Papers by Author: Yoshihiro Narita

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Authors: Daisuke Narita, Yoshihiro Narita
Abstract: Curved panels can bear more lateral load than flat plates because they can transmit the external load along curved surface in addition to load-carrying capacity by the bending stiffness. For curved panels, however, there is a critical point of the lateral load that structure can endure before it buckles. On the other hand, composites are known to have more advantages in specific strength and stiffness than conventional metal materials. The present paper proposes a semi-analytical method to predict the initial buckling loads of slightly curved panels composed of thin orthotropic composite layers under general boundary conditions. Based on the Donnell type theory, the potential strain energy is evaluated as a sum of stretching energy, stretching-bending coupling energy and bending energy, and the external work done by uniform external pressure is included in the functional. The eigenvalue equation is derived by the Ritz method to yield such initial buckling load parameters as eigenvalues. Numerical examples include a list of buckling loads and the corresponding buckling patterns for typical panels with simply supported and clamped edges.
Authors: Daisuke Narita, Yoshihiro Narita
Abstract: Despite a large number of technical papers on vibration of composite shallow shells, all the previous papers have dealt with shallow shells with uniform curvature to avoid difficulty in the analysis. Recent composite products, however, require various surface designs of thin panels from the viewpoint of industrial design, for example, in the fender and door panel designs of commercial vehicles. The present study proposes an analytical method to deal with vibration of shallow shells with non-uniform curvature. An interpolating function is introduced to represent the required surface shape and the corresponding curvature is derived as a function of the position (x,y). The obtained curvature is substituted into the total potential energy of the shell, and the procedure is shown to derive a frequency equation in the Ritz method. Numerical examples clarifies the effects of non- uniform curvature on the natural frequencies and mode shapes.
Authors: Takuji Kobayashi, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Yoshihiro Narita
Abstract: This paper discusses ratchetting deformation of lead-free solder Sn/3Ag/0.5Cu and lead-containing solder alloy Sn/37Pb with several stress amplitudes and stress ratios of the maximum stress to the minimum stress. First the uniaxial ratchetting testsare conducted with three maximum stresses and five stress ratios. The all tests are conducted using cylindrical bulk specimens of the solder alloys at 313 K. The test results show that there is the difference in the viscoplastic deformation behavior between two solder alloys. The relationship between ratchetting strain and time is estimated by Biley-Norton law to explain that the uniaxial ratchetting deformation is strongly dominated by the viscous deformation. Finally, the ratchetting deformation is simulated by the dislocation based constitutive model proposed by Estrin [1]. The simulations show that there is a possibility to simulate the uniaxial ratchetting by clarifying the dislocation mechanism of the solder alloys.
Authors: Shinya Honda, Yoshihiro Narita, Katsuhiko Sasaki
Abstract: Structural plate elements in composite structures are typically fabricated by stacking orthotropic layers, each of which is composed of reinforcing fibers and matrix materials. In this work, three optimum design approaches are compared to clarify the advantages and disadvantages for optimizing the buckling performance of laminated composite plates. The first approach is developed recently by the authors, where the buckling load is maximized with respect to the lamination parameters by a gradient method and then the optimum lay-up design is determined by minimizing the errors between the optimum parameters and parameters for all possible discrete lay-ups. The second approach is the layerwise optimization (LO) approach where the fiber orientation angle in each layer is optimized step-by-step by repeating one dimensional search. The third one is a direct application of a simple genetic algorithm (SGA). In numerical examples, three sets of results are compared to discuss on the methodology for buckling optimization.
Authors: Takuma Kawakami, Yoshihiro Narita, Katsuhiko Sasaki
Abstract: Composite materials are frequently used in automobile and other moving vehicle structures. External and internal sounds sometimes cause unpleasant effects on the users and environment, and reduction of such sound is one of the key engineering problems. This study presents an acoustic radiation analysis from forced vibration of laminated rectangular plates and proposes a design approach to reduce the sound pressure from the plates. In the analysis the sound pressure at an arbitrary point over the plate is derived and is used as an object function in the optimization. A set of the fiber orientation angles is used as the design variable, and is optimized to minimize the sound pressure at the designated point. It is shown in numerical examples that the optimum design for sound pressure reduction is possible by the present approach.
Authors: Tsuyoshi Mayama, Katsuhiko Sasaki, Yoshihiro Narita
Abstract: In the present study, a new approach is conducted to evaluate dislocation structure induced by cyclic plasticity. First, cyclic plastic loading tests are carried out up to 100 cycles with three different small strain amplitudes on SUS316L stainless steel at room temperature. The test result presents the dependence of the strain amplitude on cyclic hardening and softening behaviors. Specifically, it is found that the cyclic loading test with strain amplitude of 0.25% shows both cyclic hardening and cyclic softening, while the cyclic loading tests with strain amplitudes of 0.75% and 1.0% show no cyclic softening. Secondly, the dislocation structures of the specimens after cyclic loading are observed by using a transmission electron microscope (TEM), and this observation reveals that the dislocation structure after cyclic loading test depends on the strain amplitude. Finally, a quantitative evaluation method of the dislocation structure is also proposed. The TEM images are converted into binary images and the resolution dependence of the generated binary image is used to visualize the characteristics of the dislocation structure. The relationship between strain amplitudes of cyclic plasticity and dislocation structure organization is clarified by the evaluation method. Finally, the heterogeneity of the dislocation structure is discussed.
Authors: Takuji Kobayashi, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Yoshihiro Narita
Authors: Tsuyoshi Mayama, Katsuhiko Sasaki, Yoshihiro Narita
Abstract: The present paper investigates relationships between the macroscopic viscoplasticity and the surface morphological changes at room temperature for commercially pure titanium (CP-Ti) and austenitic stainless steel (SUS316L). Pure tensile test and tension-intermittent creep test are conducted. Both CP-Ti and SUS316L are deformed up to 16% of inelastic strain with a few unloading, and surface conditions are observed during pure tension test and tension-intermittent creep test. Qualitative surface observations and quantitative surface roughness measurements are made for the unloaded specimens. The surface roughness measurement shows that the curves plotted between surface roughness and inelastic strains are almost linear for all the present experiments. The slopes of curves depend, however, on material and type of tests, and this tendency agrees well with the qualitative surface observations by an optical microscope. The experimental results for CP-Ti suggest that different deformation mechanisms during tensile loading and creep contribute to different surface morphological changes.
Authors: Jin Qiang Li, Yoshihiro Narita
Abstract: This paper presents an analysis on the effect of ply angle for laminated composite plates on wind induced vibration. With Hamilton’s principle and the Rayleigh-Ritz method, the equation of motion for the wind induced vibration is derived. The displacements in time domain and the mean-square value of the transverse response under wind pressure are studied for laminated plates with different ply angles. From the numerically simulation results it is seen that the ply angle of the laminated plate can significantly affect the wind induced vibration. For different rectangle plate the optimal ply angles of minimum displacement is different. The analytical methodology in this paper can be expanded to other kinds of random vibration such as water flow induced vibration.
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