• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.75-76
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• 2008

• Journal of the Korean Society for Precision Engineering
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• v.25 no.9
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• pp.95-102
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• 2008

A miniature metal bellows is used to minimize the excessive flow of the cryogenic gas in Joule-Thomson micro cryocooler. It is made of metal alloy and its geometry is axisymmetric. The bellows is filled with high pressure gas. It contracts or expands in the axial direction for a wide change of temperature, because the pressure and volume inside the bellows must be satisfied with state equation of the gas. Therefore, in order to design the bellows in Joule-Thomson micro-cryocooler, it is important to evaluate deformation of the bellows under internal pressure exactly. Considering geometric nonlinearity, deformations analysis of the bellows were obtained by a commercial finite element code ANSYS, The bellows was modeled by 3-node axisymmetric shell elements with reduced integration. Experiments were also performed to prove the validity of proposed numerical analysis. The results by numerical analysis and experiments were shown in good agreements.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.266-273
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• 2002

Milli-structure components are classified as a component group whose size is between macro and micro scales, that is, about less than 20mm and larger than 1mm. The bending of these components of thin sheets has a typical phenomenon of bulk deformation because of the forming size. The recent trend towards miniaturization causes an increased demand for parts with very small dimensions. The conceptual miniature bending process enables the production of such parts with high productivity and accuracy. The stress values of the flow curve decrease with miniaturization, which means that coarse grained materials show a higher resistance against deformation, when the grain size is in the range of the sheet thickness. In this paper, a new numerical approach is proposed to simulate intergranular milli-structure in forming by the finite element method. The grain element and grain boundary element are introduced to simulate the milli-structure of strip in the bending. The grain element is used to analyze the deformation of individual grain while the grain boundary element is for the investigation on the movement of the grain boundary. Also, the result of the finite element analysis is confirmed by a series of milli-sized forming experiments.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.395-409
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• 2022

The presence of infill generally neglected in design despite the fact that infill contribution significantly increase the lateral stiffness and strength of the reinforced concrete frame structure. Several experimental studies and computational models have been proposed to capture the rational response of infill-frame interaction at global level. However, limited studies are available on explicit finite element modelling to study the local behavior due to high computation and convergence issues in numerical modelling. In the current study, the computational modelling of RC frames is done with various configurations of infill masonry in terms of types of blocks, lateral loading and reinforcement detailing employed with material nonlinearities, interface contact issues and bond-slip phenomenon particularly near the beam-column joints. To this end, extensive computational modelling of five variant characteristics test specimens extracted from the detailed experimental program available in literature and process through nonlinear static analysis in FEM code, ATENA generally used to capture the nonlinear response of reinforced concrete structures. Results are presented in terms of damage patterns and capacity curves by employing the finest possible detail provided in the experimental program. Comparative analysis shows that good correlation amongst the experimental and numerical simulated results both in terms of capacity and crack patterns.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.89-94
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• 2017

Micro-screws can be defined by their outer diameter of generally less than 1 mm. They are manufactured by head forging and thread rolling processes. In this study, the thread rolling process was numerically analyzed for a micro-screw with a diameter and pitch of 0.8 and 0.2 mm, respectively. Through finite element (FE) analysis, the effects of two design parameters (die gap and chamfer height) on the dimensional accuracy were investigated. Three combinations of chamfer heights were chosen first and the corresponding die gap candidates selected by geometric calculation. FE analyses were performed for each combination and their results indicated that the concave chamfer height should be less than 0.3 mm, while a 10 ?m difference in the die gap might cause degeneration in dimensional accuracy. These results conclude that ultra-high accuracy is required in die fabrication and assemblies to ensure dimensional accuracy in micro-screw manufacturing.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.134-141
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• 2010

This study analyzed the regional morphological and mechanical characteristics of vertebrae by using micro-computed tomography (micro-CT) and micro finite element analysis (FEA). For the present study, the $12^{th}$ human thoracic vertebral bones (an 85-years female and a 48-years male) were used. These were scanned by using micro-CT. Structural parameters were evaluated from the acquired 20 image data for fifteen $4{\times}4mm^2$ regions (five regions in respective layers of superior, middle and inferior part) in the thoracic vertebral trabecular bones. $4{\times}4{\times}4mm^3$ cubic finite element models of each regions were created at $70{\mu}m$ voxel resolution to investigate effective modulus ($E^+$). The present study indicated that there were significant differences in morphological and elastic mechanical characteristics of each region. There are close relationship between effective modulus and structural model index (SMI) in the bone of the 48-years male and between effective modulus and bone volume fraction (BV/TV) in the bone of the 85-years female. In addition, the effective modulus of central regions is about 80% stiffer than that of lateral regions at transverse plane. These findings may be likely to explain the previous result that a change of loading distribution of the vertebral trabecular bones is caused by spinal curvature and nucleus pulpous degeneration of the intervertebral disc.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.184-196
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• 2004

An Eulerian finite element analysis for the steady state rolling process is addressed. This analysis combines the crystal plasticity theory fur texture development as well as the continuum damage mechanics for growth of micro voids. Although an Eulerian analysis for steady state rolling has many advantages, it needs an initial assumption about the shape of control volume. However, the assumed control volume does not match the final shapes. To effectively predict the correct shape in an assumed control volume, a free surface correction algorithm and a streamline technique are introduced. Applications to plate rolling, clad rolling, and shape rolling will be given and the results will be discussed in detail.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.3 s.192
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• pp.108-116
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• 2007

To overcome many defects such as the high product cost, large energy consumption, and big space capacity in conventional mechanical machining, the miniaturization of machine tool and micro factory systems has been envisioned recently. The object of this paper is to research the effect of dynamic characteristic parameters in bolted-joint beams, which is widely applied to the joining of mechanical structures in order to identify structural system characteristics and to predict dynamic behavior according to scale-down from macro to micro system as the development of micro/meso-scale machine tool and micro factories. Modal parameters such as the natural frequency, damping ratio, and mode shape from modal testing and dynamic characteristics from finite element analysis are extracted with all 12 test beam models by materials, by size, and by joining condition, and then the results obtained by both methods are compared.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.1
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• pp.67-76
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• 2008

Implant requires long lasting, strong osseointegration using bio-mechanical interlocking by bone ingrowth. In regarding the size level for bone ingrowth, the micro-patterning would enhance bone response. Micro-patterning can increase the area contacting the bone tissues. Therefore, it may distribute the load to the surrounding bone tissue, more effectively. This study compared and analyzed the load distributing effect with the shape and number of micro-patterning. For the optimal comparison of threads, the assumptions different from general finite element analysis model were made. It was assumed that the implant was axisymmetric and infinitely long. The implant was assumed to be completely embedded in the infinitely long cortical bone and to have 100% bone apposition. The implant-bone interface had completely fixed boundary conditions and received an infinitely big axial load. The condition of threads were as follows. The reference model 1 had conventional thread. Model 2 had 2 micro-patterns on the upper flank of the thread. Model 3 had 2 micro-patterns on the lower flank of the thread. Model 4 had 2 micro-patterns on the upper and lower flanks of the thread. Model 5 had 3 micro patterns on the upper and lower flanks of the thread. The results were as follows: 1. The thread with micro-patterns distributed stress better than the conventional thread. 2. The thread with micro-patterns on the lower flank distributed stress better than that with micro-patterns on the upper flank. 3. The thread with 3 micro-patterns distributed stress better than that with 2 micro-patterns, However, an area with stress concentration occurred.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1697-1704
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• 2001

A finite element model for polarization switching in electro-mechanically coupled materials is proposed and applied to predict the switching behavior of a two-dimensional ferroelectric ceramic. A complicated micro-structure existing in the material is modeled as il continuum body and a simple 3 node triangle finite element with nodal displacement and voltage degrees of freedom is used for a finite element analysis. The elements use nonlinear constitutive equations, switching criterion and kinetic relation, fur representation of material response at strong electric and stress fields. The polarization state of the material is represented by internal variables in each element, which are updated at each simulation step based on the proposed constitutive equations. The model reproduces strain and electric displacement hysteresis loops observed in the material.