• The korean journal of orthodontics
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• v.27 no.6 s.65
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• pp.943-954
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• 1997

Forces needed for orthodontic tooth movement are obtained from various appliances such as orthodontic wires or elastic rubber. Orthodontic elastic rubber is widely used clinically, but permanent deformation and force decay may occur from the environmental changes, time of clinical use and the extent of the stretch, making the Prediction of force being applied difficult. The Present study examined and compared the changes in residual force between three brands of elastomeric chains (Ormco Generation II Power Chains ; brand A, RMO : Energy-Chain ; brand B, Unitek : AlastiK ; brand C) under various environmental conditions, amount of initial force, types of elastomer and the rate of extension. The characteristic physical properies of the elastomeric chains were as follows. 1. In all three brands, the residual force ratio was largest when the chains were stored in air, with no difference between water and saliva. 2. In all three brands, after 24 hours, there was no statistical difference in residual force ratio according to the initial force level. 3. In Brand A and B, the presence of filament had no correlation with the residual force ratio. In Brand C force decay was more severe when the chain contained filament. 4. In each brand, rate of extension had no effect on residual force ratio. 5. Brand B showed relatively higher residual force ratio compared to other brands.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.5
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• pp.375-384
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• 2013

Most of regions within the city of Mokpo, located on the southwest coast of the Korean Peninsula, are subjected to significant subsidence because about 70% of the city is land reclaimed from the sea (Kim et al., 2005). In this study, we aimed to estimate the rate of subsidence over Mokpo by using PALSAR L-band dataset from 2006 to 2010. Time series analysis was performed as well using GPS surveying data from 2010 to 2012. Results from these two independent datasets are then compared and analyzed over the common period of time. GPS data processing provides the results of seasonal variation on the surface, that is, via repeatedly rising and falling in association with the periodic cycle. Therefore, a time series analysis was performed to calculate the rate of ground subsidence. The deformation rates calculated for the same point are 3.89cm/yr and 2.65cm/yr from the GPS data and SAR data, respectively. SAR and GPS data processing results show a very similar pattern in terms of magnitude of annual subsidence. Thus, if the two datasets are integrated together, new modeling on ground subsidence is feasible. Lastly, subsidence was detected in a landfill area in the city of Mokpo, which has been continuously occurring through 2012.

• Fire Science and Engineering
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• v.34 no.1
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• pp.47-54
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• 2020

This paper proposes a solution to the problems of constructing and installing sway braces for existing standpipes in narrow spaces and pits. The study develops a floor-fixed sway brace for a narrow space that can support the ground area under horizontal seismic loads (X-axis, Y-axis) as well as vertical seismic loads (Z-axis). The results of structural analysis using SolidWorks simulation showed that the eccentric load was generated in the first design according to the anchored position along the vertical direction, and the problem of exceeding the allowable stress of the material along the horizontal and vertical directions. In the second design model, deformation caused by the eccentric load along the vertical direction, similar to the first design model, did not occur. The maximum strain rate was 0.17%, which is approximately 12.84% less than the first design model (Maximum strain rate of 13.01%). It was confirmed that the structural stability and durability improved. Compressive and tensile load testing of the prototypes showed that all of them meet the performance criteria of the standard.

• Journal of Mechanical Science and Technology
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• v.18 no.5
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• pp.770-779
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• 2004

This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during these various cutting conditions. A summary of the results are as follows: (1) From the SEM direct observation in cutting the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case, it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was due to the flank wear within the maximum value of $V_{max}$ being about 260 $\mu\textrm{m}$.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.3
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• pp.174-183
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• 1996

Acoustic emission(AE) response during stress corrosion cracking(SCC) of Inconel 600 alloy has been monitored to study the AE detectability of crack generation and growth by comparing the crack behavior with AE parameters processed, and to evaluate the applicability as a nondestructive evaluation(AE) by measuring the minimum crack size detectable with AE. Variously heat-treated specimens were tensioned by constant extension rate test(CERT) in various extension rate to give rise to the different SCC behavior of specimens. The AE amplitude level generated from intergranular stress-corrosion cracking(IGSCC) is higher than those from ductile fracture and mechanical deformation, which means the AE amplitude can be a significant parameter for distinguishing the An source. AE can also provide the effective means to identify the transition from the small crack initiation and formation of dominant cracks to the dominant crack growth. Minimum crack size detectable with AE is supposed to be approximately 200 to $400{\mu}m$ in length and below $100{\mu}m$ in depth. The test results show that AE technique has a capability for detecting the early stage of IGSCC growth and the potential for practical application as a NDE.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.81-94
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• 2010

This paper deals with the fracture simulation of UHPFRC girder with the interface type model. Based on the existing numerical simulation of quasi-brittle fracture in normal strength concrete, constitutive modeling for UHPFRC I-girder has been improved by including a tensile hardening at the failure surface. The finite element formulation is based on a triangular unit, constructed from constant strain triangles, with nodes along its sides and neither at the vertex nor the center of the unit. Fracture is simulated through a hardening/softening fracture constitutive law in tension, a softening fracture constitutive law in shear as well as in compression at the boundary nodes, with the material within the triangular unit remaining linear elastic. LCP is used to formulate the path-dependent hardening-softening behavior in non-holonomic rate form and a mathematical programming algorithm is employed to solve the LCP. The piece-wise linear inelastic yielding-failure/failure surface is modeled with two compressive caps, two Mohr-Coulomb failure surfaces, a tensile yielding surface and a tensile failure surface. The comparison between test results and numerical results indicates this method effectively simulates the deformation and failure of specimen.

• Nuclear Engineering and Technology
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• v.21 no.2
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• pp.111-122
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• 1989

With the Zircaloy-4 tube oxidized in high temperature (1323 K) steam for 5, 10, 30 and 60 minutes, the expanding copper mandrel test was carried out over a temperature range of 673-l173k at $\varepsilon\;=\;3.0\times10^5S\;^1$. The oxidation parameters $(K_i)$ in the present study were linearly proportional to square root of time $(Ki= \delta_{kit})$ and their rate constants ($\delta_{ki}$) are 0.281, 2.82, and 2.313 for weight gain and thickness of Zr02 and $\alpha$(0) layer, respectively. Activation energy for high temperature (873-1073k) plastic deformation of Zircaloy-4 increases from 251 KJ/mol to 323 KJ/mol with increase in oxidation time from 5 minutes to 60 minutes due to the high strengthened Zr02. With the oxide layer thickness [K ; expressed in "Equivalent Cladding Reacted" (ECR,%)] and the yield stress obtained from the mandrel test, an empirical relation was derived as ($\sigma/C)^n=K^mexp$ (Q/RT) with n=6.9, m=5.7, C=0.155, 0.138, 0.051, and 0.046 MPa for Q=251, 258, 316, 323 KJ/mol, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.499-508
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• 2016

Injection molding is a method for manufacturing many products, wherein a plasticized resin is injected into a mold at high pressure and hardened. According to the method, the product can be manufactured into various forms, and the mass production of up to tens of thousands of products is possible. The purpose of this study was to determine the process conditions for manufacturing a door latch for automobiles, through an analysis of the injection molding method. To calculate an appropriate injection flow for injection molding, a primary analysis for comparing the injection time, pressure, flow pattern, consolidation range, shear stress, shear rate, and weld line, as well as a secondary analysis for determining the conditions for stabilizing the molding temperature, holding pressure, and cooling process, were conducted. The characteristics of injection molding, and their influence on the product quality are discussed. No weld line and pores were observed on the products that had been manufactured based on the process conditions determined above. In addition, there were no flaws regarding the deformation compared to the prototype. Therefore, the manufacture of a product under the conditions determined in this study can reduce the defect rate compared to the existing production, and the process is also more competitive due to reduced production time.

• Geophysics and Geophysical Exploration
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• v.23 no.1
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• pp.1-12
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• 2020

In the development of geodynamic structures such as subduction and rift zones, a weakening mechanism is essential for localized weak zone formation in the lithosphere. Shear heating, a weakening mechanism, generates short-wavelength temperature elevation in the lithosphere; the increased temperature can reduce lithospheric strength and promote its breakup. A two-dimensional elastoplastic extensional basin model was used to conduct benchmarking based on previous numerical simulation studies to quantitatively analyze shear heating. The amount of shear heating was investigated by controlling the yield strength, extensional velocity, and strain- and temperature-dependent weakening. In the absence of the weakening mechanism, the higher yield strength and extensional velocity led to more vigorous shear heating. The reference model with a 100-MPa yield strength and 2-cm/year extension showed a temperature increase of ~ 50 K when the bulk extension was 20 km (i.e., 0.025 strain). However, in the yield-strength weakening mechanism, depending on the plastic strain and temperature, more efficient weakening induced stronger shear heating, which indicates positive feedback between the weakening mechanism and the shear heating. The rate of shear heating rapidly increased at the initial stage of deformation, and the rate decreased by 80% as the lithosphere weakened. This suggests that shear heating with the weakening mechanism can significantly influence the strength of relatively undamaged lithosphere.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.197-213
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• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.