• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.1033-1036
• /
• 2005

The effect of surface roughness on the contact fatigue was investigated in this study. To accomplish this goal, contact analysis based on the influence functions and the rectangular patch solution was performed to obtain the subsurface stress. Mesoscopic multiaxial fatigue criterion is then applied to predict fatigue damage. Suitable counting method and damage rule were used to evaluate the fatigue life of random loading caused by rough surface. As a result of the analysis, relationship between the life and roughness as well as the creack initiation depth was revealed. Below the critical roughness, It is observed that the fatigue life has hardly changed and creack is initiated around the depth at which the maximum shear stress occurs. Different behavior, however, is observed in case that the roughness is above the critical value.

• International Journal of Concrete Structures and Materials
• /
• v.18 no.1E
• /
• pp.23-28
• /
• 2006

In this study, the general theory of fractality is discussed to provide a fundamental understanding of fractal geometry applied to heterogeneous material surfaces like pavement surface and rock surface. It is well known that many physical phenomena and systems are chaotic, random and that the features of roughness are found at a wide spectrum of length scales from the length of the sample to the atomic scales. Studying the mechanics of these physical phenomena, it is absolutely necessary to characterize such multi scaled rough surfaces and to know the structural property of such surfaces at all length scales relevant to the phenomenon. This study emphasizes the role of fractal geometry to characterize the roughness of various surfaces. Pavement roughness and rock surface roughness were examined to correlate their roughness property to fractality.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.17 no.1 s.104
• /
• pp.39-44
• /
• 2006

This paper proposes a method of moments(MoM)/Monte-Carlo simulation and Physical Optics(PO) model to determine Bistatic Coherent Reflectivity of sea surfaces at various wind speeds. For the MoM simulation, a Gaussian random rough sea surface was generated based on the data of Tae-An ocean at various wind speeds and sea surface heights. The numerical results of the MoM/Monte Carlo simulations were used to verify the validity region of the PO model. It was found that the numerical result for a flat surface agrees quite well with the Fresnel reflection coefficient. The validity of the PO model on the rough sea surface is shown by using ray tracing method.

• Tunnel and Underground Space
• /
• v.26 no.6
• /
• pp.516-523
• /
• 2016

Roughness of a joint surface is one of the most important parameters that affects the mechanical and hydraulic behavior of rock mass. Therefore, various studies on making constitutive model and/or roughness quantification have been conducted in experimental and empirical manners. Advances in recent 3D printing technology can be utilized to generate a joint surface with a specific roughness. In this study, a reliable technique to generate a rough joint surface was introduced and its quantitative assessment was made. Random midpoint displacement method was applied to generate a joint surface and the distribution of $Z_2$ was investigated to assess its roughness. As a result, a certain roughness can be embodied by controlling input parameters and furthermore it was able to generate a joint surface with specific roughness anisotropy.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.06a
• /
• pp.243-250
• /
• 2000

In the partial lubrication regime, the roughness effects are most important due to the presence of interacting asperities. An average Reynolds equation using flow factors is very useful to determine effects of surface roughness on partial lubrication. In this paper, the pressure flow factors for Gaussian and non-Gaussian surfaces are evaluated in terms of kurtosis. The effect of kurtosis on pressure flow factor is investigated using random rough surface generated numerically. The pressure flow factor increases with increasing kurtosis in partial lubrication regime(h/$\sigma$<3). As h/$\sigma$increases, the pressure flow factor approach to 1 asymptotically regardless of kurtosis.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2002.10b
• /
• pp.79-80
• /
• 2002

This paper presents an experimental study of the effect of rolling speed and surface roughness on the mixed elastohydrodynamic (EHD) lubrication characteristics for point contact formed between a real, random, rough surface, steel ball and smooth glass disc. The Thin Film Colorimetic Interferometry measurement technique has been extended to give detailed information about in-contact deformation of the microgeometry. It has enabled to derive the amplitude reduction curve that shows progressive recovering of ball roughness features with increasing speed.

• Tribology and Lubricants
• /
• v.16 no.6
• /
• pp.448-454
• /
• 2000

The roughness effects are very important due to the presence of interacting asperities in partial lubrication regime. An average Reynolds equation using flow factors is very useful to determine the effects of surface roughness on mixed lubrication. In this paper, the pressure flow factors for surfaces having Gaussian and non-Gaussian distribution of roughness height are evaluated in terms of various kurtosis. The effect of kurtosis on pressure flow factors is investigated using random rough surface generated numerically. The pressure flow factor increases with increasing kurtosis in mixed lubrication regime (h/$\sigma$<3). As h/$\sigma$ increases, the pressure flow factors approach to 1 asymptotically regardless of kurtosis.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.5 no.1
• /
• pp.33-42
• /
• 1996

The high coherence of laser beam has made it possible to observe interference effects even in the light scattered from rough surfaces. That's why, when object with a scattering surface is illuminated with laser light, we do see a speckled appearance due to random interference. This sort of unique property of laser speckle has bruht into existence the new noncontaciting techniques such as speckle metrology method of measuring deformation, displacement, and vibration etc of objects with high optical sensitivity. The measurable range of speckle metrology especially used to measure in -plane information, however, is limited by some factors, the so-called strain, rotation tilt of surface and out of displacement perpendicular to the plane of analysis This restrictions severly limits the measurable range of speckle metrology by causing the decorrelation of speckle patterns. It is the purpose of this paper to give a survey on the measurable limitation of speckle photography method that is one of speckle metrology. Namely we will discuss the mutual relationships and problems of each limitations adding the restriction on the largest and smallest displacement measurable with speckle methods.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.11a
• /
• pp.280-288
• /
• 2000

In this study, flow factors are evaluated in terms of kurtosis using random rough surface generated numerically. As h/$\sigma$become large øx, øy, øfp approach to 1 and øs, øfs to 0 asymptotically regardless of kurtosis. øx, øy, øfp increase with increasing kurtosis in the mixed lubrication regime. øs, øfs is associated with an additional flow transport due to the combined effect of sliding and roughness. As h/$\sigma$ decreases øs, øfs increase up to a certain point, and then decrease toward zero. This behavior can be attributed to the increasing number of contacts in the mixed lubrication regime. øx in the presence of elastic deformation on the surface is larger than øx in the absence of it because local film thickness( h$\_$T/) increases by elastic deformation.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.25 no.1
• /
• pp.9-14
• /
• 2005

The angular dependence(profile) of backward radiated ultrasound was measured for glass specimens with random surface roughness using ultrasonic goniometer that ran changes the incident angle continuously. It was concluded that the roughened region had greater acoustic impedance than the unperturbed region. The comparison of backward radiations showed that the amplitude of peak and the area of radiation profile were increased with surface roughness. It was suggested from the sensitive dependence of the profile area that the profile of backward radiation could be applied to in the nondestructive evaluation of sulfate region. Inclined C-scan technique with the transducer inclined at Rayleigh angle showed the reverse of luminosity and the high signal to noise ratio so that it provided high resolution.