Koichi Ogawa

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (82)30.33 Total impact

  • Hiizu Ochi · Gosaku Kawai · Yoshiaki Yamamoto · Koichi Ogawa
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    ABSTRACT: Tensile strength and fatigue strength of friction-welded joints of pure titanium to tough pitch copper were statistically analyzed and validated by experimental tensile and fatigue testing. In the tensile testing, it was found that the shape parameter of the Weibull distribution increased with an increase in mean value of the tensile strength and with a decrease in dispersion of the tensile strength. The shape parameter was useful for judging the suitability of the friction welding conditions. An appropriate shape parameter could be estimated by Weibull analysis from the data of 10 pieces of joint specimens. In the fatigue testing, P-S-N curves showed that the dispersion in the fatigue life distribution of the sound joint was stabilized regardless of stress level, whereas that of a poor joint dispersed as the stress level decreased. Moreover, the guarantee fatigue life of sound joints could be estimated by Weibull analysis.
    No preview · Article · Oct 2015 · Strength, Fracture and Complexity
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    ABSTRACT: The relationship between joint strength and deformation heat input at the upset stage and the relationship between joint strength and upset burn-off length were examined on friction welded joints of 1050 pure aluminum to C I 100 tough pitch copper. Joint quality was evaluated from the tensile strength and fatigue strength. It was found that both the deformation heat input at the upset stage and the upset burn-off length correlated well with joint strength. Additionally, when the deformation heat input at the upset stage or upset burn-off length exceeded a certain value, stable tensile strength was obtained. The mixing layer, intermetallic compounds of Al-Cu were interpolated into A 1050, formed at the weld interface, and joints having a thick mixing layer fractured at the weld interface. Joint efficiencies of sound joints for the fatigue limit of the A 1050 base metal were 88-100%. Judging front the fatigue limit, sound joints could be produced when either the deformation heat input at the upset stage or the upset burn-off length exceeded a certain value. [doi: 10.2320/matertrans.L-MRA2008836]
    Preview · Article · Dec 2008 · Journal of Japan Institute of Light Metals
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    Yoshihiro Isshiki · Gosaku Kawai · Hiizu Ochi · Koichi Ogawa
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    ABSTRACT: A numerical method was proposed to predict transient temperature distribution in friction welding of two similar materials of steel. In this method, heat input was estimated using the data of thrust pressure and rotation speed which could be easily measured under a commercial friction welder. The estimated heat input was given as a boundary condition of heat flux at the weld interface, and a finite element method was used for solving an unsteady heat conduction problem of two-dimensional axis symmetry. Transient temperature distributions during whole friction welding process were calculated using variable thermal properties of the specimen materials of mild steel and stainless steel respectively. Calculated results were compared with experimental results, and the relationship between calculated temperature distribution and measured hardness distribution was investigated in the vicinity of weld interface.
    Preview · Article · Jan 2008
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    ABSTRACT: The effect of heat input on joint strength in the brake type friction welding has become clear, but the effect in the inertia type friction welding is not clear even at present. Then in this report, inertia type friction welding of 6061 aluminum alloy was carried out in order to examine the effect of unit heat input, burn-off length and burr shape on the joint strength. The heat input (mechanical work) was calculated by burn-off speed and welding pressure in the final stage. The joint strength was examined by tensile test. The final stage (welding time) of inertia type friction welding corresponding to the upset stage of brake type friction welding was searched using the relationship between heat input and joint strength. Using the most proper-final stage obtained, the relationships between unit final deformation heat input and joint strength, final burn-off length and joint strength, and burr shape and final deformation heat input were examined. Also the minimum unit final deformation heat input and minimum final burn-off length required for making a sound joint were also examined. The results showed that within this experiment the most proper-final stage (welding time) was 0.1s, and the limit unit final deformation heat input and limit final burn-off length were 19J/s and 0.3mm, respectively.
    No preview · Article · Jan 2007
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    ABSTRACT: We have developed digital phantoms to be used for a basic education on an image quality and a quantification of SPECT data. Differing from the digital phantoms developed by Castiglioni and et al, several SPECT projection data sets were generated by Monte Carlo simulations (EGS4 code) with different acquisition parameters. A physical, brain and cardiac phantoms were generated. An external shape of the physical phantom is a 200 mm diameter and 200 mm long cylinder. Three objects, each of which consists of 4 mm, 10 mm, 20 mm, 40 mm and 60 mm diameter rods (each rod is 30 mm long) , are set in. Shapes of the brain phantom were created using a MRI data set. Shapes of the cardiac phantom were created using a CT image set. Tc-99m was used for the simulations. The Monte Carlo simulations were performed, taking account of Compton scattering, photoelectric effect and degradation of a spatial resolution due to collimator aperture. SPECT acquisition parameters were collimator type, pixel length, acquired photon count, projection number and radius of detector rotation. Ideal SPECT projection data and transaxial image were generated as reference (standard) data. Several attenuation maps with different attenuation coefficients can be used for an evaluation of an attenuation correction. The triple energy window setting was used for an evaluation of a scatter correction such as the TEW method. Overall, primary and scattered photons were saved in different files. By using the proposed phantoms, spatial resolution, contrast, signal to noise ratio and quantification with SPECT data acquisition and processing parameters were evaluated. The phantoms are considered to be useful for understanding the fundamental performance on SPECT.
    No preview · Conference Paper · Jan 2007
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    ABSTRACT: The purpose of this study is to estimate temperature distribution in the vicinity of weld interface during a friction welding process involving an upset process. On the base of a simple model of friction heat input, a non-steady heat conduction analysis was carried out by finite element method. As a result from a comparison of the estimated temperature distribution with the experimental data, it turned out that the friction heat input model that allowed for the effects of temperature and linear velocity on the friction coefficient was appropriate. This heat input model could simulate adequately the change in friction heat input and temperature distribution in a friction welding process. As a result, the relationship between burn-off length and temperature distribution in upset process has been explained and also the relationship between temperature distribution and width of heat-affected zone has been obtained. This heat input model allows us to estimate temperature distribution in friction welding, from friction pressure, rotation speed and the thermal property of base metal, even where a friction-welding machine does not have a function of torque measurement.
    No preview · Article · Jan 2007
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    ABSTRACT: An approach to combine a friction heat input model with a non-steady heat conduction analysis has enabled a numerical simulation of a heat input and a transient temperature distribution in friction welding processes. This report describes the result obtained by applying this approach to the friction welding process of two similar materials of S25C carbon steel or SUS304 stainless steel. When base metals are different, the friction heat input model and the thermophysical property data are changed depending on a quality of base metal. Comparison between a calculated result and an experimental result was carried out, and appropriateness of this approach was examined. Furthermore, a difference of temperature distribution in friction welding region with the difference of thermophysical property of base metal was examined, and also the heat-affected zone was investigated. As a result, it was verified that this approach could simulate a characteristic of a welding process in brake-type friction welding. And the calculated results agreed with the experimental results on a difference of quantity of heat input to be caused by a difference of a friction welding condition. A difference of a temperature history caused in a different base metal appeared to be estimated from a calculated result, and it was confirmed that this approach was appropriate. The width of heat-affected zone was estimated by an calculated result of the maximum temperature distribution in the vicinity of friction surface by using this approach combining a friction heat input model with a non-steady heat conduction analysis.
    No preview · Article · Jan 2007
  • Kazuhiko Kowase · Koichi Ogawa
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    ABSTRACT: In a conventional X-ray CT scanner with Gd<sub>2</sub>O<sub>2</sub>S detectors, the measured data are the whole X-ray energy deposited to each detector bin. The detection of energy is performed in an integration manner, so that the contribution of photons having low energy is smaller than that of those having high energy. But if we use a semiconductor detector such as CdTe with a photon counting mode, we may obtain valuable information for the medium being imaged. For example, if we obtain some information about energy spectra for detected photons, we can enhance the contrast resolution of media having almost the same linear attenuation coefficient as soft tissues by weighing the counted photons having lower energy. To clarify the validity of our proposed method, we used a CdTe semiconductor detector and reconstructed images with projection data measured with different thresholds in counting X-ray photons.
    No preview · Conference Paper · Dec 2006
  • Koichi Ogawa · Mayuko Kishino · Tsutomu Yamakawa
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    ABSTRACT: In an X-ray CT system the energy fluence of X-rays is commonly measured with scintillation detectors in the data acquisition. To enhance the contrast in low contrast media we proposed a new concept of X-ray CT system. This technique utilized the information for an energy spectrum of X-rays. That is, we applied more than two voltages to an X-ray tube and obtained data measured with different energy spectra. Without increasing the irradiation dosage of X-rays, the contrast enhancement was carried out with arithmetic between these reconstructed images. The aim of this study is to clarify the validity of such an energy-modulated X-ray CT with simulations.
    No preview · Conference Paper · Dec 2006
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    ABSTRACT: A CdZnTe semiconductor detector, which works at room temperature, may realize a next generation gamma-camera system due to its high spatial resolution and high energy resolution. We made a prototype gamma-camera system with CdZnTe detectors to evaluate the feasibility of the semiconductor gamma-camera. This paper described our prototype system and some results obtained with this system.
    No preview · Conference Paper · Dec 2006
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    ABSTRACT: The Ono's rotary bending fatigue test and the cantilever rotary bending fatigue test were carried out on friction-welded 6061 aluminum alloy joints, and the relationship between the deformation heat input in the upset stage or the upset burn-off length and fatigue strength was examined. In the Ono's type test, sound joints, which fractured in the heat affected zone in the tensile test, fractured in the heat affected zone also and the fatigue limit of these joints was slightly lower than that of 6061 aluminum alloy base metal. This is because joints fractured in the softened area in both tensile test and Ono's type test using smoothed test specimens. While, in the cantilever type test, the fatigue limit of sound joints was a little more than or a little less than that of 6061 aluminum alloy base metal. It seems that a weld and a structure at the weld interface affected fatigue strength in the cantilever type test using notched test specimens. Judging from the fatigue limit obtained, sound joints could be produced when either the deformation heat input in the upset stage or the upset burn-off length exceeded a certain value.
    Preview · Article · Jul 2006 · Journal of Japan Institute of Light Metals
  • Takashi KURIHARA · Koichi Ogawa
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    ABSTRACT: In a simulation study the description of an object is very important for high speed calculation in photon transportation with a Monte Carlo method. For this object description we developed a maximum rectangular region (MRR) method in 2000 (TNS vol.47, No.3) thereby reducing the calculation time. In this paper we proposed a more efficient method in which we considered the location of a photon within a rectangular region. This method could reduce the calculation time as compared with the MRR method.
    No preview · Article · Jan 2006
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    ABSTRACT: Similar and dissimilar joints of 2017 and 6061 aluminum alloys were friction welded. Fatigue strength and fatigue life distribution of these joints were examined. The S-N curve showed that the fatigue strength of A2017/A2017 was almost the same as that of A2017 base metal, while that of A6061/A6061 was lower than that of A6061 base metal. The fatigue strength of A2017/A6061 was lower than that of A6061/A6061. The fatigue limit at 108 cycles of A2017 base metal, A2017/A2017, A6061 base metal, A6061/A6061 and A2017/A6061 were 120MPa, 120MPa, 70MPa, 60MPa and 55MPa, respectively. The shape parameter m and the location parameter γ in Weibull distribution function of the joints were lower than those of the base metals. These results suggest that the scatter in fatigue life distribution is larger and the smallest fatigue life is shorter for the present joints compared to the base metals.
    No preview · Article · Jan 2006 · Journal of Japan Institute of Light Metals
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    Jianbin Ju · Yasuo Suga · Koichi Ogawa
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    ABSTRACT: In automatic butt welding of relatively thin plates, it is important to control welding conditions in order to obtain a sound full-penetration weld. Recently, an intimate relationship was reported between the oscillation of the molten pool and penetration. The vibrating frequency of a molten pool decreases drastically with the transition from partial penetration to full penetration and with an increasing molten pool size. As a result, the vibration of the weld molten pool can be analyzed for an estimation of weld penetration. In this study, a new vibration method is proposed: the Pulse Shielding Gas (PSG) oscillating method. The natural vibration frequency of a molten pool is measured from the molten pool oscillation detected by an arc sensor. A control system is constructed, which controls the welding current on the basis of the measured vibration frequency. © by The International Society of Offshore and Polar Engineers.
    Preview · Article · Jun 2004
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    ABSTRACT: The relationship between the deformation heat input in the upset stage or the upset burn-off length and joint strength was examined on the friction-welded SUS304 stainless steel joints. Joint strength was evaluated by tensile test and fatigue test. It was found that the deformation heat input in the upset stage or the upset burn-off length was correlated well with tensile strength, and a stable tensile strength was obtained when the deformation heat input in the upset stage or the upset burn-off length exceeded a certain value. In the Ono's rotary bending fatigue testing, the fatigue strength of sound joints was a little less than that of SUS304 base metal. While, in the cantilever rotary bending fatigue testing, the fatigue strength of sound joints was a little more than that of SUS304 base metal. This difference probably resulted from the fatigue fracture occurred in the softened area in the Ono's type testing and at the weld interface in the cantilever type one. Judging from the fatigue limit obtained, sound joints can be produced when the deformation heat input in the upset stage or the upset burn-off length exceeds a certain value.
    No preview · Article · May 2004 · Journal of the Society of Materials Science Japan
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    ABSTRACT: Aluminum alloys to S25C carbon steel were friction welded, and the friction weldability and intermetallic formations at the weld interface of joints were investigated. Joints of A1050, A5052, A6061 and A6063 to S25C showed good-weldability, and A5056/S25C joint was somewhat poor than former one. An intermetallic compound of Al 13Fe 4 was formed at the weld interface of A5056/S25C and A6061/S25C joints, and their intermetallic formations were tend to increase with friction pressure, friction time and rotation speed. The joint strength of these joints was high when thin instermetallic conpound layer was formed under high upset pressure. Somewhat poor-weldability of A5056/S25C joint compared with A6061/S25C joint seemed a cause of the intermetallic formation accelated by high content of magnesium in A5056. Joints of A2011, A2017, A2024 and A7075 to S25C showed poor-weldability. Brittle intermetallic compounds of CuAl 2 and Al 7Cu 2Fe were formed at the weld interface of A2011/S25C joint containing a copper.
    No preview · Article · May 2004 · Journal of the Society of Materials Science Japan
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    ABSTRACT: In order to measure the heat input (quantity of heat) generated during friction welding, a new type calorimeter of acryl resin was developed, and applied to friction welding of a stainless steel. The heat input measured during friction welding was in good agreement with the values calculated from the measured values of friction torque, burn-off length, rotation speed and pressure. Being classified into friction and deformation heat inputs, the friction heat input was much greater than the deformation heat input through the friction and upset stages.
    No preview · Article · Jan 2004
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    ABSTRACT: Friction welding of aluminum alloys to copper was carried out in order to examine the weldability with particular reference to the effect of the intermetallic formation at the weld interface. The maximum joint efficiencies of A1050, 5000 and 6000 series alloys to copper were more than 80 %, while those of 2000 series and A7075 alloys joints were less than 50 % and scattered widely. For joints of A2024 and 5000 series alloys which contain rather high magnesium content, intermetallic compounds of Al-Cu-Mg system were formed at the weld interface in addition to that of Al-Cu system. In the other joints, only intermetallic compounds of Al-Cu system were formed. A mixing layer, in which pieces of copper and intermetallic compounds were incorporated into aluminum alloy, was formed near the weld interface. The mixing was very intense, in the joints with low efficiency, namely joints of A2011, A2024 and A7075 to copper, and these joints were fractured in this mixing layer and at the weld interface. On the other hand, the joints with high efficiency, namely joints of A5052 and A6061 to copper, had thin and even mixing layer. The mixing layers observed in the joints of A1050, A2017, A5056 and A6063 to copper were thinner than those of the other joints.
    No preview · Article · Aug 2003 · QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY
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    ABSTRACT: In this paper, the effect of the upset timing on joint strength of the friction welded joints of 6061 aluminum alloy was discussed by using the evaluation factors of the deformation heat input in the upset stage and the upset burn-off length. The results showed the followings. When the upset pressure was applied before the braking, the deformation heat input in the upset stage and the upset burn-off length were so large more that sound weld joints could be obtained easily, than that of the synchronized timing at the same welding parameters. In the synchronized timing, when the upset pressure was large, the actual pressure could not attain to a set up pressure. Meanwhile, when the upset pressure was applied after the braking, the deformation heat input in the upset stage and upset burn-off length were so small that sound weld joints could not obtained. Therefore, it was made clear by using effect of the upset timing in joint performance was much related with the deformation heat input and upset burn-off length. And the sound welded joints were obtained with 200 J/s or more deformation heat input and 2.5 mm or more upset burn-off length.
    No preview · Article · Feb 2003 · Journal of Japan Institute of Light Metals

  • No preview · Article · Jan 2003 · Materials Science Forum

Publication Stats

415 Citations
30.33 Total Impact Points

Institutions

  • 1991-2015
    • Osaka Prefecture University
      • Faculty of Liberal Arts and Sciences
      Sakai, Ōsaka, Japan
  • 2006
    • Osaka Electro-Communication University
      Ōsaka, Ōsaka, Japan
  • 1996-2006
    • Hosei University
      • Department of Electronics and Electrical Engineering
      Edo, Tōkyō, Japan
  • 2002
    • Osaka Sangyo University
      Ōsaka, Ōsaka, Japan
    • Osaka Institute of Technology
      • Department of Mechanical Engineering
      Ōsaka, Ōsaka, Japan
  • 1982-1991
    • Keio University
      • • Department of Radiology
      • • Department of Electronics and Electrical Engineering
      Tokyo, Tokyo-to, Japan