• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.50-58
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• 2000

A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• 마이크로전자및패키징학회지
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• 제17권3호
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• pp.33-41
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• 2010

Crack propagation mechanisms of Sn-3.0Ag-0.5Cu solder were studied in strain controlled push-pull creepfatigue conditions using the fast-fast (pp) and the slow-fast (cp) strain waveforms at 313 K. Transgranular cracking was found in the pp strain waveform which led to the cycle-dominant crack propagation and intergranular cracking in the cp strain waveform that led to the time-dominant crack propagation. The time-dominant crack propagation rate was faster than the cycle-dominant crack propagation rate when compared with J-integral range which resulted from the creep damage at the crack tip in the cp strain waveform. Clear recrystallization around the crack was found in the pp and the cp strain waveforms, but the recrystallized grain size in the cp strain waveform was smaller than that in the pp strain waveform. The cycle-dominant crack propagated in the normal direction to the specimen axis macroscopically, but the time-dominant crack propagated in the shear direction which was discussed in relation with shear micro cracks formed at the crack tip.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1097-1105
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• 1997

Because of the existence of stress interaction field made by other defects and propagating cracks, the structure may be weakened. Therefore in this study, the crack behavior in the interaction field made by two different cracks is studied experimentally. In the experiment, vertical distance between two cracks and applied stress are varied to make different stress interacted field. In addition, the effect of plastic zone is used to examine crack propagation path and rate. Three types of crack propagation in the interacted field were found, and crack propagating path and rate of two cracks were significantly changed according to different applied stress as each crack propagates. And the results are attributed to the effect of the size and shape of the plastic zone.

• 대한기계학회논문집A
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• 제30권7호
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• pp.826-832
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• 2006

For the improvement of safety and endurance in welded steel structure, it is needed to consider welding residual stress distribution and rolling directional characteristics of materials. In this study, it was investigated experimentally about characteristics of fatigue crack propagation according to welding residual stress and rolling in FCAW(flux cored arc welding) butt-jointed steel plates. SS400 steel plates of 3mm thickness were selected and tested for this study. When the angles between tensile loading direction and rolling direction in welded materials are increased from $0^{\circ}\;to\;90^{\circ}$, their fatigue crack propagation rates are increased. These results are same as predicted increments of fatigue crack propagation rate when stress ratio is increased from 0 to 0.5. When the angles of rolling direction and welding direction to tensile loading direction are $0^{\circ}\;and\;90^{\circ}$ respectively, fatigue crack propagation rate in welded material is lowest.

• 동력기계공학회지
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• 제4권4호
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• pp.41-47
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• 2000

Fatigue crack propagation rate and threshold characteristics of the SA516/70 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $25^{\circ}C$ and low temperature ranges of $-10^{\circ}C,\;-30^{\circ}C,\;-60^{\circ}C\;and\;-80^{\circ}C$ with stress ratio of R=0.1. In the logarithmic relationship between the fatigue crack propagation rate($d{\alpha}/dN$) and stress intensity factor range ${\Delta}K$, the linear relationship was obtained up to $d{\alpha}/dN=4.425{\times}10^4mm/cycle$ in the same of room temperature, but in low temperature case, the relationship was extended to the range of low crack propagation rate. The fractured specimens were examined by SEM. Tested results showed that specimen failed at low temperature exhibit the quasi-cleavage fracture formation however considerable ductility proceed final fracture.

• 한국기계가공학회지
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• 제5권4호
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• pp.65-71
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• 2006

The lightness of components required on marine and shipbuilding industry is requiring high strength of components. In particular, fatigue failure phenomena, which happen in metal, bring on danger in human life and property. Therefore, antifatigue failure technology takes an important part on current industries. In this study, it is investigated about endurance and fatigue crack propagation rate of according to welding methods such as SMAW, FCAW and SAW commonly used for welding structures in present. Endurance limits carried out highly in the order of SMAW, FCAW, SAW and fatigue crack propagation rate out lowly in the order of SMAW, FCAW, SAW. By these results, it is needed to use SMAW welding method for welding structures with small welding capacity and FCAW, SAW methods for large welding structures after consideration about economic gains and operation efficiency of welding. Fatigue crack propagation rate is more affected by strength of welding materials than endurance limit of welding materials according to welding methods.

• ETRI Journal
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• 제29권5호
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• pp.559-568
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• 2007

This paper presents a new distortion control scheme with a simple estimation model for the propagation errors incurred by dropping some parts of the bitstream in a frame dropping-coefficient dropping (FD-CD) transcoder. The primary goal of this paper is to facilitate bit-rate conversions and rate-distortion controls in the compressed domain without introducing a full decoding and reencoding system in the pixel domain. First, the error propagation behavior over several frame sequences due to coefficient dropping is investigated on the basis of statistical and empirical properties. Then, such properties are used to develop a simple estimation model for the CD distortion accounting for the characteristics of the underlying coded-frame. Finally, the proposed estimation model allows us to determine the amount of coefficient dropping and to effectively allocate rate-distortions into coded-frames. Experimental results show that the proposed estimation model accurately describes the characteristics of propagation errors adaptively in the compressed domain and can be easily applied to distortion control over different kinds of video sequences.

• 한국안전학회지
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• 제23권4호
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• pp.30-35
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• 2008

The present study has been conducted to examine the effect of grid resolution on the predicted results for electric cable fire using pyrolysis model in FDS(Fire Dynamics Simulator, version 5). The grid independent test for different grid resolutions has been performed for a PE coating cable and the grid resolution is defined by the non-dimensional characteristic length of fire and mean grid size. The calculated maximum heat release rate and mean flame spread rate were almost constant for higher grid resolution of 20${\sim}$25 and the computing time for the grid resolution takes approximately 20hours to solve flame propagation with pyrolysis model. The geometrical simplification of a electric cable dose not greatly affect on the maximum heat release rate and flame spread rate and the rectangular approximation of cable shape gives acceptable result comparing with the round cable with stepwise grid.

• 전기학회논문지
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• 제62권11호
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• pp.1571-1577
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• 2013

Electrical tree structure is one of the most important influencing factors for electrical treeing characteristics in polymers. In this paper, we focused on the structure characteristics of electrical treeing in epoxy resins (original) insulation under different high-frequency voltages (60, 500, 1000Hz). Effects of voltage frequency on the ac electrical treeing phenomena in an epoxy resins were carried out in needle-plate electrode arrangement. To measure the treeing initiation and propagation, and the breakdown rate, constant AC of 10 kV with three different voltage frequencies (60, 500 and 1,000 Hz) was applied to the specimen in needle-plate electrode specimen at $30^{\circ}C$ of insulating oil bath. At 60 Hz, the treeing initiation time was 360 min and the propagation rate was $6.85{\times}10^{-4}mm/min$, and the morphology was dense branch type. As the voltage frequency increased, the treeing initiation time decreased and the propagation rate increased. At 1,000 Hz, the treeing initiation time was 0 min and the propagation rate was $7.81{\times}10^{-2}mm/min$, and the morphology was dense bush type.

• 한국안전학회지
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• 제19권2호
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• pp.16-20
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• 2004

This paper aims to analyze fatigue fracture mechnisms with high strength aluminum alloys, which are widely used in vehicles or airplanes to prevent accidents. Usefulness of the crack opening point was proposed by using an effective stress intensity facor when evaluating the fatigue crack propagaion rate. Therefore an exact crack opening ratio can be measured for a more exact fatigue crack propagation rate. It is found that the fatigue crack propagation rate was valid within the range of experimentation as an effective stress intensity factor. Summarizing the results are as follows in this paper ; (1) It is found that the value of the crack opening ratio is constant at the rear of the specimen, U'=0.25 at the crack mouth and U'=0.45 at the crack tip, respectively regardless of the stress ratio. (2) The crack opening ratio is different according to measurement locations. The crack opening ratio value was measured at the crack mouth by a clip gage or measured behind the specimen by a strain gage. It is found that the crack opening ratio value is more accurate that any other measuring test for evaluating the crack propagation ratio test by effective stress intensity factor.