研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙飛翔工学研究系 特任教授
- 学位
- 工学博士(1991年3月 東京大学)
- 研究者番号
- 60237419
- ORCID ID
https://orcid.org/0000-0002-2403-5780- J-GLOBAL ID
- 202101015987830507
- researchmap会員ID
- R000025142
経歴
7-
2024年4月 - 現在
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2021年11月 - 2024年3月
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2018年4月 - 2021年10月
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2000年4月 - 2018年3月
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1994年4月 - 2000年9月
学歴
1-
1986年4月 - 1991年3月
委員歴
14-
2022年4月 - 2024年3月
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2014年4月 - 2024年3月
受賞
7論文
53-
AIAA Journal 62(4) 1311-1317 2024年4月 査読有りThe objective of this study is to develop a novel aircraft design approach using biomimetics as an alternative to traditional airframes. This approach is primarily inspired by the dragonfly wing, which possesses reinforcement structures composed of cross veins and longitudinal veins. These structures are assumed to regulate deformation and enhance stiffness, respectively. The cross veins were replicated using weighted centroidal Voronoi tessellation (WCVT) based on the out-of-plane displacement of the skin. In contrast, the longitudinal veins were replicated by extracting a centerline from the topology optimization (TO) results on the skin, achieved through image analysis techniques such as binarization and skeletonization. The longitudinal layout effectively reduces compliance by distributing internal loads, utilizing only essential reinforcements on the skin without increasing its mass. The WCVT layout significantly enhances the buckling resistance of the reinforced skin. As a result, the skin reinforced using both cross–longitudinal layouts from TO and WCVT exhibited a buckling load 2.7 times greater while maintaining a lower mass compared to conventional layouts.
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Composites Part A: Applied Science and Manufacturing 172 2023年9月 査読有りAn analytical approach was developed for assessing the thermal history of thermoplastic composites during tape placement for in-situ consolidation of the automated fiber placement (AFP) technique. In this study, the heat-conduction equation is developed and solved for internal energy instead of temperature because the diffusivity does not significantly change over a wide range of temperatures in the AFP process, despite the significant change in the specific heat and conductivity. The three-dimensional internal energy history is derived in an integrated form using the Green function technique. The temperature field obtained from the internal energy field agreed with the finite element solution, where the temperature-dependent thermal properties were considered. The effects of manufacturing parameters, such as the placement speed and thickness of the placed laminates, on the thermal history of laminated composites during AFP are discussed using the present approach and finite element analysiss.
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Journal of Composite Materials 57(21) 3377-3391 2023年9月 査読有りTensile tests of quasi-isotropic laminates with a circular open hole, which include a gap in the hole area, were conducted to demonstrate the effect of the gap on the strength. The test showed that the reduction in the open-hole strength owing to the gap was less significant than that in the no-hole tensile strength. A two-dimensional mechanical model of quasi-isotropic laminates with an arbitrary inclined gap was proposed and analytically solved to obtain a closed-form expression for the stress concentration. An approximate expression was provided as the sum of the global uniform stress field and the local stress field near the open hole, which was solved based on a complex variable method. The present analytical solution agrees well with the corresponding two-dimensional finite element solutions. The solution indicated that the stress increase owing to the gap is limited at the stress concentration area. The analytical results were consistent with the experimental results.
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Composite Structures 306 2023年2月15日 査読有りCompression tests of quasi-isotropic laminates with embedded gaps were conducted to reveal the effect of the gap(s) on their compressive strength. Specimens were prepared such that the gaps are located at designated relative positions on a free side edge of the gage section. An analytical solution for a two-dimensional mechanical model of quasi-isotropic laminates with an arbitrary inclined gap is used to estimate the stress changes at the free edge owing to inclined gaps in the arbitrary relative locations. The relative reductions in the compressive strengths of the specimens with different gap arrangements were consistent with the analytically estimated increases in stress. The present results indicate that the significant reduction in compressive strength is caused not only by the waviness of the laminas at the gaps but also by the stress concentration at the free boundary due to the gap ends. Moreover, it is found that the standardized compression test may not be adequate to investigate the effect of the defect introduced by automated-fiber-placement method on the strength of the laminates because the sizes of the gage section of the compression test specimens specified by standard test methods are small compared to the gap spacing.
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Mathematics in Engineering, Science and Aerospace 11(2) 453-465 2020年 査読有り筆頭著者責任著者An engineering system such as an aircraft or a satellite undergoing rigid motion can inevitably include many types of uncertainties. These may be structural parameters such as dimensions, material properties, etc., and motion variables including velocity, acceleration, and direction. Consequently, an evaluation of their effects plays an important role in structural design. In this study, a differential equation is derived for the response of a moving elastic body under uncertain conditions based on the perturbation method. The effect of the uncertainty is represented by the sensitivity of the output with respect to the uncertain parameter. The equation is applied to a rotating Euler-Bernoulli cantilever beam and numerical examples are presented. As the natural frequency depends on the rotational velocity, the strain sensitivity responses are complex.
MISC
29講演・口頭発表等
163-
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 1993年A series of creep-fatigue experiments has been conducted with 304 stainless steel, 2 1/4Cr-1Mo steel and modified 9Cr-1Mo steel at in both air and very high vacuum environment of 0.1μPa. The damage model developed by the authors to evaluate the creep-fatigue damage in vacuum is applied to the data obtained in air and a separate evaluation of the environmental effect of air on the creep-fatigue interaction is made. Fatigue damage is highly affected with the air environment which results in a time/rate-dependent life reduction being mainly controlled by a strain rate. The air environment has different effect to the different material on the evolution of creep damage. It accelerates the creep damage in 304 stainless steel, gives no effect on it in modified 9Cr-1Mo steel and reduces it in 2 1/4Cr-1Mo steel.
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American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 1993年The stability analysis of the one-step Euler method in numerical time integration of a viscoplastic constitutive equation is discussed by applying the theory of nonlinear discrete dynamic system. The algorithm is represented as a discrete dynamic system which has a fixed point. The behavior of the system is classified into three types based on the eigen value of the Jacobian at the fixed point. Some numerical experiments are conducted and it is shown that the calculations meet the present theory.
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American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 1993年A series of creep-fatigue tests has been conducted with modified 9Cr-1Mo steel at 600°C in a high vacuum environment of 0.1 mPa to assess an accumulation of creep-fatigue damage. In these tests, each test specimen has been subjected to prior creep-fatigue loading followed by subsequent fatigue loading or prior fatigue loading followed by subsequent creep-fatigue loading. A linear summation of cumulative damage of fatigue and creep life faction was smaller then unity for the former case, and larger than unity for the latter case. SEM observation showed that in the case of prior creep-fatigue loading, a crack propagated from inclusions around which cavities were observed and its appearance transformed from transgranular to intergranular type with the increase of the number of cycles of prior creep-fatigue loading, while crack mode was predominantly intergranular in the case of prior fatigue loading. It was suggested that in the case of prior creep-fatigue loading, the fatigue life becomes shorter than that predicted by the linear rule due to early initiation of a crack caused from the cavity creation. In the case of prior fatigue loading, the crack propagates different courses in each loading to lead to the life fraction which is ″larger than unity″.
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American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 1992年A series of creep-fatigue tests have been conducted with Modified 9Cr-1Mo steel at 600°C in air and in a very high vacuum environment of 10-9 torr. Strain wave forms employed include symmetric continuous cycle, unsymmetric continuous cycle, and tension or compression hold-time cycle with a strain rate from 10-6 to 10-3 1/8 and a hold-time up to 600 s. Creep-fatigue life was reduced by about one order of amgnitude in air than in vacuum, however, the life reduction decreased as the creep component of damage increased. Data were analyzed based on the overstress concept to separate the environmental effect of air from the creep-fatigue interaction behavior. The environmental effect of air decreases the fatigue life, however, it does not affect the creep component of life.
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American Society of Mechanical Engineers, Materials Division (Publication) MD 1991年A unified inelastic constitutive equation is suggested for 2 1/4Cr-1Mo steel at the elevated temperature of 550°C. In the present study, an evolution of the overstress is discussed, where the overstress is a difference between the applied stress and the internal stress. Another significant point suggested in this study is the distinction of the inelastic deformation depending on the evolution of the overstress. A mathematical model is developed based on these assumptions. Many numerical experiments have been conducted to examine the validity of the present model. In comparison with the experimental results, the present model is shown to give good descriptions for a wide variety of loading conditions, including time-dependent plasticity, stress relaxation, creep and cyclic softening.
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American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 1989年Tension-torsion biaxial creep-fatigue tests have been conducted with 304 stainless steel at 650°C under a proportional biaxial strain condition. An overstress and an internal stress were analyzed under the biaxial strain condition. Peak stress components were well prepared with Von Mises equivalent stress. However, the overstress and internal stress showed a dominant anisotropy. A long term stress relaxation test was examined under biaxial proportional straining. The result suggested that a time-dependent inelastic strain is composed of at least two origins. One is caused from a relaxation of the overstress and the other is caused from a relaxation of the internal stress. The former is much faster than the latter. The relaxation of the internal stress indicates a recovery of the anisotropy.
共同研究・競争的資金等の研究課題
1-
日本学術振興会 科学研究費助成事業 1999年 - 2001年
