• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.4
• /
• pp.337-342
• /
• 2000

We fabricated resistive superconducting fault current limiters based on YB $a_{2}$/C $u_{3}$/ $O_{7}$ thin films and investigated their quench propagation characteristics. The YB $a_{2}$/C $u_{3}$/ $O_{7}$ films was coated with a gold layer and patterned into 1 mm wide meander lines by photolithography. The quench was concluded to start locally and propagates until completed. The quench propagation characteristics were explained based on the heat transfer within the film as well as between the film and the surrounding liquid nitrogen. The quench completion time depended strongly on potential fault current amplitude and not significantly on fault angle which indicates that the quench propagation speed is affected more by heat dissipation rate than by fault current increase rate. The quench completion time was 1 msec at the fault current of 65 $A_{peak/{\ak}}$.

• Journal of Ocean Engineering and Technology
• /
• v.1 no.2
• /
• pp.83-92
• /
• 1987

Inorder ot estimate the running life of turbine rotors, fatigue crack propagation low, da/dN = C(${\DELTA}K)^m$, proposed by paris et al. has been widely applied. In this study, fatigue crack propagation rates for 16 samples of 1% Cr-Mo-V rotor steel were measured and statistical characteristics of m and C values in above equation were reviewed. The results are summarized as follows. 1. C and m follow a log-normal distribution and normal distribution, respectively. And the relation of C and shows a strong negative correlation. 2. Fatigue crack propagation equation can be expressed as da/dN=$4.11{\times}10^{-4}({\Delta}K/153.8)^m$, introducing the ralationship C=$C_oK_o^{-m}$. In this case, contribution of $C_o$ distribution to the distribution of log C shows very small compared to degrees of contribution by m.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2001.05a
• /
• pp.146-151
• /
• 2001

Low temperature fatigue crack propagation ratio and characteristics of the pressure structural steel which is used for the low temperature pressure vessels. Fatigue crack properties was studied at room temperature of $25^{\circ}C$ and low temperature ranges $-60^{\circ}C,\; -80^{\circ}C \;and\; -100^{\circ}C$ with stress ratio of R=0.05, 0.1, 0.3 in the logarithmic relationship between the fatigue crack propagation rate (da/dN) and stress intensity factor $\DeltaK$, in low temperature case the relationship was extend to the range of low crack propagation rate. The fractured specimens were examined by SEM tested. That results showed specimen failed at low temperature exhibit the quasi-cleavage fracture formation, however, considerable ductility proceed final fracture.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.6
• /
• pp.717-723
• /
• 2010

Many researchers have studied woven fabric carbon-fiber-reinforced composite (CFRP) materials but the study of fatigue crack propagation in composites has been insufficient. It has known that the crack propagation behavior differs depending on the load and the fiber direction. In this study, the fatigue crack propagation along two different fiber array directions ($0^{\circ}$, $45^{\circ}$) in plain woven CFRP composite was investigated. Fatigue crack propagation tests were conducted on the woven CFRP composite under a sinusoidal waveform load with stress ratios of 0.1 at a frequency of 10 Hz. Once the results of the tests were obtained, fatigue crack propagation rates (da/dN) were plotted against the energy release rate amplitude (${\Delta}G$), and it was observed that either mode I crack propagation or mixed mode crack propagation occurs depending on the fiber array direction.

• 한국연소학회:학술대회논문집
• /
• 2015.12a
• /
• pp.75-76
• /
• 2015

Lifted flame stabilization mechanism can be explained with constant Schmidt number from the equation of $H^{\ast}_L/d^2_o=const{\times}v_e^{(2Sc-1)/(Sc-1)}$. In this research, a method of local Schmidt number was applied in order to measure edge flame propagation velocities, and edge flame propagation velocity was calculated from the trend between lift-off height and nozzle flow rate.

• Transactions on Electrical and Electronic Materials
• /
• v.14 no.6
• /
• pp.324-328
• /
• 2013

An alternating current (AC) electrical treeing phenomena in an epoxy system with low chlorine BDGE (1,4-butanediol diglycidyl ether) was studied in a needle-plate electrode arrangement. To measure the treeing propagation rate and breakdown time, a constant AC of 10 kV with three different electric field frequencies (60, 500, and 1,000 Hz) was applied to the needle-plate electrode specimen at $130^{\circ}C$ in aninsulating oil bath. The treeing propagation rate of the DGEBA/high-chlorine BDGE system was higher than that of the DGEBA/low-chlorine BDGE system and the breakdown time of the system with high-chlorine BDGE was lower than that of the system with low-chlorine BDGE. These results implied that chlorine had a negative effect on the electrical insulation property of the epoxy system. As the electric field frequency increased, the treeing propagation rate increased and the breakdown time decreased.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.6
• /
• pp.258-269
• /
• 1999

It is important to evaluate fatigue damage of in-service material in respect to assure safety and remaining fatigue life in structure and mechanical components under cyclic load . Fatigue damage is represented by mathematical modelling with crack growth rate da/dN and cycle ration N/Nf and is detected by X-ray diffraction and ultrasonic wave method etc. But this is estimated generally by single parameter but influenced by many test conditions The characteristics of it indicates fatigue damage has complex fracture mechanism. Therefore, in this study we propose that back-propagation neural networks on the basis of ration of X-ray half-value breath B/Bo, fractal dimension Df and fracture mechanical parameters can construct artificial intelligent networks estimating crack growth rate da/dN and cycle ratio N/Nf without regard to stress amplitude Δ $\sigma$.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05c
• /
• pp.92-97
• /
• 1996

The fatigue crack propagation behavior in SA106 Gr.C main steam pipe weld joint was investigated in air environment. Crack growth rate tests were conducted on base metal and weld metal at load ratio of 0.1 and 0.3 and at frequency of 10Hz. The fatigue crack growth rates of the base metal and the weld metal were above the ASME reference line and the fatigue crack propagation rate of the weld metal was higher than those of the base metal. Fatigue crack growth rate increased with increasing the load ratio and the effect of the load ratio was more significant in the weld metal. The post weld heat treatment increased the fatigue crack growth rates of the base metal by reducing compressive residual stress and decreased those of the weld metal by reducing weld defects.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.226-227
• /
• 2005

In this study, it was investigated about endurance and fatigue crack propagation rate of according to welding methods of SMAW and FCAW commonly using for welding structures in present. Endurance limits carried out highly in the order of SMAW, FCAW and fatigue crack propagation rate out lowly in the order of SMAW, FCAW. By these results, it is needed to used SMAW welding methods for welding structures with small welding capacity and FCAW methods for large welding structures after consideration about economic gains and operation efficiency of welding. Fatigue crack propagation rate is more effected by strength of welding materials than endurance limit of welding materials according to welding methods..

• The Journal of the Acoustical Society of Korea
• /
• v.30 no.2
• /
• pp.86-91
• /
• 2011

In the underwater communications, the acoustic channel is in poor communication conditions, such as long propagation delay, narrow bandwidth, and high bit-error rate. For these bad acoustic channels, we propose an efficient automatic repeat request (ARQ) for multi-hop underwater network by using the concepts of concurrent bi-directional transmission, multiple sub-packets, and overhearing data packet instead of the acknowledgement signal. Our results show that the proposed ARQ significantly reduces the transmission latency especially in high BER compared with the existing Stop and Wait ARQ.