• 한국세라믹학회지
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• 제50권6호
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• pp.523-527
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• 2013

Ti-based coatings following laser ablation were studied to compare degradation behaviors by thermomechanical stress. TiN, TiCN, and TiAlN coatings were degraded by a Nd:YAG pulsed laser with an increase in the laser pulses. A decrease in the hardness was identified as the pulses increased, and the hardness levels were in the order of TiAlN > TiCN > TiN. The TiN showed cracks on the surface, and cracks with pores formed along the cracks were observed in the TiCN. The dominant degradation behavior of the TiAlN was surface pore formation. EDS results revealed that diffusion of substrate atoms to the coating surface occurred in the TiN. Delamination occurred in the TiN and TiCN, while the TiAlN which has higher thermal stability than the TiN and TiCN maintained adhesion to the substrate. It was considered that the decrease in the hardness of the Ti-based hard coatings is attributed to surface cracking and the diffusion of substrate atoms.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1469-1476
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• 2003

This paper provides plastic limit load solutions of cylinders with circumferential part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly-plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both external and internal cracks are considered. Furthermore, in terms of the crack shape, both semi-elliptical and constant-depth surface cracks are considered. The resulting limit load solutions are given in a closed form, and thus can be easily used in practical situations. Being based on detailed 3-D FE limit analysis, the present solutions are believed to most reliable, and thus to be valuable information for integrity assessment of piping.

• 대한기계학회논문집A
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• 제31권6호
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• pp.710-717
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• 2007

This paper presents plastic limit loads and approximate J-integral estimates for circumferential part-through surface crack at the interface between elbows and pipes. Based on finite element limit analyses using elastic-perfectly plastic materials, plastic limit moments under in-plane bending are obtained and it is found that they are similar those for circumferential part-through surface cracks in the center of elbow. Based on present FE results, closed-form limit load solutions are proposed. Welds are not explicitly considered and all materials are assumed to be homogeneous. And the method to estimate the elastic-plastic J-integral for circumferential part-through surface cracks at the interface between elbows and straight pipes is proposed based on the reference stress approach, which was compared with corresponding solutions fur straight pipes.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1428-1434
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• 2002

The ball-on-disk type sliding tests with boundary lubricated steels were carried out to verify the effect of initial spacing in surface profiles on wear and scuffing. Three kinds of surface spacing, which are closely related with initial surface micro-cracks on sliding surfaces, were produced on AISI 1045 steel surfaces using different grinding and polishing processes. Frictional forces and time to scuffing were measured, and the shape and amount of wear particles were analyzed to compare the with original surface profiles. From the tests, it was confirmed that the size of wear particles are related closely to the original spacing of the surface profile. The time to failure and amount of wear were sensitive to the surface spacing. The wider surface spacing shows much longer sliding life and smaller amount of wear than the others. Time to scuffing was increased with increasing surface pro(lie spacing. The size of wear particles increased while the wear and wear rate K were decreased with an increase in surface spacing. After the sliding tests, surface cracks of inner parts of the wear track formed due to scuffing were observed and compared among the specimens having the different surface spacing.

• 대한기계학회논문집
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• 제18권3호
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• pp.716-728
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• 1994

In this paper, fatigue tests were carried out to study the behavior of growth and coalescence of multi-surface cracks which were initiated at the semi-circular surface notches, and a simulation program was developed to predict their growth and coalescence behavior. By comparing the experimental result with those of the simulation based on SPC(surface point connection), ASME and BSI(British Standards Institution) conditions, we tried to enhance the reliance and integrity of structures. This shows that the simulation result has utility for fatigue life prediction.

• 대한기계학회논문집
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• 제17권7호
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• pp.1668-1677
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• 1993

The objective of this paper is to develop a computational model for predicting the fatigue propagation of collinear multiple surface cracks under constant amplitude and variable amplitude loadings. After examining fatigue crack growth behavior for CT specimens and single surface crack specimens, empirical equations of(11) and(12) are proposed for the prediction of fatigue life in a multiple surface crack geometry. The accuracy of the proposed model is verified using a life prediction computer program. Several case studies were performed to check the accuracy of the proposed model and to verify the usefulness of the developed program. Good agreement is observed between the numerical results based on the proposed model and the published experimental data.

• International Journal of Reliability and Applications
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• 제5권1호
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• pp.37-46
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• 2004

Coil spring of automobile suspension system is very important to safety and dynamics of passenger car and requires a highly advanced quality control during manufacturing processes. Surface cracks on the coil spring rod produced by mechanical machining and heat treatment may cause a severe accident and large cost to the manufacturer. In order to detect surface cracks of the rod, guided wave technique is applied for a fast total volumetric inspection. Pochhammer equation is studied to investigate the dispersion characteristics of the guided wave in the spring rod and optimal wave modes sensitive to the surface crack are selected experimentally to design the experimental arrangement for the generation of guided wave. Rod samples with different size of artificial axial EDM notch on the surface ranging from 50${\mu}{\textrm}{m}$ to 1 mm are examined by guided wave and inspection results discussed.

• Advances in concrete construction
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• 제3권1호
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• pp.39-54
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• 2015

Relative humidity and strains within a massive concrete cylinder (${\varphi}450mm{\times}900mm$) in the drying and the re-saturating process were measured for elucidating the process of ASR surface cracking in concrete. The expansion behavior of mortars in dry atmospheres with various R.H. values and the resaturating process was revealed. Non- or less-expansive layers were formed in near-surface regions in the concrete cylinder in the drying process, but ASR expansions actively progressed in inner portions. After resaturating, R.H. values of near-surface regions rapidly increased with time, but expansions in the regions were found to be very small. However, in the middle portions, of which R.H. values were kept 80% ~ 90% R.H. in the drying process, expansion actively progressed, resulting in further development of surface cracks in the re-saturating process.

• 대한토목학회논문집
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• 제35권2호
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• pp.481-491
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• 2015

콘크리트 표면에 발생된 균열은 구조물의 수명에 영향을 미치는 주요원인으로 작용하기 때문에 주기적인 검사와 유지관리가 필요하다. 콘크리트 표면 유지관리를 위한 실링작업은 표면에 발생된 균열을 초기에 보수하는 방법으로 시간 경과에 따른 균열의 추가생성 및 확산을 방지하는데 효과적이다. 하지만, 교량 하부의 실링작업은 열악한 작업환경으로 인하여 작업자들의 안전성 확보에 문제가 있다. 이런 이유로, 콘크리트 구조물의 유지관리를 위한 실링자동화의 필요성이 부각되고 있다. 본 논문은 콘크리트 교량 하부에 발생된 균열의 실링작업에 로봇을 적용하기 위한 두 가지 제어방법에 대하여 제안한다. 하나는, 균열의 궤적을 자동으로 추적하는 방법이다. 로봇은 카메라로부터 취득되는 영상정보로 균열의 궤적을 파악하는데, 이전 시점의 궤적 정보를 통하여 다음 이동할 시점의 정보를 유추할 수 있다면, 실시간으로 변동되는 궤적 정보에 대응이 가능하면서 자동으로 균열을 추적할 수 있다. 다른 하나는 접촉면에 일정한 힘을 유지하여 실링하는 방법이다. 장기간 외부 환경에 노출된 거친 표면에서도 로봇이 일정한 접촉력을 유지하며 실링작업을 수행한다면, 균등한 완성도를 유지할 수 있다. 이러한 균일한 힘의 유지를 위하여 임피던스를 이용한 힘 제어 기법을 제안한다. 본 논문에서는 실링 로봇에 적용하기 위하여 개발한 두 가지 제어기법들을 소개하고, 그것을 적용한 Lab Test와 Field Test를 수행한다. 이 시험결과를 토대로 로봇의 현장적용에 대한 의견을 제시한다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.103-104
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• 2022

Cracks may occur in reinforced concrete (RC) structures due to various physical and chemical factors, and the growth of cracks causes deterioration of the structure's performance. It is important to prevent the expansion of cracks through periodic diagnosis of cracks in structures. In order to enable free crack exploration even in a narrow space, a construction robot using a Mecanum wheel that can move up, down, left and right and rotate in place was designed. High-quality crack images were periodically collected through the camera, and the image fragments stored during the exploration were combined into a single photo after the exploration was completed. The robot detected cracks with a width of 0.2 mm or more on the concrete probe surface with an accuracy of about 90% or more.