• Journal of Welding and Joining
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• 제33권3호
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• pp.25-31
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• 2015

Due to environmental regulations (RoHS, WEEE and ELV) of the European Union, electronics and automotive electronics have to eliminate toxic substance from electronic devices and system. Specifically, reliability issue of lead-free solder joint have an increasing demand for the car electronics caused by ELV banning. The authors prepared engine control unit and cabin electronics soldered with Sn-3.0Ag-0.5Cu (SAC305). To compare with the degradation characteristics of solder joint strength, thermal cycling test (TC), power-thermal cycling test (PTC) and series tests were conducted. Series tests were conducted for TC and PTC combined stress test using the same sample in sequence and continuously. TC test was performed at $-40{\sim}125^{\circ}C$ and soak time 10 min for 1000 cycles. PTC test was applied by pulse power and full function conditions during 100 cycles. Combined stress test was tested in accordance with automotive company standard. Solder joint degradation was observed by optical microscopy and environment scanning electron microscopy (ESEM). In addition, to compare with deterioration of bond strength of quad flat package (QFP) and chip components, we have measured lead pull and shear strength. Based on the series test results, consequently, we have validated of series test method for lifetime and reliability of Pb-free solder joint in automotive electronics.

• KSBB Journal
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• 제17권6호
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• pp.549-554
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• 2002

한지로 된 고서적의 가수분해가 Trichoderma viride로부터 분리한 endoglucanase I, exoglucanase II와 endo-exo혼합효소 (I：I, weight ratio)에 의하여 수행되었다. Endoglucanase I, exoglucanase II와 endo-exo혼합효소에 의한 가수분해 최적pH는 각각 4.5, 5.5, 5.0으로 나타났다. 이들 결과들은 지류문화재의 열화가 산성조건에서 셀룰라아제의 활성을 증가시켜 촉진될 수 있음을 보여준다. 또한 이들 효소들에 의한 분해에 있어서 최적 분해온도는 모두 5$0^{\circ}C$를 보여주었다. 고서적의 재생펄프를 이들 효소로 처리했을 때 수율(yield)과 물리적 강도(physical strength)를 살펴보면, 수율은 이들 효소의 농도 증가와 함께 감소함을 보여 주었다. 특히 endo-exo혼합효소로 처리했을 때 가장 낮은 값을 보여 주었다. 이는 endo성분과 exo성분의 협동작용(synergistic action)에 의한 것으로 생각할 수 있다. 물리적 강도는 exo II로 처리했을 경우 농도 증가에 따라 향상됨을 보여 주었으며, exoglucanase II와 endo-exo혼합효소로 처리했을 경우는 농도에 따라 감소함을 보여 주었다. 이들 결과들은 고서적의 분해(열화)가 endoclucanase에 의한 것임을 보여 준다. 즉 지류문화재의 물리적 강도를 저하시키는 주요 성분 효소는 endoglucanase이며 지류문화재의 효과적인 보존을 위해서는 endoglucanase성분의 활성을 억제시킬 필요가 있다.

• 한국구조물진단유지관리공학회 논문집
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• 제16권3호
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• pp.1-10
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• 2012

FRP 재료는 높은 부식저항성과 강도에도 불구하고 지난 20여년 동안 심각한 환경적 노출에 의한 재료의 성능저하에 대한 문제가 제기되어 왔다. 본 연구에서는 섬유와 수지로 구성된 이질재료인 FRP보강근이 온도와 화학적 노출을 복합적으로 받는 경우에 대하여 실험적으로 분석하였다. 각기 다른 형상으로 제작된 탄소, 유리 및 하이브리드 FRP 보강근 5종류에 대하여 중량변화, 계면전단강도(ILSS), SEM 및 FT-IR분석을 수행하였으며, 모든 FRP 실험편은 최대 150일까지 알칼리 용액과 증류수에 침지시킨 다음 60, 100, 150 및 300도의 온도에서 30분동안 노출하였다. 실험결과, 또한 FRP 보강근의 성능저하는 섬유의 종류뿐 아니라 수지의 종류와 제조과정에 따라 영향을 받는 것으로 관찰되었다. 침지 초기에는 ILSS 강도가 약간 증가한 후 시간경과에 따라 강도가 감소하는 것으로 나타났다. 알칼리 용액과 증류수 용액에 의해 손상을 받은 ILSS의 차이는 무시할 수 있는 수준인 것으로 관찰되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.337-342
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• 1994

This experimental study is aiming to investigate the hysteritic behavior of high-strength R/C columns subjected to axial load and lateral load reversals. The five 1/4 scaled specimens were made of high-strength concrete with the design strength load(n=0.2f'cAg, n=0.4f'cAg) and type of transverse reinforcement. From the test results, strength and stiffness degradation of columns under higher axial load is much more serious than that under lower axial load. ductility of columns is enhansed with increasing amount of transverse reinforcement, shear strength is depended on the level of axial load.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.392-395
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• 2004

When a concrete member is damaged by fire accident, it can lose its strength. And the degradation rate of losing its strength affected by many environmental conditions. But there is few research for equation for strength evaluation of fire-damaged concrete. Besides, it is impossible to destruct structural member from the building for the evaluation. So, I will suggest a new equation for strength evaluation of fire-damaged RC beam using non-destructive test. For this purpose, the researchers are exploring the performance of non-destructive testing methods using Ultrasonic test, Schmidt Hammer test and Coring test against fire damaged concrete specimen.

• International Journal of Concrete Structures and Materials
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• 제2권2호
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• pp.115-122
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• 2008

Ductility is important in the design of reinforced concrete structures. In seismic design of reinforced concrete members, it is necessary to allow for relatively large ductility so that the seismic energy is absorbed to avoid shear failure or significant degradation of strength even after yielding of reinforcing steels in the concrete member occurs. Therefore, prediction of the ductility should be as accurate as possible. The principal aim of this paper is to present the basic data for the ductility evaluation of reinforced high-strength concrete beams. Accordingly, 23 flexural tests were conducted on full-scale structural concrete beam specimens having concrete compressive strength of 40, 60, and 70MPa. The test results were then reviewed in terms of flexural capacity and ductility. The effect of concrete compressive strength, web reinforcement ratio, tension steel ratio, and shear span to beam depth ratio on ductility were investigated experimentally.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.69-84
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• 2017

This paper presents results of an experimental investigation on the behaviour of bond between external glass fibre reinforced polymer reinforcement and concrete exposed to three different environmental conditions, namely, temperature cycles, wet-dry cycles and outdoor environment separately for extended durations. Single shear tests (pull-out test) were conducted to investigate bond strengths (pull-out strengths) of control (unexposed) and exposed specimens. Effect of the exposure conditions on the compressive strength of concrete were also investigated separately to understand the effect of changing concrete compressive strength on the pull-out strength. Based on the comparison of experimental results of exposed specimens to control specimens in terms of bond strengths, failure modes and strain profiles, the most significant degradation of pull-out strength was observed in specimens exposed to outdoor environment, whereas temperature cycles did not cause any deterioration of strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.349-352
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• 2004

In this study, a strut-and-tie models for the coupling beam based on deformations are presented. To design shear-dominated R/C coupling beams, it is important to consider shear strength deterioration with required deformations. This study proposes the method of estimating shear strength of the reinforced concrete coupling beams. The proposed method determines the strain states from target displacements based on the nonlinear truss analysis. The estimated horizontal strain of beam is then used in calculating the strength of the diagonal strut with compatibility conditions. The deterioration of shear strength of the coupling beam depends on the strength degradation of struts due to plastic deformations.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 추계 학술논문 발표대회
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• pp.137-138
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• 2017

Generally, a lot of reinforcements are used in nuclear power plant concrete structures in order to improve the structural safety, but it may cause several potential problems due to the overcrowded reinforcement, such as the degradation of concrete quality, the construction delay and the increase of construction cost. In order to resolve these problems, structural test researches and code change studies on using high-strength reinforcement (Gr.80) in unclear power plant structures are under way, and there is good progress in code change of ASM BPVC.III.2 and ACI 349. This purpose of this study is to review the code change status ASM BPVC.III.2, ACI 349 under way to use the high-strength reinforcement in nuclear power plant structures. Also I will introduce the design optimization of NPP structures with high-strength reinforcements in order to maximize the effect and minimize the problem when using the high-strength reinforcements in NPP structures.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 가을 학술논문 발표대회
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• pp.165-166
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• 2022

In this paper, the characteristics of slag cement mortar added with neutralized liquid red mud with nitric acid to reduce pH by neutralizing liquid red mud with nitric acid were reviewed to improve strength degradation of cement concrete added with liquid red mud. As a result, the compressive strength of cement mortar added with liquid red mud was higher than that of Plain on 1 and 3 days, and the strength of red mud neutralized with nitric acid was lower than that of cement mortar added with liquid red mud on 7 days, but the strength was recovered on 28th. It was found that the addition of red mud has the effect of improving the strength in the early age.