• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.1
• /
• pp.8-16
• /
• 2006

The communication through optical fiber is taking an important role of the expansion of communication network with excellent transmitting rate and quality. As the optical communication is introduced to the backbone network at first and becomes a general communication method of network, the demand of kernel parts of optical communication such as PLC(Planar Light Circuit), Coupler, and WDM(Wavelength Division Multiplexing) element increases. The alignment and the attachment technology are very important in the fabrication of optical elements. In this paper, the driving mechanism of ultra precision stage is studied with the aim of optimal design of stage. The travel and the resolution of stage are investigated. The hysteresis of the stage is generated because of PZT actuator. The hysteresis and the inverse hysteresis are modeled in X, Y, and Z-axis motion. The input data of desired displacement of the stage according to input voltage is obtained from the inverse hysteresis equation. In the result of experiments with the input data, the errors due to hysteresis are well compensated.

• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.6
• /
• pp.67-73
• /
• 2001

Three dimensional, elastic-plastic finite element(FE) analyses for circumferential through-wall cracked pipes under combined tension and bending are performed using actual tensile data of stainless steel, for two purposes. The first one is to validate the recently-proposed enhanced reference stress (ERS) method to estimate the J-integral and COD for circumferential through-wall cracked pipes under combined tension and bending. The second one is to compare those results with the GE/EPRI estimations. The FE results of the J-integral and the COD, resulting from six cases of proportional and non-proportional combined tension and bending, compare very well with those estimated from the proposed method. Excellent agreements of the proposed method with the detailed FE results provide sufficient confidence in the use of the proposed method to the Leak-Before-Break(LBB) analysis of through-wall cracked pipes under combined tension and bending.

• Tribology and Lubricants
• /
• v.22 no.5
• /
• pp.252-259
• /
• 2006

Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performances, stiffness, damping coefficient and load capacity, depend on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1 mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.1060-1064
• /
• 2010

Ground anchors are mostly used to improve the resistance capacity of retaining walls. The end of the anchor is connected to retaining wall through tendons and the forces in tendons are transferred to ground. In this study, we plan that the new anchor system increases the tension force in tendons and improves the pullout resistance characteristics of the system. In order to increase the pullout resistance capacity of existing anchor system, the new anchor system is made by attaching four steel sticks to the tip of anchor end. So the field test results showed that the pullout resistance capacity of the wedge-shaped ground anchor was acceptable to elastic displacement range.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.5
• /
• pp.535-541
• /
• 2010

In this paper, we have derived a continuum-based adjoint design sensitivity of general performance functionals with respect to Young' modulus and heat conduction coefficient for steady-state nonlinear thermoelastic problems. An adjoint equation for temperature and displacement fields is defined for the efficient computation of the coupled field design sensitivity. Through numerical examples, we investigated the mesh dependency of the topology optimization method in the thermoelastic problems. Also, comparing the dominant loading cases of thermal and mechanical ones, the loading dependency of topology design optimization in coupled multi-physics problems is investigated.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1367-1372
• /
• 2007

Over the past decade, many computational researches have been performed to investigate quantitative relationships between load-displacement and material properties. But piling-up which causes errors to estimate mechanical material properties remains the most significant unresolved issue in nano-indentation test. This study has estimated quantitative aspects of the effects of material properties, especially work hardening exponent, on piling up/sinking in response of various materials. Using FE Analysis, piling up/sinking in response when material is indented by sharp indenter is investigated to evaluate the effects of material properties. From the FE analysis result, quantitative relationships between piling up/sinking in height and material properties is assessed using dimensional analysis which is used to define scaling variables and universal functions. And nano-indentaion test is performed to verify this relation on various materials. From the result of comparison with prediction from dimensional function and experiment, the work hardening exponent was found to have greater influence on the piling up/sinking in height during the nano-indentation than other material properties, such as elastic modulus and yield stress.

• Geomechanics and Engineering
• /
• v.8 no.6
• /
• pp.829-844
• /
• 2015

In the current paper the results of a numerical simulation that were verified by a well instrumented experimental procedure for studying the arching effect over a trapdoor in sand is presented. To simulate this phenomenon with continuum mechanics, the experimental procedure is modeled in ABAQUS code using stress dependent hardening in elastic state and plastic strain dependent frictional hardening-softening with Mohr Coulomb failure criterion applying user sub-routine. The apparatus comprises rectangular trapdoors with different width that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to yield, the whole soil mass deforms elastically. However, after an immediate specified displacement, depending on the width of the trapdoor, the soil mass behaves plastically. This behavior of sand occurs due to the flow phenomenon and continues until the stress on trapdoor is minimized. Then the failure process develops in sand and the measured stress on the trapdoor shows an ascending trend. This indicates gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to establish a stable vault of sand called arching mechanism or progressive collapse of the soil body.

• Structural Engineering and Mechanics
• /
• v.45 no.1
• /
• pp.129-144
• /
• 2013

Load-carrying capacity of combined members consisted of inner and sleeved tubes subjected to axial compression was investigated in this paper. Considering the initial bending of the inner tube and perfect elasto-plasticity material model, structural behavior of the sleeved member was analyzed by theoretic deduction, which could be divided into three states: the elastic inner tube contacts the outer sleeved tube, only the inner tube becomes plastic and both the inner and outer sleeved tubes become plastic. Curves between axial compressive loads and lateral displacements of the middle sections of the inner tubes were obtained. Then four sleeved members were analyzed through FEM, and the numerical results were consistent with the theoretic formulas. Finally, experiments of full-scale sleeved members were performed. The results obtained from the theoretical analysis were verified against experimental results. The compressive load-lateral displacement curves from the theoretical analysis and the tests are similar and well indicate the point when the inner tube contacts the sleeved tube. Load-carrying capacity of the inner tube can be improved due to the sleeved tube. This paper provides theoretical basis for application of the sleeved members in reinforcement engineering.

• Structural Engineering and Mechanics
• /
• v.63 no.1
• /
• pp.89-102
• /
• 2017

In this work, we present a theoretical framework to study the thermovisco-elastic responses of homogeneous, isotropic and perfectly conducting medium subjected to inclined load. Based on recently developed generalized thermoelasticity theory with fractional order strain, the two-dimensional governing equations are obtained in the context of generalized magnetothermo-viscoelasticity theory without energy dissipation. The Kelvin-Voigt model of linear viscoelasticity is employed to describe the viscoelastic nature of the material. The resulting formulation of the field equations is solved analytically in the Laplace and Fourier transform domain. On the application of inclined load at the surface of half-space, the analytical expressions for the normal displacement, strain, temperature, normal stress and tangential stress are derived in the joint-transformed domain. To restore the fields in physical domain, an appropriate numerical algorithm is used for the inversion of the Laplace and Fourier transforms. Finally, we have demonstrated the effect of magnetic field, viscosity, mechanical relaxation time, fractional order parameter and time on the physical fields in graphical form for copper material. Some special cases have also been deduced from the present investigation.

• Smart Structures and Systems
• /
• v.22 no.1
• /
• pp.27-40
• /
• 2018

The governing equations of motion are derived for analysis of a sandwich microbeam in this paper. The sandwich microbeam is including an elastic micro-core and two piezoelectric micro-face-sheets. The microbeam is subjected to transverse loads and two-dimensional electric potential. Higher-order sinusoidal shear deformation beam theory is used for description of displacement field. To account size dependency in governing equations of motion, strain gradient theory is used to mention higher-order stress and strains. An analytical approach for simply-supported sandwich microbeam with short-circuited electric potential is proposed. The numerical results indicate that various types of parameters such as foundation and material length scales have significant effects on the free vibration responses and dynamic results. Investigation on the influence of material length scales indicates that increase of both dimensionless material length scale parameters leads to significant changes of vibration and dynamic responses of microbeam.