Papers by Author: Kenji Machida

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Authors: Kenji Machida, Kazuhiro Okazaki
Abstract: The displacement obtained from the experiment is including large error and it is impossible to evaluate the stress and the strain with high accuracy using raw displacement data. The 2-D intelligent hybrid method was applied in order to evaluate the 2-D stress field. In the infinitesimal deformation within elastic region of steel or an aluminum alloy, the quantity of displacement is less than 1 pixel, and analysis accuracy deteriorates. We need the system which can analyze the displacement more exactly in sub-pixel field. Hence, the Newton-Raphson method was applied after obtaining the displacement at any point of the image. On uniform deformation field, the infinitesimal strain was estimated with less than 0.01pixels of an error by DIC by taking into consideration only the 1st deformation gradient in the Newton Raphson method. On nonuniform deformation near the crack tip, it was estimated with about 0.018pixels error by taking the 2nd deformation gradient into consideration.
3096
Authors: Kenji Machida, Mitsuru Sato, Shinji Ogihara
Abstract: Fiber reinforced composites are heterogeneous and anisotropic. The applicability of the stress analysis methods on such heterogeneous and anisotropic materials is not well known. In the present study, an attempt is made to apply the digital image correlation method and the intelligent hybrid method to a carbon fiber reinforced plastic (CFRP) laminate. A material used is carbon/epoxy system. Laminate configuration is unidirectional. Tensile load is applied in off-axis (45 degrees) direction as well as longitudinal (0 degree) and transverse (90 degrees) directions on a CFRP laminate. Displacement, strain and stress fields due to the tensile loading in the CFRP unidirectional laminate are analyzed. The constitutive equation considering material anisotropy is built into the intelligent hybrid method used at the time of analyses. The validity of the algorithm is checked through comparison between results of the present method, experimental results from strain gauge method, and the analytical results from finite element method (FEM).
1121
Authors: Kenji Machida, Takanori Ueno
Abstract: We developed the 3-D local hybrid method to evaluate the 3-D stress field inside the specimen from displacement data on the free surface obtained from the 2-D intelligent hybrid method. When a uniform load was applied to the structure with a surface crack, high accuracy was already acquired in stress analyses. The 3-D local hybrid method was anew applied to a structure with a surface crack which is subjected to bending load. It is expected that the accuracy depends on local model size. In this study, the width, the thickness and the height of the local model were changed widely, and analyses were carried out. Then the size of the local model necessary for the analyses was examined. Assessment of analyses was performed by comparing J integral value of a whole model and a local model.
469
Authors: Shin Yokota, Hirotaka Ohnuki, Kenji Machida, Zu Guang Zhang
Abstract: Health assessment of a structure is various. In architecture and civil engineering, a natural frequency is calculated by conducting the frequency analysis of the response waveform of the structure. The natural frequency measurement has been performed with a speedometer, an acceleration sensor and a laser Doppler velocimeter, but possibility of the evaluation of the natural frequency by the digital image correlation method was examined mainly. In the case of the digital image correlation method, if a picture and time are connected, the displacement response of the structure is obtained. Hence, we considered the applicability of it to the vibration phenomenon. We carried out displacement comparison with the finite element method, and then investigated the accuracy of the displacement response waveform. Furthermore, it succeeded in assessment of the natural frequency by the frequency analysis. The health assessment of the structure is possible by using the digital image correlation method and frequency analysis.
118
Authors: Koji Tomita, Kenji Machida, Zu Guang Zhang
Abstract: Since the method of performing displacement measurement and stress assessment of material by non-contact comes to capture the spotlight, study of the digital image correlation method which adopted the pattern-matching method for asking for displacement by deformation of a surface speckle pattern has been advanced. When the configuration for an analysis was settled in the rectangle and the square region, the whole-field mesh generation was also possible, but when it became a complicated configuration, the background etc. entered and mesh generation was affected. In order to solve such a problem, even if the object for an analysis was a complicated configuration, it aimed at generating a mesh automatically and obtaining appropriate analysis output in the displacement analysis and stress analysis using the generated mesh. In addition, the validity of the result was verified by the comparison with the finite element method. By this study, the convenience and availability of the digital image correlation method was improved remarkably, and it became clear to become a leading tool in health monitoring.
112
Authors: Kenji Machida, Shohei Miyagawa
Abstract: Influence of the frequency to the temperature image obtained by an infrared thermography was investigated using specimens of three kinds of materials at four kinds of frequencies of the cyclic load. Then, the infrared hybrid method was developed to separate individual stress components. However, the influence of heat conduction is inevitable in the infrared stress measurement method. Therefore, an error arises in the infrared hybrid analysis. Then, the system which corrects the error by the inverse analysis was developed. Thereby, the accuracy of the stress intensity factor was able to be raised. Furthermore, the accuracy of hybrid method considering to heat conduction was discussed in comparison with the 3-D finite element analysis and 2-D hybrid method.
1137
Authors: Kenji Machida
Abstract: In previous studies, the elastic stress field near the crack tip was investigated by digital image correlation and the 2-D intelligent hybrid method. In this study, the 2-D nonlinear hybrid method was developed to analyze the elastic-plastic singular stress field near the crack tip from the displacement data obtained by digital image correlation. Then, the 2-D nonlinear hybrid method was carried out to evaluate stress, strain and J integral. The 3-D elastic-plastic finite element method was conducted on the same specimen as the experiment, and the validity of this approach was discussed from the comparison of the experiment and 3-D finite element method.
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Authors: Kenji Machida, Gaku Mizukami, Hirohisa Oyama
Abstract: To evaluate the 3-D stress field inside a specimen from displacement data on the free surface obtained from the 2-D intelligent hybrid method, we developed the 3-D local hybrid method based on inverse problem analysis. In a previous study, when a uniform load was applied to a structure with a surface crack, it was demonstrated that the stress field was analyzed with high accuracy. In this study, the 3-D local hybrid method was applied to a structure with a surface crack subjected to bending load. However, a suitable solution was not able to be obtained on a bending problem. Therefore, another method was applied. The relative error between the J integral value of the whole model and the local model was compared, and accuracy was investigated. First, the variation of accuracy with width and thickness was examined. If thickness is increased, the relative error decreases as found in the uniform load case. Moreover, as width increases, the relative error decreases. However, even if width and thickness become large, accuracy does not necessarily become better. Therefore, the relative error was compared and a suitable hybrid size was examined.
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