• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.155-169
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• 2002

The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024-T4 and 6061-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins' opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.30-38
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• 2023

As the number of old buildings subject to safety inspection increases, the burden on designated institutions and management entities that are responsible for safety management is increasing. Accordingly, when selecting buildings subject to safety inspection, appropriate safety inspection standards and appropriate technology are essential. The current safety inspection standards for old buildings give low scores when it is difficult to confirm damage such as cracks in structural members due to finishing materials. This causes the evaluation results to be underestimated regardless of the actual safety status of the structure, resulting in an increase in the number of aging buildings subject to safety inspection. Accordingly, this study proposed a thermal imaging technique, a non-destructive and non-contact inspection, to detect cracks inside finishing materials. A concrete specimen was produced to observe cracks inside the finishing material using a thermal imaging camera, and thermal image data was measured by exciting a heat source on the concrete surface and cracked area. As a result of the measurement, it was confirmed that it was possible to observe cracks inside the finishing material with a width of 0.3mm, 0.5mm, and 0.7mm, but it was difficult to determine the cracks due to uneven temperature distribution due to surface peeling and peeling of the wallpaper. Accordingly, as a result of performing data analysis by deriving the amplitude and phase difference of the thermal image data, clear crack measurement was possible for 0.5mm and 0.7mm cracks. Based on this study, we hope to increase the efficiency of field application and analysis through the development of technology using big data-based deep learning in the diagnosis of internal crack damage in finishing materials.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.173-180
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• 2014

In the design of tunnel segment structure, axial and moment forces are considered as significant forces. Since axial force is much greater than moment force, the whole section of segment remains in compression. Therefore crack width can be reduced. But the axial force is not considered in criteria for serviceability check. This fact leads service condition more severe compared to ultimate condition and makes the required steel reinforcement increase to meet the serviceability criteria. In this study, the effect of axial force on serviceability of tunnel segment is evaluated, experimentally and analytically. Mock-up tests on segments with actual size were performed and investigated in terms of initial crack resistance. The evaluation proves that more comprehensive design could be achieved when the axial force is considered in the procedure for the serviceability check in design of tunnel segment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.47-54
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• 2023

In this study, the tensile behavior of concrete specimens reinforced with GFRP (Glass Fiber Reinforced Polymer), BFRP (Basalt Fiber Reinforced Polymer), and CFRP (Carbon Fiber Reinforced Polymer) bars was experimentally analyzed. The tensile strength of the FRP bars is appeared to be similar to the design strength, but the elastic modulus was somewhat lower. Additionally, the specimens for tension stiffening effect were manufacured using OPC (Ordinary Portland Cement) and SFRC (Steel Fiber Reinforced Concrete), with dimensions of 150(W)×150(B)×1000(H) mm. The crack spacing of specimens was most significant for GFRP reinforcement bars, which have a lower elastic modulus and a smoother surface, while BFRP and CFRP bars, with somewhat rougher surfaces and higher elastic moduli, showed similar crack spacings. In the load-strain relationship, GFRP bars exhibited a relatively abrupt behavior after cracking, whereas BFRP and CFRP bars showed a more stable behavior after the cracking phase, maintaining a certain level of tension stiffening effect. The tension stiffening index was somewhat smaller as the diameter increased, and GFRP, compared to BFRP, showed a higher tension stiffening index.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.121-125
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• 2018

In this study, finite element analyses of crack propagation along a sinusoidal interface are performed by using cohesive elements. BK law is used for cohesive zone to consider mixed mode traction-separation relation at the crack tip on a sinusoidal interface of a double cantilever beam specimen. The shape of a sinusoidal interface crack and the cohesive strength and the cohesive energies in mixed mode cohesive laws are varied in numerical experiments, and load-displacement curves at the ends of a double cantilever beam specimen are obtained to investigate the crack propagation behavior along a sinusoidal interface.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.156-166
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• 2001

A stochastic continuum(SC) modeling technique was developed to simulate the groundwater flow pathway in fractured rocks. This model was developed to overcome the disadvantageous points of discrete fracture network(DFN) modes which has the limitation of fracture numbers. Besides, SC model is able to perform probabilistic analysis and to simulate the conductive groundwater pathway as discrete fracture network model. The SC model was formulated based on the discrete fracture network(DFN) model. The spatial distribution of permeability in the stochastic continuum model was defined by the probability distribution and variogram functions defined from the permeabilities of subdivided smaller blocks of the DFN model. The analysis of groundwater travel time was performed to show the consistency between DFN and SC models by the numerical experiment. It was found that the stochastic continuum modes was an appropriate way to provide the probability density distribution of groundwater velocity which is required for the probabilistic safety assessment of a radioactive waste disposal facility.

• Tunnel and Underground Space
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• v.9 no.1
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• pp.64-71
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• 1999

A numerical analysis was performed to investigate the effects of notched blasthole in controlling the fracture plane. Analyzed were elastic and elasto-plastic response of rock, and fracture propagation under static and dynamic load conditions. Results showed that the region exceeding the tensile strength extended up to three times the radius of a normal blasthole in elastic analysis, while fifteen times in elasto-plastic analysis. It was shown that a crack was driven from the notch tip up to the distance of 23 times the hole radius in the case of a notched blasthole with a notch of 5 mm in depth and 30 mm in length.

• Journal of the Korean Society for Railway
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• v.20 no.3
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• pp.374-381
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• 2017

Concrete sleepers, installed on majority of railroad track in this nation can, if not maintained properly, threaten the safety of running trains. In this paper, an algorithm for automatically identifying cracks in a sleeper image, taken by high-resolution camera, is developed based on Adaboost, known as the strongest adaptive algorithm and most actively utilized algorithm of current days. The developed algorithm is trained using crack characteristics drawn from the analysis results of crack and non-crack images of field-installed sleepers. The applicability of the developed algorithm is verified using 48 images utilized in the training process and 11 images not used in the process. The verification results show that cracks in all the sleeper images can be successfully identified with an identification rate greater than 90%, and that the developed automatic crack identification algorithm therefore has sufficient applicability.

• Korean Journal of Labor Studies
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• v.14 no.2
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• pp.169-200
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• 2008

노동계급은 다양한 형태의 내적 이질성을 지니고 있으며, 신자유주의 경제정책과 구조조정 과정에서 고용형태에 따른 이질성은 계급균열로 발달하며 노동계급 내적 이질성 논의의 핵심을 구성하게 되었다. 국내의 선행 연구들도 정규직과 비정규직 사이의 물질적 존재조건의 양극화 추세와 사회적 관계의 위계적 배제적 성격을 확인해 주고 있다. 하지만 정규직과 비정규직 사이의 계급균열이 극복되고 노동계급의 내적 통합과 계급형성 과정을 이룰 수 있는지에 대한 논의로 발전하지는 못했다. 본 연구는 계급균열의 극복과 노동계급 통합의 가능성을 검토하기 위해 계급균열의 핵심인 비정규직 노동자 문제를 둘러싼 정규직 비정규직의 의식 수준의 비교연구를 실시한다. 본 연구는 민주노총 공공운수연맹 노동조합원들에 대한 설문조사와 심층면접 연구를 통해 계급균열의 존재를 확인하고 그 원인과 의미를 분석하였다. 첫째, 정규직과 비정규직 노동자들은 비정규직 문제에 대한 인식을 공유하고 있지만 구체적 해결책에 대해서는 입장 차이를 보임으로써 고용형태에 따른 계급균열은 존재하며, 경제위기 이후에도 해소되지 않고 고착화되고 있음을 확인시켜 주었다. 둘째, 고용형태에 따른 계급내적 균열이 비정규직 문제 인식과 추상적 원칙 수준에서는 유의미한 의식 차이를 보이지 않지만 비정규직 문제 해결을 위한 구체적 해결책에 대해 유의미한 입장 차이를 보이는 것은 정규직과 비정규직 사이의 물질적 이해관계의 차이 때문이다. 정규직 노동자들은 비정규직 노동자들의 고용안정성과 노동조건의 개선을 허용하더라도 자신들의 이해관계가 위협받지 않는 수준에서 이루어져야 한다고 보는 것이다. 셋째, 정규직 노동자들이 추상적 원칙 수준에서는 비정규직 노동자들과 동질성을 보이지만 구체적 대안에서 차별성을 보이는 것은 정규직 노동자들의 의식의 양면성을 표현하는 것이며, 물질적 이해관계에 기초한 개인적 수준의 합리성과 계급적 원칙에 기초한 계급적 수준의 합리성이 갈등하고 있는 것이다. 넷째, 정규직 노동자들의 주관성 속에서 개인적 합리성과 계급적 합리성이 갈등하는 정도는 노동조합 가입 여부 및 소속 노동조합의 정체성, 즉 이익집단 정체성 혹은 계급조직 정체성에 의해 결정된다. 여기에 계급조직 정체성을 지닌 민주노조들이 노동계급 계급균열을 극복하고 계급형성을 이루는데 기여할 수 있다는 실천적 함의가 있다.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.3 s.151
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• pp.378-385
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• 2006

To release fashion trends in an efficient way, many of the apparel business and fashion educational institutes in land adopt fashion shows employing fashion models. Modeling rather than flat pattern making realizes the majority of the complicated design works for the fashion shows. However, for the different measurements between the dress form and the real human model, problems often occur during the modeling and fitting processes. Researches on the standard dress form development representing professional fashion models' features are therefore in urgent need to enable the related apparel business and fashion institutes to make appropriate use of the dress form in their jobs. The study has been conducted as a preliminary study using a questionnaire method ultimately to develop the female dress form. A questionnaire in the research aimed at an investigation into the actual conditions of and satisfaction with the usage and the body measurements of existed dress forms. Approximately 30 fashion-related educational institutes and 10 apparel companies responded to the survey. Data derived from the survey was analyzed using SPSS version 10.1, the statistics tool. The results throughout the research were discussed in terms of largely three categories that are; (1) the general conditions of the usage of the dress form to prepare fashion shows: e.g. the frequency of holding the fashion show in an annual term, the proportion of professional and amateur models employed for the fashion show, the methods to construct garments, types and number of dress forms utilized and etc.; (2) factors considered to purchase the dress form e.g. its functionality, shapes, sizes, duration, price, A/S condition and etc.; and(3) satisfaction with the similarity between the dress form and the human body in the relation to the body measurements. Measurements in length wise, front and back waist lengths, neck to bust point on the dress forms were apparently differed from the ones of the actual body. In particular, differed torso length measurements cause the problem to have to alter the whole silhouette, consequently, the resultant patterns as well. In girth measurements, in order of bust and waist girths, the satisfaction was low.