Papers by Author: Hideki Tonda

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Authors: Naomi Iida, Shinji Ando, Masayuki Tsushida, Hiromoto Kitahara, Hideki Tonda
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Authors: Takahiro Sakamoto, Shinji Ando, Hiromoto Kitahara, Masayuki Tsushida, Hideki Tonda
Abstract: In this present study, the fatigue behavior of titanium single crystals containing cracks growing in different crystallographic orientations has been investigated. To investigate fatigue fracture behavior of small single crystals, plain bending fatigue test method for thin sheet specimen was developed. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. In A-specimen, the notch plane and the direction are (11-20) and [1-100], respectively, the crack propagated parallel to {1-100} plane and striation-like markings were observed on the fatigue surfaces. In B-specimen with a notch of (1-100) and [11-20], the crack also propagated parallel to {1-100} plane as similar to A-specimen. These cracks are deduced to extend by alternating shear on two intersecting prismatic slip systems at the crack tip. In F-specimen with a notch of (0001) and [11-20], the crack propagated parallel to (0001) and twins were observed near the crack. As a result, S-N curves of each specimen showed strong orientation dependence and the fatigue strength of F-specimen was the highest in these specimens.
351
Authors: Shinji Ando, Takahiro Sakamoto, Yukishige Ikejiri, Masayuki Tsushida, Hideki Tonda
Abstract: Fatigue test of titanium single crystals with different crystallographic orientations has been carried. To investigate fatigue fracture behavior of small single crystals, plain bending fatigue test method for thin sheet specimen was developed. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. In A-specimen, a notch plane and the direction are (11 20) and [1100], respectively, the crack propagates parallel to {1100} plane and striation-like markings are observed on the fatigue surfaces. In B-specimen with a notch of (1100) [1120], the crack also propagates parallel to {1100} plane as similar to A-specimen. These cracks are deduced to extend by alternating shear on two intersecting prismatic slip systems at the crack tip. In F-specimen with a notch of (0001) [11 20], the crack propagates parallel to (0001) and some trace of pyramidal slip was observed on the fatigue surface. As a result, S-N curves of each specimen showed strong orientation dependence. Fatigue strength of F-specimen is higher than that of A- and B-specimen.
967
Authors: Shinji Ando, Katsuhiro Oyabu, Kousei Hirayama, Masayuki Tsushida, Hideki Tonda
Abstract: A crack propagation behavior of hcp crystal has been simulated by molecular dynamics method using Lennard-Jones type potential. A notch was introduced to model crystals with free surfaces. The size of the model was 13nm×24nm×4.6nm and about 80000 atoms were included in the model. A crack propagated by applying tensile strain on top and bottom layer of the model crystal. A definite dependence of crystallographic orientation on crack propagation behavior was obtained. In a model crystal with initial notch plane and direction were (101 0), [1 210], the crack propagated parallel to notch plane and two sets of prismatic slips were occurred at the crack. Therefore, the crack in this crystal is deduced to extend by alternating shear on two intersecting {101 0}, <1 210> prismatic slip systems. In a model crystal with (0001), [101 0] initial crack, {101 1} first order pyramidal slip occurred at crack tip and following {101 2} twin was also observed. In a model crystal with (10 1 0), [0001] initial crack, the crack propagates parallel to initial crack plane. Crack propagation rate of the crack near surface is faster than the crack in interior of the model. In this case, two prismatic slips were occurred in front of the crack. This result explains a mechanism of forming ‘Herring-born pattern’ which was observed in the titanium single crystal. Results obtained by these three models are well described the fatigue crack propagation behavior in hcp titanium crystals.
280
Authors: Takaaki Kitahara, Shinji Ando, Masayuki Tsushida, Hiromoto Kitahara, Hideki Tonda
Abstract: In general, deformation behavior of magnesium in compression is different from tensile. To investigate deformation behavior of magnesium single crystals, c-axis compression was performed. The crystals were yielded by second order pyramidal slip, and the yield stress shows anomalous temperature dependence (increased with increasing temperature) between 203K and 293K. Yield stress of c-axis compression is bigger than that of a-axis tensile. {10-13} twin and {11-24} twin occurred at 77293K and 77473K respectively. Fracture surface at 77293K was {11-24} and at 473K was {11-22}.
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Authors: Shinji Ando, Le Ping Bu, Shunsuke Tanaka, Hiromoto Kitahara, Hideki Tonda
Abstract: For development of high strength magnesium alloys, a melt stirring method was employed to Mg-Al and Mg-RE (rare earth metal) alloys. As reinforcement particle, B2O3 powder was added into melts and stirred at 953K in 10 or 20 minutes with argon atmosphere. The grain sizes of both alloys were decreased by 3wt% B2O3 addition. These results show that B2O3 have grain refinement effects to magnesium alloys. Micro Vickers hardness of Mg-Al alloy was increased by 3wt% B2O3 addition. On the other hand, the hardness of Mg-RE alloy was decreased by B2O3. Though addition of B2O3 into Mg-Al and Mg-RE systems make grain size to fine, the hardness of Mg-RE alloys decreased. The tensile properties of Mg-RE alloys with B2O3 were extremely improved by extrusion process.
271
Authors: Shinji Ando, Hideki Tonda
1031
Authors: Y. Mine, T. Yamada, Shinji Ando, K. Takashima, Hideki Tonda, Yakichi Higo, Paul Bowen
721
Authors: Shinji Ando, Kazuaki Toda, Masayuki Tsushida, Hideki Tonda, Yoshihito Kawamura
Abstract: Recently, Mg-Zn-Y alloys with superior performance, which have a long period order (LPO) phase, have been developed. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of Mg-Zn2-Y2-Zr0.2 alloy has been investigated using a plain fatigue bending testing machine, which was originally developed for thin sheet specimen. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. To estimate stress amplitude of bending, deflections at the free end of the specimen oscillating at a frequency of about 250~700Hz was measured by a laser displacement gauge. For comparison, AZ31B alloy also has been investigated. S-N curve for the Mg-Zn2-Y2-Zr0.2 alloy was obtained using a stress ratio of R=-1, and the fatigue strength was estimated as about 200MPa at 106~108 cycles. The value corresponds to about 50% of 0.2% proof strength of the alloy. Two types of fatigue surface were observed in the alloy. One is striation like pattern and the other is relatively flat surface. The former is similar to fatigue surface of AZ31B. Therefore, these two types of fatigue surface correspond to crack passing through α-Mg phase and LPO phase, respectively.
975
Authors: Masayuki Tsushida, Kazuaki Toda, Hiromoto Kitahara, Shinji Ando, Hideki Tonda
Abstract: Recently, Mg-Zn-Y alloys with superior performance, which have a long period stacking order (LPSO) phase, have been developed. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of the Mg96Zn2Y2 alloy has been investigated with a plain bending testing machine, which was originally developed for thin sheet specimen at room temperature and 523K. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. To estimate stress amplitude of bending, deflections at the free end of the specimen oscillating at a frequency of about 200~500Hz was measured by a laser displacement gauge. For comparison, AZ31B alloy also has been investigated. S-N curve for the Mg96Zn2Y2 alloy was obtained using a stress ratio of R=-1, and the fatigue strengths were estimated as 200MPa at room temperature and 120MPa at 523K at 106~107 cycles. These values correspond to about 50% of 0.2% proof strengths of the Mg96Zn2Y2 alloy. Two types of fatigue surface were observed in the Mg96Zn2Y2 alloy. One was striation-like-pattern and the other was relatively flat surface. Striation-like-pattern was similar to fatigue surface of AZ31B. Therefore, these two types of fatigue surface correspond to crack passing through α-Mg phase and LPSO phase, respectively. The feature of fracture surface at 523K was almost the same as that at room temperature.
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