• Restorative Dentistry and Endodontics
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• 제26권6호
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• pp.464-484
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• 2001

When restoring a tooth, the dentist tries to choose the ideal material for existing situation. One criterion that is considered is its suitability for restoring coronal strength. As more tooth structure is removed, the cusps are weakened and susceptible to fracture. Further, this increased deformation may cause the formation of intermittent gaps at the margin between the hard tissue and the restoration, facilitating marginal leakage. The improvements in ceramic materials now make it possible for alternatives to amalgams, composites, and cast metal to be of offered for posterior teeth. Of the materials used, ceramics most closely approximates the properties of enamel. The introduction of computer-aided design/computer-aided manufacture(CAD/CAM) systems to restorative dentistry represents a major technological breakthrough. It is possible to design and fabricate ceramic restorations at a single appointment. Additionally, CAD/CAM systems eliminate certain errors and inaccuracies that are inherent to the indirect method and provide an esthetic restoration. The aim of this investigation was to study the loading characteristics of CAD/CAM ceramic inlay and to compare the stress distribution and displacement associated with different designs of cavity(the isthmus width and cavity depth). A human maxillary left first premolar was prepared with standard mesio-occlusal cavity preparation, as recommended by the manufacturer Ceramic inlay was fabricated with CEREC 2 CAD/CIM equipment and cemented into the prepared cavity. Three dimensional model was made by the serial photographic method. The cavity width was varied $\frac{1}{3}$, $\frac{1}{2}$ and $\frac{2}{3}$ of intercuspal distance between buccal and lingual cusp tip. The cavity depth was varied 1.5mm and 2.3mm. So six models were constructed to simulate six conditions. A point load of 500N was applied vertically onto the first node of the lingual slope from the buccal cusp tip. The stress distribution and displacement were solved using ANSYS finite element program(Swanson Analysis System). (omitted)

• 한국건축시공학회지
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• 제10권2호
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• pp.105-113
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• 2010

거푸집 공사는 부실공사의 예방 및 인력절감과 저비용 고효율의 공사관리 차원에서 공법개선이 요구되고 있으며, 자재 및 공법 채용과정에서 경제성과 합리화를 꾀하는 일은 전체 공사에 큰 영향을 미친다. 공사 효율성 제고를 위한 합판계 유로폼의 대체공법과 거푸집 폐자재의 재생기술, 고기능성 거푸집, 친환경을 고려한 재생 가능한 거푸집 등 경제, 시공, 안전측면에서의 효과적인 거푸집 개발 필요성이 요구되고 있다. 이에 본 연구에서는 구조체 공사 공기를 단축하고, 인력투입을 최소화하여 원가를 절감시키고, 조립 해체 과정에서 작업의 생산성과 안전성이 확보된 사출성형방식의 합성수지계 재생유로폼 공법을 개발하는데 목적을 두고 있다. 이에 1차적으로 제반 요구성능 및 필요기술에 대하여 조사하고, 이를 바탕으로 개발기술의 타당성 검토와 기존 거푸집 및 선행기술과의 비교 분석을 실시하고, 성능 평가를 실시하였다.

• 한국강구조학회 논문집
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• 제20권1호
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• pp.81-92
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• 2008

일반적인 강구조물의 연결은 강절(rigid) 또는 활절(hinge)로 취급되고 있으나 실제 강구조물은 연결부위에서 부재간의 상대적인회전이 허용됨으로 인해 부분강절(semi-rigid)의 특성을 갖게 된다. 본 연구에서는 부분강절을 회전스프링으로 가정하여 부재 단부에 적용시킨 평면 뼈대구조물의 엄밀한 접선강도행렬을 유도하고 이를 다시 탄성강도행렬과 기하학적 강도행렬로 분리 유도함으로써 부분강절을 갖는 평면 뼈대구조물의 안정성해석을 위한 일반화된 해석방법을 제시하고자 한다. 이를 위하여, 보-기둥부재의 좌굴조건을 만족시키는 처짐함수로부터 안정함수(stability function)를 유도하고, 횡변위(sway)를 고려한 힘-변위관계와 적합조건을 고려하여 정확한 접선강도행렬을 제시하였다. 본 연구의 타당성과 실용성 제고를 위해 두 가지 방법에 의한 수치해석프로그램을 개발하였고 다양한 해석예제를 통해, 타 연구자 해석 결과와 비교하고 부분강절이 구조물의 좌굴강도에 미치는 영향에 대하여 조사한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.589-592
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• 2005

Micro-forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Micro-forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro-formability of a representative bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$, was investigated for micro-forging of U-shape pattern. Micro-formability was estimated by comparing $R_f$ values $(=A_f/A_g)$, where Ag is cross-sectional area of U groove, and $A_f$ the filled area by material. Microforging process was simulated and analyzed by applying finite element method. FEM simulation results should reasonable agreement with the experimental results when the material properties and simulation conditions such as top die speed, remeshing criteria and boundary conditions tightly controlled. The micro-formability of $Zr_{62}Cu_{17}Ni_{13}Al_8$ was increased with increasing load and time in the temperature range of the supercooled liquid state. Also, FEM Simulation using DEFORM was confirmed to be applicable for the micro-forming process simulation.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1229-1242
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• 2005

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens. Rubber specimens were heat-aged in an oven at a temperature ranging from $50^{\circ}C$ to $90^{\circ}C$ for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the strain energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.

• 수산해양기술연구
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• 제19권1호
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• pp.51-56
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• 1983

경계요소법에 의하여 U자형 홈(groove)을 가진 평판이 측면 분포하중을 받을 때 끝부에 위치할 원형 Hole의 최적 위치의 해석을 행하고 동일한 모델(model)에 대하여 실험결과를 비교하여 다음과 같은 결론을 얻게 되었다. 1. 원형 Hole이 U자형 홈(groove)에 가까이 접근하게 됨에 따라 초기의 원형 Hole은 c.-c.선에 수직방향이 그 장축이 되는 타원형으로 변화됨을 알 수 있다. 2. 원형 Hole이 U-groove에 접근함에 따라 Hole 과 Groove 사이의 Neck부는 그 횡단면응력이 인장 및 압축이 동시에 존재하다가 점점 전체가 인장역이 됨을 알 수 있다. 3. 원형 Hole이 Groove에 접근함에 따라 판재경계와 Hole 사이의 목(neck)부분은 계속적인 압축상태를 유지한다. 4. U-groove쪽의 Neck area의 응력분포는 그 최대응력치가 Hole로 접근함에 따라 가속적으로 증가하고 Hole의 찌그러짐(distortion)의 방지를 위한 Hole의 최적중심의 위치는 Neck부의 Hole 측면의 압축응력치가 0이 되지 않는 범위가 한계임을 알 수 있다.

• Advances in concrete construction
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• 제8권3호
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Smart Structures and Systems
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• 제15권1호
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• pp.99-117
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• 2015

The Stonecutters Bridge (SCB) in Hong Kong is the third-longest cable-stayed bridge in the world with a main span stretching 1,018 m between two 298 m high single-leg tapering composite towers. A Wind and Structural Health Monitoring System (WASHMS) is being implemented on SCB by the Highways Department of The Hong Kong SAR Government, and the SCB-WASHMS is composed of more than 1,300 sensors in 15 types. In order to establish a linkage between structural health monitoring and maintenance management, a Structural Health Rating System (SHRS) with relevant rating tools and indices is devised. On the basis of a 3D space frame finite element model (FEM) of SCB and model updating, this paper presents the development of an SHR-oriented 3D multi-scale FEM for the purpose of load-resistance analysis and damage evaluation in structural element level, including modeling, refinement and validation of the multi-scale FEM. The refined 3D structural segments at deck and towers are established in critical segment positions corresponding to maximum cable forces. The components in the critical segment region are modeled as a full 3D FEM and fitted into the 3D space frame FEM. The boundary conditions between beam and shell elements are performed conforming to equivalent stiffness, effective mass and compatibility of deformation. The 3D multi-scale FEM is verified by the in-situ measured dynamic characteristics and static response. A good agreement between the FEM and measurement results indicates that the 3D multi-scale FEM is precise and efficient for WASHMS and SHRS of SCB. In addition, stress distribution and concentration of the critical segments in the 3D multi-scale FEM under temperature loads, static wind loads and equivalent seismic loads are investigated. Stress concentration elements under equivalent seismic loads exist in the anchor zone in steel/concrete beam and the anchor plate edge in steel anchor box of the towers.

• Steel and Composite Structures
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• 제18권2호
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• pp.425-442
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• 2015

This paper addresses theoretically the bending and buckling behaviors of size-dependent nanobeams made of functionally graded materials (FGMs) including the thickness stretching effect. The size-dependent FGM nanobeam is investigated on the basis of the nonlocal continuum model. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a sinusoidal variation of all displacements through the thickness without using shear correction factor. The material properties of FGM nanobeams are assumed to vary through the thickness according to a power law. The governing equations and the related boundary conditions are derived using the principal of minimum total potential energy. A Navier-type solution is developed for simply-supported boundary conditions, and exact expressions are proposed for the deflections and the buckling load. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and stability responses of the FGM nanobeam are discussed in detail. The study is relevant to nanotechnology deployment in for example aircraft structures.

• Smart Structures and Systems
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• 제9권6호
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• pp.505-534
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• 2012

The present work deals with second order statistics of post buckling response of piezoelectric laminated composite cylindrical shell panel subjected to hygro-thermo-electro-mechanical loading with random system properties. System parameters such as the material properties, thermal expansion coefficients and lamina plate thickness are assumed to be independent of the temperature and electric field and modeled as random variables. The piezoelectric material is used in the forms of layers surface bonded on the layers of laminated composite shell panel. The mathematical formulation is based on higher order shear deformation shell theory (HSDT) with von-Karman nonlinear kinematics. A efficient $C^0$ nonlinear finite element method based on direct iterative procedure in conjunction with a first order perturbation approach (FOPT) is developed for the implementation of the proposed problems in random environment and is employed to evaluate the second order statistics (mean and variance) of the post buckling load of piezoelectric laminated cylindrical shell panel. Typical numerical results are presented to examine the effect of various environmental conditions, amplitude ratios, electrical voltages, panel side to thickness ratios, aspect ratios, boundary conditions, curvature to side ratios, lamination schemes and types of loadings with random system properties. It is observed that the piezoelectric effect has a significant influence on the stochastic post buckling response of composite shell panel under various loading conditions and some new results are presented to demonstrate the applications of present work. The results obtained using the present solution approach is validated with those results available in the literature and also with independent Monte Carlo Simulation (MCS).