• Computers and Concrete
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• 제21권3호
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• pp.321-333
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• 2018

Flat-slabs, being a significant structural component, not only reduce the dead load of the structure but also reduce the amount of concrete required for construction. Moreover the use of recycled aggregates lowers the impact of large scale construction to nearby ecosystems. Recycled aggregate based concrete being a quasi-brittle material shows enormous cracking during failure. Crack growth in flat-slabs is mostly in sliding mode (Mode II). Therefore sufficient sections need to be provided for resistance against such failure modes. The main objective of the paper is to numerically determine the ultimate load carrying capacity of two self-similar flat-slab specimens and validate the results experimentally for the natural aggregate as well as recycled aggregate based concrete. Punching shear experiments are carried out on circular flat-slab specimen on a rigid circular knife-edge support built out of both normal (NAC) and recycled aggregate concrete (RAC, with full replacement). Uniaxial compression and bending tests have been conducted on cubes, cylinders and prisms using both types of concrete (NAC and RAC) for its material characterization and use in the numerical scheme. The numerical simulations have been conducted in ABAQUS (a known finite element software package). Eight noded solid elements have been used to model the flat slab and material properties have been considered from experimental tests. The inbuilt Concrete Damaged Plasticity model of ABAQUS has been used to monitor crack propagation in the specimen during numerical simulations.

• 대한기계학회논문집A
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• 제30권7호
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• pp.833-840
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• 2006

The paper presents a numerical solution to the problem of a hot rigid indenter sliding over a thermoelastic Winkler foundation with a thermal contact resistance at constant speed. It is shown analytically that no steady-state solution can exist for sufficiently high temperature or sufficiently small normal load or speed, regardless of the thermal contact resistance. However the steady state solution may exist in the same situation if the thermal contact resistance is considered. This means that the effect of the large values of temperature difference and small value of force or velocity which occur at no steady state can be lessened due to the thermal contact resistance. When there is no steady state, the predicted transient behavior involves regions of transient stationary contact interspersed with regions of separation regardless of the thermal contact resistance. Initially, the system typically exhibits a small number of relatively large contact and separation regions, but after the initial transient, the trailing edge of the contact area is only established and the leading edge loses contact, reducing the total extent of contact considerably. As time progresses, larger and larger numbers of small contact areas are established, unlit eventually the accuracy of the algorithm is limited by the discretization used.

• 한국자동차공학회논문집
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• 제24권2호
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• pp.183-190
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• 2016

Engine torque is transferred to the transmission where drag torque is minimized improving fuel efficiency. This is particularly true in a wet clutch pack. This study measures slip friction when the wet clutch pack in a DCT (Dual-Clutch Transmission) is disengaged, and the friction pads are slipping. Shudder engagement velocity, and applied forces can be measured under various working conditions through these torque transfer experiments. Test results demonstrate that the design parameters, and engagement conditions of wet clutch packs can be optimized to reduce shudder and frictional vibration during engagement in a dual clutch transmission.

• International Journal of Automotive Technology
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• 제4권4호
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• pp.165-172
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• 2003

This article deals with the spin loss analysis of friction drive CVTs, especially for the cases of S-CVT and SS-CVT. There are two main sources of power loss resulting from slippage in the friction drive CVT, spin and slip loss. Spin loss, which is also a main design issue in traction drives, results from the elastic contact deformation of rotating bodies having different rotational velocities. The structure and operating principles of the S-CVT and SS-CVT are first reviewed briefly. And to analyze the losses resulting from slippage, we reviewed previous analyses of the friction mechanism. A modified classical friction model is proposed, which describes the friction behavior including Stribeck (i.e., pre-sliding) effect. It is also performed an in-depth study for the velocity fields generated at the contact regions along with a Hertzian analysis of deflection. Hertzian results were employed to construct the geometric parameters and normal pressure distributions of the contact surface with respect to elastic and plastic deformations. With analytic formulations of the relative velocity field, deflection, and friction mechanism of the S-CVT and SS-CVT, quantitative analyses of spin loss for each case are carried out. As a result, explicit models of spin loss were developed.

• Tribology and Lubricants
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• 제22권3호
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• pp.119-126
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• 2006

In this paper, the contact behavior characteristics of a primary sealing components such as a seal ring and a seal seat has been presented for a small hydro-power turbine. Using the non-linear FEM analysis, the maximum temperature, the axial displacement, radial differences between a seal ring and a seal seat, and maximum contact normal stress have been analyzed for three optimized sealing profiles in which are designed based on the FEM analysis and Taguchi's experimental method. The three primary sealing profiles between a seal ring and a seal seat are strongly related to a leakage of a water for a hydro-power turbine and wear of a primary sealing component. The computed results show that the contact rubbing area between a seal ring and a seal seat is very important for reducing a friction heating and wear in a sealing gap, and increasing a contact normal stress in primary sealing components. Based on the FEM computation, models II and III in which have a small rubbing surface of seal rings show low dilatation of primary sealing components, and high normal contact stress between a seal ring and a seal seat. Thus, the FEM computed results recommend a short contacting width of a primary sealing component for reducing a leakage and thermal distortions, and expanding a seal life. This means that a conventional primary sealing component may be switched to a reduced sealing face of seal rings.

• 소성∙가공
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• 제18권7호
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• pp.544-549
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• 2009

This study aimed to elucidate the deformation mechanism during low-temperature superplasticity of fine-grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy in the context of constitutive equation. For this purpose, initial coarse equiaxed microstructure was refined to $2.2{\mu}m$ via dynamic globularization. Globularized microstructure exhibited large superplastic elongations(434-826%) at temperatures of $650-750^{\circ}C$ and strain rate of $10^{-4}s^{-1}$. It was found that the main deformation mechanism of fine-grained material was grain boundary sliding accommodated by dislocation motion with both stress exponent (n) and grain size exponent (p) values of 2. When the alpha grain size, not sub-grain size, was considered to be an effective grain size, the apparent activation energy for low-temperature superplasticity of the present alloy(169kJ/mol) was closed to that of Ti-6Al-4V alloy(160kJ/mol).

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.27-27
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• 2003

무가압침투법으로 제조된 부피분율 10~24% SiC, TiC, B$_4$C 탄화물 입자강화 7075 Al 합금 기지 복합재료의 건식 미끄럼 마멸거동을 강화입자의 종류, 크기 및 부피 분율을 변수로 연구하였다. 미끄럼 마멸 시험은 pin-on-disk 형태의 마멸 시험기를 사용하여, AISI 52100 베어링강을 상대재로 상온 대기 중에서 실시되었다. 마멸특성의 분석과 마멸기구의 규명을 위하여 마멸면과 마멸단면을 SEM, EDS를 이용하여 분석하였다. 제조된 복합재료의 압축 시험을 통하여 측정된 항복강도와 가공경화지수는 서로 반비례하였고, 각 시편간의 경도 차는 크지 않았다. 마멸 시험결과, 크기 및 부피 분율이 7$\mu\textrm{m}$ !0%인 SiC 입자로 강화된 복합재료를 제외하고, 전체 복합재료 시편은 7075 Al 기지 합금에 비해 낮은 마멸 속도를 보였다. 10N 이하의 저하 중에서는 강화상의 종류와 상관없이 복합재료는 낮은 마멸 속도를 보였고, 25N 이상의 고하중에서는 TiC 입자강화 복합재료가 가장 낮은 마멸 속도를, SiC 입자강화 복합재료가 가장 높은 마멸 속도를 나타내었다. 강화 입자의 크기 및 부피 분율이 동일한 경우 SiC 입자로 강화된 복합재료가 가장 낮은 내마멸성을 나타내었다. 강화상의 크기 및 부피 분율이 증가함에 따라 미소 마멸에서 격렬 마멸로의 천이 하중이 증가하였다.

• 한국분말재료학회지
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• 제10권5호
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• pp.325-332
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• 2003

The effect of extrusion temperature on the microstructure and mechanical properties was studied in gas atomized TEX>$Al_{81}Si_{19}$ alloy powders and their extruded bars using SEM, tensile testing and wear testing. The Si particle size of He-gas atomized powder was about 200-800 nm. Each microstructure of the extruded bars with extrusion temperature (400, 450 and 50$0^{\circ}C$) showed a homogeneous distribution of primary Si and eutectic Si particles embedded in the Al matrix and the particle size varied from 0.1 to 5.5 ${\mu}m$. With increasing extrusion temperature from 40$0^{\circ}C$ to 50$0^{\circ}C$, the ultimate tensile strength (UTS) decreased from 282 to 236 ㎫ at 300 K and the specific wear increased at all sliding speeds due to the coarse microstructure. The fracture behavior of failure in tension testing and wear testing was also studied. The UTS of extrudate at 40$0^{\circ}C$ higher than that of 50$0^{\circ}C$ because more fine Si particles in Al matrix of extrudate at 40$0^{\circ}C$ prevented crack to propagate.

• 한국분말재료학회지
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• 제3권4호
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• pp.271-278
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• 1996

In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al-Mg-X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 $\mu$m were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively large particles occasionally at grain boundaries. The ultimate tensile strengths of Al-Mg-X alloys were found to decrease rather remarkably at 150 $^{\circ}C$ without the gain of the ductility at 150 $^{\circ}C$, which may result from segregation of $\beta$ ($Al_{3}Mg_{2}$) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed upon alloy systems. The ductility at 530 $^{\circ}C$ was found to be ~100%, suggesting that grain boundary sliding did not contribute to ductiliy despite he grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al-Mg-X alloys.

• Wind and Structures
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• 제23권4호
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• pp.301-311
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• 2016

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using $k-{\varepsilon}$ standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.