Ki-Moon Kang

The role of shape memory alloy on impact response of glass/epoxy laminates under low temperature

The paper aims to evaluate the impact response of glass/epoxy laminates with embedded shape memory alloy (SMA) subject to low velocity impact at various temperatures. For the goal, the impact tests were performed by using an instrumented impact-testing machine at three temperatures: 293K, 263K and 233K for the baseline (laminates without SMA wires) and SMA laminates (laminates with embedded SMA wires). And the resultant damages were inspected through the scanning acoustic microscope (SAM). Also, based on the impact force history and the damage configuration, the impact resistance parameters were employed to evaluate damage resistance of laminates with embedded SMA wires. As a result, it was observed that the damage resistance of glass/epoxy laminates is influenced by embedded SMA wires and embedding SMA wires into laminates does not compromise the structure any differently to laminates without wires. In fact, it has been shown that under lower temperature, the SMA laminates have a little superior damage resistance compared with the baseline laminates.

Characteristics of LiFePO4/C composite prepared by sonochemical method under multibubble sonoluminescence

LiFePO4/C composites with various weight percent of carbon nanotubes (CNT) were prepared through one-pot sonochemical method under the condition of multibubble sonoluminescence (MBSL). The electrical performance of the composites depends crucially on ultrasound irradiation time, the calcination temperature and duration and weight percent of CNTs. The best initial discharge capacity was obtained for a calcination temperature of 650 °C for 6 h, 30minutes ultrasound irradiation and with 2 wt% of CNTs. The electric conductivity of the LiFePO4/C composite with 2 wt% CNTs was approximately 3.4·10−4 S/cm. The coin cell made of LiFePO4/C composite whose average diameter is 683 nm exhibits an initial discharge capacity of 142mAh/g at 0.1 C, a flat and long voltage plateau and low ΔV between the initial charge and discharge plateaus of 0.03 V and small fade rate of capacity of 0.08% per cycle at 0.5 C. The first efficiency, the ratio of the initial discharge to the initial charge capacity, of the LiFePO4/C composite, is about 90%.

Expanding of Fire-Ball and Subsequent Shock Wave Propagation by Explosives Detonation in Underwater

A well known problem in hydrodynamics involves the sudden release of explosion energy, concentrated in a finite volume, to surroundings with uniform density. However, only similarity solutions which have no detailed information on the behavior of the fire-ball are available on this problem. In this study, we obtain a set of analytical solutions for the time dependent radius of expanding fire-ball after explosives detonation by solving continuity, Euler and energy equations with a “polytope” assumption for the fire-ball center. Subsequent spherical shock waves developed from the fire-ball in underwater are obtained by Kirkwood-Bethe hypothesis with Tait’s equation of state for water. The pressure waves emanating from the oscillating bubble in underwater, which has a notably different time scale from the shock wave generation, are obtained using the Rayleigh equation. The calculated results of period and the maximum radius of bubble developed from the fire-ball and the pressure wave from the oscillating bubble are similar to those observed.© 2011 ASME

Gaseous Bubble Nucleation Under Shear Flow

A decompression experiment of a water solution, saturated with methane gas at about 68 atm at room temperature, was done to investigate gas bubble nucleation under shear flow. A pressure reduction from 68 atm to atmospheric pressure is well below the decompression pressure required for spontaneous bubble nucleation of the methane gas, about 120 atm. The application of a shear flow from 5 minutes before to 1 minute after the decompression induced active bubble formation and the final gas content in the solution was reduced substantially, even with the application of low shear rate of 25/s.Copyright