• Restorative Dentistry and Endodontics
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• v.7 no.1
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• pp.77-83
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• 1981

The purpose of this study was to observe the bonding strength between tooth surface (enamel and dentin) and restorative filling materials which are two composite resins (Clearfil and Concise) and Glass ionomer cement, after etching with 50% phoshoric acid and 37% citric acid. To measure the bonding strength in enamel, the labial surface of upper anterior tooth was cut flatly with using carborundum disk and polished with sand paper disk, and to measure in dentin, the dentin surface was prepared by grinding upper part of posterior tooth horizontally. After washing the tooth surface with water and drying with air blast, the prepared tooth surface was etched. In glass ionomer cement, 50% phosphoric acid and 37% citric acid were used, in Clearfil 40% phosphoric acid was used and in Concise, 50% phosphoric acid and 37% citric acid were used as etchant for 1 minute. After the copper band which is 5 mm in diameter and 5 mm in height was fixed on the prepared surface and each filling material was inserted into the copper band, the hooking loop was inserted into filled material in the copper band before setting to make it easily that the load is applied on the specimen. After all specimens were immersed in water at $37^{\circ}C$ for 1 week, this specimen was placed on the load cell of tensile test apparatus, and specimen was pulled at the cross-head speed of 0.8 mm per minute. The following results were obtained 1) In glass ionomer cement, the bond strength obtained by 37% citric acid was higher than one obtained by 50% phosphoric acid in enamel and dentin surfaces. The bond strength obtained in non-etched surface was much less than one by etchants in enamel and dentin surface. 2) In Clearfil, the bond strength obtained by 40% phosphoric acid was 4 times more than one obtained by non etch ant. 3) In Concise, the bond strength obtained by 50% phosphoric acid was almost same as one obtained by 37% citric acid, and the bond strength obtained by non etch ant was much less than one obtained by etchants.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.355-360
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• 2006

The damping force of a jaw pad is determined by the displacements of main part when two lockers are locked, after the damping angle of a locker was set up in the wedge type rail damp for a container crane. In this time, of the resistance of wedge frame generates due to several factors, the damping angle of a locker to display the initial clamping force will be changed because of the reduction of displacement of extension bar. This resistance is determined by the eccentric distance between the roller and the wedge, and by the gap between the wedge frame and outer frame. In this study we measured the tensile force of both extension bar through the performance test of the prototype rail damp in order to evaluate the effect of the resistance of wedge frame on the damping force of the wedge type rail clamp.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.649-660
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• 2003

The paper presents an evaluation of the tensile strength of the expansion anchor that can cause failure in the concrete based on the design of the anchorage. Tests of the heavy-duty anchor and the wedge anchor that are domestically manufactured and installed in plain concrete members are conducted to probe the effects of the embedded depth, concrete strength, and anchors spacing. The design of post-installed steel anchors is presented using the Concrete Capacity Design (CCD) approach. The CCD method is applied to predict the concrete failure load of the expansion anchor in plain concrete under monotonic loading for important applications. The concrete tension capacity of the fastenings with heavy-duty anchors and wedge anchors in plain concrete predicted using the CCD method is compared with the test results. For the CCD method, a normalization coefficient of 9.94 is appropriale for the nominal concrete breakout strength of an anchor or a group of wedge anchors in tension. On the other hand, a normalization coefficient of 11.50 is appropriate for the nominal concrete breakout strength of an anchor or a group of heavy-duty anchors in tension.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.458-462
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• 2005

This paper deal with the optimal lamination condition of cylindrical shell applied new composite URN300 for a study of composite empirical formula. Finite element analyses for isotropic materials considered element numbers and boundary conditions are compared with existing empirical formulas to apply FE analysis for composite. And composite tensile test is done to know the composite material applied FE analysis for composite. The results of FE analyses for isotropic materials have indicated that Optimal element number and boundary condition were 1600 and both simple support. These conditions were applied in composite FE analyses. Ply orientations and lamination patterns in FE analyses for composite were considered. Ply orientations are $0^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ},\;60^{\circ},\;75^{\circ},\;and\;90^{\circ}$. Lamination patterns are $[\pm\theta/0/90]_{14s]$ and $[\pm\theta_{14}/0_{14}/90_{14}]_s$ in FE analysis. Lamination pattern $[\pm\theta_{14}/0_{14}/90_{14}]_s$ is the equivalent model of $[\pm\theta/0/90]_{14s}$. At the result of this study, the FE analyses for composite have indicated that the optimized ply orientation $75^{\circ}$ is and real model must use in FE analysis for accurate results.

• Transactions of Materials Processing
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• v.21 no.1
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• pp.49-57
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• 2012

It is difficult to estimate the properties of multilayered sheet because they are composed of one or more different materials. Plastic deformation behavior of the multilayered sheet is quite different as compared to each material individually. The deformation behavior of multilayered sheet should be investigated in order to prevent forming defects and to predict the properties of the formed part. In this study, the mechanical properties and formability of stainless steel-aluminum-magnesium multilayered sheet were investigated. The multilayered sheet needs to be deformed at an elevated temperature because of its poor formability at room temperature. Uniaxial tensile tests were performed at various temperatures and strain rates. Fracture patterns changed mainly at a temperature of $200^{\circ}C$. Uniform and total elongation of multilayered sheet increased to values greater than those of each material when deformed at $250^{\circ}C$. The limiting drawing ratio (LDR) was obtained using a circular cup deep drawing test to measure the formability of the multilayered sheet. A maximum value for the LDR of about 2 was achieved at $250^{\circ}C$, which is the appropriate forming temperature for the Mg alloy. Fracture patterns on a circular cup and thickness of formed part were predicted by a rigid-viscoplastic FEM analysis. Two kinds of modeling techniques were used to simulate deep drawing process of multilayered sheet. A single-layer FE-model, which combines the three different layers into a macroscopic single layer, predicted well the thickness distribution of the drawn cup. In contrast, the location and the time of fracture were estimated better with a multi-layer FE model, which used different material properties for each of the three layers.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.68-73
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• 2009

Recently, as titanium and titanium alloys are being increasingly used in wide areas, there are on-going researches to obtain high quality weld zone. In particular, growing interest is being drawn to laser welding, which involves low heat input and large aspect ratio in various welding processes and can facilitate shield in atmospheric condition compared with electron beam welding. The first report covered the analysis of embrittlement by the bead color of weld zone through quantitative analysis of oxygen and nitrogen and measurement of hardness as basic experiment to apply laser welding to titanium. Results indicated that the element that affect embrittlement the most was nitrogen, and as embrittlement and oxygenation go on, bead color changed to silver, gold, brown, blue and gray. This study performed butt welding of pure titanium and STS304 by using 1kW CW Nd:YAG laser, and to find out basic physical properties, evaluated welding performance by laser output, welding speed, root gap and misalignment etc, and examined mechanical properties through tensile stress and Erichsen test. The reason particles of pure titanium welded metal and HAZ are greater than STS304 is because they are pure metal and do not include many impure elements that work as nuclei in case of resolidification, thus becoming coarse columnar crystals eventually. In addition, the reason STS304 requires more energy during welding than pure titanium is because the particle size of base metal is smaller.

• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.265-269
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• 2014

Objectives: To evaluate the effect of different ultrasonic tip designs on intraradicular post removal. Materials and Methods: The crowns of forty human canine teeth were removed, and after biomechanical preparation and filling, the roots were embedded in acrylic resin blocks. The post spaces were made, and root canal molding was performed with self-cured acrylic resin. After casting (Cu-Al), the posts were cemented with zinc phosphate cement. The specimens were randomly separated into 4 groups (n = 10), as follows: G1 - no ultrasonic vibration (control); G2 - ultrasonic vibration using an elongated cylindrical-shaped and active rounded tip; G3 - ultrasonic vibration with a flattened convex and linear active tip; G4 - ultrasonic vibration with active semicircular tapered tip. Ultrasonic vibration was applied for 15 seconds on each post surface and tensile test was performed in a Universal Testing Machine (Instron 4444 - 1 mm/min). Results: G4 presented the highest mean values, however, with no statistically significant difference in comparison to G3 (p > 0.05). G2 presented the lowest mean values with statistically significant difference to G3 and G4 (p < 0.05). Conclusions: Ultrasonic vibration with elongated cylindrical-shaped and active rounded tip was most effective in reducing force required for intraradicular post removal.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.95-103
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• 2012

In order to improve the dimensional stability and mechanical performance of cement-based composites, the effect of an expansive admixture based on calcium sulphoaluminate (CSA) on the shrinkage and mechanical properties of strain-hardening cement-based composite (SHCC), which exhibits multiple cracks and pseudo strain-hardening behavior in the direct tension, is investigated. Polyethylene fibers reinforced SHCC mixtures with three levels (30, 70, and 100MPa) of compressive strength were compared through free shrinkage, compressive strength, flexural strength, and direct tensile strength measurements. The SHCC mixtures were cast with and without replacing 10% of Portland cement content with CSA admixture. According to test results, CSA admixture is effective in reducing shrinkage of SHCC material. SHCC mixture with CSA admixture exhibited a little higher strength than companion mixture without CSA admixture.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.95-104
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• 2013

Recently, application of CSG is increasing in various design construction projects. At the initial stage of cementation CSG materials show the same mechanical characteristics as soil, however, as the cementation process develops, CSG materials gradually reveal material characteristics of concrete. The hardened CSG manifests elastic behavior such as maximum strength at small strain range and rapid brittle failure. In this research, PVA fiber stiffeners were used in order to: (1) reduce such brittle behavioral characteristics; (2) improve the relatively weak tension performance of CSG materials. The binding strength between the bed materials and fiber prevents rapid brittle failure and increases tensional strength of fiber reinforced CSG materials.Test results show that fiber reinforcement alone could induce the stress-strain characteristics of CSG materials from brittle failure to ductile failure and also increase the residual strength.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.807-812
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• 2010

In this paper, the Ultrasonic Nanocrystalline Surface Modification (UNSM) surface treatment process was used to induce compressive residual stress and nanocrystalline structure by severe plastic deformation on the UNSM-treated surface. The test results for AISI304 stainless steel demonstrated that the grain size was found to be 23 nm, the dislocation density was increased by $0.2085{\times}10^{18}\;m^{-2}$, and the volume fraction of martensite is defined as 27.6% from austenite so that the surface hardness of the surface is increased from 200 Hv up to 515 Hv. The initial tensile residual stress is changed from 300 MPa to a compressive residual stress of 500 MPa after UNSM treatment. In addition, UNSM was applied under five various conditions, and the results of those conditions were defined as a function of depth quantitative.