• Carbon letters
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• v.22
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• pp.42-47
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• 2017

In this paper, the in vitro biocompatibility of graphene film (GF) with osteoblasts was evaluated through cell adhesion, viability, alkaline phosphatase activity, F-actin and vinculin expressions, versus graphite paper as a reference material. The results showed that MG-63 cells exhibited stronger cell adhesion, better proliferation and viability on GF, and osteoblasts cultured on GF exhibited vinculin expression throughout the cell body. The rougher and wrinkled surface morphology, higher elastic modulus and easy out-of-plane deformation associated with GF were considered to promote cell adhesion. Also, the biomineralization of GF was assessed by soaking in simulated body fluid, and the GF exhibited enhanced mineralization ability in terms of mineral deposition, which almost pervaded the entire GF surface. Our results suggest that graphene promotes cell adhesion, activity and the formation of bone-like apatite. This research is expected to facilitate a better understanding of graphene-cell interactions and potential applications of graphene as a promising toughening nanofiller in bioceramics used in load-bearing implants.

• Geomechanics and Engineering
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• v.14 no.6
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• pp.563-570
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• 2018

Ballast layer has an important role in vertical stiffness and stability of railway track. In most of the Middle East countries and some of the Asian ones, significant parts of railway lines pass through desert areas where the track (particularly ballast layer) is contaminated with sands. Despite considerable number of derailments reported in the sand contaminated tracks, there is a lack of sufficient studies on the influences of sand contamination on the ballast vertical stiffness as the main indicator of track stability. Addressing this limitation, the effects of sand contamination on the mechanical behavior of ballast were experimentally investigated. For this purpose, laboratory tests (plate load test) on ballast samples with different levels of sand contamination were carried out. The results obtained were analyzed leading to derive mathematical expressions for the strain modulus ($E_V$) as a function of the ballast level of contamination. The $E_V$ was used as an index for evaluation of the load-deformation characteristics and bearing capacity of track substructure. The critical limit of sand contamination, after which the $E_V$ of the ballast reduces drastically, was obtained. It was shown that the obtained research results improve the current track maintenance approach by providing key guides for the optimization of ballast maintenance planning (the timing of ballast cleaning or renewal).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.12
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• pp.1173-1179
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• 2007

In recent years, research to machine large-surface micro-features has become important because of the light guide panel of a large-scale liquid crystal display and the bipolar plate of a high-capacity proton exchange membrane fuel cell. In this study, in order to realize the systematic design technology and performance improvements of an ultra-precision machine for machining the large-surface micro-features, a structural characteristic analysis was performed using its virtual prototype. The prototype consisted of gantry-type frame, hydrostatic feed mechanisms, linear motors, brushless DC servo motor, counterbalance mechanism, and so on. The loop stiffness was estimated from the relative displacement between the tool post and C-axis table, which was caused by a cutting force. Especially, the causes of structural stiffness deterioration were identified through the structural deformation analysis of sub-models.

• Journal of Korean Foot and Ankle Society
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• v.18 no.2
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• pp.43-47
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• 2014

Hallux valgus is a lateral deviation of the first phalanx and medial deviation of the first metatarsal at the first metatarsophalangeal (MP) joint. Its incidence has increased due to developing footwear. The etiologies include fashion footwear, genetic causes, anatomical abnormality around the foot, rheumatoid arthritis, and neuromuscular disorders. Physiologic alignment of the first MP joint is maintained by congruent and symmetric alignment of the articular surface of the first proximal phalanx and first metatarsal head, physiologic relationship of the distal first metatarsal articular surface and the first metatarsal shaft axis, and stable balance of soft tissue around the first MP joint and stable tarsometatarsal joint. Several factors have been associated with hallux valgus, including pes planus, hypermobility of the first tarsometatarsal joint, flattened shape of the first metatarsal head, increased distal metatarsal articular angle, and deformation of the medial capsular integrity. History and physical examination are very important to diagnosis of hallux valgus. Simple radiography provides information on deformity, particularly in weight-bearing anteroposterior and lateral radiographs. Understanding the etiologies and pathophysiology is very important for success in treatment of patients with hallux valgus.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.90-95
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• 2005

To perform the finish outside-diameter grinding process of ferrules which are widely used as fiber optic connectors, a high-precision centerless grinding machine is necessary. In this study, the thermal characteristics of the high-precision centerless grinding machine such as the temperature distribution, temperature rise and thermal deformation, are estimated based on the virtual prototype of the grinding machine and the heat generation rates of heat sources related to the machine operation conditions. The reliability of the predicted results is demonstrated by the temperature characteristics measured from the physical prototype. Especially, the predicted and measured results show the fact that the high-precision centerless grinding machine consisted of the hydrostatic GW and RW spindle systems, hydrostatic RW feeding mechanism, RW swivel mechanism, on-machine GW and RW dressers, and concrete-filled steel bed, has very stable thermal characteristics.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.8
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• pp.693-698
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• 2015

Recently, the quality of products after the corresponding machining processes were scrutinized in the interest of maintaining a high product-quality standard. The structure and stability of machine tools are important for the prediction of product quality. A structural analysis needs to be carried out to achieve the stable design of machine tools before the initial design stage in the manufacturing process of a precision product. In this study, a structural analysis was carried out using a finite element analysis (FEA) simulation to obtain the design stability of the main parts of a grinding machine. The sizes and locations of both the maximum stress and deformation in consideration of the cutting force of the chuck, tail stock, and bearing of the grinding machine were analyzed. Finally the grinding machine was successfully developed.

• International Journal of Concrete Structures and Materials
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• v.10 no.sup3
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• pp.43-52
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• 2016

The degradation of the load-bearing capacity of reinforced concrete beams due to corrosion has a profoundly negative impact on the structural safety and integrity of a structure. The literature is limited with regard to models of bond characteristics that relate to the reinforcement corrosion percentage. In this study, uniaxial tensile tests were conducted on specimens with irregular corrosion of their reinforced concrete. The development of cracks in the corroded area was found to be dependent on the level of corrosion, and transverse cracks developed due to tensile loading. Based on this crack development, the average stress versus deformation in the rebar and concrete could be determined experimentally and numerically. The results, determined via finite element analysis, were calibrated using the experimental results. In addition, bond elements for reinforced concrete with corrosion are proposed in this paper along with a relationship between the shear stiffness and corrosion level of rebar.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.7
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• pp.120-126
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• 2009

Thermal displacement of high speed spindle is very important problem to be solved. To solve heat generation and thermal displacement problems that influence on the product accuracy, it is very important to predict thermal characteristics of the spindle and it is positively necessary to select the conditions of cooling, flow rate and preload of bearings. In this paper, 30,000rpm($1.455{\times}10^6DmN$) spindle was designed and produced. The analysis of thermal deformation for heat generation of inner spindle was carried out using commercial program $ANSYS^{(R)}$ and the result was compared with measured data using $LabVIEW^{(R)}$ and SGXI-1600, 1125 and 1126 module. Temperature distribution and thermal displacement according to spindle speed are measured. Using this method, it is possible to predict and to improve thermal characteristic of high speed spindle by control spindle speed, bearing preload and cooling rate.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1690-1695
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• 2007

Lightweight metallic truss structures with open, periodic cell are currently being investigated because of their multi-functionality such as thermal management and load bearing. The Kagome truss PCM has been proved that it has higher resistance to plastic buckling, more plastic deformation energy and lower anisotropy than other truss PCMs. The subject of this paper is an examination of the failure mechanism of Wire woven Bulk Kagome(WBK). To address this issue, the out-of-plane compressive responses of the WBK has been measured and compared with theoretical and finite element (FE) predictions. For the experiment, 2 multi-layered WBK are fabricated and 3 specimens are prepared. For the theoretical analysis, the brazed joints of each wire in WBK are modeled as the pin-joint. Then, the peak stress of compressive behavior and elastic modulus are calculated based on the equilibrium equation and energy method. The mechanical structure with five by five cells on the plane are constructed is modeled using the commercial code, PATRAN 2005. and the analysis is achieved by the commercial FE code ABAQUS version 6.5 under the incremental theory of plasticity.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.117-125
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• 2012

In recent years, polymer concrete based on polyester resin have been widely generalized and the research of polymer concrete have been actively pursued by the technical innovations. Polymer concrete is a composite consisting of aggregates and an organic resin binder that hardens by polymerization. Polymer concrete are stronger by a factor of three or more in compression, a factor of four to six in tension and flexural and a factor of two in impact when compared with portland cement concrete. In view of the growing use of polymer concrete, it is important to study the physical characteristics of the material, emphasizing the short term properties as well as long term mechanical behavior. If polymer concrete is to be used in flexural load-bearing application such as in beam, it is imperative to understand the deformation of the material under sustained loading conditions. This study is proposed to empirical and mechanical model of polymer concrete tension creep using long-term experimental results and mathematical development. The test results showed that proposed model has been used successfully to predict creep deformations at a stress level that was 20 percent of the ultimate strength and viscoelastic behavior of recycled-PET polymer concrete is linear of stress level up to 30 percent. It is expected that the present model allows more realistic evaluation of varying stresses in polymer concrete structures with a constant loading.