• Computers and Concrete
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• v.12 no.5
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• pp.585-612
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• 2013

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.36 no.5
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• pp.219-223
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• 2014

During surgical procedures, unexpected material, including surgical instruments and tissue segments, may get lost in the surgical field. Most of these should be immediately removed to prevent further complications, such as vital organ irritation, infection, and inflammatory pseudo-tumor formation. However, it is not always easy to define the exact location of the foreign body, especially if the item is very small and/or it is embedded in the soft tissue of the head and neck region. Intraoperative real-time radiological imaging with C-arm fluoroscopy can be useful to trace the three-dimensional location of small and embedded foreign bodies in the oral and maxillofacial area. We describe an unusual case of an embedded micro-screw in the intrinsic tongue muscle that had been dropped into the sublingual space during a lower alveolar bone graft procedure. The lost foreign body was accurately identified with C-arm fluoroscopy and safely removed without any further complications.

• 전자공학회논문지 IE
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• v.44 no.3
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• pp.42-50
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• 2007

In this paper, elastic and plastic adhesion index was very important in deciding adhesive characteristics and varying elastic and plastic index, dimensionless load and pull-off force were analyzed and simulated. Finally, using AFM, experimental surface roughness parameters of substrates and pull-off force between tip and substrates were produced. Using these values, pull-off forces were calculated and were compared with experimental pull-off forces. Through simulation and experiment, it was found that interaction of asperity also had very important influence on adhesive contact.

• Transactions of Materials Processing
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• v.20 no.3
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• pp.193-205
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• 2011

Because of its rustproof property, stainless steel is widely used in kitchen appliances, building materials, electronics, chemical plants and automobile exhausts. In addition, the utilization of stainless steel for fuel cell application is growing. As the demand for this material increases, it is necessary to study the basic properties of stainless steel such as corrosion resistance, heat transfer, formability, cutting or shearing ability and weldability. In this article, the mechanical properties, formability and press forming performance of stainless steel are reviewed. Since temperature and strain rate affect the press forming performance of STS304(austenitic) stainless steel, the influence of these parameters on the plastic behavior should be investigated. Moreover, measures for the prevention of ridging of STS430(ferritic) and delayed fracture of STS430, which respectively appear during and after press forming, should be considered. Recently, stainless steel sheets with a thickness lower than 0.2 mm have been widely used in applications for mobile phone, digital camera and fuel cell separator. Therefore, there is a growing interest of studying the grain size effect and plasticity at the crystal scale in order to understand the anisotropic behavior and micro forming ability of thin sheets. This review paper was written with the objective of helping engineers and researchers to understand the forming characteristics of stainless steel and to establish standards in plastic forming techniques.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.15-18
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• 2011

Up to now the incomplete texture have been manufactured through the 2D surface treatment like simple painting process or printing process. But in order to obtain 3D texture like natural object, micro scales' 3D surface structure on the surface of plastic part must be formed. In this study plastic smart phone case with 3D texture was produced by developing the surface duplication technology of natural object used electro-forming technology, by developing the press forming technology converted plane stamper to curved surface stamper and by developing the injection mold and molding technology which have been installed the curved surface stamper.

• Tribology and Lubricants
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• v.19 no.4
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• pp.230-236
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• 2003

In applications such as MEMS and NEMS devices, the adhesion force and contact load may be of the same order of magnitude and the static friction coefficient can be very large. Such large coefficient may result in unacceptable and possibly catastrophic adhesion, stiction, friction and wear. To obtain the static friction coefficient of contacting real surfaces without the assumption of an empirical coefficient value, numerical simulations of the contact load, tangential force, and adhesion force are preformed. The surfaces in dry contact are statistically modeled by a collection of spherical asperities with Gaussian height distribution. The asperity micro-contact model utilized in calculation (the ZMC model), considers the transition from elastic deformation to fully plastic flow of the contacting asperity. The force approach of the modified DMT model using the Lennard-Jones attractive potential is applied to characterize the intermolecular forces. The effect of the surface topography on the static friction coefficient is investigated for cases rough, intermediate, smooth, and very smooth, respectively. Results of the static friction coefficient versus the external force are presented for a wide range of plasticity index and surface energy, respectively. Compared with those obtained by the GW and CEB models, the ZMC model is more complete in calculating the static friction coefficient of rough surfaces.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.41
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• pp.20.1-20.7
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• 2019

Background: The purpose of this study was to evaluate the effects of botulinum toxin A (BTX) injection into the anterior belly of the digastric muscle on a growing rat. Methods: Ten Sprague Dawley rats were used in this study. When the rats were 13 days old, 0.5 units of BTX was injected into the anterior belly of the digastric muscle for the experimental group (n = 5). For the control, the same volume of normal saline was injected (n = 5). The rats were sacrificed at 60 days old, and the skulls were harvested for micro-computed tomography (μCT) analysis. Results: In anthropometric analysis, the zygomatic arch and mandibular bi-condylar width were significantly lower in the experimental group than those in the control group (P = 0.025 and 0.027, respectively). The maxillary point width was significantly higher in the experimental group than that in the control group (P = 0.020). Conclusion: BTX injection into the anterior belly of the digastric muscle had effects on the maxillofacial bony width in growing rats.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.33 no.6
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• pp.467-477
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• 2011

Purpose: The objective of this study was to examine the affected period and the amount of bone formation during osteogenesis of intramembranous bone using low-intensity pulsed ultrasound (LPUS) $in$ $vivo$. Methods: Xeno-bone (Bio-oss) and autogenous bone were grafted bilaterally into mini-pig mandibles. The left mandible served as the control and the other mandible was treated with 3 MHz, 160 mW (output, 0.8 mW) ultrasound stimulation for 7 days 15 minutes per day. The mini-pigs were sacrificed at 1, 2, 4, and 8 weeks, and micro computed tomography (${\mu}CT$), a microscopic examination, and a statistical analysis were performed on the specimens. Results: Based on a computerized image analysis of the ${\mu}CT$ scans, the experimental group had an average 150% more new bone formation than that in the control group. The effect of LPUS continued during the post operative 2 weeks. The histomorphological microscopic examination showed similar results. Conclusion: Our results suggest the LPUS had an effect on early intramembranous bone formation in vivo.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.1
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• pp.66-71
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• 2004

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good cast-ability in spite of hexagonal closed-packed crystal structure of pure magnesium. In this study, it is studied about the forming characteristics of press forging of AZ31 magnesium alloy by MSC/MARC in case of material having one boss and MSC/Supeiforge in case of material having multi-boss with heat transfer analysis during deformation at elevated temperature. For these results it is simulated about temperature distribution, strain distribution, and stress distribution of AZ31 Magnesium alloy. During the press forging, foot regions of bosses showed greater temperature rise than other areas of AZ31 sheet. Finally the plastic strain of AZ31 sheet did not remarkably vary with increasing temperature from 373 to 473K, while it significantly increased as the forming temperature increased from 473 to 573K, which is related with the change in micro-structures, such as dynamic re-crystallization occurring during the deformation process.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.4
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• pp.345-349
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• 2014

In this study, an age-hardened 6061-T6 alloy sheet was used, which is commonly utilized for auto parts. The junction strength characteristics in relation to the stirring speed and welding speed were studied in accordance with the friction stir welding rotation of the tool pin. Micro hardness measurements of A type and B type pins, for a welding speed of 400 mm/min and a tool rotational speed 3000 rpm, were obtained as Hv104 and Hv111, respectively. For a welding speed of 200 mm/min and a tool rotational speed of 2000 rpm, we obtained Hv48 and Hv50 for A and B type pins, respectively. Microstructure observation showed that the stirring portion was fine and uniform, which occurred because of its plastic deformation. In the thermomechanically affected zone, partial recrystallization was present because of the plastic deformation. The crystal grains in the heat affected zone were coarsened due to the heat generated by friction stir welding.