusaburo Hosoya, Yutaka Wakabayashi, Kiyotaka Masaki, Ta ...
Article type: Article
Pages
383-384
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) with shot-peening (SP) treatment, and influences of the SP treatment on fatigue property and fracture morphology were investigated. As results, the fatigue strength of shot-peened ADI specimens was improved in the region of under (10)^7 cycles. But, the S-N curve of shot-peened ADI and that of non shot-peened ADI crossed at near (10)^8 cycles, and the fatigue strength of shot-peened ADI specimens was lower than that of non shot-peened ADI in the region of over (10)^8 cycles. In order to investigate the causes, the hardness distribution and the residual stress distribution in the surface layer of the SP treated specimens was measured and the fracture surfaces of all failed specimens were observed using a field emission scanning electron microscopy (FE-SEM) after the fatigue test. The stress at the crack initiation point was calculated in consideration of the stress gradient and the residual stress for shot-peened ADI specimen. The fatigue facture mechanism was discussed in detail.
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Xuelan L. Yue, Shinichi Nishida, Nobusuke Hattori
Article type: Article
Pages
385-386
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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A conventional surface strengthening technique, hard rolling, was employed to improve the fatigue properties of A17075. The results show that the fatigue strength of hard-rolled specimens is increased around 70% compared with that of the non-hard-rolled specimens. In agreement with this, the hard-rolled specimens exhibite a much lower fatigue crack growth rate, indicating that after hard rolling, fatigue crack initiation and propagation are obviously delayed. The improvement of fatigue properties is analyzed in terms of the microstructural change and the residual stress induced by hard rolling.
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Wenxian SUN, Shinichi NISHIDA, Nobusuke HATTORI
Article type: Article
Pages
387-388
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Some of the authors have been continually researching the effect of plastic deformation on fatigue properties and considerably clarified that it is one of the effective and low cost way to improve the fatigue properties. In this study, fatigue test had been performed to investigate the effect of roller working on notched specimen using eutectoid steel-one of the most important materials for industrial components. The result of the test shows that the cold rolling improved the fatigue limit of this kind of material significantly. The fatigue limit of roller-worked specimen does not necessarily increase with the increase in plastic deformation value. There exists an optimum value by roller working for improving the fatigue strength. The fracture surface is observed with SEM, the residual stress was measured by X-way method and the reason of the improvement is analyzed in the paper.
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Yukinori KUSANAGI, Saho HONMA, Noriyuki HISAMORI, Kenichi TAKAI, Akira ...
Article type: Article
Pages
389-390
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Metallic materials are widely used for orthopedic implants like artificial hip joints that bear high loads throughout its use. However, they are not capable of bonding directly to living bone. This problem will be solved if the metallic material forms hydroxyapatite (HAp) on its surface enabling living bone to bond to the metal. In this study we tried to evaluate fatigue crack propagation properties of bone-induced Ti-6Al-4V alloys in simulated body fluid (SBF), which simulates the human blood plasma in terms of ion concentrations. Bone-inducing function was added on Ti-6Al-4V alloys by coating HAp through surface treatment The fatigue crack propagation test of bone-induced Ti-6Al-4V alloys was performed under a SBF environment at 37℃. The result of the fatigue test is analyzed in terms of the fatigue crack extension rate (da/dN) vs. the stress intensity factor plots (⊿k). At stable crack propagation filed in the da/dN- ⊿k curve, the crack propagation rates of the HAp coated Ti-6Al-4V alloys and alkali-heat treatment Ti-6Al-4V alloys specimens were higher than the Ti-6Al-4V alloys without the coating. This difference is possibly caused by the stress corrosion cracking (SCC). The SEM observations of fatigue fracture surface during stable crack extension showed the evidence of SCC that occurs during fatigue crack extension in SBF environment that is observe in the coated Ti-6Al-4V and Alkali-Heat Treatment Ti-6Al-4V alloys specimens.
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Yutaka YAMAMOTO, Katsumi SAKAGUCHI, Masahiro OTAKA, Akio SAYANO, Yasua ...
Article type: Article
Pages
391-392
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The fatigue life of austenitic stainless steel in LWR water environment tends to reduce remarkably with decreasing strain rate and increasing temperature. In this study, based on fatigue tested data conducted in simulated LWR water environments, the effects of these parameters on fatigue life reduction have been examined quantitatively, and a method to estimate the fatigue life correction factor F_<en> in BWR and PWR water environment respectively has been proposed for austenitic stainless steels. The research was carried out by the Japan Power Engineering and Inspection Corporation (JAPEIC) which was entrusted by the Ministry of Economy, Trade and Industry (METI).
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Masahiro OTAKA, Katsumi SAKAGUCHI, Yutaka YAMAMOTO, Akio SAYANO, Yasua ...
Article type: Article
Pages
393-394
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Fatigue lives of carbon and low-alloy steels in LWR water environment decrease with decreasing strain rate, and increasing temperature and dissolved oxygen content. The fatigue life correction factor, F_<en'> has been proposed as a method to assess the fatigue life reduction in such environments. This paper describes a revised model for calculating F_<en>. In this revised model, sulfur content and water flow rate are considered for calculating F_<en>. It is found that this revised model shows better correlation with test data than the previous models. The research was carried out by the Japan Power Engineering and Inspection Corporation (JAPEIC) which was entrusted by the Ministry of Economy, Trade and Industry (METI).
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