• Tribology and Lubricants
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• v.11 no.1
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• pp.27-36
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• 1995

Maximum allowable PV values of oilless composite bearing materials (70% epoxy-resin/30% Graphite) were measured and compared at various types of test rigs that have different contact geometry and the operating conditions. Test results showed that material failure was mainly characterized by the sharp increase in both coefficient of friction and surface temperature, and different PV values were measured under different Contact geometry. The discrepancy in measurement of PV values was analyzed in the light of theoretical frictional heating analysis. Results show that surface temperature rise depends on its contact geometry, and PV values could be overestimated in the testing conditions of high sliding velocity. Test data of different contact geometry were normalized by using a normalized contact pressure and sliding velocity; it showed a good correlation. This work suggests that normalized PV values could be more effective in evaluating bearing materials than conventional PV values for a design parameter of journal bearings.

• Journal of the Korean Ceramic Society
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• v.19 no.1
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• pp.24-34
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• 1982

The effect of the several variables on wetting of AISIB1113 steel by molten glass was studied by Sessible-drop method. Experimental variables were temperature, firing atmospheres, Fe2O3 addition to the sealing glass and steel surface conditions. The degree of wetting in terms of contact angles between molten glass and metal tested at different test conditions was analyzed by using Young's equation. The results showed that contact angles in H2 atmosphere in the glass metal systems were high but in N2 atmosphere, were small for studied glass metal systems. Especially, when the glass drop was in contact with oxidized steel in N2 atmosphere, The best adherence with contact angle of approximately 9°was obtained. In the case of Fe2O3 addition in glass contact angles subtantially increased due to the increase of surface tension of glass. Wetting phenomena were also discussed under the basis of these experimental results.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.3
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• pp.5-10
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• 2004

Electric contacts serve the purpose of transmitting electric signals across two conducting components. In this paper, the effects of contact conditions such as surface roughness, oxidation, and contamination were investigated with respect to electrical resistance variation of a connector in a direct current circuit. Such change in the electrical resistance is particularly important for low power circuits. The experimental results showed that compared with the effects of contact surface scratch or oxidation, the effect of contamination on the resistance variation was the most significant. In order to minimize failure due to electrical resistance change at the contact region, proper sealing to prevent contamination from entering the interface is needed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.188-191
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• 1997

In the recent sheet metal forming simulations, it increases to adopt the dynamic explicit method for an effective computation and the elastic-plastic formulation for stress recovery. It is inevitable in the dynamic explicit method that some noises occur and sometimes partly spoil results of simulations. It is severer when complicated contact conditions are included in simulations. An effective method to control these noises is introduction of damping effects. In this paper, the concept of contact damping is introduced in order to suppress noises due to complicated contact conditions. This is checked by analyzing a simple sheet metal forming process(U-bending). From the computational results, it is shown that the contact damping can effectively control the noises due to contacts and develop more reliable internal stress states.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.582-590
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• 2007

Imperfectly jointed interface serves as mechanical waveguide for elastic waves and gives rise to two distinct kinds of guided wave propagating along the interface. Contact acoustic nonlinearity (CAN) is known to plays major role in the generation of these interface waves called generalized Rayleigh waves in non-welded interface. Closed crack is modeled as non-welded interface that has nonlinear discontinuity condition in displacement across its boundary. Mathematical analysis of boundary conditions and wave equation is conducted to investigate the dispersive characteristics of the interface waves. Existence of the generalized Rayleigh wave(interface wave) in nonlinear contact interface is verified in theory where the dispersion equation for the interface wave is formulated and analyzed. It reveals that the interface waves have two distinct modes and that the phase velocity of anti-symmetric wave mode is highly dependent on contact conditions represented by linear and nonlinear dimensionless specific stiffness.

• Biomolecules & Therapeutics
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• v.31 no.4
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• pp.388-394
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• 2023

Nitric oxide (NO) is a signaling molecule that plays a crucial role in numerous cellular physiological processes. In the skin, NO is produced by keratinocytes, fibroblasts, endothelial cells, and immune cells and is involved in skin functions such as vasodilation, pigmentation, hair growth, wound healing, and immune responses. NO modulates both innate and adaptive immune responses. As a signaling molecule and cytotoxic effector, NO influences the function of immune cells and production of cytokines. NO is a key mediator that protects against or contributes to skin inflammation. Moreover, NO has been implicated in skin sensitization, a process underlying contact dermatitis. It modulates the function of dendritic cells and T cells, thereby affecting the immune response to allergens. NO also plays a role in contact dermatitis by inducing inflammation and tissue damage. NO-related chemicals, such as nitrofatty acids and nitric oxide synthase (NOS) inhibitors, have potential therapeutic applications in skin conditions, including allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD). Further research is required to fully elucidate the therapeutic potential of NO-related chemicals and develop personalized treatment strategies for skin conditions.

• Steel and Composite Structures
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• v.29 no.3
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• pp.333-348
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• 2018

An analytical method is developed for analysing the contact buckling response of infinitely long, thin corrugated plates and flat plates restrained by a Winkler tensionless foundation and subjected to linearly varying in-plane loadings, where the corrugated plates are modelled as orthotropic plates and the flat plates are modelled as isotropic plates. The critical step in the presented method is the explicit expression for the lateral buckling mode function, which is derived through using the energy method. Simply supported and clamped edges conditions on the unloaded edges are considered in this study. The acquired lateral deflection function is applied to the governing buckling equations to eliminate the lateral variable. Considering the boundary conditions and continuity conditions at the border line between the contact and non-contact zones, the buckling coefficients and the corresponding buckling modes are found. The analytical solution to the buckling coefficients is also expressed through a fitted approximate formula in terms of foundation stiffness, which is verified through previous studies and finite element (FE) method.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1002-1009
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• 2004

Direct contact air conditioning systems, in which heat and mass are transferred directly between air and water droplets, have many advantages over conventional indirect contact systems. The purpose of this research is to investigate the cooling and heating performances of direct contact air conditioning system for various inlet parameters such as air velocity, air temperature, water flow rate and water temperature. The experimental apparatus comprises a wind tunnel, water spray system, scrubber, demister, heater, refrigerator, flow and temperature controller, and data acquisition system. The inlet and outlet conditions of air and water are measured when the air contacts directly with water droplets as a counter flow in the spray section of the wind tunnel, and the heat and mass transfer rates between air and water are calculated. The droplet size of the water sprays is also measured using a Malvern Particle Analyzer. In the cooling conditions, the outlet air temperature and humidity ratio decrease as the water flow rate increases and as the water temperature, air velocity and temperature decrease. On the contrary, the outlet air temperature and humidity ratio increase in the heating conditions as the water flow rate and temperature increase and as the air velocity decreases.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.143-149
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• 2013

A new finite element model for the hydrostatic extrusion of a biaxial bar is introduced. In this model, a penalty contact algorithm, which is adopted to replace the traction boundary conditions due to the fluid in the container of the extruder, is incorporated into a consistent penalty finite element formulation for the viscoplastic deformation of a work piece during hydrostatic extrusion. Two parameters, introduced in the penalty contact algorithm in this study, a critical penalty contact pressure $P_0$ and a critical penalty contact distance $D_c$, are carefully examined for various process conditions. The proposed finite element model is applied to the hydrostatic extrusion of a Cu-clad Al bar. The extrusion loads and thickness ratios of the clad materials by the proposed model are compared in detail to values from experiments reported in the literature. Finally, it is concluded that the proposed finite element model is useful in practical implementations.

• Tribology and Lubricants
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• v.23 no.5
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• pp.187-194
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• 2007

The profile of the roller in the axial direction is the main design factor in order to increase endurance life against the contact fatigue due to the stress concentration along the edge of the roller. Even under the elas-tohydrodynamic lubrication (ehl) conditions, the stress concentration along the edge of the roller greatly worsens the fatigue life both for the roller and contacting body. In this study, roller contacts of finite axial length are studied for the film thickness and pressure of ehl. For the real contact behaviors under the ehl conditions, multigrid and multi-level method is applied so that much higher loading conditions can be investigated. Several axial profiles of roller are investigated to verify how both ehl film and pressure are generated and some of them are recommended for the ehl contact condition.