• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.97-105
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• 2001

현장타설말뚝의 건전도 평가에서 충격반향, 충격응답기법과 같은 비검측공 시험법을 적용하는 사례가 점차로 증가되는 추세에 있다. 비검측공시험법의 적용성을 체계적으로 평가하기 위해 수행된 일련의 연구결과 중에서 본 논문에서는 시험법의 결함탐지 능력을 평가하기 위해 수행된 해석적 연구결과에 관해 논한다. 이 연구에서는 시험법의 결함탐지능력에 대한 제반 영향인자 중에서 결함의 유형, 위치 및 크기의 영향을 평가하고자 하였다. 이를 위해서 여러 가지 조건에서 말뚝머리에 작용하는 충격하중에 대한 흙-말뚝 구조의 동적응답을 ABAQUS를 이용한 유한요소법으로 해석하였다. 이로부터 얻은 신호를 충격반향 혹은 충격응답기법으로 처리.분석하여 각 시험법의 결함탐지 능력을 평가해 보았다. 연구결과 이들 두 기법 모두 결함의 위치와 유형은 비교적 정확하게 탐지하는 것으로 나타났다. 그러나 충격응답기법을 이용하여 추정한 결함 크기는 신뢰도가 매우 낮았다. 이 문제를 해소하여 시험법의 적용성을 향상시키기 위해서는 측정된 동적응답신호를 이용하여 적절한 역계산 기법을 개발하여 적용할 필요가 있다는 결론을 얻었다.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.111-120
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• 2003

A new stress path test method, which is more suitable f3r evaluating settlements of clay deposits, was introduced. This new method is basically based on back pressure equalization concept and makes it possible to estimate deformations corresponding to all points on a specific stress path by only one test. As a result, deformation characteristics of a clay deposit can be predicted by a few tests and the more practical application of stress path method can be realized. In addition, anisotropic deformation behaviors following arbitrary stress paths also can be experimentally measured by this test method. Experimental applicability of the proposed method was confirmed by performing various stress path tests on remolded kaolinite samples and the actual process to evaluate overall deformation characteristics and settlements was also presented.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.3-3
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• 1998

KF-16 항공기용 F100-229 엔진 부품 중 국내에서 생산되는 부품에 대한 초도품 품질보증방법의 일환으로 내구성시험을 국내에서 수행하였다. 그동안 국내에서의 항공기 엔진산업은 사용중인 엔진의 정비 혹은 민항기 엔진 일부 부품을 기계 가공하여 납품하는 수준이었으므로 특별한 품질보증 시험이 요구되지 않았으나, KFP 사업을 시작하면서 일부 주요부품은 국내에서 직접 생산하여 KF-16 항공기용 엔진에 장착하게 되므로 완제 엔진을 조립 생산할 수 있는 능력의 확보뿐만 아니라 적절한 품질보증 대책이 요구되었다. 이에 따라 국내 생산된 완제 엔진의 조립성과 일부 단품에 대한 품질보증 확보방안으로 엔진의 개발 및 부품개량시 설계수명 및 설계규격의 만족여부를 검증하는 시험인 엔진 내구성시험(Engine Accelerated Mission Test)기법을 적용하여 1차와 2차에 걸쳐 품질보증시험을 수행하였다. 시험결과 완제 엔진의 조립성, 추진성능, 부품의 내구도 확인에 의한 품질보증 적합성 여부를 확인할 수 있었으며, 본 시험평가 기법을 통하여 시험 후 부품의 검사 및 평가방법과 기준을 제시하였고, 군용 엔진 내구성시험의 요구조건, 시험절차, 시험항목 등을 확립하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.39-47
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• 2005

An acoustic emission technique is applied to the tensile tests of the plastic specimen under the different test speeds and the structural integrity evaluation of the plastic shell structure. Several AE characteristics are acquired from the tensile tests and they are proven to be useful parameters in evaluating its structural integrity. The results shows that tensile strength has almost constant value over some higher speed region while revealing some increasing tendency in strength as the test speeds up in lower speed region. The crack initiation loads and locations are accurately evaluated during the static compression testing of the plastic shell structures by using acoustic emission technique.

• 기계와재료
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• v.21 no.3
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• pp.6-19
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• 2009

소비자의 요구수준 향상으로 제품의 구조 및 성능이 점점 복잡해지고 부품수는 증가함에 따라, 시스템을 구성하는 부품의 고장발생으로 인한 경제적 손실예방, 안전성 확보 등을 위하여 신뢰성 중심의 종합적인 품질보증에 대한 요구가 점점 증대되고 있다. 본 글에서는 이러한 구성부품의 신뢰성 제고를 위하여 신뢰성평가센터가 2000년부터 현재까지 약 10년 동안 지속적으로 수행하고 있는, 기본 성능시험을 비롯한 내환경성시험, 안정성시험, 수명시험 등의 종합적이고 체계적인 신뢰성 시험평가와 신뢰성인증 시스템에 대하여 고찰하고, 그 과정에서 독창적으로 정립한 13단계의 한국적 신뢰성 인증기법에 대해 설명하고자 한다.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.309-323
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• 2005

Dynamic stiffness of subsurface materials is one of the most important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various borehole seismic testing techniques have been, thus, developed and used during past several decades. Moreover, recent rush of underground-space projects and increasing size of structures put more stress on reliable site investigation techniques in estimating stiffness of rock mass. In this paper, a new technique called 'in-hole seismic test' has been implemented to measure the dynamic stiffness of rock masses at subsurface foundations and tunnel-faces. The reliance of in-hole seismic test was evaluated by comparing the testing results at several rock sites with those of other borehole techniques and the technique tunnls out to be an efficient and accurate in-situ testing technique.

• Journal of the Korean GEO-environmental Society
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• v.2 no.4
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• pp.5-14
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• 2001

The NDT(Non-Destructive Testing) technique, detecting defects without damaging foundations, has, lately, been a matter of concern. In this study, the applicability of the borehole methods(CSL, CT, PS) and the surface reflection methods(SE, IR) to the evaluation of integrity of drilled shaft was investigated through field test. Ten drilled shafts, 0.4 m in diameter and 7.0 m long each, were constructed, one shaft with no defect and nine shafts intentionally with the combination of the common defects such as soft bottom, necking, bulging, cave-in, and/or weak concrete. Analysing each NDP test result on the constructed drilled shafts, an optimum combination of the NDP methods as well as the applicability of each NDP method to detecting defects of drilled shaft have been investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.8
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• pp.780-788
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• 2009

AE technique was applied to the static structural test of the composite wing structure to evaluate the structural integrity and damage. During the test, strain and displacements measurement technique were used to figure out for static structural strength. AE parameter analysis and source location technique were used to evaluate the internal damage and find out damage source location. Design limit load test, the 1st and 2nd design ultimate load tests and fracture test were performed. Main AE source was detected by an sensor attached on skin near by front lug. Especially, at the 1st design ultimate test, strain and displacements results didn't show internal damage but AE signal presented a phenomenon that the internal damage was formed. At the fracture test, AE activities were very lively, and strain and displacements results showed a tendency that the load path was changed by severe damage. The internal damage initiation load and location were accurately evaluated during the static structural test using AE technique. It is certified from this paper that AE technique is useful technique for evaluation of internal damage at static structural strength test.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.207-218
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• 2013

One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.17-25
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• 2005

The bender element method is an experimental technique to determine very small strain ($<10^{-3}\%$), elastic shear modulus of a soil, $G_{max}$ by measuring the velocity of shear wave propagation through a sample. Bender elements have been applied as versatile transducers to measure small strain modulus of wet or dry soils in various laboratory apparatus. In this paper, bender element (BE), resonant column (RC) and torsional shear (TS) tests were performed on Toyoura sand at various testing conditions using the modified Stokoe type RC/TS testing equipment capable of performing BE test. Based on the results, applicabilities of the testing method using bender element were evaluated by comparing the values of $G_{max}$ obtained from RC/TS and BE testing methods. For more dependable evaluation, the loading frequency of each testing method was considered for the results obtained for samples in saturated condition by adapting Biot's theory.