• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.299-307
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• 1991

A unified correlation of the interfacial friction factor for air-water and steam-water flows in inclined rectangular channels has been developed. The correlation was expressed in the form of a power law of the liquid and the gas Reynolds number, and the liquid-to-gas viscosity ratio. In addition, a relation between the equivalent roughness and the intensity of wave height fluctuation of the interface has been investigated. A new dimensionless intensity of fluctuation including a liquid film Reynolds number is proposed. It has been shown that the dimensionless equivalent roughness, which is calculated from the Nikuradse equation, can be uniquely related to this dimensionless intensity of fluctuation for both air-water and steam-water flows.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.17-24
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• 2007

An experimental investigation was carried out for 4 different types of the aluminum foam heat sinks which were inserted into the annulus. The purpose of this study is to examine the feasibility of a heat sink with high performance forced convective water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kW/m^2$ and Reynolds number ranged from 120 to 9,000. Experimental results show that the departure from the Darcy's law is evident from the pressure loss and the friction factor is much higher while the significant enhancement in Nusselt number is obtained, and average Nusselt number of aluminum foam with high pore density is much higher than that of aluminum foam with low pore density. Correlations for the friction factor is proposed and used for design of thermal applications.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.227-233
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• 2015

In this paper, the effect of flow stress, friction, temperature, and velocity on finite element predictions of metal flow lines after cylindrical upsetting is presented. An actual three-stage hot forging process involving an upsetting step is utilized and experimental metal flow lines are measured to study the effect of the various process variables. It was found that temperature and velocity for reasonable values of friction have little influence on metal flow lines especially those located deep within the cylinder but that flow stress has a direct influence on the flow lines. It was shown that a pure power law material model cannot reflect the real flow stress of hot material because it underestimates the flow stress especially around the dead-metal zone for the upsetting of a cylindrical specimen. It is thus recommended that a proper lower limit of flow stress be assumed to alleviate this issue.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.3
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• pp.157-162
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• 2005

This paper presents an adaptive compensator using the fuzzy systems for robot manipulator with unknown frictions. In general, frictions are neglected or dynamic frictions are only considered in robot control theories. The proposed control method considers viscous frictions as well as dynamic frictions. Using the property that the frictions of joints are decoupled, SISO-fuzzy systems are utilized to approximate each friction. The stability of overall control system is proven and the adaptive laws are derived based on Lyapunov stability theorey. To verify the validity of the proposed control strategy, the results of computer simulations are shown for 2-link robot manipulator. The ability of approximating of the fuzzy system is also shown.

• Transactions on Electrical and Electronic Materials
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• v.6 no.6
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• pp.249-255
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• 2005

In recent years, a novel tiny piezoelectric linear motor converting a radial mode vibration to a longitudinal mode vibration driven by the impact force has been developed for a camera optical module. The tiny piezoelectric motor is consisted of a shaft, mobile element, and piezoelectric transducer. In this work, the frictional coefficient and static friction force of the interface between the shaft and the mobile element have been investigated according to their respective materials. It was found that two combinations, namely Pyrex glass or stainless steel for the shaft and stainless steel (SUS) for the mobile element, exhibited good dynamic behaviors in the tiny ultrasonic linear motor, which was newly developed based on operating concepts based on Newton's law.

• Steel and Composite Structures
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• v.28 no.1
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• pp.111-121
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• 2018

It has been argued that fracture energy of composite laminates depends on their thickness and number of layers. In this paper a modified direct energy balance approach (DEBA) has been developed to evaluate the mode-II shear fracture energy for E-glass/Epoxy laminates from finite element model at an arbitrary thickness. This approach considers friction and damage/plasticity deformations using cohesive zone modeling (CZM) and nonlinear finite element modeling. The presence of compressive stress and resulting friction was argued to be a possible cause for the thickness dependency of fracture energy. In the finite element modeling, CZM formulation has been developed with bilinear cohesive constitutive law combined with friction consideration. Also ply element have been developed with shear plastic damage model. Modified direct energy balance approach has been proposed for estimation of mode-II shear fracture energy. Experiments were performed on laminates of glass epoxy specimens for characterization of material parameters and determination of mode-II fracture energies for different thicknesses. Effect of laminate thickness on fracture energy of transverse crack tension (TCT) and end notched flexure (ENF) specimens has been numerically studied and comparison with experimental results has been made. It is shown that the developed numerical approach is capable of estimating increase in fracture energy due to size effect.

• Transactions of Materials Processing
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• v.4 no.2
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• pp.131-140
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• 1995

In this paper damage propagation of a material during forming is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. The stiffness degradation of the loaded material is chosen as a damage measure. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. To simulate contact condition, extended interior penalty method with modified coulomb friction law is adopted. The displacement control method along with the modified Riks' continuation technique is used to solve the incremental iterative equations. As numerical examples, upsetting problem and backward extrusion problem are simulated and the results of damage propagation and $J_2$ stress contours with and without friction are presented.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.138-143
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• 2007

Superplastic forming/diffusion bonding (SPF/DB) processes were analyzed using a 3-D rigid visco-plastic finite element method. A constant-triangular element based on membrane approximation and an incremental theory of plasticity are employed for the formulation. The coulomb friction law is used for interface friction between tool and material. Pressure-time relationship for a given optimal strain rate is calculated by stress and pressure values at the previous iteration step. In order to improve the contact searching, hierarchical search algorithm has been applied and implemented into the code. Various geometries including sandwich panel and 3 sheet shape for 3-D SPF/DB model are analyzed using the developed program. The validity fer the analysis is verified by comparison between analysis and results in the literature.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.2
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• pp.84-91
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• 2011

The purpose of this study is to find how to be formed the wet film thickness during the low friction coating process for a piston skirt with application to the theory of screen printing. In other words, the general expressions predicting the pressure under a blade and the volume of coating fluid passing through the blade edge are derived. Using these expressions, the coating thickness on a piston skirt during a sample blade coating process can be quantitatively assessed.

• Transactions of Materials Processing
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• v.24 no.5
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• pp.323-331
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• 2015

Impact extrusion is an economical and productive process that can replace the multistage deep drawing process for producing deep rectangular cases. In the current work, a three-dimensional finite element analysis of the impact extrusion process of a commercial purity aluminum alloy (AA1070) was performed to predict loads, material flow, and deformed shapes using the Hansel-Spittel rheology law, which describes the flow stress at various temperatures and strain rates. The role of various process parameters such as friction, clearance between punch and die, aspect ratio and thickness of billet on the process and the shapes was analyzed.