• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.432-439
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• 2015

MEMS solid thruster module is composed of solid thruster and its control board. It was developed for the purpose of an academic research. Therefore, thermo-mechanical design and verification for space usage were not considered in the design phase. To mount it on a cube satellite without any design modification, technical efforts at the system level structure design is required. In this study, we proposed a structural design concept to mount the MEMS thruster module by using brackets for guaranteeing structure safety under launch loads and easier mating and de-mating of MEMS thruster module during test phase. The effectiveness of the design has been verified through structural analysis and vibration test. In addition, electrical connection method using spring pins between MEMS thruster and control board is effective for guaranteeing the structural safety under launch vibration loads.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.83-88
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• 2004

Recently, High Tensile Steel is adapt to thin plate on the steel structure and marine structure is used widely. It is possible for buckling happens great. Specially, Initial deflection of ship structure happens in place absence necessarily by heat processing of welding or cutting etc. This Initial Deflection is exerted negative impact when thin plate absence complicated nonlinear behaviour accompanied secondary buckling. As a result, must idealize initial deflection that occurrence is possible to endow stability and accuracy in the hull structure or marine structure and reflect in early structure design considering secondary buckling. Longi direction of compressive load interacts and analyzed finite element series analysis that apply various kinds initial deflection shape measured actually on occasion that is arranged simply supported condition in this research. Applied ANSYS (elasto-plasticity large deformation finite element method) to be mediocrity finite element program for analysis method and analysis control used in Newton-Raphson method ＆ Arc-length method.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.109-116
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• 2011

In this study, we estimated the dynamic tensile strength and strain rate from Brazilian tensile test using Split Hopkinson Pressure Bar (SHPB) system. A pulse shaping technique, which controls the shape of the impactinduce incident waves, was used for achieving the dynamic stress equilibrium and constant strain rate before fracture of rock samples. Three kinds of rock type, Inada granite, Kimachi sandstone and Tage tuff were prepared as 50mm in diameter and 26 mm in thickness. The high-speed videography system was used to observe the fracture processes of the rock samples. As the results of the tests, the ratio of dynamic tensile strength and static tensile strength was 11.9 for Inada granite, 8.5 for Kimachi sandstone and 9.2 for Tage tuff.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.49-60
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• 2002

Welding is essential in ship production since welding is very popular method for joining two or more metals. However, welding causes residual stress and distortion and these give a bad influence to the structure strength and assembly of ship blocks. Therefore, prediction and treatment of residual stress and distortion is a key to accuracy control in shipyard. In this paper, a computational procedure, based on thermal-elastic-plastic 3-dimensional FEA, has been suggested to simulate butt and fillet welding process. In the simulation process, temperature distribution at each time step is obtained by heat transfer analysis and then thermal deformation analysis is done with obtained temperature distributions to find the residual stress and distortion. In heat transfer analysis, enthalpy method is used to realize phase change at melting temperature. Also element birth and death method is used to simulate adding of weld metal in both heat transfer analysis and thermal elastic plastic analysis. The proposed procedure is verified by related researches and the results show good agreement with those of related researches.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.9-20
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• 2005

This study was carried out to select most efficient bonding methods of geogrid at the interface of old concrete pavement before placing asphalt overlay layer for reflection cracking retardation. Three bonding methods, a RSC-4 emulsified asphalt, a compound and an unsaturated polyester resin (UPR) were compared in this study. Three types of asphalt mixture (AC 60-80, RLDPE 8%, PG 76-22) and a dense-graded aggregate were used for overlay asphalt pavement. A reinforcing material which consists of a woven fabric underneath a glass fiber grid was used. An expedite test method which is for simulating mixed mode (mode I and II) fracture test was performed using a wheel tracker in laboratory. Cracking development by load repetition was measured as fatigue life (number of load cycle) and expansion of specimen body were measured for each test specimen. The results showed that UPR was the best and RSC-4 the next. But considering field applicability, RSC-4 was considered as an appropriate choice for bonding reinforcing material.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.753-756
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• 2008

HPFRCC (High-Performance Fiber Reinforced Cementitious Composites), which is relatively more ductile and has the characteristic of high toughness with high fiber volume fractions, can be used in structures subjected to extreme loads and exposed to durability problems. In the case of using PVA(polyvinyl alcohol) fibers, it is noted by former studies that around 2% fiber volume fractions contributes to the most effective performance at HPFRCC. In this study, therefore, compressive and flexural tests were implemented to evaluate the compressive and flexural capacities of HPFRCC while the total fiber volume fractions was fixed at 2% and two different PVA fibers were used with variable fiber volume fractions to control the micro-crack and macro-crack with short and long fibers, respectively. Moreover, specimens reinforced with steel and PVA fiber simultaneously were also tested to estimate their behavior and finally find out the optimized mixture. In the result of these experiments, the specimen consists of 1.6% short fibers (REC 15) and 0.4% long fiber (RF4000) outperformed other specimens. When a little steel fibers added to the mixture with 2% PVA fibers, the flexural capacity was increased, however, when high steel fiber volume fractions applied, the flexural capacity was decreased.

• Journal of Korean Association for Spatial Structures
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• v.8 no.6
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• pp.49-57
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• 2008

The seismic isolation systems could be used to reduce the seismic response of a structure. The natural period of a structure with seismic isolation system got be long to avoid the prominent seismic period. The purpose of this study is to analyzed the seismic behavior of the truss arch that is supported to column with LRB. Truss arch structures subjected to horizontal seismic have large horizontal and vertical response unlike seismic behavior of normal rahmen structures. When seismic load is applied to the truss arch with isolation systems, the horizontal acceleration response of the truss arch is reduced and the vertical seismic response is remarkably reduced. Also, the seismic behaviors of the truss arch with strengthen column as like lattice column are very similar to that of the truss arch supported to directly foundation. The Seismic Isolation system can be applied to reduce efficiently the seismic response of the spacial structure with not strong column.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.61-70
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• 2003

The behaviour of an earth and rock-fill dam is complicated due to reservoir water and various materials in zoned dams. Different materials with a wide range of permeability and seasonal variation of reservoir water result in the time dependent post-constructional behaviour. In aged dams it is often required to control water level to keep the dams safe. In this case information on the post-constructional dam behaviour is important. However, present geotechnical knowledge does not fully support the occasion. In this study the post-constructional behaviour of a dam is investigated using coupled finite element models for series of idealized water reservoir cases: impoundment, draw down, seasonal fluctuation with different rising and falling speeds. Numerical results were analysed in respect of geotechnical parameters such as load transfer, hydraulic fracturing potential and stress paths. It is shown that the control of water level is an important factor while operating dams.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.55-63
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• 2015

Prefabrication technologies are making bridge construction safer and less disruptive to the environment and traveling public, making bridge designs more constructible and, improving the quality and durability by shifting site work to a more controllable environment. Modular bridge substructures with concrete-filled steel tube (CFT) piers and composite pier caps were suggested to realize accelerated bridge construction. The precast segmental pier cap consists of a composite pier table and precast prestressed segments on the table. The pier table has embedded steel section to mitigate stress concentration at the connection by small tubes. Each bridge pier has four or six CFT columns which connect to the pier cap. Shear strength of the pier cap was obtained by extending vertical reinforcing bars from the table to the precast segment. Transverse prestressing was introduced to control tensile stresses by service loadings. Structural performance of the proposed modular system was evaluated by static tests. Design requirements of the composite pier cap were satisfied by continuous reinforcing bars and prestressing tendons. Standardized modular substructures can be effectively utilized for the fast replacement or construction of bridges.

• Composites Research
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• v.12 no.6
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• pp.22-30
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• 1999

Since the surface diffusion processed $Nb_3Sn$ superconducting tape has the advantage of having large overall critical current density. it is used for the construction of open type MRI superconducting magnets. However one of the disadvantages of this tape is that $Nb_3Sn$ compound often exhibited multiple cracking due to its intrinsic brittleness when subjected to mechanical loading such as bending and winding during the fabrication process for superconducting coil. This will eventually cause the severe degradation of critical current density. Therefore it is important to understand the microscopic deformation behavior of this kind of superconducting tape under the mechanical loading.In this study, acoustic emission(AE) was used to clarify microscopic deformation behavior at room temperature for $Nb_3Sn$ superconducting tape which was strengthened and stabilized with copper. For this purpose, special attention was paid to AE characteristics including AE event, energy, and amplitude distribution which were associated with microscopic mechanism of deformation of $Nb_3Sn$ superconducting tape under tensile load.