• Journal of the Korean GEO-environmental Society
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• v.18 no.8
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• pp.17-21
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• 2017

This paper is to grasp the use of impact-echo response signal induced from impacting an object for the assessment of compressive strength of construction materials nondestructively and to propose the test results. For this study, an impact device was devised and used for impacting an object by an initial rotating free falling impact and following repetitive impacts from the rebound action which eventually disappears. Concrete test specimens which had been mixed for different strengths were tested and the impact echo response signal was measured for each test specimen. The total sound signal energy which is assessed from integrating the impact-echo response signal was compared with the directly measured compressive strength for each specimen. The comparison showed that the total sound signal energy has a direct relationship with the directly measured compressive strength and the results clearly indicated that the compressive strength of construction materials can be assessed nondestructively using total sound signal energy which is assessed from integrating the impact-echo response signal induced from impacting an object.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.110-117
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• 1999

In order to ultrasonically evaluate creep cavities pure copper samples were subjected to creep test and their microstructures were examined. Ultrasonic velocities. frequency-dependent magnitude spectra and attenuations were measured on a series of copper samples obtained from the different stages of creep test. Velocities measured in three directions with respect to the loading axis decreased and their anisotropy increased as a function of the creep-induced porosity. The anisotropic behavior could be attributed to the progressive change of pore shape and preferred orientation as the creep advanced. The 2% porosity by volume decreased the longitudinal and shear wave velocities by 11% and 4%, respectively. Furthermore, both velocities decreased nonlinearly with the porosity. As the creep damage developed, the magnitude spectra lost high frequency components and their central frequencies shifted to lower values. The attenuation showed almost linear behavior in the frequency range used. Normalized velocity, central frequency shift and attenuation slope were selected as nondestructive evaluation parameters. These results were presented and showed good relations with the porosity content.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1C
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• pp.19-27
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• 2011

This paper evaluates the applicability of wave-based nondestructive methodologies and a penetration test for compaction quality measurements during road construction. To evaluate the physical and mechanical properties of compacted subgrade soil layers, soil stiffness gauge (SSG), time domain reflectometry (TDR), and miniature electro-mechanical systems (MEMS) accelerometers were used to nondestructively evaluate the soil response during and after compaction and dynamic cone penetrometer (DCP) profiles were used to evaluate the soil shear strength after compaction was completed. At the field site, two types of soils were compacted with four different compaction equipments and energies. Field testing results indicate that soil parameters evaluated by different testing methods, which are SSG, TDR, MEMS accelerometer, and DCP, are highly correlated. In addition, it is shown that the physical and mechanical tests deployed in this study can be used as alternative methods to the conventional compaction quality evaluation methods when assessing the overall quality and the engineering response of compacted lifts.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.40-48
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• 2012

Steel corrosion in concrete is a main cause of deterioration and early failure of concrete structures. A novel integration of electromagnetic heat induction and infrared (IR) thermography is proposed for nondestructive detection of steel corrosion in concrete, by taking advantage of the difference in thermal characteristics of corroded and non-corroded steel. This paper focuses on experimental investigation of the concept. An inductive heater is developed to remotely heat the embedded steel from concrete surface, which is integrated with an IR camera. Concrete samples with different cover depths are prepared. Each sample is embedded with a single rebar in the middle, resulting an identical cover depth from the front and the back surfaces, which enable heat induction from one surface and IR imaging from the other simultaneously. The impressed current (IC) method is adopted to induce accelerated corrosion on the rebar. IR video images are recorded during the entire heating and cooling periods. The test results demonstrate a clear difference in thermal characteristics between corroded and non-corroded samples. The corroded sample shows higher rates of heating and cooling than those of the non-corroded sample. This study demonstrates a potential for nondestructive detection of rebar corrosion in concrete.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.2
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• pp.75-82
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• 2022

Nondestructive method to predict buckling load for the propellant tank of launch vehicle should be evaluated. Vibration correlation technique can predict the global buckling load of unstiffened cylindrical structure with geometric initial imperfection using correlation of natural frequency and compressive load from compressive test below the buckling load. In this study, vibration and buckling tests of a thin metal unstiffened propellant tank model subjected to internal pressure and compressive loads were performed and the test results were used for VCT to predict global buckling load. For the vibration test of thin structure, non-contact excitation method using a speaker was used. The response was measured with piezoelectric polymer(PVDF) sensor. Prediction results of VCT were compared with the measured buckling load in the test and the nondestructive global buckling load prediction method was verified.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.4
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• pp.349-354
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• 2013

The non-destructive testing using infrared thermography is extended to a variety of industries and non-destructive testing of welds using infrared thermography is also in progress in various ways. Currently, a non-destructive testing of electrical resistance spot welds which is mainly used is Radiography Testing. This study detected area of spot welds nugget using optical-infrared thermography. In the results, it is possible for detecting defects of nugget in a short period of time using pulse-infrared thermography.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.518-525
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• 2012

In this study, the feasibility of hyperspectral reflectance imaging technique was investigated for the discrimination of viable and non-viable lettuce seeds. The spectral data of hyperspectral reflectance images with the spectral range between 750 nm and 1000 nm were used to develop PLS-DA model for the classification of viable and non-viable lettuce seeds. The discrimination accuracy of the calibration set was 81.6% and that of the test set was 81.2%. The image analysis method was developed to construct the discriminant images of non-viable seeds with the developed PLS-DA model. The discrimination accuracy obtained from the resultant image were 91%, which showed the feasibility of hyperspectral reflectance imaging technique for the mass discrimination of non-viable lettuce seeds from viable ones.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.104-112
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• 2015

Non-contact surface wave transmission (SWT) measurements are used to evaluate the depth of a surface-breaking crack in concrete slabs. The author propose a measurement model that includes an appropriate configuration of the source and receivers, and a transmission function for the given configuration. A series of numerical simulations using a 3D finite element model is used to obtain the transmission function. Then, validity of a proposed model is verified through experimental studies. Two air-coupled sensors are used to measured surface waves across surface-breaking cracks with varying depths from 0mm to 100mm with intervals of 10mm in a concrete slab ($1500{\times}1500{\times}180mm^3$) in laboratory. As a result, the proposed method is demonstrated as to be effective for charactering the depth of a surface-breaking crack in concrete bridge deck with an average error of 10%. A discussion on practical applications of the proposed method is also included in this article.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.81-86
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• 2005

This paper proposes a non-destructive ESPI technique to quantitatively evaluate defects inside a semiconductor package. The inspection system consists of the ESPI system, a thermal loading system and an adiabatic chamber. The technique is high feasibility for non-destructive testing of a semiconductor and overcomes the weaknesses of previous techniques, such as time-consumption and difficult quantitative evaluation. Most defects are classified as delamination defects, resulting from the insufficient adhesive strength between layers and from non-homogeneous heat spread. Ninety percent of the tested samples had delamination defects which originated at the corner of the chip and nay be related to heat spread design.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.25-28
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• 1999

국내에 건설되어 거의 20∼30년 가동되고 있는 발전설비, 석유화학 플랜트 등 거대설비 기기의 건전성(integrity) 및 신뢰성 확보와 잔존수명 예측을 위해서는 구조물 내부 또는 표층부에 존재하는 결 함의 특성을 아는 것과 함께 그 재료의 특정 부위에 어느정도의 응력이나 변형이 있는가를 아는 것이 매우 중요하다. 일반적으로 강 용접부의 비파괴적 결함검출에는 주로 SV파(vertically shear wave)와 SH파(horizontally shear wave)라 불리는 횡파를 이용한 초음파사각탐상법이 실용화되어 이용되고 있다. 그러나 비파괴적인 방법에 의한 실험적인 잔류응력 측정, 변형해석법에는 전기 저항 및 자기 스트레인 게이지법, X선회절법, 광탄성법(photoelasticity), 모아레(Mohr's)법, 레이저스펙클(Laser speackle)법, 응 력도료법, Barkhausen Nosise법, Caustics법 등이 제시되어 있으나 그 유용성 면에서는 아직 해결되야할 문제가 많이 남아 있는 실정이다. 응력이나 변형을 해석하는 방법으로 이론적 방법, 계산적 방법 실험적 방법이 잇다. 이론적 방법에는 재료 역학적으로 취급하는 방법, 탄성론 등이 있고, 계산적인 방법에는 유한요소법이 있지만, 이론적 방법이나 계산적 방법만으로는 해석이 불가능한 경우가 많기 때문에 실험 적 방법이 필요하게 된다. 이 글에서는 파괴 시험 또는 다른 비파괴평가기술에 비해 간편한 측정, 높은 측정정도, 시험결과 도출의 신속성, 검사비용의 절감 등 많은 장점을 가지고 있고 실험적으로 유용성이 일부 검증되고 있는 음탄성법(Acoustoelasticity)에 의한 잔류응력 측정법에 관해 소개하고자 한다.TEX> mg/L(평균 49 mg/L)로 비교적 안정적인 처리효율을 보여주었다. 본 연구결과 HVC 공정은 화학약품 사용량의 절감 및 이에 따른 화학슬러지 발생량의 감소를 기대 할 수 있는 친환경기술로 유지관리비를 최소화할 수 있는 장점이 있었다. 않은 사람들 중 미래의 검진실행의지에 건강소식지가 영향을 미친 경우는 48.7%였다. 보건교육을 받은 후 유방암 자가검진 실천율은 사업군에서 53.9%로 받기 전의 27.3%보다 증가하였으나 대조군의 경우는 별 차이가 없었다. 연령별로는 60대가 가장 높았고 사업군에서 검진율의 증가분은 30대가 가장 컸다. 교육수준별로는 사업군은 고졸이, 대조군은 전문대졸이 가장 높았고 사업군에서 검진율의 증가분은 고졸에서 가장 컸다. 보건교육 후 유방암과 관련된 건강지식의 정도는 사업군이 3.7점으로 대조군보다 유의하게 높았으며, 유방암 자가검진법을 실천하는 사람들의 동기는 ‘일반 대중매체의 영향’이 가장 많았으며 건강소식지가 동기인 경우도 20.4%였다. 사업군에서 건강소식지가 유방암 자가검진법 실천에 영향을 미친 경우가 79.6%였으며 유방암 자가검진법에 관한 보건교육을 받고 실천하지 않은 사람들 중 미래의 실천의지에 건강소식지가 영향을 미친 경우는 43.6%였다. 이상의 소견에서 지역주민을 대상으로 인쇄매체를 통한 보건교육은 인쇄물만으로도 쉽게 실천 할 수 있는 유방암 자가검진법이 가장 효과적이었으며, 자궁암검진에 관해서도 검진을 받을 수 있도록 지역사회의 보건의료의 하부구조를 정비하여 제도적 장치를 마련하고 정보를 제공한다면 자궁암검진 실천율도 증가할 것이다.고 12.9% 의 발달율을 보여 유의적인 차이를 보이지 않았다. 이상의 결과로 보아 핵이식 수정란을 효율적으로 생산하기 위하여