• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.595-602
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• 2004

In this study, the roughness of fracture surfaces in cementitious material has been characterized by roughness number (RN). A systematic experimental investigation was carried out to examine the dependency of fracture parameters on the aggregate sizes as well as the loading rates. Three aggregate sizes (0.1875 in, 0.5 in, and 0.75 in) and two loading rates (slow and fast loading rate) were used. A total of 52 compression tests and 53 tension tests were performed. All fracture parameters exhibited an increase, to varying degrees, when aggregates were added to the mortar matrix. The fracture surfaces of the specimens were digitized and analyzed. Fracture roughness was monotonically increased as maximum aggregate sizes increase.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• Tribology and Lubricants
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• 제16권2호
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• pp.106-113
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• 2000

Effects of surface roughness on bearing performances are investigated numerically in this study, especially for the parallel thrust bearing. Although mating surfaces are parallel and separated by thin fluid film, the pressure distribution is formed due to asperities. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation is applied to predict the effects of surface roughness between hydrodynamic and mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness. The correlation length is proposed to get the minimum load for the parallel thrust bearing for various sliding conditions.

• 한국기계가공학회지
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• 제9권6호
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• pp.29-35
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• 2010

Recently the industry high-speed machining has been applied to the automotive, aircraft, electronics parts machining because the effect of cost savings, machining time reduction and productivity improvement. In this study recently the aircraft structural aluminum alloy 7075 used in cutting the ball end-mill on the surface roughness terms most affect the parameters of the spindle speed and feed rate on the surface roughness of the work-piece according to the cutting depth is to investigate. Cutting depth at 0.3 mm has the lowest surface roughness.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.66-69
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• 2003

This paper presents the procedures for the evaluation of the maximum surface roughness and the shapes of the cut remainder employing the ridge method. The shapes and the heights of the cut remainder are estimated by overlapping adjacent ridges in consideration of the various machining parameters: the feedrate. the path interval. The maximum surface roughness in plane cutting modes are derived as a function of the maximum effective cutter radius, R$\_$eff,max/. and the path interval ratio, $\tau$$\_$fp/, The predicted results are compared with the values estimated by the conventional roughness model.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.115-119
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• 1996

An estimation of surface roughness value is a very important and difficult issue in grinding process. The definition of the D.A.R.F(Dimensionless Average Roughness Factor) has been made including the absolute average and tile standard deviation that are the parameters of the AE(Acoustic Emission) sign. The theoretical equation of the surface roughness applying the D.A.R.F has been derived from the regressive analysis and specified with respect to the availability through the experimental approach on the machine.

• 한국기계가공학회지
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• 제18권10호
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• pp.42-47
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• 2019

Helical machining is an efficient method for machining holes using an endmill. In this study, a surface roughness prediction model was constructed for improving the productivity of hole machining. Experiments were conducted to form holes by the helical machining of AL6061-T4 aluminum sheets and correlation analysis was performed to examine the relationships between the variables based on the measured results. Meanwhile, a regression analysis technique was used to construct and evaluate the prediction model. Through these analyses, the parameter which has the greatest influence on the surface roughness when the hole is formed by the helical machining is the feed, followed by the number of revolutions of the endmill. Moreover, for the axial feed of the endmill, it was concluded that the influence of the surface roughness is small compared to the other two parameters but it is a factor worth considering to improve the accuracy when constructing the predictive model.

• Design & Manufacturing
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• 제11권1호
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• pp.50-54
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• 2017

In this study, researches were conducted as follows. First, as the basic experiment, the cutting speed, feedrate, and the depth of cut were set as the process parameters, and by setting the surface roughness as the factor of measurement for each of the combinations, and the analysis about cutting tendency of the material was conducted by proceeding the turning process of Co-Cr-Mo alloy. Second, by setting the feature of the surface roughness according to the 'turning processing condition' that was confirmed in the previous experiment, and by applying the Taguchi Method, the conditions that influence the features of the surface roughness according to the 'turning processing condition' of Co-Cr-Mo was analyzed, and also by measuring the surface roughness according to each of the 'cutting conditions', the optimal processing condition was generated. As the result of analysis, it was possible to understand that the factor that mostly affects the surface roughness was the cutting speed, followed by the dept of cutting and transfer speed, and as for the optimal processing condition, it was possible to find that the cutting speed was 5,000rpm, and the depth of cut was 0.1mm, and the feedrate was 0.003mm/rev, and the value of the surface roughness at this point is $0.197{\mu}m$.

• Journal of Computational Design and Engineering
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• 제3권1호
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• pp.1-13
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• 2016

The increase of consumer needs for quality metal cutting related products with more precise tolerances and better product surface roughness has driven the metal cutting industry to continuously improve quality control of metal cutting processes. In this paper, two different approaches are discussed. First, design of experiments (DOE) is used to determine the significant factors and then fuzzy logic approach is presented for the prediction of surface roughness. The data used for the training and checking the fuzzy logic performance is derived from the experiments conducted on a CNC milling machine. In order to obtain better surface roughness, the proper sets of cutting parameters are determined before the process takes place. The factors considered for DOE in the experiment were the depth of cut, feed rate per tooth, cutting speed, tool nose radius, the use of cutting fluid and the three components of the cutting force. Finally the significant factors were used as input factors for fuzzy logic mechanism and surface roughness is predicted with empirical formula developed. Test results show good agreement between the actual process output and the predicted surface roughness.

• 한국기계가공학회지
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• 제16권3호
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• pp.125-130
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• 2017

In this study, the influence of various factors on surface roughness was investigated using the Taguchi experimental method through high-speed machining processing. Feed rate, pitch, tool diameter, and depth of cut are widely applied to high-speed machining conditions for mold production. Each of these factors was implemented and classified into three levels; then, after high speed machining, surface roughness was measured, the S/N ratio was analyzed, and the influence on the surface roughness of control factors was analyzed quantitatively by ANOVA. Using this information, a mathematical model for predicting surface roughness was derived from multiple regression analysis. This mathematical model enables the surface roughness value after high-speed machining to be predicted at the production stage, before machining, for a wide range of machining conditions.