• Journal of Industrial Technology
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• v.19
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• pp.75-79
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• 1999

Rotary bending fatigue tests were performed to investigate the effects of 2-phase matrix structure on fatigue limit with prepared specimens in high strength ductile irons. Two types of the specimens with different microstructures have been used. Series A has sorbite and series B has bainite. Fatigue limits of both specimens are improved comparing with as cast specimen. The fatigue limit is higher in series B than in series A. The reason why the fatigue limit of series A shows inferiority to that of series B is due to the transition of micro fatigue cracks to mesocrack occurs very rapidly, so increased stress intensity factor drives the fatigue crack growth. The higher fatigue limit of series B which has bainite is caused by the ${\gamma}$ layer contained in microstructure impede the rapid growth of micro fatigue crack to mesocrack and ${\alpha}$ layer around graphite has the higher capacity for the absorption of plastic deformation energy than sorbite.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.847-854
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• 2007

The battery electrode of a mobile phone is made of layered polymer coated on aluminum foils and the hot rolling process is applied to increase the density per volume of an electrode for a high capacity battery. The flatness of batteries surfaces should be less than $2{\mu}m$. To satisfy the required flatness, the deformation of roll surface due to bending and heating of the roll should be minimized. Complicated hot oil paths of $100^{\circ}C$ inside the roll are required for heating the polymer layers. FEA was used to calculate thermal deformations and temperatures distributions of the roller. Based on FEA, a modified surface curvature called a crown roll was suggested and this gave the area of 30% improved flatness compared with a flat roll. The flat roll satisfied the flatness of $2{\mu}m$ in the length of 340 mm and the crown roll resulted in the longer length of 460 mm. Experiments to measure the temperature distribution and thermal strain were performed and compared with FEA. There were only 6% difference between two results.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.51-60
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• 2018

The foundations are classified into shallow and deep, which have important differences: in terms of geometry, the behavior of the soil, its structural functionality, and its constructive systems. The shallow foundations may be of various types according to their function; isolated footings, combined footings, strip footings, and slabs foundation. The isolated footings are of the type rectangular, square and circular. The combined footing may be rectangular, trapezoidal or T-shaped in plan. This paper presents a new model for T-shaped combined footings to obtain the most economical contact surface on the soil (optimal dimensioning) to support an axial load and moment in two directions to each column. The new model considers the soil real pressure, i.e., the pressure varies linearly. The classical model uses the technique of test and error, i.e., a dimension is proposed, and subsequently, the equation of the biaxial bending is used to obtain the stresses acting on each vertex of the T-shaped combined footing, which must meet the conditions following: The minimum stress should be equal or greater than zero, and maximum stress must be equal or less than the allowable capacity that can withstand the soil. To illustrate the validity of the new model, numerical examples are presented to obtain the minimum area of the contact surface on the soil for T-shaped combined footings subjected to an axial load and moments in two directions applied to each column.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.24-35
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• 2014

An experimental study on the structural behavior of connection types between approach slab and integral abutment has been done for three typical bar connections. Typical hinge style reinforcing bar detail for its connection is preferred in order to accommodate rotation of the approach slab among engineers. However, the straight horizontal bars can be used as connection detail accomodate structural capacity. Total six specimens with three types of rebar detail are tested for direct tensile and bending load. The characteristic structural behaviors are carefully monitored and all the strain gauge data obtained are analyzed. It is shown that the structural performance of all the specimens well exceed its design allowance. Several design suggestions are given based on careful reviews on the experiment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5392-5395
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• 2013

Application of electric wheelchair, sort of wheelchair which is playing important role in transporting patients and old people, has been increasing. In this study, we designed the electric wheelchairs' driving system. Using the multi-step gear, the driving system can get great power, even though the small capacity of motors. First, we designed the multi-step gear, test its bending strength and contact strength, as well as verified its performance. We installed 'B-type electric brake(Multiple plate clutch, Anti-magnetization) in same axle of the driving system, so it is possible to stop under huge torque and small size. Using this driving system of the multi-step gear which we designed, it's possible to improve driving gear efficiency 30% up and create the high-competitive electric wheelchair. And, it is easy to repair and control.

• Structural Engineering and Mechanics
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• v.16 no.4
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• pp.371-390
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• 2003

The concept of the seismic slit shear wall was proposed in the early 1990's. A series of experimental and theoretic studies on the wall with reinforced concrete short connecting beams cast in the slit were carried out. In this paper another type of slit shear wall is studied. It is one with vertical slit purposely cast within the wall, and the rubber belt penetrated by a part of web shear reinforcement as seismic energy-dissipation device is filled in the slit. Firstly, an experiment under cyclic loading was carried out on two shear wall models, one slit and the other solid. The failure mechanism and energy-dissipation capacity are compared between the two different models, which testifies the seismic performance of the slit wall improved significantly. Secondly, for engineering practice purpose, a macroscopic analytical model is developed to predict the nonlinear behavior of the slit shear wall under cyclic loading. The mechanical properties of each constituent elements of this model are based on the actual behavior of the materials. Furthermore, the effects of both the axial force and bending moment on the shear behavior are taken into account with the aid of the modified compression-field theory. The numerical results are verified to be in close agreement with the experimental measurements.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1193-1219
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• 2015

The purpose of this study is to evaluate the seismic performance of high-rise reinforced concrete (RC) box-type wall structures commonly used for most residential buildings in Korea. For this purpose, an analytical model was calibrated with the results of the earthquake simulation tests on a 1:5 scale 10-story distorted model. This calibrated model was then transformed to a true model. The performance of the true model in terms of the stiffness, strength, and damage distribution through inelastic energy dissipation was observed with reference to the earthquake simulation test results. The model showed high overstrength factors ranging from 3 to 4. The existence of slab in this box-type wall system changed the main resistance mode in the wall from bending moment to tension/compression coupled moment through membrane actions, and increased the overall resistance capacity by about 25~35%, in comparison with the common design practice of neglecting the slab's existence. The flexibility of foundation, which is also commonly neglected in the engineering design, contributes to 30~50% of the roof drift in the stiff direction containing many walls. The possibility of concrete spalling and reinforcement buckling and fracture under the maximum considered earthquake (MCE) in Korea appears to be very low when compared with the case of the 2010 Concepcion, Chile earthquake.

• Structural Engineering and Mechanics
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• v.41 no.4
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• pp.509-525
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• 2012

In recent years, CFRP material usage in strengthening applications gradually became widespread. Especially, the studies on the strengthening of shear deficient reinforced concrete beams with CFRP strips are chosen as a subject to numerous experimental studies and research on this subject are increased rapidly. The most important variable, that is affected on the failure mode of CFRP strips and that is needed for determining the shear capacity of the strengthened reinforced concrete beams, is the strain distribution between CFRP strips and concrete. Numerous experimental studies are encountered in the literature about the determination of strain distribution between CFRP strips and concrete. However, these studies mainly focused on the CFRP strips under axial tension. There are very limited numbers of experimental and analytic studies examining the strain distribution between concrete and CFRP strips, which are under combined stresses due to the effects of shear force and bending moment. For this reason, existing experimental study in the literature is used as model for ANSYS finite element software. Nonlinear finite element analysis of RC beams strengthened against shear with CFRP strips under reverse cyclic loading is performed. The strain distributions between CFRP strips and concrete that is obtained from finite element analysis are compared with the results of experimental measurements. It is seen that the experimental results are consisted with the results derived from the finite element analysis and important findings on the strain distribution profile are reached by obtaining strain values of many points using finite element method.

• Journal of Power System Engineering
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• v.14 no.5
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• pp.17-23
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• 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.