• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.5 s.39
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• pp.35-43
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• 2004

Small-scale models have been frequently used for seismic performance tests because of limited testing facilities and economic reasons. However, there are not enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry is not well consistent in the inelastic seismic behavior. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to aggregate size. Therefore, it is desirable that different material is used for small-scale models. Thus, a modified similitude law could be derived depending on geometric scale factor, equivalent modulus ratio and ultimate strain ratio. In this study, compressive strength tests are conducted to analyze the equivalent modulus ratio of micro-concrete to normal-concrete. Then, equivalent modulus ratios are divided into multi-phase damage levels, which are basically dependent on ultimate strain level. Therefore, an algorithm adaptable to the pseudodynamic test, considering equivalent multi-phase similitude law based on seismic damage levels, is developed. Test specimens, consisted of prototype structures and 1/5 scaled models as a reinforced concrete column, were designed and fabricated based on the equivalent modulus ratios already defined. Finally quasistatic and pseudodynamic tests on the specimens are carried out using constant and variable modulus ratios, and correlation between prototype and small-scale model is investigated based on their test results. It is confirmed that the equivalent multi-phase similitude law proposed in this study could be suitable for seismic performance tests on small-scale models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.116-124
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• 2015

The objective of this study is to evaluate the effects of the replacement levels of grinded fly-ash on the repaired mortar based on a polymer. The main parameters are the curing temperature and replacement levels of grinded fly-ash. The curing temperature and the replacement levels of grinded fly-ash are varied at $40^{\circ}C$, $20^{\circ}C$ and $5^{\circ}C$, and between 0% and 35% of the total binder by weight, respectively. The flow in fresh mortar and compressive strengths according to ages, the relationship of stress-strain, elastic modulus and modulus rupture in hardened mortar, as well as scanning the electron microscopy and the X-ray diffraction of mortar, were measured, respectively. The test results showed that the flow, elastic modulus and modulus rupture are great in mortar specimens with 20~30% of the replacement levels of grinded fly-ash. In addition, compressive strengths according to ages were affected by the replacement levels of grinded fly-ash and the curing temperature indicated that the strength development ratio of mortar with 20% of the replacement levels of grinded fly-ash was greater than others. In the prediction of the compressive strength specified by the ACI 209 code, the strength development at an early and late age can be generalized by the functions of the replacement levels of grinded fly-ash and the curing temperature. In the analysis of scanning the electron microscopy and the X-ray diffraction, the number and intensity of peaks increased and the form of CSH gels on the surface of the particle of grinded fly-ash was observed.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.689-697
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• 2002

The dynamic loads and load-point displacements of concrete three-point bend (TPB) specimens had been measured. The average crack velocities measured with strain gages were 0.16 ㎜/sec ∼ 66 m/sec. The fracture energy for crack extension was determined from the difference of the kinetic energy for the load-point velocity and the strain energy without permanent deformation from the measure external work. For all crack velocities, there were micro-cracking for 23 ㎜ crack extension, stable cracking for 61 ㎜ crack extension at the maximum strain energy, and then unstable cracking. The unstable crack extension was arrested at 80 ㎜ crack extension except the tests of 66 m/sec crack velocity. The tests less than 13 ㎜/sec crack velocity and faster than 1.9 m/sec showed static and dynamic fracture behaviors, respectively. In spite of much difference of the load and load-point displacement relations for the crack velocities, the crack velocities of dynamic tests did not affect on fracture energy rate during the stable crack extension due to the reciprocal action of kinetic force, crack extension and strain energy. During stable crack extension, the maximum fracture resistances of the dynamic tests was 147％ larger than that of the static tests.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.143-143
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• 2017

CrAlN 코팅은 높은 경도, 낮은 표면 조도 등의 상온에서의 우수한 기계적 특성 이외에 고온에서 안정한 합금상의 형성으로 인하여 우수한 내산화성 및 내열성을 보유하여 공구 코팅으로의 적용 가능성이 크다. 그러나 최근 공구사용 환경의 가혹화로 인하여 코팅의 내마모성 및 내열성 등의 물성 향상을 통한 공구의 수명 향상이 필요시 되고 있으며, 다양한 코팅 물질을 활용하여 다층 코팅을 합성함으로써 난삭재용 공구 코팅의 물성을 높이는 연구들이 진행되고 있다. 본 연구에서는 CrAlN 코팅과 WC-Co 6wt.% 모재 사이에 CrZrN, CrN, CrN/CrZrSiN 등의 중간층을 합성하여 CrAlN 코팅의 상온 및 고온 특성을 향상시키는 연구가 진행되었다. 합성된 코팅의 구조 및 물성을 분석하기 위해 field emission scanning electron microscopy(FE-SEM), nano-indentation, atomic force microscopy(AFM) 및 ball-on-disk wear tester를 사용하였다. 코팅의 고온 특성을 확인하기 위해 코팅을 furnace에 넣어 공기중에서 30분 동안 annealing 한 후에 nano-indentation을 사용하여 경도를 측정하였고, $500^{\circ}C$ annealing 코팅의 표면 조도 분석 및 $500^{\circ}C$에서 마찰마모시험을 실시하였다. CrAlN 코팅의 상온 특성을 분석한 결과, 모든 코팅의 경도(35.5-36.2 GPa)와 탄성계수(424.3-429.2 GPa)는 중간층의 종류에 상관없이 비슷한 값을 보인 것으로 확인됐다. 그러나, CrN/CrZrSiN 중간층을 증착한 CrAlN 코팅의 마찰계수는 0.33로 CrZrN 중간층을 증착한 CrAlN 코팅의 마찰계수(0.41)에 비해 향상된 값 보였으며, 코팅의 마모율 및 마모폭도 비슷한 경향을 보인 것으로 보아 코팅의 내마모성이 향상된 것으로 판단된다. 이것은 중간층의 H/E ratio가 코팅의 내마모성에 미치는 영향에 의한 결과로 사료된다. H/E ratio는 파단시의 최대 탄성 변형율로써, 모재/중간층/코팅의 H/E ratio 구배에 따라 코팅 내의 응력의 완화 정도가 변하게 된다. WC 모재 (H/E=0.040)와 CrAlN 코팅(H/E=0.089) 사이에서 CrN, CrZrSiN 중간층의 H/E ratio는 각각 0.076, 0.083 으로 모재/중간층/코팅의 H/E ratio 구배가 점차 증가함을 확인 할 수 있었고, 일정 응력이 지속적으로 가해지면서 진행되는 마모시험중에 CrN과 CrZrSiN 중간층이 WC와 CrAlN 코팅 사이에서 코팅 내부의 응력구배를 완화시키는 역할을 함으로써 CrAlN 코팅의 내마모성이 향상된 것으로 판단된다. 내열성 시험 결과, CrN/CrZrSiN 중간층을 증착한 코팅은 $1,000^{\circ}C$까지 약 28GPa의 높은 경도를 유지한 것으로 확인 되었다. $500^{\circ}C$ annealing 후 진행된 표면 조도와 마모시험 결과, 모든 코팅의 조도 값 및 마찰계수는 상온 값에 비해 증가하였으며 CrN/CrZrSiN 중간층을 증착한 CrAlN 코팅의 변화량이 가장 낮은 값을 보였다. 이는 CrZrSiN 중간층 내에 존재하는 $SiN_x$ 비정질상이 고온 annealing시에 산소 차폐막 역할을 하여, 코팅내의 잔류 산소에 의한 산화작용을 효과적으로 방지함으로써 코팅의 고온 특성이 향상된 것으로 판단된다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.1
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• pp.33-40
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• 1994

Effects of blanching on protein composition and texture in geoduck muscle during frozen storage at $-20^{\circ}C$ were investigated. In frozen muscle, sarcoplasmic protein and myofibrillar protein were decreased, while alkali-soluble protein increased rapidly. During the storage of the blanched muscle(at $95^{\circ}C$ for 2 min.), sarcoplasmic and myofibrilla protein showed slow decreases. The muscle blanched for 2 min(BM) showed the best texture among the samples treated with various blanching times(at $95^{\circ}C$ for 1, 2, 3, and mins). In comparing the textures of BM with raw muscle, hardness of BM was similar raw muscle, and elasticity and stress relaxation of BM revealed lower levels than those of raw muscle, but break elongation and toughness were higher. In the changes of texture of raw muscle and BM during the frozen storage, as the storage time lengthened, hardness and toughness of both muscles were stronger, and both stress relaxations showed greatly decreases during initial storage(7 days), and break elongation level of raw muscle showed rapid increases in 100 days but there were no changes in that of BM, Elasticity of raw muscle gradually reduced during storage while that of BM increased.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.4
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• pp.147-154
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• 1996

This study wag performed to evaluate the engineering properties of permeable polymer concrete with stone dust and fly ash and unsaturated polyester resin. The following conclusions were drawn. 1. The highest strength was achieved by stone dust filled permeable polymer concrete, it was increased 17% by compressive strength, 188% by bending strength than that of the normal cement concrete, respectively. 2. The water permeability was in the range of 3.O76~4.152${\ell}/ cm{^2}/h$, and it was largely dependent upon the mix design. These concrete can be used to the structures which need water permeability. 3. The static modulus of elasticity was in the range of $1.15{\times} 10^5kg/cm^2$, which was approximately 53 56% of that of the normal cement concrete. 4. The poisson's number of permeable polymer concrete was in the range of 5.106~5.833, which was less than that of the normal cement concrete. 5. The dynamic modulus of elasticity was in the range of $1.29{\times} 10^5~1.5{\times} 10^5 kg/cm^2$, which was approximately less compared to that of the normal cement concrete. Stone dust filled permeable polymer concrete was showed higher dynamic modulus. The dynamic modulus of elasticity were increased approximately 7~13% than that of the static modulus. 6. The compressive strength, bending strength, elastic modulus, poisson's ratio, longitudinal strain and horizontal strain were decreased with the increase of poisson's number and water permeability at those concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.125-134
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• 1990

In order to utilize coal ash, which we go to great expense to scrap, as subba se course material, this study attempts to examine the deformation characteristics of coal ash with the addition of some cement when repeated loads are applied. The material of coal ash is obtained from Young dong and Youngwol thermal power plant. The results are : Unconfined compression strength shows rectilineal increase in propotion to the cement addition ratio. Within the scope of repeated loads of experimental condition, modulus of elasticity tends to decrease while compression strength shows about 21% increase.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.625-634
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• 1986

The strain distribution on a welded aluminum alloy transition joint produced by a static tensile load has been measured using a moire method combined with photoelastic coating method. The test specimens were made of aluminum alloy 6061-T6 and 2014-T6 butt welded with ER-4043 filler metal, and were post welded heat treated (solid solution heat treatment 502.deg. C 70min.) and precipitated (artificial aging 171.deg. C 600min.) to cause an abrupt change of mechanical properties between the base metals and weld metal. The photoelastic epoxy rubber was cemented on the specimen grating which had been reproduced on the specimen surface by using an electropolishing. The measurements were compared with strains computed by Finite Element Analysis. The following results were abtained. (1) The maximum strain were distributed along the center line in the transverse directiion of the weld metal. (2) The strain gradient along the fusion line increased approaching the V-groove tip and the maximum value was observed at a quarter of width from the V-groove tip. (3) The moire method combined with photoelastic coating was proved very useful for real time strain measurement in the welded aluminum alloy transition joint.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.636-642
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• 1989

In this paper, 3-dimensional fracture phenomena in the local area near the notch tip between the surface and the center of a composite bar which is consisted of two different materials were investigated by using embedded dyeing grids with the pitch of 50.8.mu. It was confirmed that the maximum strain near the notch tip occurred not at the notch front but at the curvature beginning point of the notch which is in the interior of z/W = 0.3 - 0.35 from the surface and a notch was initiated from that point. And that the strain near the notch front between the center and z/W = 0.65 - 0.7 toward the surface was in a state of compression.

• Journal of Korean Association for Spatial Structures
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• v.9 no.2
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• pp.77-82
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• 2009

ETFE is the abbreviation of Ethlene Tetra Fluoro Ethlene, a sort of colorless and transparent granules. The advantage of ETFE film has chemical resistance, anti-stick property, very lightly material. The thickness of ETFE film is used to from 50 ${\mu}m$ to 300 ${\mu}m$ and have superior ability of daylight transmission and elongation, while the strength is lower than of fabric membrane. The tensile strength of ETFE film changes from 40Mpa to 60Mpa and the tensile strain at break can get to about 300-400%. The mechanical characteristic test of ETFE film is described in this paper. The tensile strain at break, the tensile strength and the stress-strain curve are obtained from the test. And then it was analyzed stress-strain characteristic by temperature and mechanical characteristic by cycling load.