• 한국주조공학회지
• /
• 제10권4호
• /
• pp.332-341
• /
• 1990

The structure and tensile properties of the unidirectionally solidified Al-33wt.%Cu alloy have been investigated. Casted Al-33wt.%Cu alloy was unidirectionally solidified with rates (R) between 1㎝/hr and 24cm/hr maintaining the thermal gradient(G) at solid-liquid interface, $32^{\circ}C/cm$ and $21^{\circ}C/cm$. The entectic struture was varied according to the growth condition(G/R radio). When G/R ratio was larger than $8.5{\times}10^3$ $^{\circ}C/cm^2/sec$ the lamellar structure was formed, and colony structure was formed when G/R ratio was smaller than $8.5{\times}10^3$ $^{\circ}C/cm^2/sec$. The interlamellar spacing(${\gamma}$) in the above alloy system was vaired with the growth rate(R) According to "${\gamma}^2{\cdot}R＝8.8{\times}10＾{-11}cm^2/sec$" relationship. The yield stress (${\sigma}$0.001) and UTS for samples in the as-grown condition increased with the interlamellar spacing decrease and the values corresponding to colony structure are lower than those corresponding to amellar structure with the same lamellar spacing. The yield stress for samples in aged condition did not change with the interlamellar spacing.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.385-390
• /
• 2001

This paper presents a nonlinear analysis technique with slip, the effects of slip modulus and composite action by shear connector on behavior and capacity in composite structure of sandwich system. As a results of this study, it proved that the slip modulus, in case of shear behavior, seldom influence load-resistance capacity such as yield and ultimate load, but in case of flexural behavior, it appropriately influence load-resistance capacity because of stress redistribution by slip. In case of flexural behavior, analysis result for perfect-composite results in over-estimation and perfect-slip results in under-estimation on behavior and capacity. Therefore, it is desirable to model steel-concrete interface with partial-composite. The effects of slip on behavior and capacity are less in case of positive composite than loosely composite, and it proved that composite action by shear connector improve the load-resistance capacity of this system.

• Structural Engineering and Mechanics
• /
• 제41권5호
• /
• pp.645-662
• /
• 2012

Deteriorative effects of steel corrosion on the structural response of reinforced concrete are simulated for varying degrees of corrosion. The simulation approach is based on a three-dimensional irregular lattice model of the bulk concrete, in which fracture is modeled using a crack band approach that conserves fracture energy. Frame elements and bond link elements represent the reinforcing steel and its interface with the concrete, respectively. Polylinear stress-slip properties of the link elements are determined, for several degrees of corrosion, through comparisons with direct pullout tests reported in the literature. The link properties are then used for the lattice modeling of reinforced concrete beams with similar degrees of corrosion of the main reinforcing steel. The model is successful in simulating several important effects of steel corrosion, including increased deflections, changes in flexural cracking behavior, and reduced yield load of the beam specimens.

• Structural Engineering and Mechanics
• /
• 제58권4호
• /
• pp.731-743
• /
• 2016

Plastic behaviors, based on the von Mises yield criterion, of circular discs containing a purely elastic, circular inclusion under uniform temperature loading are studied with the finite element analysis. Temperature-dependent mechanical properties are considered for the matrix material only. In addition to analyzing the plane stress and plane strain disc, a 3D thin disc and cylinder are also analyzed to compare the plane problems. We determined the elastic irreversible temperature and global plastic collapse temperature by the finite element calculations for the plane and 3D problem. In addition to the global plastic collapse, for the elastically hard case, the plane stress problem and 3D thin disc may exhibit a local plastic collapse, i.e. significant pile up along the thickness direction, near the inclusion-matrix interface. The pileup cannot be correctly modeled by the plane stress analysis. Furthermore, due to numerical difficulties originated from large deformation, only the lower bound of global plastic collapse temperature of the plane stress problem can be identified. Without considerations of temperature-dependent mechanical properties, the von Mises stress in the matrix would be largely overestimated.

• Journal of Mechanical Science and Technology
• /
• 제18권3호
• /
• pp.453-459
• /
• 2004

TiNi/ Al6061 shape memory alloy (SMA) composite was fabricated by hot press method to investigate the microstructure and mechanical properties. Interface bonding between TiNi reinforcement and A1 matrix was observed by using SEM and EDS. Pre-strain was imposed to generate compressive residual stress inside composite. A tensile test for specimen, which under-went pre-strain, was performed at high temperature to evaluate the variation of strength and the effect of pre-strain. It was shown that interfacial reactions occurred at the bonding between matrix and fiber, creating two inter-metallic layers. And yield stress increased with the amount of pre-strain. Acoustic Emission technique was also used to nondestructively clarify the microscopic damage behavior at high temperature and the effect of pre-strain of TiNi/ Al6061 SMA composite.

• Korea-Australia Rheology Journal
• /
• 제11권3호
• /
• pp.233-240
• /
• 1999

In order to understand the flow behavior of Electrorheological (ER) fluid, dynamic simulation has been intensively performed for the last decade. When the shear flow is applied, it is easy to carry out the simulation with relatively small number of particles because of the periodic boundary condition. For the squeezing flow, however, it is not easy to apply the periodic boundary condition, and the number of particles needs to be increased to simulate the ER system more realistically. For this reason, the simulation of ER fluid under squeezing flow has been mostly performed with some representative chains or with the approximation that severely restricts the flow geometry to reduce the computational load. In this study, Message Passing Interface (MPI), which is one of the most widely-used parallel processing techniques, has been employed in a dynamic simulation of ER fluid under squeezing flow. As the number of particles used in the simulation could be increased significantly, full domain between the electrodes has been covered. The numerical treatment or the approximation used to reduce the computational load has been evaluated for its validity, and was found to be quite effective. As the number of particles is increased, the fluctuation of the normal stress becomes diminished and the prediction in general was found to be qualitatively In good agreement with the experimental results.

• Geomechanics and Engineering
• /
• 제5권5호
• /
• pp.379-399
• /
• 2013

In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength ($s_u$) and the strain at 50% yield stress (${\varepsilon}_{50}$). This approach may ignore various features for a particular soil which may lead to un-conservative or over-conservative design as not all the data points in the stress-strain relation are used. However, with the increasing ability to simulate soil-structure interaction problems using highly developed computers, the trend has shifted towards a more theoretically sound basis. In this paper, principles of Mobilized Strength Design (MSD) concept is used to construct a continuous p-y curves from experimentally obtained stress-strain relationship of the soil. In the method, the stress-strain graph is scaled by two coefficient $N_C$ (for stress) and $M_C$ (for strain) to obtain the p-y curves. $M_C$ and $N_C$ are derived based on Semi-Analytical Finite Element approach exploiting the axial symmetry where a pile is modelled as a series of embedded discs. An example is considered to show the application of the methodology.

• Steel and Composite Structures
• /
• 제13권3호
• /
• pp.277-293
• /
• 2012

The interaction between steel tube and concrete core is the key design considerations for concrete-filled steel tube columns. In a concrete-filled steel tube (CFST) column, the steel tube provides confinement to the concrete core which permits the composite action among the steel tube and the concrete. Due to construction faults and plastic shrinkage of concrete, the debonding separation at the steel-concrete interface weakens the confinement effect, and hence affects the behaviour and bearing capacity of the composite member. This study investigates the axial loading behavior of the concrete filled circular steel tube columns with debonding separation. A three-dimensional nonlinear finite element model of CFST composite columns with introduced debonding gap was developed. The results from the finite element analysis captured successfully the experimental behaviours. The calibrated finite element models were then utilized to assess the influence of concrete strength, steel yield stress and the steel-concrete ratio on the debonding behaviour. The findings indicate a likely significant drop in the load carrying capacity with the increase of the size of the debonding gap. A design formula is proposed to reduce the load carrying capacity with the presence of debonding separation.

• 드라이브 ㆍ 컨트롤
• /
• 제14권2호
• /
• pp.23-29
• /
• 2017

In this study, a flexible multi-body dynamic simulation model of a knuckle boom crane is developed to evaluate the stress of spindle and rack gears under dynamic working conditions. It is difficult to predict potential critical damage to a knuckle boom crane if only the static condition is considered during the development process. To solve this issue, a severe working scenario (high speed with heavy load) was simulated as a boundary condition for testing the integrity of the dynamic simulation model. The crane gear model is defined as a flexible body so contact analysis was performed. The functional motion of a knuckle boom crane is generated by applying forces at each end of the rack gear, which was converted from hydraulic pressure measured for the experiment. The bending and contact stress of gears are theoretically calculated to validate the simulation model. In the simulation, the maximum stress of spindle and rack gears are observed when the crane abruptly stops. Peak impact force is produced at the contact interface between pinion and rack gears due to the inertia force of the boom. However, the maximum stress (bending/contact) of spindle and rack are under the yield stress, which is safe from damage. By using the developed simulation model, the experiment process is expected to be minimized.

• 한국진공학회지
• /
• 제9권2호
• /
• pp.162-166
• /
• 2000

플라즈마 화학증착법(Plasma Enhanced Chemical Vapor Deposition, PECVD)을 이용하여 양질의 $Si_3N_4$ 금속-유전막-금속(Metal-Insulator-Metal, MIM) 커패시터를 구현하였다. 유전체인 $Si_3N_4$와 전극인 Al의 계면반응을 억제시키기 위해 티타늄 나이트라이드(TiN)를 확산 장벽으로 사용한 결과 MIM 커패시터의 전극과 유전체 사이의 계면에서는 어떠한 hillock이나 석출물도 관찰되지 않았다. 커패시턴스와 전류전압 특성분석으로부터 양질의 MIM 커패시터 특성을 보이는 $Si_3N_4$의 최소 두께는 500 $\AA$이며, 그 두께 미만에서는 대부분의 커패시터가 전기적으로 단락되어 웨이퍼 수율이 낮아진다는 사실을 알 수 있었다. 투과전자현미경(transmission Electron Microscope, TEM)을 이용한 단면 미세구조 관찰을 통해 $Si_3N_4$층의 두께가 500 $\AA$ 미만인 커패시터의 경우에 TiN과 $Si_3N_4$의 계면에서 형성되는 슬릿형 공동(slit-like void)01 의해 커패시터의 유전특성이 파괴된다는 사실을 알게 되었으며, 열 유기 잔류 응력(thermally-induced residual stress) 계산에 기초하여 공동의 형성 기구를 규명하였다.