• Title/Summary/Keyword: cracks parameters

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Prediction of Fretting Fatigue Life for Lap Joint Structures of Aircraft (항공기 겹침이음 조립구조의 프레팅 피로수명 예측)

  • Kwon, Jung-Ho;Joo, Seon-Yeong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.7
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    • pp.642-652
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    • 2009
  • Most of lap jointed aircraft structures encounter the fretting damages, which provoke fretting cracks prematurely and lead to significant reduction of fatigue life. In the case of ageing aircrafts especially, this fretting fatigue problem is a fatal threat for the safety and airworthiness. Recently, as the service life extension program(SLEP) of ageing aircrafts has become a hot issue, the prediction of fretting fatigue life is also indispensable. On these backgrounds, a series of experimental tests of fretting fatigue on bolted lap joint specimens, were performed. And the fretting crack initiation and propagation life of each specimen were evaluated using existing and newly proposed prediction models with the fretting parameters obtained from the FEA results for elasto-plastic contact stress analyses. The validations of prediction models were also discussed, comparing the prediction results with experimental test ones.

Soft Sedimentary Rock Slopes Design of Diversion Tunnel

  • Jee, Warren Wangryul
    • Proceedings of the Korean Society for Rock Mechanics Conference
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    • 2007.10a
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    • pp.63-79
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    • 2007
  • Several remedial works were attempted to stabilize the collapsed area of the inlet slopes of diversion tunnel, but prevention of any further movement was being only carried out at beginning stage by filling the area with aggregates and rock debris, after several cracks had been initiated and developed around the area. The extra specialty developed folding zone is consisted with highly weathered Greywacke and Black shale. The suggested solution is to improve the properties of the rock mass of failed area by choosing the optimum level of reinforcement through the increment of slope rock support design so as to control the movement of slopes during the re-excavation. The Bakun hydroelectric project includes the construction of a hydroelectric power plant with an installed capacity of 2,520MW and a power transmission system connecting to the existing transmission networks in Sarawak and Western Malaysia. The power station will consist of a 210m height Concrete Faced Rockfill Dam. During the construction of the dam and the power facilities the Balui River has to be diverted of the tunnels is 12m and the tunnel width is 16m at the portal area. This paper describes the stability analysis and design methods for the open cut rock slopes in the inlet area of the diversion tunnels. The geotechnical parameters employed in stability calculations were given as a function of four defined Rock Mass Type (RMT) which were based on RMR system from Bieniawski. The stability calculations procedure of the rock slopes are divided into two stages. In the first stage, it is calculated for the stability of each "global" slope without any rock support and shotcrete system. In the second stage, it is calculated for each "local" slope stability with berms and supported with rock bolts and shotcrete. The monitoring instrumentation was performed continuously and some of the design modification was carried out in order to increase the safety of failed area based on the unforeseen geological risks during the open cut excavation.

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Development of Analytical Model for Cement Concrete Pavements Considering Joint Behavior (줄눈부의 거동을 고려한 시멘트콘크리트 포장체의 해석모델 개발)

  • 변근주;이상민;임갑주
    • Magazine of the Korea Concrete Institute
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    • v.2 no.4
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    • pp.91-98
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    • 1990
  • Joints are provided in cement concrete pavements to control transverse and longitudinal cracking that occur due to restrained deformations caused by moisture and temperature variations in the slab. But the constuction of joints reduces the load-carrying capacity of the pavement at the joints, and pavements have been deteriorated by cracks at the slab edges along the joints due to traffic loads. Therefore, it is important to analyze the behavior of joints accurately in the design of cement concrete pavements. In this study, the mechanical behavior of cement concrete pavement slabs is analyzed by the plate-finite element model, and Winkler foundation model is adopted to analyze the subgrades. The load transfer mechan¬ism of joints are composed of dowel action, aggregate interlocking, and tied-key action, and the analytical pro¬gram is developed using these joint models. Using this numerical model as an analysis tool, the effects of joint parameters on the behavior of pavements are investigated.

Analytical Study on the Development of High-Performance Orthotropic Steel Deck considered the Fatigue Behaviors of Structural Details (구조 상세부의 피로거동을 고려한 고성능 강바닥판 개발에 관한 해석적 연구)

  • Kyung, Kab Soo;Shin, Dong Ho;Kim, Kyo Hun
    • Journal of Korean Society of Steel Construction
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    • v.18 no.4
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    • pp.417-426
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    • 2006
  • Various fatigue damages have been reported in orthotropic steel deck structures put upon girders. These damages are caused by complex behaviors of the deck, which is directly subjected to vehicle loads. To estimate the causes of fatigue cracks at the welded connected parts of the trough rib and the flor beam, and the trough rib and the deck plate, in orthotropic steel deck structures, FE analyses were first, performed in this study. Parameter studies were carried out to suggest effective structural details that consider fatigue, in which the main parameters are the thickness of the deck plate, the shape of the connection of the trough rib and the flor beam such as the slit form, and the welding length. This study suggests that the effective structural details improved the fatigue strength and discusses.

Quantitative Evaluation of Concrete Damage by X-ray CT Methods (마이크로 포커스 X-ray CT를 이용한 콘크리트 손상균열의 정량적 평가)

  • Jung, Jahe
    • The Journal of Engineering Geology
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    • v.28 no.3
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    • pp.455-463
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    • 2018
  • This study developed a method to quantitatively measure the size of cracks in concrete using X-ray CT images. We prepared samples with a diameter of 50 mm and a length of 100 mm by coring cracked concrete block that was obtained by chipping. We used a micro-focus X-ray CT, then applied the 3DMA method (3 Dimensional Medial axis Analysis) to the 3D CT images to find effective parameters for damage assessment. Finally, we quantitatively assessed the damage based on sample locations, using the damage assessment parameter. Results clearly show that the area near the chipping surface was damaged to a depth of 3 cm. Furthermore, X-ray methods can be used to evaluate the porosity index, burn number, and medial axis, which are used to estimate the damage to the area near the chipping surface.

Modelling of tension-stiffening in bending RC elements based on equivalent stiffness of the rebar

  • Torres, Lluis;Barris, Cristina;Kaklauskas, Gintaris;Gribniak, Viktor
    • Structural Engineering and Mechanics
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    • v.53 no.5
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    • pp.997-1016
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    • 2015
  • The contribution of tensioned concrete between cracks (tension-stiffening) cannot be ignored when analysing deformation of reinforced concrete elements. The tension-stiffening effect is crucial when it comes to adequately estimating the load-deformation response of steel reinforced concrete and the more recently appeared fibre reinforced polymer (FRP) reinforced concrete. This paper presents a unified methodology for numerical modelling of the tension-stiffening effect in steel as well as FRP reinforced flexural members using the concept of equivalent deformation modulus and the smeared crack approach to obtain a modified stress-strain relation of the reinforcement. A closed-form solution for the equivalent secant modulus of deformation of the tensioned reinforcement is proposed for rectangular sections taking the Eurocode 2 curvature prediction technique as the reference. Using equations based on general principles of structural mechanics, the main influencing parameters are obtained. It is found that the ratio between the equivalent stiffness and the initial stiffness basically depends on the product of the modular ratio and reinforcement ratio ($n{\rho}$), the effective-to-total depth ratio (d/h), and the level of loading. The proposed methodology is adequate for numerical modelling of tension-stiffening for different FRP and steel reinforcement, under both service and ultimate conditions. Comparison of the predicted and experimental data obtained by the authors indicates that the proposed methodology is capable to adequately model the tension-stiffening effect in beams reinforced with FRP or steel bars within wide range of loading.

Study on Fatigue Life of Continuously Reinforced Concrete Pavement with Design Parameter (설계변수별 연속철근 콘크리트 포장의 피로수명 연구)

  • Park, Jong-Sup;Kang, Young-Jong
    • Journal of the Korean Society of Hazard Mitigation
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    • v.7 no.5
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    • pp.1-10
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    • 2007
  • A laboratory investigation is conducted to characterize and quantify fatigue lives of continuously reinforced concrete pavements (CRCP) with initial design parameters. Eight specimens scaled were made based on results of finite-element analyses and stress-strain curve comparisons. Static tests were firstly performed to obtain magnitudes of static failure loads and to predict crack patterns before fatigue tests. The fatigue lives measured in the study were compared based on each initial design parameter. The comparison indicates that the fatigue lives of CRCP specimens with initial cracks increases with increasing the initial crack spacing, and CRCP specimens with reinforcements at top of the concrete slab have more fatigue lives than those with reinforcements at midheight of the concrete slab. In addition, the fatigue lives were significantly affected by soil conditions under the CRCP specimens. The results obtained in the study can be used for maintenance and retrofit of the continuously reinforced concrete pavements.

Defect Monitoring of a Wind Turbine Blade Surface by using Surface Wave Damping (표면파 기반의 풍력발전기 블레이드 표면상태 실시간 모니터링에 관한 연구)

  • Kim, Kyung-Hwan;Yang, Young-Jin;Kim, Hyun-Bum;Yang, Hyung-Chan;Lim, Jong-Hwan;Choi, Kyung-Hyun
    • Clean Technology
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    • v.23 no.1
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    • pp.90-94
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    • 2017
  • These days much efforts are being dedicated to wind power as a potential source of renewable energy. To maintain effective and uniform generation of energy, defect preservation of turbine blade is essential because it directly takes effects on the efficiency of power generation. For the effective maintenance, early measurements of blade defects are very important. However, current technologies such as ultrasonic waves and thermal imaging inspection methods are not suitable because of long inspection time and non-real time inspection. To supplement the problems, the study introduced a method for real time defect monitoring of a blade surface based on surface wave technology. We examined the effect of various parameters such as micro-cracks and peelings on the propagation of surface wave.

Application and Design of Eddy Current based on FEM for NDE Inspection of Surface Cracks with Micro Class in Vehicular Parts (자동차부품의 마이크로급 표면크랙 탐상을 위한 FEM 를 기반한 와전류 센서 디자인 및 적용)

  • Im, Kwang-Hee;Lee, Seul-Ki;Kim, Hak-Joon;Song, Sing-Jin;Woo, Yong-Deuk;Na, Sung-Woo;Hwang, Woo-Chae;Lee, Hyung-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.32 no.6
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    • pp.529-536
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    • 2015
  • A defect could be generated in bolts for a use of oil filters for the manufacturing process and then may affect to the safety and quality in bolts. Also, fine defects may be imbedded in oil filter system. So it is very important that such defects be investigated and screened during the multiple manufacturing processes. Therefore, in order effectively to evaluate the fine defects, the FEM simulations were performed to make characterization in the crack detection of the bolts and the parameters such as number of turns of the coil, the coil size, applied frequency were calculated based on the simulation results. Simulations were carried out for the defect signal of eddy current probe. Exciter and receiver were utilized. In this paper, the FEM simulations were performed in both bobbin-type and pancake-type probe, both probes were optimized under Eddy current FEM simulations and the results of calculation were discussed.

A Study on the Anti-Spalling Performance of High-Strength Concrete Members by covered Engineered Cementitious Composite (ECC로 피복된 고강도콘크리트 부재의 폭렬억제성능에 관한 연구)

  • Lee, Jae-Young;Kim, Jae-Hwan;Han, Byung-Chan;Park, Sun-Gyu;Kwon, Young-Jin
    • Fire Science and Engineering
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    • v.22 no.4
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    • pp.85-94
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    • 2008
  • The purpose of this study is to obtain the fundamental fire resistance performance of engineered cementitious composites (ECC) under fire temperature in order to use the fire protection material in high-strength concrete structures. The present study conducted the experiment to simulate fire temperature by employing of ECC and investigated experimentally the explosion and cracks in heated surface of these ECC. In the experimental studies, 5 HSC specimens are being exposed to fire, in order to exami ne the influence of vari ous parameters (such as depth of layer=20, 30, 40 mm; construction method=lining and repairing type) on the fire performance of HSC structures. Employed temperature curve were ISO 834 criterion (3 hr), which are severe in various criterion of fire temperature in building structures. The numerical regressive analysis and proposed equation to calculate ambient temperature distribution is carried out and verified against the experimental data. By the use of proposed equation, the HSC members subjected to fire loads were designed and discussed.