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Kobayashi T.,Mechanical Design and Analysis Corporation | Mihara Y.,Mechanical Design and Analysis Corporation | Fujii F.,Gifu University
Shell Structures: Theory and Applications - Proceedings of the 10th SSTA 2013 Conference | Year: 2014

In design of modern lightweight structures, it is of technical importance to ensure safety against buckling under the applied loading conditions. If the analysis process traces unstable paths under the global loaddisplacement response with negative stiffness, the arc-length method is effectively usable. However, if instability is localized, global solution methods may not work. The latest general purpose finite element codes provide automatic mechanisms for stabilizing unstable quasi-static problems by automatic addition of viscous damping to the model. When local instability occurs, deformation rate of that portion begins to increase and, consequently, locally released strain energy is dissipated due to the appended artificial damping effect. Elastic buckling of thin-walled shells is typically a local instability phenomenon. In this paper,we traced the successive path jumping behavior of elastic thin shells using the artificial damping method. The automatic seamless simulation provides good agreement with the experimentally observed buckling process well covering deep post-buckling region.


Kanda Y.,Shibaura Institute of Technology | Zama K.,Shibaura Institute of Technology | Kariya Y.,Shibaura Institute of Technology | Mikami T.,Mechanical Design and Analysis Corporation | And 4 more authors.
Proceedings of the ASME InterPack Conference 2009, IPACK2009 | Year: 2010

The effect of viscoelasticity of underfill on the reliability analysis of flip-chip package by using FEA has been investigated in this study. The analytical result on thermal warpage of a package is different depending on whether the underfill is assumed to be elastic or viscoelastic. The difference is prominent in materials with low Tg, specifically during the cooling process. The viscoelastic effect of the underfill on the fatigue life of the solder bumps is also appears in materials with low Tg, and the predicted fatigue life of a package is about twice as short if the underfill is assumed to be elastic instead of viscoelastic. Thus, the differences in the assumption regarding the viscoelastic properties of the underfill affect the reliability analysis of the packages under thermal cycling condition using FEA. Copyright © 2009 by ASME.


Tanaka M.,Keio University | Tanaka M.,Toyota Central R and D Laboratories Inc | Noguchi H.,Keio University | Fujikawa M.,Mechanical Design and Analysis Corporation | And 7 more authors.
CMES - Computer Modeling in Engineering and Sciences | Year: 2010

This paper describes the development of a proper constitutive model of woven fabrics and its implementation in nonlinear finite shell elements in order to simulate the large deformation behavior of cloth. This work currently focuses on a macroscopic continuum constitutive model that is capable of capturing the realistic mechanical behavior of cloth that is characterized by two families of yarns, i.e., warp and weft. In this study, two strategies are considered. One is a rebar layer model and the other is a polyconvex anisotropic hyperelastic material model. The latter avoids non-physical behavior and can consider the effect of the interaction between the warp and the weft, whereas the former cannot do so. These material models are implemented in a four-node shell element in Abaqus/Standard (S4R type) via the UMAT user-subroutine. These models can be used to predict the outcome of uniaxial tensile tests and compute the contact pressure exerted by clothing on the human body. The resultant pressure distribution can then be used to design a form of cloth that provides more comfortable fitting. © 2010 Tech Science Press.


Kobayashi T.,Mechanical Design and Analysis Corporation | Mihara Y.,Mechanical Design and Analysis Corporation | Fujii F.,Gifu University
Thin-Walled Structures | Year: 2012

In terms of the buckling problem related to elastic cylindrical shells under axial compression, experimental results have shown that after primary buckling, secondary buckling occurs accompanied by successive reductions in the number of circumferential waves at every path jumping. In this paper, we traced this successive buckling of the elastic cylindrical shells using the latest general-purpose finite element technology with a static stabilizing method. The study accomplished a fully automatic and seamless simulation of successive path jumping in the deep post-buckling region and showed good agreement with Yamaki's experimental results and Esslinger's high-speed photography. © 2012 Elsevier Ltd. All rights reserved.


Mlhara Y.,Mechanical Design and Analysis Corporation | Kobayashijeii T.,Mechanical Design and Analysis Corporation | Fujit F.,Mechanical Design and Analysis Corporation
Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A | Year: 2011

For the buckling problem of circular cylindrical shells under axial compression, experimental results show that after the primary buckling, the secondary buckling takes place accompanying successive reductions in the number of the circumferential waves at every path jumping. In this paper we traced this successive buckling of circular cylindrical shells using the latest in general-purpose FEM technology with the static stabilizing method with the aid of artificial damping for the local instability. The studies accomplish a fully automatic and seamless simulation of the successive path jumping in the deep postbuckling region, and show a good agreement with Yamaki's experimental results. © 2011 The Japan Society of Mechanical Engineers.


Kobayashi T.,Mechanical Design and Analysis Corporation | Mihara Y.,Mechanical Design and Analysis Corporation | Yamashita K.,TOYOBO Co. | Nonomura C.,TOYOBO Co. | And 3 more authors.
SAE Technical Papers | Year: 2013

Thermoplastic polyester elastomer (TPEE) possesses the properties of both rubber and engineering plastic. The most important feature of this material lies in its ability to combine the superior repulsion elasticity and flexibility of rubber with the rigidity of engineering plastic. This enables it to exhibit durability against fatigue, even when exposed repeatedly to large deformation. The most remarkable feature of TPEE is such that it can realize material properties with very small strain rate dependency. The authors have had their ample experiences with applying TPEE to large damper members in the civil engineering structures, such as fenders surrounding the piers of bridges to absorb the impact energy caused by ship collisions and the aseismatic connectors built in bridge structures. This paper attempts to develop shock absorbing components of small sizes with light weight for automobile applications. Locating TPEE shock absorbers inside the crash box (members connecting the bumper system to the main body) may be thought as a typical application of the TPEE products. In order to achieve weight saving of the shock absorbing components, it is effective to utilize the buckling behaviors of thin walled structures. With regard to the buckling simulations of cylindrical shell structures, the authors have been working to develop analysis procedures for obtaining stable solutions utilizing the latest general-purpose finite element technology. This report shows that the experimental results could successfully be reproduced by applying the simulation technique to the honeycomb-shaped shock absorbing components. For realizing a desirable load-displacement relationship, this report also shows how to modify the shape of the components. Copyright © 2013 SAE International.


Kobayashi T.,Mechanical Design and Analysis Corporation | Mihara Y.,Mechanical Design and Analysis Corporation
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2010

In designing a modern lightweight structure, it is of technical importance to assure its safety against buckling under the applied loading conditions. For this issue, the determination of the critical load in an ideal condition is not sufficient, but it is further required to clarify the postbuckling behavior, that is, the behavior of the structure after passing through the critical load. One of the reasons is to estimate the effect of practically unavoidable imperfections on the critical load, and the second reason is to evaluate the ultimate strength to exploit the load-carrying capacity of the structure. For the buckling problem of circular cylindrical shells under axial compression, a number of experimental and theoretical studies have been made by many researchers. In the case of the very thin shell that exhibits elastic buckling, experimental results show that after the primary buckling, secondary buckling takes place accompanying successive reductions in the number of circumferential waves at every mode shift on systematic (one-by-one) basis. In this paper, we traced this successive buckling of circular cylindrical shells using the latest in general-purpose FEM technology. We carried out our studies with three approaches: the arc-length method (the modified Riks method); the static stabilizing method with the aid of (artificial) damping especially, for the local instability; and the explicit dynamic procedure. The studies accomplished the simulation of successive buckling following unstable paths, and showed agreement with the experimental results. Copyright © 2009 by ASME.


Mikami T.,Mechanical Design and Analysis Corporation | Kobayashi T.,Mechanical Design and Analysis Corporation
Proceedings of the ASME InterPack Conference 2009, IPACK2009 | Year: 2010

The rapid assembly of printed circuit boards to meet the desired goal of thinning the board creates more complexity in the reflow process, to control the occurrence of warpage in the board. Therefore, certain methods are preferred for simply yet accurately predicting the amount of warpage inevitable in the reflow process. Responding to such a need, the study was carried out aiming to provide a specific numerical method based on the multilayered plate theory, resulting in a simple procedure capable of supplying an accurate estimation of the warped deformation of the board. The estimation results derived from this method were compared with the FEM analysis results and confirmed to be in good agreement. Application of this method is designed for ease of use to estimate the warpage at any stage of planning and design. Copyright © 2009 by ASME.


Kobayashi T.,Mechanical Design and Analysis Corporation | Oi S.,Mechanical Design and Analysis Corporation | Sato M.,Mechanical Design and Analysis Corporation | Tanaka M.,Keio University | And 4 more authors.
ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers | Year: 2012

This paper describes the development of knitted fabric models for finite element analysis to simulate the large deformation behavior of garments and their clothing pressure distribution on the human body. In this study, for the modeling of cloth materials, two analytical approaches are investigated: a rebar layer model combined with isotropic hyperelastic shell elements and an anisotropic hyperelastic material model with a polyconvex strain energy function defined by the UMAT user-subroutine. These material models are implemented in the four-node shell element S4R of Abaqus/Standard and achieved adequate performance in predicting the deformation behavior of fabric test specimens and the computation of the contact pressure distribution on the human body caused by clothing. This study presents a fully automatic and seamless simulation of the clothing process for pantyhose and T-shirts, and the results show a good agreement with the experimental results.

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