Papers by Author: Kenji Machida

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.

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.

Abstract: Most measurement by experiment is about a structure surface and it is dramatically difficult to measure the stress state inside a structure. Although the stress analysis of a big structure is possible by the 3-D finite element method, great time, labor, and expense are needed for modeling and calculation. Then, we developed the 3-D local hybrid method which analyzes only the local model of a structure and can evaluate the stress field inside it from surface data obtained by easy measurement. In previous studies, the good result was obtained with the surface cracked specimen subjected to uniform tension and a cantilever subjected to bending. However, with an actual structure, it is not thought that simple bending deformation which is produced under an experiment environment arises. In this study we examined whether the 3-D local hybrid method would be able to apply to the structure subjected to bending and torsion by using the displacement on front surface and the displacement of upper and lower sides of a local model. It was clarified that the 3-D local hybrid method is very useful to the 3-D stress analysis of the structure subjected to the complicated loading (uniform, bending and torsion, etc.).

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 newly applied to 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 full model and the local model.

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.

Abstract: Recently, the influence of heat conduction has been considered to be a big problem. Then, the influence of heat conduction was investigated by the experiment which changed the material, thickness of the specimen and frequency of a cyclic load. Then, the infrared hybrid method was developed to separate individual stress components. However, it has the influence by heat conduction in the infrared stress measuring method. Therefore, an error will arise 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.

Abstract: The thickness dependency of the temperature image obtained by an infrared thermography was investigated using specimens with three kinds of metal materials of different heat conduction and four kinds of thickness of the specimens. Then, the infrared hybrid method was developed to separate each stress components. However, it contains the influence of heat conduction in the infrared stress measurement method. Therefore, heat conduction error will arise in the infrared hybrid analysis. Then, the new system which corrects the error by an heat conduction inverse analysis was developed. Thereby, the accuracy of the stress intensity factor was able to be raised using heat conduction inverse analysis. Furthermore, the accuracy of hybrid method taking heat conduction into consideration was discussed in comparison with 3-D finite-element analysis and the 2-D infrared hybrid method.

Abstract: The wings of a dragonfly have many complicated structures. The configuration of the costal vein of the wings of a dragonfly is different from them of other insects. So, we paid attention to the configuration of the costal vein of the wings in this study. In order to know the functions and structures of the wings of a dragonfly, several 3-D models of the wing of Anotogaster Sieboldii were created, and calculated with the 3-D finite element method. In addition, we created a 3-D model of the wing of Hybris Subjacens which has the configuration of original wing, and compared the models of Anotogaster Sieboldii and Hybris Subjacens. As a result, it was clarified that the arch configuration of the costal vein controls the bending and the torsion of the wings.

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).