• 한국의류산업학회지
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• 제15권4호
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• pp.620-629
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• 2013

This study examines the rustling sound characteristics of electrospun nanofiber web laminates according to layer structures. This study assesses mechanical properties and frictional sounds (such as SPL); in addition, Zwicker's psychoacoustic parameters (such as Loudness (Z), Sharpness (Z), Roughness (Z), and Fluctuation strength (Z)) were calculated using the Sound Quality Program (ver.3.2, B&K, Denmark). The result determined how to control these characteristics and minimize rustling sounds. A total of 3 specimens' frictional sound (generated at 0.63 m/s) was recorded using a Simulator for Frictional Sound of Fabrics (Korea Patent No. 10-2008-0105524) and SPLs were analyzed with a Fast Fourier Transformation (FFT). The mechanical properties of fabrics were measured with a KES-FB system. The SPL value of the sound spectrum showed 6.84~58.47dB at 0~17,500Hz. The SPL value was 61.2dB for the 2-layer PU nanofiber web laminates layered on densely woven PET(C1) and was the highest at 65.1dB for the 3-layer PU nanofiber web laminates (C3). Based on SPSS 18.0, it was shown that there is a correlation between mechanical properties and psychoacoustic characteristics. Tensile properties (LT), weight (T), and bending properties (2HB) showed a high correlation with psychoacoustic characteristics. Tensile linearity (LT) with Loudness (Z) showed a negative correlation coefficient; however, weight (T) with Sharpness (Z) and Roughness (Z), and bending hysteresis (2HB) with Roughness (Z) indicated positive correlation coefficients, respectively.

• Journal of Ship and Ocean Technology
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• 제1권1호
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• pp.35-47
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• 1997

The consequences associated with ships running aground depend very much on the soil characteristics of the sea bed and the geometrical shape of the ship bow. The penetration into the sea bed depends on these factors and the penetration is an important factor for the ship motion because it influences the ship heave and pitch motions as well as the friction between the ship and the soil. In this paper a rational calculation model is presented for the sea bed soil reaction forces on the ship bottom. The model is based on the assumption that the penetration of the ship bow generates a flow of pore water through the grain skeleton of the soil. The flow is governed by Darcy\`s law and it is driven by the pressure of the pore water at the bow. In addition to this pore water pressure, the bow is subjected to the effective stresses in the grain skeleton at the bow surface. These stresses are determined by the theory of frictional soils in rupture. Frictional stresses on the bow surface are assumed to be related to the normal pressure by a simple Coulomb relation. The total soil reaction as a function of velocity and penetration is found by integration of normal pressure and frictional stresses over the surface of the bow. The analysis procedure is implemented in a computer program for time domain rigid body analysis of ships running aground and it is verified in the paper through a comparison of calculated stopping lengths, effective coefficients of friction, and sea bed penetrations with corresponding experimental results obtained by model tests as well as large, scale tests.

• 한국결정성장학회지
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• 제16권3호
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• pp.121-126
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• 2006

HVOF thermal spray coating of Co-alloy T800 is progressively replacing the classical hard coatings such as chrome plating because of the very toxic $Cr^{6+}$ ion known as carcinogen causing lung cancer. For the study of the possibility of replacing of chrome plating, the wear properties of HVOF Co-alloy T800 coatings are investigated using the reciprocating sliding tester both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$. The possibility as durability improvement coating is studied for the application to the high speed spindles vulnerable to frictional heat and wear. Wear mechanisms at the reciprocating sliding wear test are studied for the application to the systems similar to the sliding test such as high speed spindles. Wear debris and frictional coefficients of T800 coatings both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$ are drastically reduced compared to those of non-coated surface of parent substrate Inconel 718. This study shows that the coating is recommendable for the durability improvement coatings on the surfaces vulnerable to frictional heat. The sliding surfaces are weared by the mixed mechanisms such as oxidative wear, abrasion by the sliding ball slurry erosion by the mixture of solid particles and small drops of the melts and semi-melts of the attrited particles cavitation by the relative motions among the coating, sliding ball, the melts and semi-melts. and corrosive wear. The oxide particles and the melts and semi-melts play roles as solid and liquid lubricant reducing the wear and friction coefficient.

• Tribology and Lubricants
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• 제38권6호
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• pp.235-240
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• 2022

Atomically-thin 2D nanomaterials can be easily deformed and have surface corrugations which can influence the frictional characteristics of the 2D nanomaterials. Chemical vapor deposition (CVD) graphene can be grown in a wafer scale, which is suitable as a large-area surface coating film. The CVD growth involves cooling process to room temperature, and the thermal expansion coefficients mismatch between graphene and the metallic substrate induces a compressive strain in graphene, resulting in the surface corrugations such as wrinkles and atomic ripples. Such corrugations can induce the friction anisotropy of graphene, and therefore, accurate imaging of the surface corrugation is significant for better understanding about the friction anisotropy of CVD graphene. In this work, the combinatorial analysis using friction force microscopy (FFM) and transverse shear microscopy (TSM) was implemented to unveil the friction anisotropy of CVD bi-layer graphene. The periodic friction anisotropy of the wrinkles was measured following a sinusoidal curve depending on the angles between the wrinkles and the scanning tip, and the two domains were observed to have the different friction signals due to the different directions of the atomic ripples, which was confirmed by the high-resolution FFM and TSM imaging. In addition, we revealed that the atomic ripples can be easily suppressed by ironing the surface during AFM scans with an appropriate normal force. This work demonstrates that the friction anisotropy of CVD bilayer graphene is well-correlated with the corrugated structures and the local friction anisotropy induced by the atomic ripples can be controllably removed by simple AFM scans.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.88-93
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• 1995

The ball screw preloaded for high nigidity and accuracy increases frictional resistance, therefore, its temperature and positioning error rise. In this paper, 2 diamensional temperature distributions of a ball screw with preload are analyzed according to the rotational speeds and stop times by a finite element method. The theremal behaviors of a ball screw are measured to examine the analyzed datum. The examined results show that the trends of temperature rising and axial distributions in steady state are nearly extimate but the temperature low. The differences of temperature ate seems to be caused by not exact heat transfer coefficients. More than an hour is consumed for calculation by FEM. So the modified lumped method for the real-time estimation of the thermal distribution is proposed. The estimated temperature of a ball serw by the modified lumped method is more exactly estimated than by FEM, nd that method takes less than several millisec. Moreover it can be used to estimate heat transfer coefficients.

• Tribology and Lubricants
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• 제39권3호
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• pp.118-122
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• 2023

In our study, we develop a finite element model based on Archard's wear law to predict the cumulative wear and the evolution of the tool profile in friction stir welding (FSW) applications. Our model considers the rotational and translational behaviors of the tool, providing a comprehensive description of the wear process. We validate the accuracy of our model by comparing it against experimental results, examining both the predicted cumulative wear and the resulting changes to the tool profile caused by wear. We perform a detailed comparison between the predictions of the model and experimental data by manipulating non-dimensional coefficients comprising model parameters, such as element sizes and time increments. This comparison facilitates the identification of a specific non-dimensional coefficient condition that best replicates the experimentally observed cumulative wear. We also directly compare the worn tool profiles predicted by the model using this specific non-dimensional coefficient condition with the profiles obtained from wear experiments. Through this process, we identify the model settings that yield a tool wear profile closely aligning with the experimental results. Our research demonstrates that carefully selecting non-dimensional coefficients can significantly enhance the predictive accuracy of finite element models for tool wear in FSW processes. The results from our study hold potential implications for enhancing tool longevity and welding quality in industrial applications.

• 소성∙가공
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• 제3권1호
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• pp.51-62
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• 1994

Cup drawing test and U-bending test were performed to evaluate the friction characteristics of sheet materials for the different deformation modes involved in stamping process. The coefficient of friction calculated from the each test was compared to that obtained from the draw bead friction test. It was clarified that the cup drawing test could be simply used for evaluating the friction characteristic of sheet material in deep drawing process with high contacting pressure. However the U-bending test is suitable to evaluate the frictional characteristic of sheet material in bending process with low contacting pressure.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.343-346
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• 2004

In recent years, various forms of indentation testing have been increasingly used to determine the material properties of specimens. This technique, particularly the nano-indentation method , has been extended to the testing of coating systems in order to calculate the individual properties of the thin coatings and the substrates. However, the interpretation of the test data to achieve this is complex and continues to be a widely studied subject. Based on the finite element method of coated surfaces indented by a Berkovich diamond tip, this paper describes methods for combining FEM and experimental indentation testing to determine coating modulus and hardness independent of substrate effects. Using this proposed methodology, testing and FEM to measure coefficients of friction of sheet steel for outer panel were studied.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.253-259
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• 1997

A software for design of turbine bearings has been developed based on both the theoretical analysis and experimental investigation. Static and dynamic performance, i.e. load capacity, frictional loss, temperature distribution, stiffness and damping coefficients, stability etc., can be obtained by using this software taking into account the effects of three dimensional variation of lubricant viscosity, turbulence and inlet pressure. A performance test rig was developed by self-design and technology, which was used to verify static and dynamic characteristics and to investigate the proper boundary conditions for theoretical analysis. Consequently HANJUNG has developed the self-design technology for design of turbine bearings for power plants.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.129-132
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• 2005

This study analyzes the behavior of adhesion and friction according to the pore size of nanohoneycomb structures in atomic force microscope (AFM). Anodic aluminum oxide (AAO) films are fabricated as nanohoneycomb structures. According to the pore diameters of the nanohoneycomb structures, the adhesive forces and the frictional coefficients arc obtained in AFM, and the behaviors are analyzed in the view of the contact area between the sphere particle and nanohoneycomb substrate. The effective Young's moduli of the nanohoneycomb structures are measured from the nanoindentation tests, and the contact areas at zero applied load are calculated by combining the porosity of the nanohoneycomb structures and the contact radius determined from JKR and DMT theory.