• Journal of the Korean Geotechnical Society
• /
• v.22 no.9
• /
• pp.15-22
• /
• 2006

Single segmented mooring lines were tested in a geotechnical centrifuge for the purpose of calibrating the analytical solution developed for the analysis and design of various mooring lines associated with underwater drag/permanent anchors. The model mooring lines included steel ball chains and wire cables placed at various depths within the soft clayey seafloor soil. The mooring lines were loaded to preset tensions at the water surface under an elevated acceleration inside the centrifuge to simulate the field stress conditions experienced by the prototype mooring lines. This paper describes the calibration of two factors that are used as part of the input parameters in the analytical solution of mooring lines and considers the effect of chasing wires that were used in the experiment to determine the locations of the mooring lines.

• Journal of Korean Ophthalmic Optics Society
• /
• v.16 no.3
• /
• pp.229-235
• /
• 2011

Purpose: The present study was performed to evaluate the safety of ophthalmic lenses in domestic market since eyeglasses wearers could be exposed to the negligent accident by damaged ophthalmic lenses. Method: Totally, 160 ophthalmic lenses (NK55, ${n_{d}}$ = 1.56) with the refractive powers of -3D, -6D, +3D, +6D manufactured by 4 companies in domestic market were evaluated using drop ball test. In accordance with FDA standard, steel ball (~16 g) was freely dropped on these ophthalmic lenses from 127 cm high and the surfaces of lenses were observed. Results: From the study, center thicknesses of NK55 ophthalmic lenses manufactured by 4 different companies showed somewhat different numbers even though the lenses had the same refractive index and powers. All convex lenses of +3D, +6D were evaluated as the safe lenses since there was no damage such as crack and broken found on the lens surfaces after drop ball testing. However, some noticeable broken was shown on the surfaces of concave lenses with relatively thinner center thickness. Especially, 59(73.8%) of total 80 concave lenses with the refractive power of -3D and -6D classified as unacceptable lenses to FDA standard. Conclusions: From the results, the negligent accident by damaged ophthalmic lenses should be considered as well as the correction of visual acuity, design and price when customers purchase eyeglasses. Thus, the enforcement regulation like drop ball testing of uncut ophthalmic lens could be suggested to guarantee the safety of ophthalmic lenses in domestic market.

• The Journal of Korean Academy of Prosthodontics
• /
• v.33 no.4
• /
• pp.611-633
• /
• 1995

The pupose of this study was to compare the fracture strength of five kinds of all-ceramic crowns(Vintage, Dicor Empress-staining, Empress-layering, In-Ceram) luted with glass ionomer cerment and composite resin cement and to evaluate the effect of cements on the fracture stregth of all ceramic crowns. Five groups of twelve uniform sized all-ceramic crown specimens were fabricated. Six specimens of each group were cemented with glass ionomer cement(Fuji G.I. Cement) and the remaining six specimens of each group were etched, silane-treated, and cemented with composite resin cement(Bistite resin cement). The crowns were stored in water$(37^{\circ}C)$ for 1 day prior to loading in an Instron, using a steel ball(diameter 4mm) at a crosshead speed of 0.5mm/min. The crowns were angled $30^{\circ}$, so the steel ball contacted with the crowns 2mm lingual from the mid-incisal edge. The results obtained were summarized as follows ; 1. With G.I. cement, mean fracture load(Kg) Were : Intage : $18.33{\pm}1.47$ ; Empress-staining : $23.92{\pm}6.67$ ; Dicor : $24.0{\pm}5.81$ ; Empress-layering : $26.92{\pm}2.80$ ; In-Ceram : $51.58{\pm}6.87$ ; ANOVA revealed a significant difference existed(p<0.05) between the group A(Vintage, Dicor, Empress-staining, Empress-layering) and group B(In-Ceram). 2. With Resin cement, mean fracture load(Kg) were : Intage : $22.75{\pm}4.97$ ; Dicor : $42.75{\pm}7.07$ ; Empress-staining : $44.08{\pm}7.99$ ; Empresslayering : $50.42{\pm}5.43$ ; In-Ceram : $52.58{\pm}6.51$ ; ANOVA revealed a significatnt difference existed(p<0.05) between the group A(Vintage) and B(Dicor, Empress-staining Empress-alyering, In-Ceram). 3. Resin cement significantly increased the fracture strength of the all-ceramic crowns for Dicor(156%), Empress-staining(185%), Empress-alyering(187%)(p<0.05); but did not increase the fracture strength of Vintage(128%) and In-Ceram(101%)(p>0.05). 4. Majority of the all-ceramic crowns show a wedge fracture extending through proximal surfaces to an apex, usually apical third(with G.I. cement) or middle third(with Resin cement) of the facial surface.

• The Journal of Korean Academy of Prosthodontics
• /
• v.39 no.3
• /
• pp.260-272
• /
• 2001

All-ceramic restorations have had a more limited life expectancy than metal ceramic restorations because of their low strength. Their relatively lower strength and resistance to fracture have restricted the use of all-ceramic crowns to anterior applications where occlusal loads are lower. But there has been increasing interest in all-ceramic restorations because patients are primarily concerned with improved esthetics. Many efforts have been made to in prove the mechanical properties of dental ceramics. This study was designed to elucidate the influence of the luting agent on the strength of the Empress 2 crown (staining technique) cemented on human teeth. Seventy extracted human permanent molar teeth were chosen. Teeth were prepared for Empress 2 crowns with milling machine on a surveyor. A dental bur was placed in the mandrel that was positioned so that the long axis of the bur was perpendicular to the surveyor base. Dimensions of the Empress 2 crown preparation were $6^{\circ}$ taper on each side, $1.5{\pm}0.1mm$ shoulder margin, and 4mm crown height. The luting cements used in this study were as follow: 1. Uncemented 2. Zinc phosphate cements (Confi-Dental) 3. Conventional glass ionomer cement : Fuji 1 (GC) 4. Resin-modified glass ionomer cements : Fuji plus (GC) 5. Adhesive cements : Panavia F (Kuralay), Variolink II (Vivadent), Choice (Bisco). Fracture test using Instron. The crowns were loaded in compressive force to evaluate the effect of these cements on the breaking strength of these all-ceramic crowns. A steel ball with a diameter of 4mm was placed on the occlusal surface and load was applied to the steel ball by a cylindrical bolt with a crosshead speed of 0.5mm per minute until fracture occurred. The fractured surface was examined using Scanning Electron Microscopic Image (SEM) to discover the correlation between fracture strength and bonding capacity. Within the limitation of this in vitro study design, the results were as follows : 1. fomentations significantly increased the fracture resistance of Empress ceramic crowns compared to control. Uncemented (206.9 N): ZPC (812.9 N): Fuji 1 (879.5 N): Fuji Plus (937.7 N): Choice (1105.4 N): Variolink II (1221.1 N): Panavia F (1445.2 N). 2. Resin luting agent, treated by a silane bond enhancing agents, yielded a significant increase in fracture resistance. In some of the Panavia F group, a fracture extended into dentin. 3. According to SEM images of fractured Empress crowns, the stronger the bond at both interfaces(crown and die), the more fracture strength was acquired.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.4
• /
• pp.299-304
• /
• 2007

There are to be some cracks on the material degradation part or the stress concentration parts of the main members, which carry on over-loads, of structures. Because these cracks can be used to evaluate the structural health status, it is important to monitor the crack growth for maintaining the structural safety. In this study, the fiber Bragg grating sensor with a drop ball was developed as a sensor for crack growth detection of an existing crack. The crack growth detection sensor was constructed with three parts: a probe part, a wavelength controling light source and receiver part, and an impact part. The probe part was just formed with a fiber Bragg grating optical fiber The wavelength controling light source part was composed of a current supplying circuit, a DFB laser diode, and a TEC controling circuit for wavelength control. Also, the impact part was just implemented by dropping a steel ball. The performance of this sensor was confirmed by the experiments of the crack detection with an aluminum plate having one existing crack. According to these experiments, the difference of the sensor signal outputs was correlated with the crack length. So, it was confirmed that this sensor could be applied to monitor the crack growth.

• Journal of the Korean Society of Safety
• /
• v.31 no.6
• /
• pp.25-31
• /
• 2016

This paper has analyzed the structure, applicable regulations and the resistance characteristics of insulation ring type of CSST (Corrugated Stainless Steel Tubing for Gas). With the flammability test conducted in accordance with KS C IEC 60811-1-1, the evaluation of insulation resistance, temperature characteristics, and reliability has been conducted. An insulation ring type CSST consists of protective coating, tube, nut, insulation ring, packing, socket, and ball valve. Connecting an insulation ring type CSST to gas tubings for gas appliance is not permitted, moreover, the product shall be installed inside a sleeve pipe in case of buried installation such as the ceiling. Damages on protective coating and tube were detected when fire was applied to the test sample with a portable torch for 60 seconds. The insulation resistance of a normal product was $49.59M{\Omega}$, while that of the product completed the flammability test reduced to $9.21M{\Omega}$. The mean insulation resistance within the confidence Interval of 95% using the mini tap program 17 was $49.59M{\Omega}$ and the mean insulation resistance within the confidence interval reduced to $9.21M{\Omega}$. In the normal distribution analysis of 95% confidence interval, the value-P of the normal product was stable at 0.075 and AD(Anderson-Darling) statistic value was turned out to be 0.063, which is very normal, and the standard deviation was analyzed as 0.2586. The value P of the product completed the flammability test resulted in 0.005, the AD was 1.355 and the standard deviation reduced to 0.07908.

• The Journal of Korean Academy of Prosthodontics
• /
• v.35 no.2
• /
• pp.417-430
• /
• 1997

The purpose of this study was to compare the fracture resistance of copy-milled and conventional In-Ceram crown. Four groups of ten uniform sized all-ceramic crowns were fabricated. In-Ceram Spinell and In-Ceram Alumina crowns were fabricated as control group, Celay In-Ceram Spinell and Celay In-Ceram Alumina crowns were fabricated as test group. All specimen were cemented on stainless steel master die with resin cement, and stored in $37^{\circ}C$ water for 1 day prior to loading in Instron testing machine. Using a steel ball at a crosshead surfed of 0.5mm/min, the crowns were loaded at $30^{\circ}C$ angle until catastrophic failure occurred. The results obtained were as follows : 1. With the value of $984.8N{\pm}103.67N$, the strength of Celay In-Ceram Alumina crowns had a significantly higher fracture strength than conventional In-Ceram Alumina crowns ($876.2N{\pm}92.20N$) (P<0.05) 2. The fracture strength of Celay In-Ceram Spinell crowns($706.3{\pm}70.59N$) was greater than that of conventional In-Ceram Spinell crowns($687.4{\pm}90.26N$), but there was no significant difference(P>0.05). 3. The In-Ceram Alumina crowns had a significantly higher fracture strength than In-Ceram Spinell crowns in both methods(P<0.05). 4. Ther order of fracture strength was as followed : Celay In-Ceram Alumina, In-Ceram Alumina, Celay In-Ceram Spinell and In-Ceram Spinell crowns

• Journal of the Korean institute of surface engineering
• /
• v.38 no.3
• /
• pp.95-99
• /
• 2005

Quaternary Ti-Cr-Si-N coatings were synthesized onto steel substrates (SKD 11) using a hybrid method of arc ion plating (AIP) and sputtering techniques. For the Syntheses of Ti-Cr-Si-N coatings, the Ti-Cr-N coating process was performed substantially by a multi-cathodic AIP technique rising Cr and Ti targets, and Si was added by sputtering Si target during Ti-Cr-N deposition. In this work, comparative studies on microstructure and evaluation of mechanical properties between Ti-Cr-N and Ti-Cr-Si-N coatings were conducted. As the Si was incorporated into Ti-Cr-N coatings, the Ti-Cr-Si-N coatings showed largely increased hardness value of approximately 42 GPa than one of 28 GPa for Ti-Cr-N coatings. The average friction coefficient of Ti-Cr-N coatings largely decreased from 0.7 to 0.35 with increasing Si content up to 20 at. $\%$. In addition, wear behavior of Ti-Cr-N coatings against steel ball was much improved with Si addition due to the surface smoothening effect and tribe-chemical reaction.

• Journal of the Korean institute of surface engineering
• /
• v.47 no.5
• /
• pp.263-268
• /
• 2014

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, $2.2{\mu}m$ thick NCD films were deposited on sintered 3 mm diameter SiC balls at $600^{\circ}C$ in a 2.45 GHz microwave plasma CVD system. Bare $ZrO_2$ and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against $ZrO_2$, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, $ZrO_2$ and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

• Journal of the Korean institute of surface engineering
• /
• v.51 no.4
• /
• pp.249-255
• /
• 2018

High temperature and low temperature gaseous nitriding was performed in order to study of the surface hardening and wear properties of the nitrided AISI 410 Martensitic stainless steels. High temperature gaseous nitiridng (HTGN) was carried out using partial pressure $N_2$ gas at $1,100^{\circ}C$ for 10 hour, and Low temperature gaseous nitiridng (LTGN) was conducted in a gas mixture of NH3 and N2 at $470^{\circ}C$ for 10 hour. The nitrided samples were characterized by microhardness measurements, optical microscopy and scanning electron microscopy. The phases were identified by X-ray diffraction and nitrogen concentration was analyzed by GD-OES. The HTGN specimen had a surface hardness of about $700HV_{0.1}$, $350{\mu}m$ of case depth. A ${\sim}50{\mu}m$ thick, $1,250HV_{0.1}$ hard nitrided case formed at the surface of the AISI 410 steel by LTGN, composed nitrogen supersaturated expanded martensite and ${\varepsilon}-Fe_{24}N_{10}$ iron nitrides. Additionally, the results of the wear tests, carried out LTGN specimen was low friction coefficient and high worn mass loss of ball. The increase in wear resistance can be mainly attributed to the increase in hardness and to the lattice distortion caused by higher nitrogen concentration.