• Journal of Korean Association for Spatial Structures
• /
• v.19 no.3
• /
• pp.101-109
• /
• 2019

In order to develop the compatible damping device in various vibration source, a hybrid wall-type damper combining slit and friction damper in parallel was developed. Cyclic loading tests and two-story RC reinforced frame tests were performed for structural performance verification. As a result of the 5-cyclic loading test according to KBC-2016 and low displacement cyclic fatigue test, The hybrid wall type damper increased its strength and the ductility was the same as that of the slit damper. In addition, As a result of the two-layer frame test, the reinforced frame had about twice the strength of the unreinforced frame, and the story drift ratio was satisfied to Life Safety Level.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.12
• /
• pp.513-518
• /
• 2019

Friction Stir Welding is a welding technique for metal materials that utilizes the heat generated by friction between the material to be welded and the welding tool that rotates at high speed. In this study, a numerical analysis method was used to analyze the change in the internal temperature of the welded material during friction stir welding. As the welding target material, AZ31 magnesium alloy was applied and the welding phenomenon was considered a flow characteristic, in which a melting-pool was formed. FLUENT was used as the numerical tool to perform the flow analysis. For flow analysis of the welding process, the welding material was assumed to be a high viscosity Newtonian fluid, and the boundary condition of the welding tool and the material was considered to be the condition that friction and slippage occur simultaneously. Analyses were carried out for various rotational speeds and the translational moving speed of the welding tool as variables. The analysis results showed that the higher the rotational speed of the welding tool and the slower the welding tool movement speed, the higher the maximum temperature in the material increases. Moreover, the difference in the rotational speed of the welding tool has a greater effect on the temperature change.

• Steel and Composite Structures
• /
• v.24 no.2
• /
• pp.239-248
• /
• 2017

Friction dampers are displacement dependent energy dissipation devices which dissipate earthquake energy through friction mechanism and widely used in improving the seismic behavior of new structures and rehabilitation of existing structures. In this paper, the cyclic behavior of a friction damper with different friction materials is investigated through experimental tests under cyclic loading. The damper is made of steel plates, friction pads, preloaded bolts and hard washers. The paper aims at investigating the hysteretic behavior of three friction materials under cyclic loading to be utilized in friction damper. The tested friction materials are: powder lining, super lining and metal lining. The experimental results are studied according to FEMA-356 acceptance criteria and the most appropriate friction material is selected by comparing all friction materials results.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.6
• /
• pp.57-62
• /
• 2000

An experimental study has been performed to investigate friction characteristics of pre-coated metals widely used in domestic appliances. Seven-coated sheet metals are tested by using three friction mechanism such as straight pulling, frictionless roller, and non-rotational roller with three kinds of cylindrical rollers. In this experiment, effects of friction mechanism, blank thickness, and roller diameter on friction coefficient, surface roughness, and scoring factor have been investigated From the experimental results, it has been found that tested pre-coated sheet metals have low friction coefficients ($\mu$ = 0.15~0.20) because films coated on sheets take a role of lubricants. Friction coefficients of pre-coated metals decrease with increasing roller-diameters. Surface of pre-coated metals can be improved by decreasing the blank thickness

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.337-340
• /
• 2002

The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The flow field of an annulus has been numerically solved using a finite volume method. The pressure losses and Skin-friction coefficients have been measured for the fully developed flow of water and $0.2{\%}$ aqueous solution of sodium carboximethy1 cellulose (CMC), respectively at inner cylinder rotational speed of $0{\~}600rpm$. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. Consequently the critical(axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of Taylor vortices.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.23 no.4
• /
• pp.345-349
• /
• 2014

In this study, an age-hardened 6061-T6 alloy sheet was used, which is commonly utilized for auto parts. The junction strength characteristics in relation to the stirring speed and welding speed were studied in accordance with the friction stir welding rotation of the tool pin. Micro hardness measurements of A type and B type pins, for a welding speed of 400 mm/min and a tool rotational speed 3000 rpm, were obtained as Hv104 and Hv111, respectively. For a welding speed of 200 mm/min and a tool rotational speed of 2000 rpm, we obtained Hv48 and Hv50 for A and B type pins, respectively. Microstructure observation showed that the stirring portion was fine and uniform, which occurred because of its plastic deformation. In the thermomechanically affected zone, partial recrystallization was present because of the plastic deformation. The crystal grains in the heat affected zone were coarsened due to the heat generated by friction stir welding.

• Steel and Composite Structures
• /
• v.51 no.2
• /
• pp.173-183
• /
• 2024

This study investigates a new seismic retrofit system that utilizes rotational friction dampers and axial springs. The retrofit system involves a steel frame with rotational friction dampers (RFD) at beam-column joints and linear springs at the corners, providing energy dissipation and self-centering capabilities to existing structures. The axial spring acts as a self-centering mechanism that eliminates residual deformations, while the friction damper mitigates seismic damage. To evaluate the seismic performance of the proposed retrofit system, a series of cyclic loading tests were carried out on a steel beam-column subassembly equipped with the proposed devices. An analytical model was then developed to validate the experimental results. A performance point ratio (PPR) was presented to optimize the design parameters of the retrofit system, and a performance-based seismic design strategy was developed based on the PPR. The retrofit system's effectiveness and the presented performance-based design approach were evaluated through case study models, and the analysis results demonstrated that the developed retrofit system and the performance-based design procedure were effective in retrofitting structures for multi-level design objectives.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.181-186
• /
• 2002

Lately, as going on increasing in the demand of high power density(power/weight), it is necessary for hydraulic axial piston pump/motor to operate more high pressure and speed. But in these condition, there are some trouble like as friction loss. To reduce this friction loss, hydrostatic bearing is used far axial piston pump/motor frequently. In general, it is difficult to measure accurate friction torque of spherical hydrostatic bearing in the use of the existing devices. So, we have developed the measurement device using the reaction torque sensor to obtain the pure friction torque, fitted in the casing. In this report, we intend to make an introduction about this measurement device for friction torque of the spherical wear part and clarify the effect of friction characteristics on supply pressure and rotational speed with three types of pocket size by using this measurement device.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.22 no.4
• /
• pp.230-234
• /
• 2010

This study examined the effect of wall friction on deformation characteristics of the cellular bulkhead, in terms of artificial wall friction based on the results of model tests according to the existing penetration ratio and loading height. 1. The effect of wall friction on deformation characteristics of the cellular bulkhead turned out to be less as the loading height decreases and the penetration ratio increases. The yield load also becomes less as wall friction decreases. 2. The ratio of the rotational displacement to the horizontal displacement of the cellular bulkhead becomes less as the loading height decreases and the penetration ratio increases. Hence it is concluded that the effect of wall friction has close relationship with the rotational displacement.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.324-329
• /
• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of $0.1\sim0.4%$ aqueous solution of sodium carbomethyl cellulose (CMC), respectively at inner cylinder rotational speed of $0\sim600rpm$. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficients due to the rotation in uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.