• KCI Concrete Journal
• /
• 제11권3호
• /
• pp.65-77
• /
• 1999

A portland cement was reinforced by incorporating carbon fiber(CF), silica powder, and impregnating the pores with styrene monomers which were polymerized in situ. The effects of type, length, and volume loading of CF, mixing conditions, curing time and, curing conditions on mechanical behavior as well as freeze-thaw resistance and longer term stability of the carbon-fiber reinforced cement composites (CFRC) were investigated. The composite Paste exhibited a decrease in flow values linearly as the CF volume loadings increased. Tensile, compressive, and flexural strengths all generally increased as the CF loadings in the composite increased. Compressive strength decreased at CF loadings above approx. 3% in CFRC having no impregnated polymers due to the increase in porosity caused by the fibers. However, the polymer impregnation of CFRC improved all the strength values as compared with CFRC having no Polymer impregnation. Tensile stress-strain curves showed that polymer impregnation decreased the fracture energy of CFRC. Polymer impregnation clearly showed improvements in freeze-thaw resistance and drying shrinkage when compared with CFRC having no impregnated polymers.

• 한국정밀공학회지
• /
• 제29권9호
• /
• pp.938-945
• /
• 2012

To design and estimate material failures of Type III pressure vessels, which have excellent stability and performance, various modeling techniques have been introduced. This paper provided a hybrid modeling technique composed of ply-based modeling for a cylinder part and laminate-base modeling technique for a dome part for enhancing modeling efficiency. The ply-based modeling technique provided accurate ply stresses directly for predicting material failure, on the other hand, additional manipulations in stress calculations, which may cause some errors, were needed for the case of the laminate-based modeling technique. The ply stresses in fiber, transverse and in-plane shear directions were compared with the corresponding material strengths to predict material failure.

• 로봇학회논문지
• /
• 제12권2호
• /
• pp.116-123
• /
• 2017

Wearable robots are receiving great attention from the public, as well as researchers, because its motivation is to improve the quality of lives of people. Above all, complete paraplegic patients due to spinal cord injury (SCI) might be the most adequate target users of the wearable robots, because they definitely need physical assistance due to the complete loss of muscular strength and sensory functions. Furthermore, the medical care of complete paraplegics by using the wearable robots have significantly reduced the mortality rate and improved the life expectancy. The requirements of the wearable robot for complete paraplegics are actuation torque, locomotion speed, wearing sensation, robust gait stability, safety, and practicality (i.e., size, volume, weight, and energy efficiency). A WalkON Suit is the wearable robot that has satisfied the requirements of the wearable robot for complete paraplegics and participated in the powered exoskeleton race of Cybathlon 2016. In this paper, configuration of the WalkON Suit, human-machine interface, gait pattern, control algorithm, and evaluation results are introduced.

• 한국생산제조학회지
• /
• 제23권4호
• /
• pp.337-344
• /
• 2014

While implicit integration methods such as Newton's method have excellent stability for the analysis of stiff and constrained mechanical systems, they have the drawback that the evaluation and LU-factorization of the system Jacobian matrix required at every time step are time-consuming. This paper proposes a Jacobian update-free Newton's method in order to overcome these defects. Because the motions of all bodies in a vehicle model are limited with respect to the chassis body, the equations are formulated with respect to the moving chassis-body reference frame instead of the fixed inertial reference frame. This makes the system Jacobian remain nearly constant, and thus allows the Newton's method to be free from the Jacobian update. Consequently, the proposed method significantly decreases the computational cost of the vehicle dynamic simulation. This paper provides detailed generalized formulation procedures for the equations of motion, constraint equations, and generalized forces of the proposed method.

• 센서학회지
• /
• 제23권1호
• /
• pp.42-45
• /
• 2014

Recently, tremendous application utilizing electrospun nanofibers have been actively reported due to its several advantages, such as high surface to volume ratio, simple fabrication and high-throughput manufacturing. In this paper, we developed highly sensitive and consistent nanofiber humidity sensor by electrospinning. The humidity sensor was fabricated by rapid electrospinning (~2 sec) $TiO_2$/PVP/LiCl mixed solution on the micro-interdigitated electrode. In order to evaluate the humidity sensing performances, we measured current response using DC bias voltage under various relative humidity levels. The results show fast response / recovery time and marginal hysteresis as well as long-term stability. In addition, with the aid of micro-interdigitated electrode, we can reduce a total resistance of the sensor and increase the total reaction area of nanofibers across the electrodes resulting in high sensitivity and enhanced current level. Therefore, we expect that the electrospun nanofiber array for humidity sensor can be feasible and promising for diverse humidity sensing application.

• 한국화재소방학회논문지
• /
• 제27권3호
• /
• pp.72-79
• /
• 2013

최근 건축물은 재료의 고강도화 및 단면형상 최적화를 바탕으로 초고층화, 장대화 및 복합화 추세로 발달하고 있으나, 화재 위험성에 의한 구조적 거동에 관한 연구는 매우 미진한 실정이다. 특히 고강도 구조용 강재로 구성된 강구조 건축물의 구조부재에 대한 화재 노출 시 거동평가를 위한 기초적인 자료조차 거의 없는 실정이다. 따라서 본 연구에서는 고층 강구조 건축물에 활용되고 있는 고강도 구조용 강재의 고온 시 구조적 내력 평가를 위한 기계적 특성과 열적 특성 자료 도출을 목적으로 항복강도, 탄성계수 그리고 열전도율 등을 측정하고, 이를 일반 구조용 강재의 특성과 비교분석을 통하여 상대적 안전성을 평가한다.

• 동력기계공학회지
• /
• 제14권5호
• /
• pp.17-23
• /
• 2010

In recent, the capacity of a commercial wind power has reached the range of 6 MW, with large plants being built world-wide on land and offshore. The rotor blades and the nacelle are exposed to external loads. Wind power system concepts are reviewed, and loadings by wind and gravity as important factors for the mechanical performance of the materials are considered. So, the mechanical properties of fiber composite materials are discussed. Plain woven fabrics Carbon Fiber Reinforced Plastics (CFRP) are advanced materials which combine the characteristics of the light weight, high stiffness, strength and chemical stability. However, Plain woven CFRP composite have a lot of problems, especially delamination, compared with common materials. Therefore, the aim of this work is to estimate the mechanical properties using the tensile specimen and to evaluate strain using the CNF specimen on plain woven CFRP composites. For the strain, we tried to apply to plain woven CFRP using Digital Image Correlation (DIC) method and strain gauge. DIC method can evaluate a strain change so it can predict a location of fracture.

• 대한기계학회논문집A
• /
• 제26권4호
• /
• pp.587-595
• /
• 2002

Recent trend changes a criterion for evaluation of humors that environmental problems are raised as a global issue. Burners with higher thermal efficiency and lower oxygen in the exhaust gas, evaluated better. To comply with environmental regulations, burners must satisfy the NO/sub x/ and CO regulation. Consequently, 'good burner'means one whose thermal efficiency is high under the constraint of NO/sub x/ and CO consistency. To make existing burner satisfy recent criterion, it is highly recommended to develop a feedback control scheme whose output is the consistency of NO/sub x/ and CO. This paper describes the development of a real time flame diagnosis technique that evaluate and diagnose the combustion states, such as consistency of components in exhaust gas, stability of flame in the quantitative sense. In this paper, it was proposed on the flame diagnosis technique of burner using Neuro-Fuzzy algorithm. This study focuses on the relation of the color of the flame and the state of combustion. Neuro-Fuzzy loaming algorithm is used in obtaining the fuzzy membership function and rules. Using the constructed inference algorithm, the amount of NO/sub x/ and CO of the combustion gas was successfully inferred.

• Structural Engineering and Mechanics
• /
• 제68권6호
• /
• pp.721-733
• /
• 2018

The modal frequency responses of functionally graded (FG) sandwich doubly curved shell panels are investigated using a higher-order finite element formulation. The system of equations of the panel structure derived using Hamilton's principle for the evaluation of natural frequencies. The present shell panel model is discretised using the isoparametric Lagrangian element (nine nodes and nine degrees of freedom per node). An in-house MATLAB code is prepared using higher-order kinematics in association with the finite element scheme for the calculation of modal values. The stability of the opted numerical vibration frequency solutions for the various shell geometries i.e., single and doubly curved FG sandwich structure are proven via the convergence test. Further, close conformance of the finite element frequency solutions for the FG sandwich structures is found when compared with the published theoretical predictions (numerical, analytical and 3D elasticity solutions). Subsequently, appropriate numerical examples are solved pertaining to various design factors (curvature ratio, core-face thickness ratio, aspect ratio, support conditions, power-law index and sandwich symmetry type) those have the significant influence on the free vibration modal data of the FG sandwich curved structure.

• 한국수소및신에너지학회논문집
• /
• 제34권4호
• /
• pp.369-380
• /
• 2023

There is no clear standard for estimating the power distribution of fuel cells and batteries to meet the required power in hydrogen electric vehicles. In this study, a hydrogen electric vehicle simulation model equipped with a vehicle electric component model including a fuel cell system was built, and a power distribution strategy between fuel cells and batteries was established. The power distribution model was operated through two control strategies using step control and fuzzy control, and each control strategy was evaluated through data derived from the simulation. As a result of evaluation through the behavior data of state of charge, fuel cell current and balance of plant, fuzzy control was evaluated as a proper strategy in terms of control stability and durability.