• Interaction and multiscale mechanics
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• v.3 no.3
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• pp.213-234
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• 2010

A multiscale method is presented for analysis of thin slab structures in which the microstructures can not be reduced to two-dimensional plane stress models and thus three dimensional treatment of microstructures is necessary. This method is based on the classical asymptotic expansion multiscale approach but with consideration of the special geometric characteristics of the slab structures. This is achieved via a special form of multiscale asymptotic expansion of displacement field. The expanded three dimensional displacement field only exhibits in-plane periodicity and the thickness dimension is in the global scale. Consequently by employing the multiscale asymptotic expansion approach the global macroscopic structural problem and the local microscopic unit cell problem are rationally set up. It is noted that the unit cell is subjected to the in-plane periodic boundary conditions as well as the traction free conditions on the out of plane surfaces of the unit cell. The variational formulation and finite element implementation of the unit cell problem are discussed in details. Thereafter the in-plane material response is systematically characterized via homogenization analysis of the proposed special unit cell problem for different microstructures and the reasoning of the present method is justified. Moreover the present multiscale analysis procedure is illustrated through a plane stress beam example.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.2
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• pp.195-204
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• 2017

Predicting the failure life of automated manufacturing systems can reduce overall downtime, maintenance costs, and total plant operation costs. Therefore, there is a growing interest in fatigue failure mechanisms as the safety or service life assessment of manufacturing systems becomes an important issue. In particular, fretting fatigue is caused by repeated tangential stresses that are generated by friction during small amplitude oscillatory movements or sliding between two surfaces pressed together in intimate contact. Previous studies in fretting fatigue have observed size effects related to contact width such that a critical contact width exists where there is drastic change in the fretting fatigue life. However, most of them are the two-dimensional finite element analyses based on the plane strain assumption. The purpose of this study is to investigate the contact size effects on the three-dimensional finite element model of a finite width of a flat specimen and a cylindrical pad exposed to fretting fatigue. The contact size effects were analyzed by means of the stress and strain averages at the element integration points of three-dimensional finite element model. This study shows that the fretting fatigue life of manufacturing systems can be predicted by three-dimensional finite element analysis based on SWT critical plane model.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2218-2221
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• 1998

Data compression of 3 dimensional objects has limitations such as large data size, slow processing time, uncertainties of noise and measurement errors. Recently, along with activities of information transmission in internet, the researches in 3 dimensional information processing become a very important issue as the exchanges of large data are available. In this paper, we propose a data compression algorithm which first estimates the surfaces of 3 dimensional objects and then apply them to the FCV(Fuzzy c-Varieties) Clustering to obtain 3 dimensional edges and vertices, and represent the results.

• Fibers and Polymers
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• v.5 no.1
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• pp.12-18
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• 2004

A parametric body model generation system has been developed. Using various mathematic and geometric algorithms of this system, a three-dimensionally scanned human body can be converted into a resizable body model. Once a parametric body model is formed, its size and shape can be modified instantaneously by providing appropriate anthropometric data. To facilitate the subsequent pattern arrangement process for garment drape simulation, a bounding box generation algorithm has been developed in this study. Also the model can be converted into a set of parametric surfaces that it can also be used for three-dimensional garment pattern design system.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.1
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• pp.21-27
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• 2002

Inspection and shape measurement of three-dimensional objects are widely needed in industries for quality monitoring and control. A number of visual or optical technologies have been successfully applied to measure three-dimensional surfaces. However, those conventional visual or optical methods have inherent shortcomings such as occlusion and variant surface reflection. X-ray vision system can be a good solution to these conventional problems, since we can extract the volume information including both the surface geometry and the inner structure of any objects. In the x-ray system, the surface condition of an object, whether it is lambertian or specular, does not affect the inherent characteristics of its x-ray images. In this paper, we propose a three-dimensional x-ray imaging method to reconstruct a three dimensional structure of an object out of two dimensional x-ray image sets. To achieve this by the proposed method, two or more x-ray images projected from different views are needed. Once these images are acquired, the simultaneous algebraic reconstruction technique(SART) is usually utilized. Since the existing SART algorithms have several shortcomings such as low performance in convergence and different convergence within the reconstruction volume of interest, an advanced SART algorithm named as USART(uniform SART) is proposed to avoid such shortcomings and improve the reconstruction performance. Because, each voxel within the volume is equally weighted to update instantaneous value of its internal density, it can achieve uniform convergence property of the reconstructed volume. The algorithm is simulated on various shapes of objects such as a pyramid, a hemisphere and a BGA model. Based on simulation results the performance of the proposed method is compared with that of the conventional SART method.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.66-71
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• 2003

Profiles of naturally fractured surfaces of three sedimentary rock samples were plotted from the measured data using a mechanical profilometer. Fractal dimension of these profiles were computed and statistical F-test indicates that fractal dimension (FD) values can be used as a parameter for distinguishing the rock types. The comparison between FD values and a commonly used profile-roughness parameter called the Mayer's $Z_2$ parameter shows the superiority of the FD values as roughness estimator. Two-dimensional fractal roughness parameters of the same naturally fractured rock surfaces were also studied from their scanning electron microscopic (SEM) images at various magnification levels. The most suitable level of magnification of the SEM images for the study of the 2-D fractal roughness parameter was identified. The values of 2-D fractal roughness parameter for three different rocks were also compared using different methods of fractal dimensioning.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.2
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• pp.64-72
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• 1995

A series of cubical triaxial tests with three independent principal stresses was per- formed on Baekma river sand( # 40~100). It was found that the major principal strain at failure remained approximately constant for b values larger than about 0.3 for both the drained and undrained condition, and thereafter increased as b value decreased. The test results showed that the direction of the strain increment at failure form acute angles with the failure surfaces for both the drained and undrained condition. The results were thus not in agreement with the normality condition from classic plasticity theory. Howev- er, it was found that the projections of the plastic strain increment vectors on the octahe- dral plane were perpendicular to the failure surface in that plane. Failure strength in terms of effective stress anlaysis was greatly influenced by the variation of intermediate principal stress and so was failure criterion. The effective stress failure surfaces for both the drained and undrained condition were estimated quite well by use of Lade's failure criterion.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.230-234
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• 1997

Reverse engineering involves digitizing a three-dimensional model or part converting the data to a CAD database description and manufacturing by CNC. Currently, the digitization is done through measurements taken manually by a CMM or touch probe mounted on a CNC machinetool. Some reverse engineering techniques require close integration between the data collection method and the surface-fitting algorithms. Accurate surface data are collected by input to the surface fitting method. This study has been found that both the smoothness of surfaces and accuracy of surface fitting are related with the degree of the interpolated surfaces.

• Korean Journal of Computational Design and Engineering
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• v.11 no.3
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• pp.157-163
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• 2006

Surfaces of many engineering structures, especially, those of ships are commonly made out of either single- or double-curved surfaces to meet functional requirements. The first step in the fabrication process of a three-dimensional design surface is unfolding or flattening the surface, otherwise known as planar development, so that manufacturers can determine the initial flat plate which is required to form the design shape. In this paper, an algorithm for optimal approximated development of a general curved surface, including both single- and double-curved surfaces, is established by minimizing the strain energy of deformation from its planar development to the design surface. The unfolding process is formulated into a constrained nonlinear programming problem, based on the deformation theory and finite element. Constraints are subjected to the characteristics of the fabrication method. And the design surface, or the curved shell plate is subdivided by automatic mesh generation.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.697-704
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• 2000

This study presents methodology and tools for remote measurement of the orientation of the rock parting surfaces. Two close circuit video camera capture the pictures of a rock excavation surface while a laser beam scans the surface. Positions of the laser beams in the two digital images are recognized by image processing. Using the stereoscopic concept, three dimensional coordinations of the rock surface and the orientation of the rock parting planes are calculated. Point, cross and line type laser beams are tested for better image processing results and measurement accuracy of the coordinates. According to a simple accuracy test, cross beam show better results than the point beam. However, line beam show more promising results for the measurement of the rock parting surfaces.