• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.6 s.171
• /
• pp.159-167
• /
• 2005

This work focuses on the effects of crack free friction on Mode II stress intensity factors, $K_{II}$, for a vertical surface crack in a two-dimensional finite element model of TiN/steel subject to rolling contact. Results indicate that maximum $K_{II}$ values, which occur when the load is adjacent to the crack, may be significantly reduced in the presence of crack face friction. The reduction is more significant for thick coatings than for thin. Crack extension and increased layer thickness result in increased $K_{II}$ values. The effect of crack face friction on compressive $K_I$ values appears negligible. Comparative results are presented for $MoS_2/steel$ and diamond-like carbon(DLC)/Ti systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.431-437
• /
• 1996

The natural frequencies of annular plates in contact with water were theoretically derived and its validity was checked by experiments. The experimental frequency response functions of the annular plates were obtained using the impact hammer method. Comparison of the FRF obtained using the impact hammer and the fRF using shaker attached showed that the former was better than the latter due to the mass effect and additional constraint from the instrumentation. It was found that the experimentally extracted natural frequencies of annular plates in contact with water were in good agreement with those theoretical values.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.864-868
• /
• 2005

This paper develops an analysis model of a piezoelectric transducer. The transducer considered in this paper is a bolt-clamped Langevin-type transducer, which consists of a couple of piezoelectric discs, a couple of metal blocks for added mass effect, and a bolt to tighten them. A new analytical model for the transducer has been developed by taking into account the contact area between the piezoelectric ceramic and the metal block. The analysis model is verified by calculating the variations of the resonance frequency due to the contact area and comparing them with reported experimental results.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.6
• /
• pp.576-581
• /
• 2007

Ultrasonic nonlinearity has been considered as a promising method to evaluate the micro damage of material; however, its magnitude is so small that its measurement is not easy. Especially, when we use contact PZT transducer, if the contacting pressure is not kept in constant during the measurement then there exists extraneous fluctuation in the measured nonlinearity caused by the unstable contact condition, In this paper, we developed a pneumatic control system to keep the contacting pressure of transducer in constant during the measurement and analyzed the effect of contacting pressure to the ultrasonic nonlinearity measurement As a result, we found that the pressure of transducer in our measurement system should be greater than 170 kPa to measure the ultrasonic nonlinear parameter in stable with no dependency on the contacting pressure.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.8
• /
• pp.38-43
• /
• 2019

Electrowetting on dielectric (EWOD) is a unique method of shape control of small-volume droplets in microfluidic biochips that relies on modification of surface wetting characteristics using electrical methods. In this study, the droplet shape control on various dielectric surfaces by the EWOD and the effect of droplets on the contact angle as well as the shape were investigated. The droplet used in the experiment was on a sample substrate with $5{\mu}l$ of de-ionized water (DIW) using a micropipette, and wettability was measured with a contact angle meter. This study is expected to be helpful for the development of various micro-total-analysis-systems (${\mu}TAS$) and microfluidic systems with MEMS technology.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.5
• /
• pp.402-409
• /
• 2006

For the design of a liquid direct contact cooling system, thermal and hydraulic analysis has been carried out. Well-known Zukauskas correlations are used to estimate the Nusselt number between the liquid refrigerant columns and the inlet airflow. The inlet air velocity is set at a typical value used in an actual showcase. For a constant column number, the best nozzle arrangement is determined for the maximum heat transfer. Heat transfer increases as the transverse pitch of the refrigerant column decreases. Among all the cases dealt with in the present study, the staggered arrangement with 140-columns of $14{\times}10$ shows the best thermal peformance and the expected temperature drop is $27.8^{\circ}C$. The effect of downstream refrigerant columns on the overall thermal performance is investigated as well.

• Membrane and Water Treatment
• /
• v.10 no.5
• /
• pp.387-394
• /
• 2019

Membrane distillation (MD) is one of the water treatment processes which involves the momentum, heat and mass transfer through channels and membrane. In this study, CFD modeling has been used to simulate the heat and mass transfer in the direct contact membrane distillation (DCMD). Also, the effect of operating parameters on the water flux is investigated. The result shows a good agreement with the experimental result. Results indicated that, while feed temperature is increasing in the feed side, water flux improves in the permeate side. Since higher velocity leads to the higher mixing and turbulence in the feed channel, water flux rises due to this increase in the feed velocity. Moreover, results revealed that temperature polarization coefficient is rising as flow rate (velocity) increases and it is decreasing while the feed temperature increases. Lastly, the thermal efficiency of direct contact membrane distillation is defined, and results confirm that thermal efficiency improves while feed temperature increases. Also, flow rate increment results in enhancement of thermal efficiency.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.5
• /
• pp.91-96
• /
• 2018

The oleophobic property of surfaces modified with micro-post structures are investigated for a range of micro-post diameter ($11-23{\mu}m$) and pitch ($20-40{\mu}m$). The contact angle of an oil droplet on surfaces with various micro-post dimensions was calculated using the Cassie-Baxter model and did not show a good agreement with the measured contact angle. From measurement, the micro-post with diameter of $23{\mu}m$ and pitch of $32{\mu}m$ was found to have the highest contact angle ($134.3^{\circ}$).

• Journal of Ceramic Processing Research
• /
• v.19 no.6
• /
• pp.525-529
• /
• 2018

The antireflective (AR) coated poly methyl methacrylate (PMMA) substrate was deposited by atomic layer deposition (ALD) on a self-assembled monolayer (SAM) to improve hydrophobicity and mechano-chemical properties of organic thin films. The water contact angles (WCA) were tested to characterize the surface wettability of SAM octadecyltrichlorosilane (OTS) films. Results showed that a contact angle of $105.9^{\circ}$ was obtained for the SAM films with an annealing process, and the highest WCA of $120^{\circ}$ was achieved for the films prepared by the SAM and ALD multi-process. The surface morphology of the SAM films with different assembly times and varying number of ALD cycles was obtained by atomic force microscopy (AFM). The maximum light transmittance for the SAM films on the PMMA substrate reached 99.9% at a wavelength of 450 nm. It was found that the SAM surfaces were not affected at all by the ALD process.

• Journal of the Korean Society for Precision Engineering
• /
• v.10 no.4
• /
• pp.206-215
• /
• 1993

The finite element method is applied to analyze the mechanism of metal cutting, especially micro metal cutting. This paper introduces some effects, such as constitutive deformation laws of workpiece material, friction of tool-chip contact interfaces, tool rake angle and also simulate the cutting process, chip formation and geometry, tool-chip contact, reaction force of tool. Under the usual plane strain assumption, quasi-static analysis were performed with variation of tool-chip interface friction coefficients and tool rake angles. In this analysis, cutting speed, cutting depth set to 8m/sec, 0.02mm, respectively. Some cutting parameters are affected to cutting force, plastic deformation of chip, shear plane angle, chip thickness and tool-chip contact length and reaction forces on tool. Several aspects of the metal cutting process predicted by the finite element analysis provide information about tool shape design and optimal cutting conditions.