• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1994.04c
• /
• pp.6-6
• /
• 1994

Har dmaterials such as cemented carbides with or without coated layer, cermets, ceramics and diamond or c-BN high pressure sintered compact are used for cutting tools, wear -resistant parts, rock drilling bits and/or high pressure vessels. These hardmaterials contain not only hard phase, but also second consituent as the element for forming ductile phase and/or sintering aid, and the mechanical properties of each material depend on (1) the amount of the second constituent as well as (2) the grain size of the hard phase. The hardness of each material mainly depends on these two factors. The fracture strength, however, largely depends on other microstructur a1 factors as well as the above two factors. For all hardmaterials, the fracture strength is consider ably affected by (3) the size of microstructur a1 defect which acts as the fracture source. In cemented carbides, the following factors which are generated mainly due to the addition of the second constituent are also important; (4) the variation of the carbon content in the normal phase region free from V-phase and graphite phase, (5) the precipitation of $Co_3$ during heating at about $800^{\circ}C$,(6) the domain size of binder phase, and (7) the formation of ${\beta}$-free layer or Co-rich layer near the surface of sintered compacts. For cemented carbides coated with thin hard substance, the important factors are as follows; (8) the kind of coated substance, (9) the formation of ${\eta}$-phase layer at the interface between coated layer and substrate, (10) the type of residual stress (tension or compression) in the coated layer which depends on the kind of coating method (CVD or PVD), and (11) the properties of the substrate, and (12) the combination, coherency and periodicity of multi-layers. In the lecture, the details of these factors and their effect on the strength will be explained.

• Journal of the Korean Chemical Society
• /
• v.9 no.4
• /
• pp.185-189
• /
• 1965

Korean acid clays and silica gel were put into action on benzene solution of dye, such as aniline yellow, o-nitro aniline and oil orange, and then the adsorptivity of dye in nonaqueous solution was measured, with the result that adsorptivity was greater with silica than acid clays and it had no relation to acidity. And when chemical compounds, such as amine, alcohol, halogen derivative, were added to each dye solution by 10%(in volume), the change of the adsorptivity of dye by solid acid(that is, the interfered adsorption rate) decreased in order of amine > alcohol > halogen derivative, and in homologue the smaller the molecular weight, the larger was the effect. So adsorption in nonaqueous solution was a selective adsorption of chemical compounds which contained negative groups such as amine and hydroxyl radicals, and it had no relation to surface tension and showed inverted phenomenon of Traube series. It is guessed that the inverted phenomenon (the interfered adsorption phenomenon) was due to the polar chemical adsorption between active $SiO_2$ which was an origin of solid acid and the adsorbed substances, considering that the order of inversion was nearly in accord with dipole moment of added solvents. The results of this study led to find adsorption mechanism and inverted phenomenon of Traube series in nonaqueous solution.

• Proceedings of the KIEE Conference
• /
• 2006.07c
• /
• pp.1621-1622
• /
• 2006

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristic s were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Also we observed the movement characteristics of PZT actuator with LDV(Laser Doppler Vibrometer) system, oscilloscope and dynamic signal analyzer. Missing nozzles caused by bubbles in chamber were monitored by their resonance frequency. Using the water based ink of viscosity of 4.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets up to 20kHz, 4.4m/s and above 8pL at the different applied driving waveforms.

• Applied Microscopy
• /
• v.28 no.4
• /
• pp.465-475
• /
• 1998

The cryoprotection, section retrieval and embedding methods were studied for the preservation of ultrastructure of ultracryomicrosections in immunoelectron microscopy. The results obtained were as follows. 1. The cryoprotection of ultrastructure with a mixture containing 1.7 M sucrose and 15% polyvinylpyrrolidone was better than that with 2.3 M sucrose. The stretching caused by surface tension and the electron lucent holes decreased more in the cryosections infused with 2.3 M sucrose than in those with the mixture. 2. The difference between section retrieval solutions in cases of cryoprotection with 2.3 M sucrose was that the destructive .effects such as electron lucent holes and stretching between myofribrils were less in a mixture containing 1% methylcellulose and 2.3 M sucrose than in 2.3 M sucrose. The difference was obscure in the mixture containing 1.7 M sucrose and 15% PVP, but the destructive effects were slightly less in a mixture containing 1% mthylcellulose and 2.3 M sucrose than in 2.3 M sucrose or 1% methylcellulose. 3. The embedding of cryosection on drying with 2% PVA or 2% methylcellulose exhibited some protective effect during observation with transmission electron microscope, but made the ultrastructure more obscure. 4. Mitochondrial membrane and cristae and myofilaments were well delinated in sections infused with 2.3 M sucrose and retrieved with 1% methylcellulose and 2.3 M sucrose. In summary, it is suggested that the cryoprotection with 2.3 M sucrose and section retrieval with a mixture containing 1% methylcellulose and 2.3 M sucrose are good for the ultrastructure of cryosections.

• Proceedings of the KIEE Conference
• /
• 2007.07a
• /
• pp.1542-1543
• /
• 2007

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristics were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Using the water based ink of viscosity of 11.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets through 64 nozzles average velocity of 4.05 m/s with standard deviation of 0.06 m/s and average diameter of $29.2\;{\mu}m$ with standard variation of $0.5\;{\mu}m$.

• Nuclear Engineering and Technology
• /
• v.27 no.2
• /
• pp.226-233
• /
• 1995

The wall thickness of a pressure tube is increased in order to reduce the probability of failure in a pressure tube of CANDU type reactor. It is presented here that the variation of wall thickness changes stress, hydrogen concentration and delayed hydride cracking in Zr-2.5Nb pressure tube. When the wall thickness is increased from 4.2 mm to 5.2 mm, the stress exerted on the tube and the deuterium taken up during operation are reduced by 19％. Further, the calculated allowable depth of the surface flaw over which delayed hydride cracking(DHC) is susceptible increases by 50％. DHC initiation is controlled by the stress and by the hydrogen concentration in the pressure tube. The results are therefore very significant in such a respect that increased wall thickness may reduce DHC initiation. Ac the wall thickness increases the hydrostatic tension will increase. Its impact on the acceleration of the crack growth rate of DHC deserves further studies.

• Membrane Journal
• /
• v.15 no.1
• /
• pp.22-33
• /
• 2005

Asymmetric PVDF membranes were prepared by the phase inversion from casting solutions containing PVDF, NMP as solvent and 1,4-dioxane, DGDE, acetone, or GBL as additives by immersing them in water. The effects of various additives on the casting solution properties, permeation properties, and membrane structures were investigated. Low miscibility of 1,4-dioxane, DGDE and acetone with the coagulant (water) compared with NMP resulted in reducing the membrane pore size. When DGDE is used as an additive, the pore size was reduced because of its incipient sharp interface formation in the water. GBL increased membrane pore size because of its polarity compared to that of NMP. The PVDF membranes with various pore sizes could be obtained by controlling the amount of additive. The effect of mixed solvent (aqueous and non-aqueous solution) on permeation through membrane was investigated. Not only solution viscosity but surface tension affected solvent permeation.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.7
• /
• pp.573-580
• /
• 2021

Paraffin wax is attracting many attentions for promising solid fuel of hybrid rocket because of its higher regression than other fuels. However, even with paraffin fuel combustion, unsteady low-frequency oscillation of combustion pressure is still observed. And, this is related to the formation of liquid layer and the entrainment of fuel droplets entering the axial combustion gas flow. This study investigates the effect of additional combustion of fuel droplets on the occurrence of low-frequency combustion instability. On the other hand, the formation of fuel droplets depends on Weber Number (the ratio of the inertial force to the surface tension of the liquid) and Reynolds Number of the oxidizer flow. Therefore, a laboratory-scale hybrid rocket was used to monitor the occurrence of combustion instability while changing We number. A series of combustion tests were conducted to control We number by changing the oxidizer flow rate or adding LDPE (low density polyethylene) to base fuel. In the results, it was confirmed that there is a critical We number above which the low-frequency combustion instability occurs.

• The Journal of the Convergence on Culture Technology
• /
• v.9 no.5
• /
• pp.159-165
• /
• 2023

This study was limited to the underwater search part among water accidents on the inland water surface, and analyzed five underwater search methods and lifesaving time at 5m underwater. The subjects of the experiment were 10 people. The semi-circle search took the longest with 259 seconds, and the modified round-trip search took 78.60 seconds, showing a significant difference with an average of 180.04 seconds. Subjects B and D showed similar values, with average underwater search times of 199 seconds and 202 seconds, respectively. Subject C showed a significantly higher average underwater search time of 209 seconds. The reason seems to be from increased anxiety and excessive tension due to poor underwater watch. Subject A showed a significantly lower underwater search time of 187 seconds. The reason seems to be the result of E's experience being the most among the test subjects and his rich diving experience in the Han River with poor visibility. As for convenience, semicircle search showed a low score of 6~7, and modified reciprocal search showed a high score of 8~9. The most suitable rescue method as an underwater search method in the Han River where visibility is poor is determined to be a modified round-trip search method.

• Journal of the Korea Concrete Institute
• /
• v.24 no.2
• /
• pp.195-204
• /
• 2012

In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.