Jin Oh Chung, Sang Ryul Go, Jeong Hee Kim, Jong Geun Choi, Hyang Rae Kim and Hee Bum Choi
The purpose of this paper is to investigate surroundings for transfer film formation and removal, the effect of the transfer film formation on friction coefficients, the effect of…
Abstract
Purpose
The purpose of this paper is to investigate surroundings for transfer film formation and removal, the effect of the transfer film formation on friction coefficients, the effect of four different abrasive components, ZrO2, ZrSiO4, Al2O3 and Fe3O4, on transfer film formation and the effect of lubricating component MoS2 on transfer film formation and friction coefficients.
Design/methodology/approach
Two different MoS2 contents of 5.5 and 8.5 per cent were added to friction materials with no MoS2 content, which have four different abrasive components, ZrO2, ZrSiO4, Al2O3, Fe3O4. Friction tests composed of three different stages were conducted for those materials, and the friction surfaces of the counterpart disks were examined by scanning electron microscopy (SEM) to access the formation of transfer film at each stage.
Findings
For the transfer film formation, high temperature was a prerequisite, but the magnitude of deceleration rate was not important. The effect of the transfer film formation was to reduce the friction coefficients for most friction materials. Friction coefficients of materials which contain lubricating component MoS2 were higher than those which contain no MoS2 for most friction materials. The effect of the lubricating component MoS2 was to suppress the formation of transfer film, thus resulting in increase in friction coefficients.
Research limitations/implications
The transfer film was rather thin, with thickness of 1-2 µm for most friction materials. That hindered the examination of mechanical properties of the transfer film, such as hardness.
Practical implications
This research explained the surroundings for transfer film formation, and its effect on friction coefficients. The research suggests to suppress the formation of transfer film to make friction materials with high friction coefficient, and the lubricating component MoS2 can be used for the purpose.
Social implications
Development of high-friction-brake materials conventionally depends on the use of strong abrasive components, which may induce attacking of counterpart disks. The enhancement of friction coefficients with addition of MoS2 content is expected to open a new prospect in development of high-performance friction materials, which can be applicable to brake pads for racing cars.
Originality/value
The study is in pursuit of the transfer film formation in successive friction stages, which revealed the conditions for transfer film generation and removal. Specimen preparation for SEM observation of cross section of friction surface was painstaking to not damage the developed friction surface. The study revealed the effect of different abrasive components on transfer film formation and the effect of lubrication contents of MoS2 on transfer film formation and friction coefficients.
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Jin Oh Chung, Sang Ryul Go, Hee Bum Choi and Tae Kwan Son
This paper aims to investigate the temperature dependence of transfer film formation and friction coefficients in NAO friction materials with four different abrasive components…
Abstract
Purpose
This paper aims to investigate the temperature dependence of transfer film formation and friction coefficients in NAO friction materials with four different abrasive components, ZrO2, ZrSiO4, Al2O3 and Fe3O4.
Design/methodology/approach
8.5% SnS2 was added as a lubricating component to friction materials. Friction tests comprised 100 times of consecutive braking application for each friction material under constant temperature of 300°C, 400°C, 500°C and 600°C. After the friction tests, the friction surfaces of the counterpart disks were examined by scanning electron microscope to access the formation of transfer film.
Findings
Coefficients of friction depended on not only friction temperature but also friction history which is related to development of transfer film. The effect of the transfer film formation was to reduce the friction coefficients for most friction materials. Quantities of the transfer film formation varied with friction materials; at low temperature below 400° the transfer film formation was most active in the Fe3O4 materials, while at 600° it was the most active in the Al2O3 material. The effect of the lubricating component SnS2 was to suppress the formation of transfer film, thus enhancing friction coefficients.
Social implications
The enhancement of friction coefficients with addition of small amount of lubricating components such as SnS2 is expected to open a new approach in developing high performance-brake pads.
Originality/value
Temperature was the controlling parameter in the present test. Under these test modes, transfer film could be fully developed to access the role of the transfer film.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0427/
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Heesun Chung, Bum-Joon Kim, Eugenia Y. Lee and Hee-Yeon Sunwoo
This study aims to examine whether debt financing creates incentives for private firms to engage in earnings management via classification shifting. Especially, the authors…
Abstract
Purpose
This study aims to examine whether debt financing creates incentives for private firms to engage in earnings management via classification shifting. Especially, the authors examine whether debt-induced financial reporting incentives differ depending on the type of debt (i.e. public bonds versus private loans) and whether such incentives are influenced by the characteristics of external auditors (i.e. initial audits and auditor size).
Design/methodology/approach
The study uses data on 93,427 Korean private firms from 2001 to 2016. Classification shifting is measured by the positive correlation between non-core expenses and unexpected core earnings estimated with ordinary least squares.
Findings
The empirical analyses reveal that private firms engage in classification shifting as do public firms. Importantly, classification shifting is observed only in private firms that have outstanding debt, but not in private firms without debt. Among debt-financing private firms, classification shifting is more prevalent for firms that issue public debt than for firms that only use private debt. In addition, classification shifting of debt-financing private firms is more successful when they are audited by new auditors that are one of the non-Big 4 firms.
Research limitations/implications
The study provides evidence of classification shifting in private firms, which is novel to the literature. However, the inferences in the study depend on the validity of the model for detecting classification shifting.
Practical implications
This study helps lenders enhance their understanding on the financial reporting behaviors of borrowing firms. The results in this study suggest that lenders should be cautious in using core earnings for their investment decisions.
Originality/value
This study contributes to the literature by providing novel evidence of classification shifting in private firms. In addition, the authors contribute to the literature on debt-induced incentives for financial reporting.
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Chung Hyuk Park and Bum‐Hee Lee
To propose a new haptic modeling and contact analysis algorithm (modified long element method (MLEM)) to efficiently model deformation, to estimate elasticity, and to provide the…
Abstract
Purpose
To propose a new haptic modeling and contact analysis algorithm (modified long element method (MLEM)) to efficiently model deformation, to estimate elasticity, and to provide the characterization of contact with deformable objects, which is important in teleoperation and haptic system.
Design/methodology/approach
Widely used finite element method for haptic rendering and visualization of deformable objects has limitations in real‐time applications because of its massive calculations and the absence of physical modeling. Using long elements method (LEM), the authors propose the MLEM which is capable of real‐time deformation rendering and elasticity estimation with reliable physical modeling. The authors applied MLEM to a simple haptic system composed of the three‐link SNU DD‐robot and a force‐feedback joystick.
Findings
An efficient, real‐time haptic modeling for deformable objects has been developed. MLEM provides physically accurate deformation modeling in real time, and estimates the elasticity of objects at contact, providing contact characterization based on material properties.
Research limitations/implications
MLEM has been applied to SNU DD‐robot, and displayed real‐time haptic visualization in 2D space. It can be applied easily to any haptic system with force sensors, and may have impacts on the applications of teleoperation, robot‐aided surgery and human‐robot interaction.
Originality/value
This paper offers a practical tool to the engineers in the haptics field for visualization of deformation. The efficient algorithm of MLEM can be placed on any haptic system with force sensors, and will improve the efficiency and accuracy of teleoperated haptic systems with real‐time analysis of haptic contact.
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From 1953 to 1961, the South Korean economy grew slowly; the average per capita GNP growth was a mere percent, amounting to less than $100 in 1961. Few people, therefore, look for…
Abstract
From 1953 to 1961, the South Korean economy grew slowly; the average per capita GNP growth was a mere percent, amounting to less than $100 in 1961. Few people, therefore, look for the sources of later dynamism in this period. As Kyung Cho Chung (1956:225) wrote in the mid‐1950s: “[South Korea] faces grave economic difficulties. The limitations imposed by the Japanese have been succeeded by the division of the country, the general destruction incurred by the Korean War, and the attendant dislocation of the population, which has further disorganized the economy” (see also McCune 1956:191–192). T.R. Fehrenbach (1963:37), in his widely read book on the Korean War, prognosticated: “By themselves, the two halves [of Korea] might possibly build a viable economy by the year 2000, certainly not sooner.”