• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.5
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• pp.51-60
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• 2009

To secure the structural safety of structures and members against earthquakes, the plastic deformation capacity demand of members should be accurately predicted. In the present study, a method for the evaluation of the plastic deformations of members for moment frames was developed. To facilitate the practical use of the proposed method in equivalent seismic design, the plastic deformations of members were evaluated based on the results of elastic analysis, without using nonlinear analysis. The plastic deformation demands of members were formulated as functions of story drift demand, redistributed moment and member stiffness. Story drift demand and moment redistribution were directly determined from elastic analysis. The proposed method was applied to an 8 story-2 bay moment frame, and the predicted plastic deformations were verified using nonlinear analysis. The results showed that the proposed method could be used to accurately predict the member plastic rotations with simple calculations. The proposed method can be applied both to the earthquake design of new structures and to the performance evaluation of existing structures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.621-629
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• 1992

This study is concerned with an application of the Boundary Element Method to 2-dimensional elastoplastic stress analysis on the material nonlinearities. The boundary integral formulation adopted an initial stress equation in the inelastic term. In order to determine the initial stress increment, the increment of initial elastic strain energy due to elastic increment in stressstrain curve was used as the convergence criterion during iterative process. For the validity of this procedure, the results of B.E.M. with constant elements and NISA with linear elements where compared on the thin plate with 2 edge v-notches under static tension and the thick cylinder under internal pressure. And this paper compared the results of using unmedical integral with the results of using semi-analytical integral on the plastic domain integral.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.504-508
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• 2010

In conventional diagnostic ultrasound strain imaging, when displaying strain image on a monitor, human visual characteristics are utilized such that hard regions are displayed as dark and soft regions are displayed as bright. Thus, hard regions representing tumor or cancer are displayed as dark, decreasing the contrast inside the lesion. Because the lesion area is stiff and thus displayed as dark, a method of inverting the image brightness and thereby increasing the contrast in the lesion for better diagnostic purposes is proposed wherein a postcompression signal is extended in the time domain by a factor corresponding to the reciprocal of the amount of the applied compression using a technique termed globally uniform stretching. Experiments were carried out to verify the proposed method on an ultrasound elasticity phantom with radio-frequency data acquired from a diagnostic ultrasound clinical scanner. It is found that the new method improves the contrast-to-noise ratio by a factor of up to about 1.8 compared to a conventional strain imaging method that employs a reversed gray color map without globally uniform stretching.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.72-78
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• 2008

In this study, advanced (fluid-structure interaction (FSI)) analysis system has been developed in order to predict turbine cascade performance with blade deformation effect due to aerodynamic loads. Intereference effects due to the relative movement of the rotor cascade with respect to the stator cascade are also considered. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation k-ω SST turbulence models are solved to accurately predict fluid dynamic loads considering flow separation effects. A fully implicit time marching scheme based on the (coupled Newmark time-integration method) with high artificial damping is efficiently used to compute the complex fluid-structure interaction problem. Predicted aerodynamic performance considering structural deformation effect of the blade shows somewhat different results compared to the case of rigid blade model. Cascade performance evaluations for different elastic axis positions are importantly presented and its aeroelastic effects are investigated.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.21-27
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• 2007

Nickel bumps for ACF(anisotropic conductive film) flip chip application were fabricated by electroless and electro plating and their mechanical properties and impact reliability were examined through the compressive test, bump shear test and drop test. Stress-displacement curves were obtained from the load-displacement data in the compressive test using nano-indenter. Electroplated nickel bumps showed much lower elastic stress limits (70MPa) and elastic moduli ($7.8{\times}10^{-4}MPa/nm$) than electroless plated nickel bumps ($600-800MPa,\;9.7{\times}10^{-3}MPa/nm$). In the bump shear test, the electroless plated nickel bumps were deformed little by the test blade and bounded off from the pad at a low shear load, whereas the electroplated nickel bumps allowed large amount of plastic deformation and higher shear load. Both electroless and electro plated nickel bumps bonded by ACF flip chip method showed high impact reliability in the drop impact test.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.39-46
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• 2019

A stiffness-gradient soft PDMS/hard PDMS/FPCB stretchable package of the island-bridge structure was processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff flexible printed circuit board (FPCB) as the island substrate, and its effective elastic modulus and stretchable deformation characteristics were analyzed. With the elastic moduli of the soft PDMS, hard PDMS, and FPCB to be 0.28 MPa, 1.74 MPa, and 1.85 GPa, respectively, the effective elastic modulus of the soft PDMS/hard PDMS/FPCB package was analyzed as 0.58 MPa. When the soft PDMS of the soft PDMS/hard PDMS/FPCB package was stretched to a tensile strain of 0.3, the strains occurring at hard PDMS and FPCB were found to be 0.1 and 0.003, respectively.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.55-63
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• 2007

Deformational characteristics of subgrade soils are important properties in the mechanistic analysis and design of pavement system. In this study, to evaluate the effect of specimen construction methods on deformational characteristics of subgrade soils in Korea, resonant column tests were performed for specimens constructed by various methods. Specimen construction method affected to the modulus value but the variation in the normalized modulus reduction curve was almost identical. The effects of specimen construction method on modulus are decreased with increasing confining pressure. The average maximum variation in the modulus value with different specimen construction methods was estimated as 16.8%. The differences in the modulus value of the specimens with same water content and dry density conditions that made by gyratory compaction and impact compaction were very small within 5.2%. The impact compaction method was proposed as a specimen construction method for determining the design input parameter testing considering that impact compaction method is much simpler and require less expensive specimen construction equipment and setup than gyratory compaction method.

• International Journal of Highway Engineering
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• v.1 no.2
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• pp.155-168
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• 1999

Asphalt pavement tends to rut in high temperature and to crack in cold temperature. The performance of asphalt pavement can be deteriorated by korean weather condition which has the four distinct seasons. In this study, the typical sections that may minimize rutting and fatigue were analyzed through the numerical model tests. The layered elastic theory , finite element method and visco elastic theory were utilized for these numerical model tests. From the various numerical model tests, it is found that an optimum design procedure was recommended. It was increasing the thickness of asphalt stabilized base with fixing the wearing course as 5cm the minimum specified thickness. The section was most beneficial in resting rutting and fatigue. From the analysis of the relative index on tensile strain and cost analysis, it was recommended that the thickness ratio of subbase and asphalt concrete is 1.0$\sim$2.5.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.129-134
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• 2010

The influence of the strain-rate on the thermomechanical characteristics of shape memory alloys (SMAs) is numerically investigated. The three-dimensional SMA constitutive equations of strain-rate effect is developed. The strain-rate effect is taken into account by introducing a coupling equation between the production rate of martensite and the temperature change. For the numerical results, the SMA algorithm is implemented into the ABAQUS finite element program. Numerical simulation shows that the pseudoelasticity of SMA may significantly be changed by considering the strain-rate due to the temperature change.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.89-95
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• 1989

In this study, it is attempted to examine (1) the residual deformation and elastic deformation induced from the repeated loads (up to the maximum of 100,000 times) on fully compacted soil specimen, the relation between stress and strain by performing the unconfined compressive test, after repeated loads and (2) the effect of water content, dry density, number of cycle, repeated loads, etc. on the effect of the stress-strain relation. The rate of deformation caused by repeated loads greatly depends on to the condition whether the water content is above or below the plastic limit. It is possible to estimate the initial tangent modulus of soil by means of modulus of elastic deformation obtained by putting repeated loads on the clay soil.