• 한국재료학회지
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• 제14권6호
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• pp.436-442
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• 2004

Elastic and plastic deformation behaviors of the high purity aluminum and the silica glass were studied using nanoindentation and finite element analysis(FEA) techniques. Berkovich- and cone-type indenters were used for the nanoindentation test. Deformation behaviors and nanoindent profiles of elastic, elastic-plastic or plastic materials were clearly visualized by FEA simulation. Effects of the penetration depth and strain hardening on the deformation behavior were examined. Pile-up and sink-in behaviors were studied by using FEA technique. Degree of pile-up or sink-in was found to be a function of the ratio of elastic modulus to yield strength of materials. FEA was found to be an effective method to study deformation behaviors of materials under nanoindentation, especially in the case when pile-up or sink-in phenomena occurred.

• Structural Engineering and Mechanics
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• 제38권6호
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• pp.753-765
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• 2011

The radial vibration behaviors of a circular cylindrical composite piezoelectric transducer (CPT) are investigated. The CPT is composed of a piezoelectric ring polarized in the radial direction and an elastic ring graded in power-law variation form along the radial direction. The governing equations for plane stress state problem under the harmonic excitation are derived and the exact solutions for both piezoelectric and functionally graded elastic rings are obtained. The characteristic equations for resonant and anti-resonant frequencies are established. The presented methodology is fit to carry out the parametric investigation for composite piezoelectric transducers (CPTs) with arbitrary thickness in radial direction. With the aid of numerical analysis, the relationship between the radial vibration behaviors of the cylindrical CPT and the material inhomogeneity index of the functionally graded elastic ring as well as the geometric parameters of the CPTs are illustrated and some important features are reported.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.543-546
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• 2000

Static and dynamic experiments were done to study on the restitution behaviors of strings. The elastic and viscoelastic model were compared. To apply a linear viscoelastic model (Kelvin model) to longitudinal behaviors of strings, static and dynamic tensile tests were done. Using their results, it should be intended to acquire damped stress (Stress related to velocity), and to calculate the viscoelastic coefficient. Fixing both ends, string was pushed by the loadcell attached to the tensile tester. The experimental results were in accordance with the calculated results using the Kelvin model acquired from the results of longitudinal tensile test. But the results of falling mass experiments, the behaviors of strings were near to elastic model. The clamping condition of strings in both sides has an effected on the value of COR. The smaller contact area, the grower the value of COR.

• Advances in nano research
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• 제16권3호
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• pp.313-324
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• 2024

The main aims of this study are to develop a new nonlocal quasi-3D theory for the free vibration behaviors of the functionally graded sandwich nanobeams. The sandwich beams consist of a ceramic core and two functionally graded material layers resting on elastic foundations. The two layers, linear spring stiffness and shear layer, are used to model the effects of the elastic foundations. The size-effect is considered using nonlocal elasticity theory. The governing equations of the motion of the functionally graded sandwich nanobeams are obtained via Hamilton's principle in combination with nonlocal elasticity theory. Then the Navier's solution technique is used to solve the governing equations of the motion to achieve the nonlocal free vibration behaviors of the nanobeams. A deep parametric study is also provided to demonstrate the effects of some parameters, such as length-to-height ratio, power-law index, nonlocal parameter, and two parameters of the elastic foundation, on the free vibration behaviors of the functionally graded sandwich nanobeams.

• 한국지반공학회논문집
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• 제28권11호
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• pp.87-99
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• 2012

국내에서 출토되는 퇴적암, 화성암 및 변성암군중 출토빈도가 높은 9개 암종을 대상으로 함수에 의한 탄성계수의 저감거동을 분석하였다. 일축압축강도 기준으로 20MPa 범위로 5개단계로 분활하여 단계별, Group별로 함수 저감거동을 분석한 결과는 5개 퇴적암 전부와 화성암군인 안산암을 포함한 모집단은 단일 저감거동을 보이며, 화성암군인 화강암, 유문암과 변성암군인 편마암은 또 다른 동일 거동을 보이며, 더욱이 저감속도가 퇴적암군을 포함한 모집단에 비해서 2배이상 빠르며 탄성계수의 잔존값도 매우 낮게 나타났다.

• Geomechanics and Engineering
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• 제12권5호
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• pp.863-870
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• 2017

With the increasing interest in using bacterial biofilms in geo-engineering practices, such as soil improvement, sealing leakage in earth structures, and hydraulic barrier installation, understanding of the contribution of bacterial biofilm formation to mechanical and hydraulic behavior of soils is important. While mechanical properties of soft gel-like biofilms need to be identified for appropriate modeling and prediction of behaviors of biofilm-associated soils, elastic properties of biofilms remain poorly understood. Therefore, this study investigated the microscale Young's modulus of biofilms produced by Shewanella oneidensis MR-1 in a liquid phase. The indentation test was performed on a biofilm sample using the atomic force microscopy (AFM) with a spherical indentor, and the force-indentation responses were obtained during approach and retraction traces. Young's modulus of biofilms was estimated to be ~33-38 kPa from these force-indentation curves and Hertzian contact theory. It appears that the AFM indentation result captures the microscale local characteristics of biofilms and its stiffness is relatively large compared to the other methods, including rheometer and hydrodynamic shear tests, which reflect the average macro-scale behaviors. While modeling of mechanical behaviors of biofilm-associated soils requires the properties of each component, the obtained results provide information on the mechanical properties of biofilms that can be considered as cementing, gluing, or filling materials in soils.

• 세라미스트
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• 제23권1호
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• pp.101-109
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• 2020

In this study, the phase transition behaviors of lead-free (Na_1/2Bi_1/2TiO₃)_(1-x)-(BaTiO₃)_x (NBT-BT) are investigated by using Brillouin spectroscopy. The elastic properties, sound velocity and absorption coefficient of NBT-BT are characterized as a function of temperature along different crystallographic axes. The temperature dependences of the elastic constants of NBT-BT near the morphotropic phase boundary are determined for the first time. The unpoled NBT-BT single crystals exhibits the typical relaxor behaviors, presenting broad acoustic and dielectric anomalies. The application of electric field induced discontinuous changes in the elastic properties at ~110℃, which indicates field-induced phase transition occurred. The electric field also changes the dielectric constant from more relaxor-like to ferroelectric-like dielectric behavior.

• Composites Research
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• 제12권1호
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• pp.59-67
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• 1999

보강섬유의 굴곡을 가지는 일방향성 graphite/epoxy 복합재료의 비선형거동에 대하여 이론 및 실험을 통하여 고찰하였다. 해석모델에서 공액에너지밀도와 순차적 해석방법을 이용하여 보강섬유의 굴곡에 의한 재료적 비선형 특성 및 기하학적 비선형 특성을 모두 고려하였으며, 이를 이용하여 보강섬유의 굴곡정도에 따른 복합재료의 기계적 특성값의 변화 및 인장/압축 거동을 일정한 보강섬유의 굴곡을 가지는 모델, 재료의 중심에서 바깥쪽으로 갈수록 보강섬유의 굴곡이 점차 줄어드는 모델 그리고 재료의 일부분에만 보강섬유의 굴곡이 존재하는 모델에 대하여 예측하였다. 그리고 여러 굴곡 정도에 대한 일정한 보강섬유의 굴곡을 가지는 두꺼운 복합재료를 제작하고 인장/압축 실험을 수행하여 그 결과와 예측 결과를 비교하였다. 실험 결과는 예측 결과와 잘 일치하였으며, 보강섬유의 굴곡이 복합재료의 기계적 특성에 큰 영향을 미침을 알 수 있었다.

• Steel and Composite Structures
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• 제25권6호
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• pp.671-684
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• 2017

Elastic-plastic shear buckling behaviors of the web-post in a Castellated Steel Beam (CSB) with hexagonal web openings under vertical shear force were investigated further using Finite Element Model (FEM) based on a sub-model, which took the upper part of the web-post under horizontal shear force to represent the whole web-post under vertical shear force. A simplified design method for the web-post elastic-plastic shear buckling strength was proposed based on simulation results of the sub-model. Proper boundary conditions were applied to the sub-model to assure that its behaviors were identical to those of the whole web-post. The equation to calculate the thin plate elastic shear buckling strength was adopted as the basic form to build the design equation for elastic-plastic buckling strength of the sub-model. Parameters that might affect the elastic-plastic shear buckling strength of the whole web-post were studied. After obtaining the vertical shear buckling strength of a sub-model through FEM, the shear buckling coefficient k can be obtained through the back analysis. A practical calculation method for k was proposed through curving fitting the parameter study results. The elastic-plastic shear buckling strength of the web-post calculated using the proposed shear buckling coefficient k agreed well with that obtained from the FEM and test results. And it was more precise than those obtained from EC3 based on the strut model.

• Steel and Composite Structures
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• 제21권1호
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• pp.109-122
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• 2016

Concrete creep, while significantly changing the static behaviors of concrete filled steel tube (CFST) structures, do alter the structures' dynamic behaviors as well, which is studied quite limitedly. The attempt to investigate the influence of concrete creep on the dynamic property and response of CFST arch bridges was made in this paper. The mechanism through which creep exerts its influence was analyzed first; then a predicative formula was proposed for the concrete elastic modulus after creep based on available test data; finally a numerical analysis for the effect of creep on the dynamic behaviors of a long-span half-through CFST arch bridge was conducted. It is demonstrated that the presence of concrete creep increases the elastic modulus of concrete, and further magnifies the seismic responses of the displacement and internal force in some sections of the bridge. This influence is related closely to the excitation and the structure, and should be analyzed case-by-case.