• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.46-49
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• 2003

Cu have been widely used as signal transmission materials for electrical electronic components owing to its high electrical conductivity. However, it's size have been limited to small ones due to its poor mechanical properties, Until now, strengthening of the copper at toy was obtained either by the solid solution and precipitation hardening by adding alloy elements or the work hardening by deformation process. Adding the at toy elements lead to reduction of electrical conductivity. In this aspect, if carbon nanofiber is used as reinforcement which have outstanding mechanical strength and electric conductivity, it is possible to develope Cu matrix nanocomposite having almost no loss of electric conductivity. It is expected to be innovative in electric conduct ing material market. The unidirectional alignment of carbon nanofiber is the most challenging task developing the copper matrix composites of high strength and electric conductivity In this study, the unidirectional alignment of carbon nanofibers which is used reinforced material are controlled by drawing process in order to manufacture the intermediary materials for the carbon nanofiber reinforced Cu matrix nanocomposite and align mechanism as well as optimized drawing process parameters are verified via experiments and numerical analysis. The materials used in this study were pure copper and the nanofibers of 150nm in diameter and of $10~20\mu\textrm{m}$ In length. The materials have been tested and the tensile strength was 75MPa with the elongation of 44% for the copper it is assumed that carbon nanofiber behave like porous elasto-plastic materials. Compaction test was conducted to obtain constitutive properties of carbon nanofiber. Optimal parameter for drawing process was obtained by experiments and numerical analysis considering the various drawing angles, reduction areas, friction coefficient, etc Lower reduction areas provides the less rupture of cu tube is not iced during the drawing process. Optimal die angle was between 5 degree and 12 degree. Relative density of carbon nanofiber embedded in the copper tube is higher as drawing diameter decrease and compressive residual stress is occurred in the copper tube. Carbon nanofibers are moved to the reverse drawing direct ion via shear force caused by deformation of the copper tube and alined to the drawing direction.

• Composites Research
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• v.29 no.4
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• pp.194-202
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• 2016

A graphene film, two-dimensional carbon sheet, is a promising material for future electronic devices and so on. In graphene applications, the effect of substrate on the atomic/electronic structures of graphene is significant, so we studied an interaction between graphene film and substrate. To study the effect, we investigated the graphene films grown on Ni substrate with two crystal face of (111) and (100) by Raman spectroscopy, comparing with graphene films transferred on $SiO_2/Si$ substrate. In our study, the doping effect caused by charge transfer from Ni or $SiO_2/Si$ substrate to graphene was not observed. The bonding force between graphene and Ni substrate is stronger than that between graphene and $SiO_2/Si$. The graphene films grown on Ni substrate showed compressive strain and the growth of graphene films is incommensurate with Ni (100) lattice. The position of 2D band of graphene synthesized on Ni (111) and (100) substrate was different, and this result will be studied in the near future.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.421-434
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• 2019

It is of great significance to study the mechanical properties and failure mechanism of the defected rock for geological engineering. The defected sandstone modeling with power-law distribution of pre-cracks was built in this paper by Particle Flow Code software. Then the mechanical properties of sandstone and the corresponding failure process were meticulously analyzed by changing the power-law index (PLI) and the number of pre-cracks (NPC). The results show that (1) With the increase of the PLI, the proportion of prefabricated long cracks gradually decreases. (2) When the NPC is the same, the uniaxial compressive strength (UCS) of sandstone increases with the PLI; while when the PLI is the same, the UCS decreases with the NPC. (3) The damage model of rock strength is established based on the Mori-Tanaka method, which can be used to better describe the strength evolution of damaged rock. (4) The failure mode of the specimen is closely related to the total length of the pre-crack. As the total length of the pre-crack increases, the failure intensity of the specimen gradually becomes weaker. In addition, for the specimens with the total pre-crack length between 0.2-0.55 m, significant lateral expansion occurred during their failure process. (5) For the specimens with smaller PLI in the pre-peak loading process, the concentration of the force field inside is more serious than that of the specimens with larger PLI.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.1
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• pp.99-107
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• 2001

Manufacture of fishing vessel is needed the effective material for light, strength, fire and corrosion of water in order to improve durability by high-speed and fishing. These fishing vessel can be divided into FRP and AI alloys fishing vessel. FRP fishing vessel is light and effective for strength but highly ignited and susceptible to heat during the manufacturing ship by-produce noxious component for human. In the case of a scrapped ship, it cause environmental pollution. On the other hand, aluminum is a material in return for FRP and has merit of high-strength and lightness. It's more heat proof and durable than FRP and superior to prevent from corrosion. Al alloys fishing vessel development is rising as an urgent matter. But, al alloy has some defect of bad weldability, welding transformation, cracks and overcost of construction. Therefore this study is to develop the new welding joint shape solving aluminum defects and mechanical behavior. First of all, strength was compared and reviewed by analysis of plate, stiffen plate, new model simplified by using plate theory. On the base of this result, plate and new model of temperature distribution, weld residual stress and strength of tensile, compressive force were compared and reviewed by finite element computer program has been developed to deal with heat conduction and thermal elasto plastic problem. Also, new model is proved application possibility and excellent mechanic by strength comparison is established to tensile testing result.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.525-534
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• 2006

Column-to-beam pinned connections can cause local moment to the web of a steel tube due to the distance of eccentricity between the row of bolts and the column flange, which possibility deteriorates the load capacity of column. In this study, a square hollow section tubular used finite element analysis of a square hollow section tubular column was carried out, and the column width and thickness, existence and non-existence of internal reinforcement, and existence and non-existence of compressive force were taken as variables to examine the load capacity deterioration of a square column caused by moment. To guarantee the reliability of the finite element results, some specimens were fabricated and tested. The yield line method was applied to suggest the strength formulas of the square tubular column to the beam pinned connections. Based on the study results, the column strength the moment of the square hollow section tubular column to the beam pined connections improved with the increase in the w to strength limitations, a no-reinforcement type of square hollow section tubular column was proposed, and if the limitation values were not satisfied, the reinforcement of the internal column was made mandatory. Therefore, the horizontal -reinforcement type considered the strength increase, and the fabrication of the square hollow section tubular column was ar column that considered its load capacity with the moment for the no-reinforcement and the horizontal-reinforcement types.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.543-551
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• 2006

Cold-formed steel studs that are being used as load-bearing members of wall panels for steel houses have a problem with their insulation due to the heat bridging of their web. Some additional thermal insulating materials should be used. To solve this problem, the new-concept hybrid stud, which consists of a galvanized steel sheet (t = 1.0 m - 12.0 m) and a GFRP panel (t = 4.0-6.0 mm), has recently been developed. An investigation on the structural behavior and the strength capacity of this new hybrid stud has been conducted so that it can be used in load-bearing wall panels of residential buildings. This paper describes the axial compression-torsion test results of the hybrid studs under both axial compression and torsion using ATTM. The main factors of the test were the stud length, the magnitude of the initial compressive force, and the loading method of the monotonic or cyclic loading. The torsion was applied increasingly while the initial compression was kept constant to the failure of the hybrid section. The advanced analysis results obtained form the finite element procedure that considered the material properties of the high-strength galvanized steel and the GFRP were compared with the test results for verification.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.87-92
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• 2014

The Ground anchor is reinforcement to resist pull-out through ground that is used supports structure. The pull-out resistance of anchor is constructed by skin friction resistance from compression borehole wall in expanded wings and bearing pressure from the ground. Especially, underreamed ground anchor is reinforcement that adopts active reinforcement to prevent deformation of ground using bearing resistance generated reaming anchorage. This study is conducted to calculate bearing resistance of underreamed ground anchor. Realistic model tests were fulfilled to determine bearing resistance of anchor, and correlate results of tests to Uniaxial Compressive Strengths (UCS) of ground models that assumed weathered rock condition in 8 case. In a comprehensive series of the tests, the bearing resistances were measured by pull-out tests. The bearing resistances derived from tests have a linear correlation with UCS. We also suggest empirical equation between bearing resistance and UCS of rocks by single linear regression analyses. In test results of this study, the bearing resistances were evaluated approximately 13 times higher than UCS of the grounds, and it is qualitatively similar to numerical values of pull-out force derived from theory.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.91-105
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• 2015

In the current work, a series of three-dimensional (3D) finite element analyses have been performed to study the effects of the locations of pile tips on the behaviour of single piles to adjacent tunnelling. In the numerical modelling, several key issues, such as tunnelling-induced pile head settlements, axial pile forces, interface shear stresses and apparent factors of safety have been studied. When the pile tips are inside the influence zone which considers the relative pile tip location with respect to the tunnel position, tunnelling-induced pile head settlements are larger than those computed from the greenfield condition. However, when the pile tips were outside the influence zone, an opposite trend was observed. When the pile tips were inside the influence zone, tunnelling-induced tensile pile forces developed; however, when the pile tips were outside the influence zone, tunnelling-induced compressive pile forces were mobilised, associated with larger settlements of the surrounding soil than the pile settlements. It has been shown that the increases in the tunnelling-induced pile head settlements have resulted in reductions of the apparent factor of safety by about 50% when the pile tips are inside the influence zone, therefore severly affecting the serviceability of piles. The pile behaviour, when considering the location of pile tips with regards to the influence zone, has been analysed in great detail by taking the tunnelling-induced pile head settlements, axial pile force and apparent factor of safety into account.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.345-371
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• 1994

Restorative procedures can lead to weakening tooth due to reduction and alteraton of tooth structure. It is essential to prevent fractures to conserve tooth. Among the several parameters in cavity designs, cavity isthmus and depth are very important. In this study, MO amalgam cavity was prepared on maxillary first premolar. Three dimensional. finite element models were made by serial photographic method and cavity depth(1.7mm, 2.4mm) and isthmus (11 4, 1/3, 1/2 of intercuspal distance) were varied. linear, eight and six-nodal, isoparametric brick elements were used for the three dimensional finite element model. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. Three types model(B, G and R model) were developed. B model was assumed perfect bonding between the restoration and cavity wall. Both compressive and tensile forces were distributed directly to the adjacent regions. G model(Gap Distance: 0.000001mm) was assumed the possibility of play at the interface simulated the lack of real bonding between the amalgam and cavity wall (enamel and dentin). When compression occurred along the interface, the forces were transferred to the adjacent regions. However, tensile forces perpendicular to the interface were excluded. R model was assumed non-connection between the restoration and cavity wall. No force was transferred to the adjacent regions. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, von Mises stress, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as follows: 1. G model showed stress and strain patterns between Band R model. 2. B model and G model showed the bending phenomenon in the displacement. 3. R model showed the greatest amount of the displacement of the buccal cusp followed by G and B model in descending order. G model showed the greatest amount of the displacement of the lingual cusp followed by B and R model in descending order. 4. B model showed no change of the displacement as increasing depth and width of the cavity. G and R model showed greater displacement of the buccal cusp as increasing depth and width of the cavity, but no change in the displacement of the lingual cusp. 5. As increasing of the width of the cavity, stress and strain were not changed in B model. Stress and strain were increased on the distal marginal ridge and buccopulpal line angle in G and R model. The possibility of the tooth fracture was increased. 6. As increasing of the depth of the cavity, stress and strain were not changed in B and G model. Stress and strain were increased on the distal marginal ridge and buccopulpal line angle in R model. The possibility of the tooth fracture was increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.604-609
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• 2020

There are various methods of finishing concrete surfaces, and when considering workability, the spray method is effective, but rebound occurs. The allocation of rebound occurrence control should be adjusted according to the materials used. Thus, a basic study was conducted on multiple techniques for reducing the rebound incidence that are suitable for surface finishing materials containing a photocatalyst. A prior study derived the reduction effect and optimal mix ratio for photocatalytic performance. Based on that study, the rebound reduction was verified according to the specifications of the content and the mechanical durability characteristics of the mixed materials. Rebound, compressive strength, flexural rigidity, and table flow tests were done. The flow was fixed at 170±10 mm considering the workability of the mortar spray equipment. For the experimental variables, the rebound number was adjusted to the silica sand variables relative to the cement weight, and silica sands No. 5 and No. 7 were used. The results show the highest compression strength in the final S-1 variable, and the amount of rebound was minimized. These results were sufficiently filled with the bindings of the silica pores, which increased the binding force between the aggregates, resulting in a lower amount of rebound.