• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1536-1540
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• 1997

Recently, many advanced technologies in electronics, mechanics, material and computer science have been applied to medictine and they have changed the method of diagnosis and treatment to more quantitative way than before. Now day, with the aid of this technology, the device for the minimal invasive diagnosis and treatment is being developed for the convenience and safety of patients. this paper introduces application of senso and MEMS(Micro Electro Mechnical System) in medicine and biotechnology, which are essential factor for the realization of minimal invasive diagnosis and treatment.

• Selected Papers of The Society of Naval Architects of Korea
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• v.2 no.1
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• pp.106-128
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• 1994

An elasto-plastic-damage constitutive model for ductile materials is proposed within the framework of a thermodynamic approach of continuum damage mechanics (CDM) in which internal irreversible thermodynamic changes of micro-structure of materials such as plastic deformation and damage evolution are considered as thermodynamic state variables. The new constitutive model can predict not only the elasto-plastic behaviors but also the sequential stiffness degradation process of ductile materials more rationally.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.631-644
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• 1996

Geomaterials such as soil and rock are composed of discrete elements of microstructures with different grains and microcracks. The studies of these microstructures are of increasing interest in geophysics and geotechnical engineering relating to underground space development We first show experimental results undertaken for direct observation of microcrack initiation and propagation by using a newly developed experimental system, and next a homogenization method for treating a viscoelastic behavior of a polycrystalline rock.

• Geomechanics and Engineering
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• v.11 no.2
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• pp.253-267
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• 2016

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

• Structural Engineering and Mechanics
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• v.89 no.3
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• pp.225-238
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• 2024

In this paper, a quasi-3D hyperbolic shear deformation theory for the bending responses of a functionally graded (FG) porous micro-beam is based on a modified couple stress theory requiring only one material length scale parameter that can capture the size influence. The model proposed accounts for both shear and normal deformation effects through an illustrative variation of all displacements across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the micro-beam. The effective material properties of the functionally graded micro-beam are assumed to vary in the thickness direction and are estimated using the homogenization method of power law distribution, which is modified to approximate the porous material properties with even and uneven distributions of porosity phases. The equilibrium equations are obtained using the virtual work principle and solved using Navier's technique. The validity of the derived formulation is established by comparing it with the ones available in the literature. Numerical examples are presented to investigate the influences of the power law index, material length scale parameter, beam thickness, and shear and normal deformation effects on the mechanical characteristics of the FG micro-beam. The results demonstrate that the inclusion of the size effects increases the microbeams stiffness, which consequently leads to a reduction in deflections. In contrast, the shear and normal deformation effects are just the opposite.

• Structural Engineering and Mechanics
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• v.69 no.4
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• pp.439-455
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• 2019

This research deals with thermo-electro-mechanical buckling analysis of the sandwich nano-beams with face-sheets made of functionally graded carbon nano-tubes reinforcement composite (FG-CNTRC) based on the nonlocal strain gradient elasticity theory (NSGET) considering various higher-order shear deformation beam theories (HSDBT). The sandwich nano-beam with FG-CNTRC face-sheets is subjected to thermal and electrical loads while is resting on Pasternak's foundation. It is assumed that the material properties of the face-sheets change continuously along the thickness direction according to different patterns for CNTs distribution. In order to include coupling of strain and electrical field in equation of motion, the nonlocal non-classical nano-beam model contains piezoelectric effect. The governing equations of motion are derived using Hamilton principle based on HSDBTs and NSGET. The differential quadrature method (DQM) is used to calculate the mechanical buckling loads of sandwich nano-beam as well as critical voltage and temperature rising. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various HSDBTs, length scale parameter (strain gradient parameter), the nonlocal parameter, the CNTs volume fraction, Pasternak's foundation coefficients, various boundary conditions, the CNTs efficiency parameter and geometric dimensions on the buckling behaviors of FG sandwich nano-beam. The numerical results indicate that, the amounts of the mechanical critical load calculated by PSDBT and TSDBT approximately have same values as well as ESDBT and ASDBT. Also, it is worthy noted that buckling load calculated by aforementioned theories is nearly smaller than buckling load estimated by FSDBT. Also, similar aforementioned structure is used to building the nano/micro oscillators.

• Corrosion Science and Technology
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• v.4 no.3
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• pp.100-107
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• 2005

Reinforcing steel bars in reinforced concrete structures are protected from corrosion by passive film on the steel surface inside concrete with high alkalinity. However, when the passive film breaks down due to chloride ion ingressed into the RC structures, a corrosion initiates at the surface of steel bars. Then, internal pressure by volume expansion of corrosion products in reinforcing bars induces cracking and spalling of cover concrete, which reduces not only durability performance but also structural performance in RC structures. In this paper, a service life prediction of RC structures is carried out by using a micro-mechanics based corrosion model. The corrosion model is composed of a chloride penetration model to evaluate the initiation of corrosion and an electric corrosion cell model and an oxygen diffusion model to evaluate the rate and the accumulated amounts of corrosion. Then, a corrosion cracking model is combined to the models to evaluate critical amount of corrosion product for initiation cracking in cover concrete. By implementing the models into a finite element analysis program, a time and space dependent corrosion analysis and a service life prediction of RC structures due to chloride attack are simulated and the results of the analysis are compared with test results. The effect of crack width on the corrosion and the service life of the RC structures are analyzed and discussed.

• Composites Research
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• v.31 no.5
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• pp.251-259
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• 2018

In this paper, statistical volume element modeling method was developed for multi-scale progressive failure analysis of fiber reinforced composite materials. Big-size statistical volume elements (BSVEs) was considered to minimize the size effect in the micro-scale, by including as many fibers as possible. For that purpose, a mesh cutting method is suggested and adapted into the fiber model generator that creates finite element domain rapidly. The fiber defect model was also developed based on the experimental distribution of the fiber strength. The size effects from the local load sharing (LLS) are evaluated by increasing the fiber inclusion in the micro-scale model. Finally, continuum damage mechanics (CDM) model to the fiber direction was extracted from numerical analysis on BSVEs. And it was compared with strength prediction from typical representative volume element (RVE) model.

• Structural Engineering and Mechanics
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• v.65 no.5
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• pp.573-585
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• 2018

This article presents strain gradient elasticity-based procedures for static bending, free vibration and buckling analyses of functionally graded rectangular micro-plates. The developed method allows consideration of smooth spatial variations of length scale parameters of strain gradient elasticity. Governing partial differential equations and boundary conditions are derived by following the variational approach and applying Hamilton's principle. Displacement field is expressed in a unified way to produce numerical results in accordance with Kirchhoff, Mindlin, and third order shear deformation theories. All material properties, including the length scale parameters, are assumed to be functions of the plate thickness coordinate in the derivations. Developed equations are solved numerically by means of differential quadrature method. Proposed procedures are verified through comparisons made to the results available in the literature for certain limiting cases. Further numerical results are provided to illustrate the effects of material and geometric parameters on bending, free vibrations, and buckling. The results generated by Kirchhoff and third order shear deformation theories are in very good agreement, whereas Mindlin plate theory slightly overestimates static deflection and underestimates natural frequency. A rise in the length scale parameter ratio, which identifies the degree of spatial variations, leads to a drop in dimensionless maximum deflection, and increases in dimensionless vibration frequency and buckling load. Size effect is shown to play a more significant role as the plate thickness becomes smaller compared to the length scale parameter. Numerical results indicate that consideration of length scale parameter variation is required for accurate modelling of graded rectangular micro-plates.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.567-573
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• 2014

Since the development of microelectromechanical systems (MEMS) technology for the medical field, various micro-fluid transfer systems have been studied. This paper proposes a micro-piezoelectric pump that imitates a stomach's peristalsis by using two separate piezoelectric elements, in contrast to existing micro-pumps. This piezoelectric pump is operated by using the valve-less traveling wave of peristalsis movement. If the piezoelectric plates at the two separated plates are actuated at the input voltage, a traveling wave occurs between the two plates. Then, the fluid migrates by the pressure difference generated by the traveling wave. Finite element analysis was performed to understand the mechanics of the combined system with piezoelectric elements, elastic structures, and fluids. The effects of design variables such as the chamber height and number of ceramics on the flow rate of the fluid were examined.