• 인터넷정보학회논문지
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• 제11권6호
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• pp.111-122
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• 2010

디지털 융합을 위한 교육은 다양한 학문과 기술들이 컴퓨터를 중심으로 융합하는 것이므로 교육 범위와 방법이 매우 상이하다. 따라서 교육 계획과 강의전략을 정형화하기 어렵기 때문에 개념적인 정보를 제한적으로 추천하는 문제점이 있다. 본 논문에서는 스피어만 상관 계수를 이용하여 교육 계획과 강의 전략을 제시하기 위한 시스템을 제안한다. 이 시스템은 학계와 산업계의 요구를 기반으로 한 정보로부터 강의 전략 연관성을 찾아 서열화하고, 사용자의 상황과 특성에 적합한 강의 전략 정보를 목록으로 제공하여, 제한적인 개념적 정보 추천의 단점을 해결한다. 성능 실험은 기존의 서비스 시스템들과 비교하여 효과성을 측정하여 정확도와 재현율로 표현하였으며, 성능 실험 결과 정확도는 90.4%, 재현율은 77.6%로 나타났다.

• 융복합기술연구소 논문집
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• 제5권1호
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• pp.7-12
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• 2015

Sheet metal formability can be defined as the ability of metal to deform without necking or fracture into desired shape. Every sheet metal can be deformed without failure only up to a certain limit, which is normally known as forming limit curve(FLC). In this paper, the dome stretching tests and tensile tests have been performed to obtain forming limit curve of aluminum alloy. During the experiment, failure strain is measured using digital image correlation(DIC) method. DIC method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. DIC results demonstrated the usefulness and ability to determine a strain.

• Journal of Information Processing Systems
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• 제13권2호
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• pp.305-320
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• 2017

The selection of subset size is of great importance to the accuracy of digital image correlation (DIC). In the traditional DIC, a constant subset size is used for computing the entire image, which overlooks the differences among local speckle patterns of the image. Besides, it is very laborious to find the optimal global subset size of a speckle image. In this paper, a self-adaptive and bidirectional dynamic subset selection (SBDSS) algorithm is proposed to make the subset sizes vary according to their local speckle patterns, which ensures that every subset size is suitable and optimal. The sum of subset intensity variation (${\eta}$) is defined as the assessment criterion to quantify the subset information. Both the threshold and initial guess of subset size in the SBDSS algorithm are self-adaptive to different images. To analyze the performance of the proposed algorithm, both numerical and laboratory experiments were performed. In the numerical experiments, images with different speckle distribution, different deformation and noise were calculated by both the traditional DIC and the proposed algorithm. The results demonstrate that the proposed algorithm achieves higher accuracy than the traditional DIC. Laboratory experiments performed on a substrate also demonstrate that the proposed algorithm is effective in selecting appropriate subset size for each point.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.75-85
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• 2016

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to $300^{\circ}C$. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress-strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress-strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study.

• 한국생산제조학회지
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• 제24권4호
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• pp.434-440
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• 2015

A smart phone is a multimedia device that is a necessity for modern people. It includes a wireless networking system to share information and pictures. However, numerous smart phones are discarded every year, since they have a very fast technology development cycle. This paper presents the development of a telemetry algorithm to measure displacement and strain with a discarded smart phone and digital image correlation methods. To implement the measurement algorithm, the LabVIEW 2010 program development platform was used. In order to verify reliability, an open hole tension test was conducted using a smart phone and a universal test machine. In addition, the measurement results from the smart phone were compared with FEM analysis results.

• 한국항공우주학회지
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• 제43권10호
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• pp.896-901
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• 2015

온도 구배에 의한 날개 외피의 열변형 특성을 연구하기 위하여 비행체 날개의 포켓 형상을 본 딴 프레임 외피 구조 시편을 제작하였다. 날개에 발생하는 온도 구배 현상을 효과적으로 모사하기 위하여 프레임 외피 시편의 프레임에 수냉 시스템을 개발, 적용하였다. 공력 특성에 영향을 미치는 날개 외피의 면외 열변형을 정량적으로 평가하기 위하여 디지털 영상 상관 기법(Digital Image Correlation technique, DIC)을 사용하고, 면외 변위 측정 불확도 평가를 통해 측정 정확도를 분석하였다. SUS304 소재로 만들어진 프레임 외피 구조 시편의 시험을 수행하여 온도에 따른 외피의 면외 변형 특성을 성공적으로 획득하였다.

• Earthquakes and Structures
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• 제7권5호
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• pp.609-626
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• 2014

The capabilities of a high-resolution Digital Image Correlation (DIC) system are presented within the context of deformation measurements of full-scale concrete columns tested under reversed cyclic loading. The system was developed to have very high-resolution such that material strains on the order of the cracking stain of concrete could be measured on the surface of full-scale structural members. The high-resolution DIC system allows the measurement of a wide range of deformations and strains that could only be inferred or assumed previously. The DIC system is able to resolve the full profiles of member curvatures, rotations, plasticity spread, shear deformations, and bar-slip induced rotations. The system allows for automatic and objective measurement of crack widths and other damage indices that are indicative of cumulated damage and required repair time and cost. DIC damage measures contrast prevailing proxy damage indices based on member force-deformation data and subjective damage measures obtained using visual inspection. Data derived from high-resolution DIC systems is shown to be of great use in advancing the state of behavioral knowledge, calibrating behavioral and analytical models, and improving simulation accuracy.

• 한국생산제조학회지
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• 제23권5호
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• pp.498-504
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• 2014

Displacements and strains are very important for material evaluation as critical factors to a machine's life cycle and safety. Typically, the strain gauge has been employed to measure displacement and strain. However, this contact-type measurement method has disadvantages that are not quantified under the test conditions of a specific object shape, surface roughness, and temperature. In this paper, the measurement of deflection and flexural strain due to the three-point bending test is presented, employing Digital Image Correlation (DIC) methods. In order to ensure measurement reliability, DIC and universal test machine methods were compared by measuring the deflections and flexural strains developed by such bending tests.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.372-380
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• 2012

The optical method Digital Speckle Correlation Measurement (DSCM) has been extensively applied due its capability to measure the entire displacement field over a body surface. A formula of displacement measurement errors by the gradient-based DSCM method was derived. The errors were found to explicitly relate to the image grayscale errors consisting of sub-pixel interpolation algorithm errors, image noise, and subset deformation mismatch at each point of the subset. A power-law dependence of the standard deviation of displacement measurement errors on the subset size was established when the subset deformation was rigid body translation and random image noise was dominant and it was confirmed by both the numerical and experimental results. In a gradient-based algorithm the basic assumption is rigid body translation of the interrogated subsets, however, this is in contradiction to the real circumstances where strains exist. Numerical and experimental results also indicated that, subset shape function mismatch was dominant when the order of the assumed subset shape function was lower than that of the actual subset deformation field and the power-law dependence clearly broke down. The power-law relationship further leads to a simple criterion for choosing a suitable subset size, image quality, sub-pixel algorithm, and subset shape function for DSCM.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3205-3214
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• 2022

The aim of this study is to provide a clear and accessible method to obtain accurate true-stress strain data, and to extend the limited material data beyond the ultimate tensile strength (UTS) for AISI 304L. AISI 304L is used for the outer construction for some types of nuclear transport packages, due to its post-yield ductility and high failure strain. Material data for AISI 304L beyond UTS is limited throughout literature. 3D digital image correlation (DIC) was used during a series of uniaxial tensile experiments. Direct method extracted data such as true strain and instantaneous cross-sectional area throughout testing such that the true stress-strain response of the material up to failure could be created. Post processing of the DIC data has a considerable effect on the accuracy of the true stress-strain data produced. Influence of subset size and smoothing of data was investigated by using finite element analysis to inverse model the force displacement response in order to determine the true stress strain curve. The FE force displacement response was iteratively adapted, using subset size and smoothing of the DIC data. Results were validated by matching the force displacement response for the FE model and the experimental force displacement curve.