• Journal of the Korean Society for Heat Treatment
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• v.8 no.1
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• pp.32-43
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• 1995

Ti-6Al-4V alloy are widely used in chemical and aircraft industries for their good corrosion resistance and high strength to weight ratio. Surface alloying of Ti alloy by $CO_2$ laser is able to produce few hundred micrometers thick TiN surface-alloyed layer with high hardness on the substrate very simplely by injecting reaction gas($N_2$) into a laser-generated melt pool and adjust the hardness to the specific requirements of the individual application by changing of laser processing parameters. This research has been investigated the effect of such parameters on TiN surface-alloying of Ti-6Al-4V alloy by $CO_2$ laser. The maximum hardness of TiN surface-alloyed zone waw obtained by injecting 100% $N_2$ gas and it was decreased as the amount of $N_2$ gas in Ar and $N_2$ gas mixture was decreased. As scanning speed was increased, the hardness and depth of TiN surface-alloyed zone was decreased at constant laser power. The surface hardness after double scanning laser treatment is higher than that of single scanning. At constant laser power, the surface roughness is increased after the surface alloying if laser scanning speed is decreased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.421-428
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• 2012

In this study, the effects of surface oxide film formation on the fatigue behavior of 7075-T6 aluminum alloy were analyzed in terms of the corrosion time of the alloy. The aluminum material used is known to have high corrosion resistance due to the passivation phenomenon that prevents corrosion. Aluminum alloys have been widely used in various industrial applications such as aircraft component manufacturing because of their lighter weight and higher strength than other materials. Therefore, studies on the fatigue behavior of materials and passivation properties that prevent corrosion are required. The fatigue behavior in terms of the corrosion time was analyzed by using a four-pointing bending machine, and the surface corrosion level of the aluminum material in terms of the corrosion time was estimated by measuring the surface roughness. In addition, fractographic analysis was performed and the oxide films formed on the material surface were studied by scanning electron microscopy (SEM). The results indicated that corrosion actively progressed for four weeks during the initial corrosion phase, the fatigue life significantly decreased, and the surface roughness increased. However, after four weeks, the corrosion reaction tended to slow down due to the passivation phenomenon of the material. Therefore, on the basis of SEM analysis results, it was concluded that the growth of the surface oxide film was reduced after four weeks and then the oxide film on the material surface served as a protection layer and prevented further corrosion.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.2
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• pp.83-94
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• 2009

The aim of this study was to investigate the shear bond strength between zirconia ceramic and resin cement according to various surface treatments. The surface of each zirconia ceramic was subjected to one of the following treatments and then bonded Rely X Unicem or Rely X ARC resin cement; (1) Rocatec system and $50{\mu}m$ surface polishing, (2) No treatment and $50{\mu}m$ surface polishing, (3) Rocatec system and $1{\mu}m$ surface polishing, (4) No treatment and $1{\mu}m$ surface polishing. Each of eight bonding group was tested in shear bond strengths by universal testing machine(Z020, Zwick, Ulm, Germany) with crosshead speed of 1mm/min. The results were as follows; 1. Rocatec treatment groups showed greater bonding strengths than No Rocatec groups. There was significant difference of among groups(P<0.001) 2. For Rocatec groups, $50{\mu}m$ surface roughness groups showed greater bonding strengths than $1{\mu}m$ surface roughness groups.(P<0.001) But for No Rocatec groups, There was no significant difference of among groups(P>0.05) 3. Rely X Unicem groups showed greater bonding strengths than Rely X ARC groups. There was significant difference of among groups(P<0.01) Within the conditions of this study, Rocatec treatment was an effective way of increasing zirconia bonds to a resin cement, even in the case of self-adhesive resin cement.

• Journal of Advanced Research in Ocean Engineering
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• v.2 no.2
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• pp.86-98
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• 2016

In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.303-316
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• 1987

The purpose f this study was to evaluate the effect of resin film thickness on the tensile bond strength and to compare the tensile bond strengths of 4 differently treated metal surfaces. For the experiment, seventy metal specimens were cast with Verabond and divided into I, II, III, groups. The metal specimens in group I were electrolytically etched and cemented with Panavia under finger pressure. Cement film thickness was regulated with metal spacers. The metal specimens in Group II were treated by 4 methods, such as electrolytic etching method, salt-roughened method, EZ-oxisor method , chemical etching method and cemented with Panavia. In group III, electrolytically etched metal specimens were cemented with Hy-Bond. The etched surface of metal specimens and the cement film thickness were examined under the scanning electron microscope. Results were as follows; 1. The tensile bond strength showed no significant difference between $30{\mu}m,\;80{\mu}m,\;130{\mu}m$ film thicknessspecimens. 2. There was no significant difference in the tensile bond strength between the 4 differently treated metal specimens. 3. The tensile bond strength showed significant difference between Panavia and Hy-Bond. 4. Scanning electron microscope photograph revealed that tile interdendritic eutectic was removed in electrolytically etched metal surfaces hilt even dendritic arm was removed in Chemically etched metal surfaces. 5. The metal surfaces which were air-abraded with $50{\mu}m$ aluminum oxide showed roughness and small crack on scanning electron microscope photograph.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.2
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• pp.1-6
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• 2015

Transmission of a tracked vehicle designed for multiple functions such as steering, gear-shifting, and braking is a core component of heavy vehicle to which the power is transferred based on combined technology of various gears, bearing, and fluid machineries. Robustness and durability of transmission, however, have been issued due to a large number of driving units and sub-components inside its body. The bevel gears are major components for the transmission of power in a transmission. Increasing the tooth surface roughness and chamfering of the bevel gears, especially, we aim to improve the quality of transmission. In this study, design structural evaluation is conducted on bevel gears of transmission for tracked vehicle using the ROMAX-DESIGNER program. By doing so, design safety of the bevel gears has been evaluated based on the gear strength theory of ANSI/AGMA 2003 B97 standard.

• Journal of Welding and Joining
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• v.11 no.2
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• pp.42-52
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• 1993

The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.

• Journal of Industrial Technology
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• v.6
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• pp.33-38
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• 1986

The aim of this study is to find out the relationships between the microstructures of SM45C(AISI1045) steel and fatigue crack propagation behaviour. Three microstructures such as (i) as received (fully annealed). (ii) water quenched and tempered, and (iii) oil quenched and tempered were used for fundamental mechanical testing and fatigue crack proagation test. The microstructures of (ii) and (iii) showed superior in tensile strength to (i). Resistance against fatigue crack propagation was higher in structure (i), while tensile properties were better in structures (ii) and (iii). It is believed due to that the enhancement of roughness of fracture surface obsered in structure (i) increases ${\Delta}Kth$ and lowers fatigue crack growth rate. However it does not necessarily mean the quenched and tempered structures (ii) and (iii) are undesirable for the engineering component because fatigue limit in low cycle test appears usually higher in the microstructures of higher strength.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.46 no.6
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• pp.16-25
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• 2014

This study was investigated in optimum condition of pulping of ramie and the mechanical properties of non-woven fabric for the performance of ramie/cotton panty liner. The result of pulping condition on ramie was most suitable for type I (mixed NaOH with $Na_2CO_3$ in 30%:70%). The sample (I) was showed yield value of 68.2% and the best fibrillation and lignin removal rate. The non-woven fabrics of ramie/cotton were made in range of ramie content of 0, 15 and 30%. As ramie content increased, so were increased in air permeability, compressive strength and compression recovery rate. But surface roughness and compressional energy were decreased. Therefore, the non-woven fabrics of ramie/cotton are very suitable in hygienic goods for female panty liner. The ramie panty liner showed a little decrease in absorption and strength, as increasing the amount of ramie. But the performance of ramie panty liner was appeared beyond standard values used by usual panty liner.

• Proceedings of the Korean Society for Quality Management Conference
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• 1998.11a
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• pp.680-695
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• 1998

The objective of this study is to optimize the responses of the creep feed ceramic grinding process simultaneously by an off-1ine multicriteria optimization methodology. The responses considered as objectives are material removal rate, flexural strength, normal grinding force, workpiece surface roughness and grinder power. Alumina material was ground by the creep feed grinding mode using superabrasive grinding wheels. The process variables optimized for the above objectives include grinding wheel specification, such as bond type, mesh size, and grit concentration, and grinding process parameters, such as depth of cut and feed rate. A weighting method transforms the multi-objective problem into a single-objective programming format and then, by parametric variation of weights, the set of non-dominated optimum solutions are obtained. Finally, the multi-objective optimization methodology was tested by a sensitivity analysis to check the stability of the model.