• Title/Summary/Keyword: Internal defects

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Effect of Hot Isostatic Pressing on Elimination of Internal Defects in IN738LC Superalloy for Gas Turbine Blade (HIP 처리에 의한 가스터빈 블레이드용 IN738LC 초합금의 내부결함 소멸 효과)

  • Park, Young-Kyu;Kim, Soo-Hyung;Kim, Jae-Cheol;Lee, Young-Chan;Kim, Doo-Soo;Choi, Cheol;Kim, Gil-Moo
    • Journal of Korea Foundry Society
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    • v.19 no.5
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    • pp.427-432
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    • 1999
  • Most investment castings contain some porosities and microcavities. In this study, we investigated the elimination trends of various internal defects in IN738LC investment castings for industrial gas turbine blade by hot isostatic pressing. The results showed that cylindrical defects which are under $0.6mm{\Phi}{\times}7mm$ size are mostly eliminated and aspect ratio of defects is more sensitive factor than their cross section shape in removing these defects. Increasing hot isostatic pressure and holding time doesn't affect the elimination trend of cylindrical defects over $0.6mm{\Phi}{\times}7mm$ size because first step(plastic deformation) of HIP densification doesn't occur under these HIPping conditions.

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DEFECT EVALUATION IN RAILWAY WHEELSETS

  • Kwon, Seok-Jin;Lee, Dong-Hyong;Seo, Jung-Won;You, Won-Hee
    • Proceedings of the KSR Conference
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    • pp.1940-1945
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    • 2007
  • The wheelsets are one of most important component: damages in wheel tread and press fitted axle are a significant cost for railway industry. Since failure in railway wheelset can cause a disaster, regular inspection of defects in wheels and axles are mandatory. Ultrasonic testing, acoustic emission and eddy current testing method and so on regularly check railway wheelset in service. However, it is difficult to use this method because of its high viscosity and because its sensitivity is affected by temperature. Also, due to noise echoes it is difficult to detect defects initiation clearly with ultrasonic testing. It is necessary to develop a non-destructive technique that is superior to conventional NDT techniques in order to ensure the safety of railway wheelset. In the present paper, the new NDT technique is applied to the detection of surface defects for railway wheelset. To detect the defects for railway wheelset, the sensor for defect detection is optimized and the tests are carried out with respect to surface and internal defects each other. The results show that the surface crack depth of 1.5 mm in press fitted axle and internal crack in wheel could be detected by using the new method. The ICFPD method is useful to detect the defect that initiated in the tread of railway wheelset.

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Internal Quality Evaluation and Age Identification of Fresh Korean Ginseng using Magnetic Resonance Imaging (자기공명영상을 이용한 수삼의 내부 품질평가 및 연근판정)

  • 임종국;김철수;이승조;김성민
    • Journal of Biosystems Engineering
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    • v.28 no.2
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    • pp.157-166
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    • 2003
  • The purpose of this study is to characterize the internal physical properties of fresh Korean ginsengs (Panax ginseng C.A. Meyer) through a magnetic resonance imaging (MRI) technique. Current external visual inspection cannot determine internal quality of ginsengs successfully. Relaxation time constants, T$_1$ and T$_2$*, were obtained from a series of MR images. Calculated Ti values were varied with different physiological states of ginseng tissues. Internal imaging information was obtained nondestructively from fresh ginsengs. One- and two-dimensional image analyses were performed. One-dimensional image analysis showed a potential of age identification of ginsengs rapidly. Internal quality of normal and abnormal ginsengs was evaluated using two-dimensional MR images. Various types of internal defects such as internal cavity and rotten spot were visualized clearly. The MRI technique had a feasibility to detect internal defects of fresh ginsengs effectively.

Effect of Shrinkage Defect on Fracture Impact Energy of A356 Cast Aluminum Alloy (A356 알루미늄 합금의 파단 충격에너지에 대한 수축공결함의 영향)

  • Chul, Hwang-Seong;Kwak, Si-Young
    • Journal of Korea Foundry Society
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    • v.34 no.1
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    • pp.22-26
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    • 2014
  • Internal defects, such as shrinkage during casting, cause stress concentrations and initiate cracking. Therefore, it is important to understand the effects of internal defects on the mechanical properties including the impact behavior. This study evaluates the effects of internal casting defects on the impact performance of A356 Al-alloy castings. The internal shrinkage defects in the casting impact specimen are scanned using an industrial Computed Tomography (CT) scanner, and drop impact tests are performed with varing impact velocities on the A356 casting aluminium specimen ($10mm{\times}10mm$ section area) in order to locate the fracture energy under an impact load. The specimens with defects with a diameter less than 0.35 mm exhibit equivalent fracture impact energies of approximately 32 J and those with a 1.7 mm diameter defect reduced the fracture impact energy by 35%.

Defect Monitoring In Railway Wheel and Axle

  • Kwon, Seok-Jin;Lee, Dong-Hyoung;You, Won-Hee
    • International Journal of Railway
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    • v.1 no.1
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    • pp.1-5
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    • 2008
  • The railway system requires safety and reliability of service of all railway vehicles. Suitable technical systems and working methods adapted to it, which meet the requirements on safety and good order of traffic, should be maintained. For detection of defects, non-destructive testing methods-which should be quick, reliable and cost-effective - are most often used. Since failure in railway wheelset can cause a disaster, regular inspection of defects in wheels and axles are mandatory. Ultrasonic testing, acoustic emission and eddy current testing method and so on regularly check railway wheelset in service. However, it is difficult to detect a crack initiation clearly with ultrasonic testing due to noise echoes. It is necessary to develop a non-destructive technique that is superior to conventional NDT techniques in order to ensure the safety of railway wheelset. In the present paper, the new NDT technique is applied to the detection of surface defects for railway wheelset. To detect the defects for railway wheelset, the sensor for defect detection is optimized and the tests are carried out with respect to surface and internal defects each other. The results show that the surface crack depth of 1.5 mm in press fitted axle and internal crack in wheel could be detected by using the new method. The ICFPD method is useful to detect the defect that initiated in railway wheelset.

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A Study on Scattered Fields Analysis of Ultrasonic SH-Wave from Multi-Defects by Boundary Element Method (경계요소법을 이용한 다중결함의 SH형 초음파 산란장 해석에 관한 연구)

  • Lee, Jun-Hyeon;Lee, Seo-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.23 no.11
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    • pp.1878-1885
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    • 1999
  • Ultrasonic technique which is one of the most common nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristic of scattering sign al from internal defects. Therefore, a numerical analysis of ultrasonic scattering field due to defect profiles is absolutely needed for the accurate, quantitative estimation of internal defects. In this paper, the SH-wave scattering by multi-cavity defects and inclusion using Elastodynamic Boundary Element Method is studied. The effects of shape and distance of defects on transmitted and reflected fields are considered. The interaction of multi-cavity defects in SH-wave scattering is also investigated. Numerical calculations by the BEM have been carried out to predict near field solution of scattered fields of ultrasonic SH-wave. The presented results can be used to improve the detection sensitivity and pursue quantitative nondestructive evaluation for inverse problem.

Analysis of Error Rate in the Variations of Shearing Amount in Measuring the Internal Defect using a Shearography (전단간섭계를 이용한 압력용기 내부 결함 측정시 전단량 변화에 따른 오차분석)

  • Hong, Kyung-Min;Kang, Young-June;Choi, In-Young;Ahn, Yong-Jin;Yoon, Suk-Bum
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.21 no.5
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    • pp.726-732
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    • 2012
  • Pipe and Pressure Vessels that is used in power plant and chemical industry have many Internal Defects that is corrosion caused by the flow of fluid. These Internal Defects that have possibility of explosion are very dangerous because it can not see from the outside. This days many companys using NDT method to find an Internal Defect. Most of the NDT methods have limitations that are constraint of shape and materials. But Sheargoraphy have many advantages compared conventional NDT method. It has very fast measuring speed, non-destructive and non contacting measurement. As well as it hasn't constraint of shape and materials. As a paper on the analysis of measurement of error, the important factors were the Shearing Amount and pressure, and discovered measurement of the Internal Defect of the object by using shearography. The optimal Shearing Amount and pressure was discovered and utilized.

Measurement of Inner Defects and out of Plane Deformation of Pressure Vessel in Piping of Circulation System Using Shearography (전단간섭법을 이용한 배관 순환 시스템에서의 압력용기 내부결함 및 면외변형 측정)

  • Kang, Chan-Geun;Kim, Hyun-Ho;Jung, Hyun-Il;Choi, Tae-Ho;Jung, Hyun-Chul;Kim, Kyeong-Suk
    • Journal of the Korean Society for Nondestructive Testing
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    • v.34 no.5
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    • pp.349-355
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    • 2014
  • Wall thinning defects can occur in the pressure vessels used in a variety of industries. Such defects are related to the flow velocity. Considering the fact that such vessels constitute up to 70 or 80% of the plant structures in a power plant, it is important to measure internal defects as part of a safety evaluation. In this study, optical measurement were applied in a non-destructive evaluation using shearography to ensure the safety and improve the reliability of a power plant through the non-contact, non-destructive evaluation of pressure vessels. In order to verify whether the pressure vessels contained faults, experimental and analytical investigation were conducted to measure any internal defects and out-of-plane deformation from inner temperature changes and pressure changes in the piping of the circulation system. The most important factors in this research were the thickness, width, and length of a defect. An increase in these could confirm an increase in the deformation. Thus, internal defects in a pressure vessel were measured using shearography, which made it possible to ensure the reliability and integrity of the pipe.