Papers by toshiya nakamura
The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experim... more The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experiments. The two bars are restrained to the same length and are subjected to a constant load. One bar sees cyclic temperature variations, while the other bar is kept at constant temperature. The material models employed are rate independent plasticity (kinematic hardening) and the viscoplasticity theory based on overstress (VBO) matched to represent the cyclic neutral 6061 T6 aluminum alloy elastic and inelastic deformation behavior. For simplicity, temperature-independent material properties were assumed. Numerical analyses were performed to investigate the effects of rate of thermal loading and temperature range. Elastic-inelastic shake down is ultimately achieved due to work hardening. There is a strain range increase until it reaches a steady value. Kinematic hardening and VBO predict almost the same strain range, which, for the case of VBO, is nearly rate-independent. The behavior for both material models is very different for the mean strain. For VBO, the number of cycles to shakedown is rate-dependent and is considerably larger than for kinematic hardening. Finally, the steady-state mean strain and strain range are computed directly for VBO.
Springer eBooks, 2009
Fatigue crack growth rates in an FSW butt joint panel were obtained in order to evaluate the effe... more Fatigue crack growth rates in an FSW butt joint panel were obtained in order to evaluate the effect of residual stress on crack growth behavior. Two angles between the weld line and loading direction, and two distances between the weld line and the center of the starter notch were employed to investigate the effect of the residual stress field on the crack growth rate and path, and the effect of the initial distance on crack growth acceleration in tensile residual stress field. The test results indicate that the crack growth rate and path on the weld line are merely affected by the angle between the weld line and the loading direction. Furthermore, the acceleration of crack growth was not affected by the distance between the weld line and the initial notch. Under this test condition, the maximum principle stress is not the primary factor determining the direction of crack growth; rather, the direction of the maximum stress range seems to be the primary factor.
Journal of Pressure Vessel Technology-transactions of The Asme, Aug 1, 1997
The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experim... more The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experiments. The two bars are restrained to the same length and are subjected to a constant load. One bar sees cyclic temperature variations, while the other bar is kept at constant temperature. The material models employed are rate independent plasticity (kinematic hardening) and the viscoplasticity theory based on overstress (VBO) matched to represent the cyclic neutral 6061 T6 aluminum alloy elastic and inelastic deformation behavior. For simplicity, temperature-independent material properties were assumed. Numerical analyses were performed to investigate the effects of rate of thermal loading and temperature range. Elastic-inelastic shake down is ultimately achieved due to work hardening. There is a strain range increase until it reaches a steady value. Kinematic hardening and VBO predict almost the same strain range, which, for the case of VBO, is nearly rate-independent. The behavior for both material models is very different for the mean strain. For VBO, the number of cycles to shakedown is rate-dependent and is considerably larger than for kinematic hardening. Finally, the steady-state mean strain and strain range are computed directly for VBO.
Jsme International Journal Series A-solid Mechanics and Material Engineering, 1998
Journal | MESA, May 25, 2020
An engineering system such as an aircraft or a satellite undergoing rigid motion can inevitably i... more 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.
Nenji Taikai koen ronbunshu, 2007
Nucleation and Atmospheric Aerosols, 2012
ABSTRACT Thermal analysis is required in the design of the structure of atmospheric reentry vehic... more ABSTRACT Thermal analysis is required in the design of the structure of atmospheric reentry vehicles, which are subjected to severe aerodynamic heating. However, prediction of aerodynamic heating is difficult owing to highly complex physical phenomena. Inverse heat conduction analysis, the methodology to estimate heat flux on boundaries and entire temperature distribution from limited number of temperature measurement, is expected to solve this problem and to contribute to improving structural integrity. Present study develops computational method of transient inverse heat conduction analysis using finite element method and pseudo-inverse matrix. The developed inverse analysis code is applied to a reentry vehicle in order to examine the present method and to discuss the computational stability and regularization methods. Sequential function specification (SFS) method and rank reduction are employed to improve the accuracy and stability of the inverse analysis. The results of the numerical simulation reveal that the present method works effectively in solving inverse problem stably by using the combination of SFS method and rank reduction. Especially, the rank reduction is quite efficient at regularization. SFS method requires proper number of future time steps.
Aerospace Science and Technology, Dec 1, 2012
Pseudo-inverse matrix Quasi-Newton method Finite element method Operational load and stress data ... more Pseudo-inverse matrix Quasi-Newton method Finite element method Operational load and stress data are useful for structural integrity management and damage prognosis of aerospace systems. Identifying aerodynamic loads by monitoring strain is not easy because the loads are distributed continuously over the structure's surface. In this study, we propose a flexible method for interpolating a continuous load distribution in order to identify the full-field aerodynamic load from strain data acquired at a number of discrete points. Our method uses the conventional finite element method and pseudo-inverse matrix, and we further extend it by coupling with an aerodynamical equation. Numerical simulations show that this extension improves the estimation accuracy when only a limited amount of strain data is available. The effects of measurement error are also discussed. It is concluded that the rank reduction method improves the estimation accuracy and that use of a proper aerodynamical restriction can suppress the adverse effect of measurement error.
Aerospace Science and Technology, May 1, 2006
Thermal analysis plays an important role in the structural design of atmospheric reentry vehicles... more Thermal analysis plays an important role in the structural design of atmospheric reentry vehicles, which are subjected to severe aerodynamic heating. It is sometimes difficult to assess the design safety margin because of uncertainties in the predicted heat flux and the material properties used in the thermal analyses. However, probabilistic techniques allow the effects of uncertainties to be analyzed, and the present study demonstrates the probabilistic thermal analysis of the PARTT reentry vehicle using the Monte Carlo technique to investigate the probabilistic temperature responses. The temperature responses were found to depend significantly on time and location, and reliability was predicted at all locations. The peak temperature of the vehicle's main structure was found to be strongly correlated with heat shield temperature, and analysis of the contributions of random parameters showed that heat flux and heat shield emissivity significantly affect the peak temperature. These results indicate that the thermal design of the heat shield shell is very important for the whole structure. It is expected that such information will provide good insight for the design of a reentry vehicle's structure.
M & M Zairyo Rikigaku Kanfarensu, 2019
Nucleation and Atmospheric Aerosols, 2014
Fiber Bragg Grating (FBG) sensors have widely been used to monitor temperature and strain distrib... more Fiber Bragg Grating (FBG) sensors have widely been used to monitor temperature and strain distributions as a part of the structural health monitoring system. Since FBG has the sensitivity to the variations in both temperature and strain, a compensation is required to separate the strain or temperature data from the sensor output which is the shift of the grating’s Bragg wavelength. The present study develops a computational inverse thermoelastic analysis method to separately identify the thermal and mechanical boundary conditions (loads) from the output of the FBG sensor. Numerical study has been made for a corrugate-core sandwich integral thermal protection system (TPS) to examine the method. The discussion is focused on the computational stability. The results reveal that the identification of the mechanical load is less stable than that of the heat flux. It is also shown that the condition number of a coefficient matrix serves as the index of the stability of the inverse analysis.
International Journal of Pressure Vessels and Piping, 1992
Comparison of two new surface treatment procacaso, ll.ler4ndu~d shock wevso and primary explosive... more Comparison of two new surface treatment procacaso, ll.ler4ndu~d shock wevso and primary explosive: application to fatigue behaviour.
Jsme International Journal Series A-solid Mechanics and Material Engineering, 2001
Recent development of the strain sensor based on optical fiber technology enables one to obtain s... more Recent development of the strain sensor based on optical fiber technology enables one to obtain strain data with high spatial density. The objective of the present study is to reconstruct the stress field from the measured strain data. Since the strain can be measured only along the fiber direction, an inverse elastic analysis is inevitable to reproduce the two-dimensional stress field which has three components of plane stress tensor. Due to the ill-posed nature of the inverse elastic problem, the stability of the analysis strongly depends on the modeling of the displacement and/or load conditions on the boundary, and their degree of freedom. A trial is made in this study where the stress distribution is deduced from the stress functions. The advantage of using the stress functions is that the stress equilibrium and strain compatibility are automatically satisfied, resulting a sound restriction to the possible solution. We use the complex stress functions given by the series of analytic functions, then the problem turns to be finding the proper set of coefficient that makes the best fitting to the measured strain data. Numerical examples are presented that are the stress concentration problems around a hole in a plate. It is demonstrated that the present method reconstructs the stress field around the hole and the estimated stress agrees with the FE analysis result.
Kotsu, Butsuryu Bumon Taikai koen ronbunshu, 2010
Japan Aerospace Exploration Agency ， 6 − 13 −10sawa ， Mitaka ， T ()kyo The Aviation Program Group... more Japan Aerospace Exploration Agency ， 6 − 13 −10sawa ， Mitaka ， T ()kyo The Aviation Program Group of Japan Aerospace Explorat 三 〇n Agency (APGIJAXA) is ⊂ onducting research of advanced and fUndamental aeronautical technologies based Qn social and industrial needs derived丘 om diversifying technological reqUirements and increasing air transport in the future ， The background includes the ongoing development of the f 丘st passengerjet aircraft produced in Japan after almost 50 years ． The primary goals is to develop the cutting −edge technologies which can be applied to the development of competitive aircraft in the world market ， T ｛) achieve this ， JAXA lau エ 1ched a research project in 2003 which covers wide variety of aeronautical science and technologies ． This arti ⊂le describes the Qutline of the project ．
Transactions of the Japan Society of Mechanical Engineers. A, 2002
Transactions of the Japan Society of Mechanical Engineers. A, 2000
한국항공우주학회 학술발표회 논문집, Nov 1, 2008
One of the goals of JAXA’s Aviation Program Group (APG) is to develop the cutting-edge technologi... more One of the goals of JAXA’s Aviation Program Group (APG) is to develop the cutting-edge technologies and make them available in the development of competitive aircraft in the world market. To achieve this, JAXA launched a research project in 2003 which covers wide variety of aeronautical science and technology: computational fluid dynamics (CFD), advanced optical measuring methods in wind tunnel test, aero-acoustic analysis (computational aero-acoustics, CAA) to reduce airframe noise, computational tool to analyze transonic flutter behavior, analysis and test of crashworthiness, composite materials and structures, and control systems. This article describes JAXA’s efforts conducted in the project in some details. Some of these activities have been contributing to the development of MRJ, the first jet passenger aircraft under development in Japan.
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Papers by toshiya nakamura