• Journal of Welding and Joining
• /
• v.31 no.4
• /
• pp.47-53
• /
• 2013

SCMH2 steel is widely used in the industrial members of car and tractor. This study focused on material properties and evaluation technology of the SCMH2 steel regarding the surface treatment followed by carburizing and nitriding, by means of impact test, hardness test. and fatigue test including HCF (high cycle fatigue) and VHCF (very high cycle fatigue). Drop weight impact tester (Instron, 9250 Hv) and Cantilever type rotating-bending fatigue tester (YRB200, 3150 rpm) were used to characterize the SCMH2 standard specimen before and after carburizing/nitriding. In order to understand those effects on fatigue characteristics and material properties, the fractured surfaces were carefully observed and analyzed by SEM (scanning electron microscope) and EDS (energy-dispersive X-ray spectroscopy).

• Journal of Welding and Joining
• /
• v.20 no.1
• /
• pp.55-61
• /
• 2002

The automobile is made up of about twenty thousand parts. Some parts are formed by pressing and combined by spot welding. Among them, steel palate of fuel tank is formed in the metal mold and bending parts are jointed by spot and seam welding. To find weldability conditions of spot welding, clearance between two welding steel plates was made and after spot welding, weldability is evaluated by means of tensile shear load, nugget size and shape. Specimen used in this study was a mild steel of 1.2mm thickness and electrode was Cu-Cr alloy of 6mm diameter. When spot welding started, the clearance of two steel plates was changed 0mm, 3mm and 5mm step by step. The fractured surface of specimen after this test was observed by Optical Microscope to measure microstructure and nugget shape. When clearance of two specimen was 3mm and 5mm, strength and nugget size was decreased and nugget shape was not clear.

• 한국신재생에너지학회:학술대회논문집
• /
• 2006.06a
• /
• pp.438-441
• /
• 2006

The groundwater level was originally above the surface at the Onyang spa area. However, it is now 98-138m depth below the surface deu to the artificial pumping from boreholes. The fluctuations of the piezometric head were observed in 4 boreholes. Transmissivity estimated from the pumping rate and the drawdown is about $577.51 m^2/day$ The transmissivity of Onyang spa area is much larger than common values of fractured aqui for the drawdown of the piezometric head by artificial pumping is widely spreaded out in that area. The drawdown related to each pumping rate was analyzed and the formula between drawdown and pumping rate was made by a regression analysis. The formula can be applied for the condition of enough groundwater flowing into the Onyang spa area

• Journal of the Korean institute of surface engineering
• /
• v.34 no.4
• /
• pp.337-341
• /
• 2001

TiN coating of high speed end mill is recently generalized. The study of coating layer using ion plating is mainly about the coating method and the why of the longer life of coated tools. In CNC machning process, metal cutting isn't carry out until the tools including the end-mill and so on are fractured. Namely, it is difficult precision processing when the cutting force of the cutting tool is near the limit the fracture cutting force. So, the estimate of the life by wear and fracture is important. Therefore, this study is about the method to estimate the capacity of the coating layer in relation to the tendency of cutting force and the influence of the cutting capacity of coated end-mill by the condition N2, Ar, temperature. The cutting length is in inverse proportion to the cutting force ratio. So, the life of the TiN coated end mill can be predicated by the ratio of the increase of the cutting force.

• The Journal of Korean Academy of Prosthodontics
• /
• v.52 no.2
• /
• pp.67-73
• /
• 2014

Purpose: The purpose of present study is to compare mechanical properties and microstructural characteristics of fractured surface for cast, 3-D printing laser sintered and CAD/CAM milled cobalt-chromium (Co-Cr) alloy specimens and to investigate whether laser sintered technique is adequate for dental applications. Materials and methods: Thirty six flat disc shape Co-Cr alloy specimens were fabricated for surface hardness test and divided into three groups according to the manufacturing methods; 12 specimens for casting (n=12), 12 specimens for laser sintered technology (n=12) and 12 specimens for milled technology (n=12). Twelve dumbbell shape specimens for each group were also fabricated for a tensile test. Statistical comparisons of the mechanical properties for the alloys were performed by Kruskal-Wallis test followed by Mann-Whitney and Bonferroni test. The microstructural characteristics of fractured surfaces were examined using SEM. Results: There were significant differences in the mean Vickers hardness values between all groups and the cast specimen showed the highest (455.88 Hv) while the CAD/CAM milled specimen showed the lowest (243.40 Hv). Significant differences were found among the three groups for ultimate tensile strength, 0.2% yield stress, elongation, and elastic modulus. The highest ultimate tensile strength value (1442.94 MPa) was shown in the milled group and the highest 0.2% yield strength (1136.15 MPa) was shown in the laser sintered group. Conclusion: Different manufacturing methods influence the mechanical properties and microstructure of the fractured surfaces in Co-Cr alloys. The cast Co-Cr alloy specimens showed the highest Vickers hardness, and the CAD/CAM milled specimens revealed the highest tensile strength value. All alloys represent adequate mechanical properties satisfying the ISO standards of dental alloy.

• Restorative Dentistry and Endodontics
• /
• v.16 no.2
• /
• pp.126-142
• /
• 1991

The purpose of this study was to evaluate the effect of various dentin surface treatments on shear bond strength, microhardness and fracture mode before and after thermocycling. Recently extracted 75 human molars were used. The teeth were sagittal sectioned faciolingually to obtain 150 specimens. They were randomly divided into six groups. Mesial and distal dentinal surfaces of specimens were exposed by grinding and treated respectively with GC-DENTIN CONDITIONER. 10-3 solution of 4-Meta, Cleansar and Primer of GLUMA, Scotchprep of Scotchbond 2, DENTIN CONDITIONER and PRIMER A, B of ALL BOND according to the manufacturers directions. Specimens of one group were not treated. Adhesive agent of Scotchbond 2, were applied and cured on the treated dentin surfaces. After P-50 were cured on them, specimens were stored in 31c water for 24 hours before shear bond strength measurement Shear bond strength was measured in 10 specimens of each group. 10 specimens of each group were thermocycled in $20^{\circ}C$, $60^{\circ}C$,$20^{\circ}C$, $4^{\circ}C$, $20^{\circ}C$ water in order, for 30 seconds respectively, 100 times a day for 7 days. After thermocycling shear bond strength was measured. Microhardness was checked on treated dentin surface and fractured dentin surface in 10 specimens respectievly. Francture modes were observed with SEM The following results were obtained. 1. Before thermocycling. shear bond strengths in the specimens treated with DENTIN CONDITIONER and PRIMER A, B of ALL BOND were significantly higher than those in other specimens(P<0.01). 2. After thermocycling. shear bond strengths in the specimens treated with Cleanser and Primer of GLUMA, Scotchprep of Scotchbond 2 and DENTIN CONDITIONER and PRIMER A, B of AIL BOND were significantly higher than those in specimens not: treated, treated with GC-DENTIN CONDITIONER and 10-3 solution of 4-Meta(P<0.01). Shear bond strengths in the specimens treated with GC-DENTIN CONDITIONER and PRIMER A, B of ALL BOND were significantly higher than those in other specimens except those treated with Scotchprep of Srotchbond 2(P<0.01). 3. Shear bond strengths after thermocycling were reduced in the specimens not treated, treated with GC-DENTIN CONDITIONER and 10-3 solution of 4-Meta and were increased in the specimens treated with Cleanser and Primer of GLUMA, Scotchprep of Scotchbond 2, without significance, compared with those before thermocycling. In the specimens treated with DENTIN CONDITIONER and PRIMER A, B of ALL BOND, shear bond strengths after thermocycling were significantly increased, compared with those before thermocycling(P<0.01). 4. Microhardnesses in the fractured surfaces after shear bond strength measurement were significantly increased in the specimens treated with 10-3 solution of 4-Meta and significantly decreased in the specimens treated with DENTIN CONDITIONER and PRIMER A, B of ALL BOND, compared with those in the treated dentin surfaces(P<0.01). 5. In the specimens treated with Cleanser and Primer of GLUMA, Scotchprep of Scotchbond 2 and DENTIN CONDITIONER and PRIMER A, B of ALL BOND, cohesive fracture modes were observed more than adhesive fracture modes.

• Transactions of the Korean hydrogen and new energy society
• /
• v.31 no.1
• /
• pp.49-56
• /
• 2020

Epoxy/carbon composite was used to prepare a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC). Phenol novolac-type epoxy and diglycidyl ether of bisphenol A (DGEBA)-type epoxy mixture was used as a matrix and graphite powder, carbon fiber (CF) and graphite fiber (GF) were used as carbon materials. In order to improve the mechanical properties of the bipolar plate, surface-modified CF was incorporated into the epoxy/carbon composite. To determine the cure temperature of the epoxy mixture, differential scanning calorimetry (DSC) analysis was performed and the data were introduced to Kissinger equation in order to get reaction activation energy and pre-exponential factor. Tensile and flexural strength was obtained by using universal testing machine (UTM). The surface morphology of the fractured specimen and the interfacial morphology between epoxy matrix and CF or GF were observed by a scanning electron microscopy (SEM).

• Journal of Power System Engineering
• /
• v.21 no.3
• /
• pp.37-44
• /
• 2017

In this study, failure analysis of the angular pin for molding machines to aluminum component molding was carried out. SM45C steel was used for the angular pin, it was surface hardened by the induction surface hardening heat treatment. The cross section of damaged angular pin was observed, and micro Vickers hardness value from the fractured part was measured. Brittle fracture was occurred from the fracture surface of angular pin, therefore, impact toughness value was evaluated by V-notch Charpy impact test. It was confirmed that the impact absorption energy was high when was tempered at a high temperature for a long time, and the toughness was slightly increased. Also, 2-parameter Weibull statistical analysis was investigated in order to evaluate the reliability of the measured micro Vickers hardness values and absorbed energy. The micro Vickers hardness and absorbed energy well followed a two-parameter Weibull probability distribution, respectively. The reverse design against angular pin was proposed as possible by using test results.

• Journal of Power System Engineering
• /
• v.12 no.3
• /
• pp.50-54
• /
• 2008

Various Sialon ceramics were fabricated by hot-pressing mixtures of $Si_3N_4$ with additive $Y_2O_3$ and $Al_2O_3$. The polished specimen of SiAlON $I{\sim}III$ went on increasing in strength by heat treatment, heat treated non-polished specimen were similar or up to polished specimen in strength. The polished specimen of both SiAlON IV and V showed a very high strength, but were not Increasing of strength by heat treatment. All specimens were fractured on the surface and at the inner flaws. Surface fractures were initiated from the polished surface flaw and corner flaw. Inner fractures were initiated from an internal defect.

• Elastomers and Composites
• /
• v.25 no.4
• /
• pp.280-290
• /
• 1990

The effect of surface treatment of kaolinite with silane coupling agent on the reinforcement of SBR was investigated. The possibility of the practical use of kaolinite as an organic filler was also scrutinized and it was found that the reinforcement of SBR was improved by modifying surface of the cheap inactive inorganic filler with organic silane coupling agents. 3-Chloropropyltrimethoxysilane(C-series), 3-mercaptopropyltrimethoxysilane(M-series) and 3-aminopropyltriethoxysilane(A-series) were used as coupling agents. To test the material properties of vulcanized and unvulcanized SBR, Mooney viscosity, modulus, elongation and fractured surface measurements by SEM were carried out by changing the amount of silane coupling agents. Torqe of the unvulcanized SBR following the measurement of the degree of vulcanization was to be increased as the amount of silane was increasing, and Mooney viscosity of M-series and A-series was also increased.