• Computers and Concrete
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• 제27권2호
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• pp.99-109
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• 2021

Experimental and discrete element methods were used to investigate the effects of echelon non-persistent joint on the failure behaviour of joint's bridge area under uniaxial compressive test. Concrete samples with dimension of 150 mm×100 mm×50 mm were prepared. Uniaxial compressive strength and tensile strength of concrete were 14 MPa and 1MPa, respectivly. Within the specimen, three echelon non-persistent notches were provided. These joints were distributed on the three diagonal plane. the angle of diagonal plane related to horizontal axis were 15°, 30° and 45°. The angle of joints related to diagonal plane were 30°, 45°, 60°. Totally, 9 different configuration systems were prepared for non-persistent joint. In these configurations, the length of joints were taken as 2 cm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increase by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

• Journal of Genetic Medicine
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• 제15권2호
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• pp.72-78
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• 2018

Purpose: Physicians' attitudes may have a strong influence on women's decision regarding prenatal screening options. The aim of this study is to assess the physicians' attitudes toward prenatal screening for fetal aneuploidy including non-invasive prenatal testing (NIPT) in South Korea. Materials and Methods: Questionnaires were distributed and collected at several obstetrics-gynecological conferences and meetings. The questionnaire included 31 multiple choice and 5 fill-in-the-blank questions. Seven questions requested physicians' demographic information, 17 questions requested information about the NIPT with cell-free fetal DNA, and 12 questions requested information about general prenatal screening practices. Results: Of the 203 obstetricians that completed the survey. In contrast with professional guidelines recommending the universal offering of aneuploidy screening, only 53.7% answered that prenatal aneuploidy testing (screening and/or invasive diagnostic testing) should be offered to all pregnant women. Physicians tended to have positive attitudes toward the clinical application of NIPT as both primary and secondary screening methods for patients at high-risk for fetal trisomy. However, for patients at average-risk for fetal trisomy, physicians tended to have positive attitudes only as a secondary screening method. Physicians with more knowledge about NIPT were found to tend to inform their patients that the detection rate of NIPT is higher. Conclusion: This is the first study to investigate expert opinion on prenatal screening in South Korea. Education of physicians is essential to ensure responsible patient counseling, informed consent, and appropriate management after NIPT.

• 비파괴검사학회지
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• 제20권4호
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• pp.290-295
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• 2000

최근 역타시공법 등에 의한 콘크리트 구조물의 시공이 증가 추세에 있다. 이 경우, 자주 발생되는 신 구타설 콘크리트 시공이음부의 공극은 향후 구조물의 구조적인 특성과 내구성 등에 큰 영향을 미치게 된다. 그러나 현재 제안되고 있는 비파괴 검사법으로는 효과적으로 이음부 공극을 평가하기에 많은 한계가 있다. 본 연구에서는 시공이음부의 콘크리트 충전상태를 평가하기 위해 철골철근 콘크리트와 무근 콘크리트 시험체내에 공극을 모의제작한 후, 초음파속도 측정을 실시하고, 화상처리기법을 이용하여 비교적 용이하게 해석 가능한 방법에 대해 검토하였다.

• 한국지반공학회논문집
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• 제16권1호
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• pp.99-106
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• 2000

기존의 Oedometer 시험은 간단한 시험장치의 편리함으로 인해 널리 이용되어 왔다. 그러나 이 방법은 장시간의 시험기간, 각 단계 하중에서의 불규칙적인 응력상태, 매우 연약한 점토에 대한 시험의 어려움 및 시료의 포화문제와 같은 여러 문제점을 노출하게 되었다. 따라서 이런 단점을 보완 할 수 있는 시험 방법의 하나로 일정 변형률 압밀시험 이 개발되어 널리 이용되고 있다. 본 논문에서는 세가지 변형률을 이용한 CRS시험을 실시하였으며, 이 결과를 수정된 Wissa(1971)의 비선형 이론을 이용해 해석하고, 기존의 Oedometer시험 및 직접투수시험과 비교분석함으로서 CRS시험의 효율성 및 적용성 유무를 판단하고자 한다.

• Journal of Welding and Joining
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• 제32권5호
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• pp.50-57
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• 2014

Friction Stir Welding (FSW) is a complex process with several mutually interdependent parameters. A slight difference from known settings may lead to imperfections in the stirred zone. These inhomogeneities affect on the mechanical properties of the FSWed joints. In order to prevent the failure of the welded joint it is necessary to detect the most critical defects non-destructive. Especially critical defects are wormhole and lack of penetration (LOP), because of the difficulty of detection. Online thermography is used process-accompanying for defect detecting. A thermographic camera with a fixed position relating to the welding tool measures the heating-up and the cool down of the welding process. Lap joints with sound weld seam surfaces are manufactured and monitored. Different methods of evaluation of heat distribution and intensity profiles are introduced. It can be demonstrated, that it is possible to detect wormhole and lack of penetration as well as surface defects by analyzing the welding and the cooling process of friction stir welding by passive online thermography measurement. Effects of these defects on mechanical properties are shown by tensile testing.

• Smart Structures and Systems
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• 제19권5호
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• pp.513-521
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• 2017

The purpose of this paper is to study the capabilities of the impulse response method in length and flaw detecting for concrete piles and provide a suggested method to find small-size flaws in piles. In this work, wavelet transform is used to decompose the recorded time domain signal into a series of levels. These levels are narrowband, so the mix of different dominant bandwidths can be avoided. In this study, the impulse response method is used to analyze the signal obtained from the wavelet transform to improve the judgment of the flaw signal so as to detect the flaw location. This study provides a new way of thinking in non-destructive testing detection. The results show that the length of a pile is easy to be detected in the traditional reflection time or frequency domain method. However, the small flaws within pile are difficult to be found using these methods. The proposed approach in this paper is able to greatly improve the results of small-size flaw detection within piles by reducing the effects of any noise and clarifying the signal in the frequency domains.

• Computers and Concrete
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• 제15권3호
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• pp.473-484
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• 2015

In this study, the availability of Schmidt hammer has been investigated as a reliable method to determine the quality of concrete in irrigation networks. For this purpose, the 28-day compressive strength of concrete material used in the construction irrigation channel of Bafra lowland, which is one of the most fertile plains in Turkey was examined by means of concrete compression and as well as concrete Schmidt hammer in laboratory conditions. This study was carried out on cylindrical samples to represent the everyday concrete party ($150m^3$) produced by contractor firm as 3 replications. The statistical analysis of experimental data showed that the correlations between the values of 28-day compressive strength of Schmidt hammer and the rebound number was found to be 0.98. Differences of the compressive strength between compression testing and Schmidt hammer were statistically significant at P<0.01. In this context, it was found that the reliability of compressive strength of the concrete compression test are excellent, also the reliability of compressive strength of Schmidt hammer are fair in assessing the quality of concrete irrigation channels.

• Corrosion Science and Technology
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• 제2권6호
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• pp.266-271
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• 2003

Safety diagnosis of various structural components and facilities is indispensable for preventing catastrophic failure of material by time-dependent and environment accelerating degradation. Also, this diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive procedure and complex procedure of specimen sampling. So, a non-destructive and simple mechanical testing method using small specimen is needed. Therefore, an advanced indentation technique was developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. In this paper, we characterized the tensile properties including yield and tensile strengths of the V-modified Cr-Mo steels in petro-chemical and thermo-electrical plants. And also, the effects of hydrogen-assisted degradation of the V-modified Cr-Mo steels were analyzed in terms of work-hardening index and yield ratio.

• Interaction and multiscale mechanics
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• 제3권2호
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• pp.173-191
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• 2010

Damage detection plays a very important role to the maintenance of bridge structures. Traditional damage detection methods are usually based on structural dynamic properties, which are acquired from pre-installed sensors on the bridge. This is not only time-consuming and costly, but also suffers from poor sensitivity to damage if only natural frequencies and mode shapes are concerned in a noisy environment. Recently, the idea of using the dynamic responses of a passing vehicle shows a convenient and economical way for damage detection of bridge structures. Inspired by this new idea and the well-established tap test in the field of non-destructive testing, this paper proposes a new method for obtaining the damage information through the acceleration of a passing vehicle enhanced by a tapping device. Since no finger-print is required of the intact structure, this method can be easily implemented in practice. The logistics of this method is illustrated by a vehicle-bridge interaction model, along with the sensitivity analysis presented in detail. The validity of the method is proved by some numerical examples, and remarks are given concerning the potential implementation of the method as well as the directions for future research.

• 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.