• Title/Summary/Keyword: Reverse bending method

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A study on reduction of pre-crack deviation in CTOD specimen using reverse bending method (Reverse Bending을 통한 CTOD 시험 예비균열 형상균일화에 관한 연구)

  • Jeong, Sehwan;Park, Dong-Hwan;Kim, Hyeon-Su;Shin, Sang-Beom;Park, Tae-Jong
    • Journal of Welding and Joining
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    • v.33 no.2
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    • pp.62-68
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    • 2015
  • This study investigates the appropriate range of reverse bending load for the CTOD test of thick weld by observing improvement of pre-crack shape and determination of the limit applicable load. In order to do it, the effect of the amount of the reverse bending load on the maximum deviation of the pre-crack length was investigated by the extensive tests, and the variation of plastic zone size in way of the crack tip under reverse bending load were evaluated by FEA. With the results obtained by the experiments and FEA, the proper range of reverse bending load was suggested. The effectiveness of the reverse bending method was verified by examining the pre-crack straightness after CTOD tests of thick weld specimens with various thickness and strength.

An Optimum Design of Pipe Bending Process Using High Frequency Induction Heating and Dynamic Reverse Moment (고주파 유도가열 및 동적 반력 모멘트를 이용한 파이프 벤딩 공정의 최적설계)

  • Lee, H.W.;Jung, S.Y.;Woo, T.K.;Kim, C.
    • Transactions of Materials Processing
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    • v.19 no.2
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    • pp.79-87
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    • 2010
  • The Pipe bending process using high frequency local induction heating is an advanced technique to bend pipes with a small bending radius and a large diameter. Even though the pipe bending process is a quite widespread engineering practice, it depends heavily upon trial and error method by field engineers with several years of experience. So it is necessary to develop an integrated methodology for optimum design of the pipe bending process. During hot pipe bending using induction heating, outward wall thickness of a pipe is thinned due to tensile stress and the reduction of wall thickness is not allowed to exceed 12.5%. Taguchi method and dynamic reverse moment is proposed to maintain a reduction ratio of thickness within 12.5%, when D/t ratio is high. An application of the proposed approach was compared with those of the finite element analysis and has good in agreements.

Process Design of the Hot Pipe Bending Process Using High Frequency Induction Heating (고주파 유도가열을 이용한 열간 파이프 벤딩 공정 설계)

  • Ryu, Gyeong-Hui;Lee, Dong-Ju;Kim, Dong-Jin;Kim, Byeong-Min;Kim, Gwang-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.9
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    • pp.110-121
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    • 2001
  • During hot pipe bending using induction heating, the wall of bending outside is thinned by tensile stress. In design requirement, the reduction of wall thickness is not allowed to exceed 12.5%. So in this study, two methods of bending, one is loading of reverse moment and the other is loading of temperature gradient, have been investigated to design pipe bending process that satisfy design requirements. For this purpose, finite element analysis with a bending radius 2Do(outer diameter of pipe) has been performed to calculate proper reverse moment and temperature gradient to be applied. Induction heating process has been analyzed to estimate influence of heating process parameters on heating characteristic by finite difference method. Then pipe bending experiments have been performed for verification of finite element and finite difference analysis results. Experimental results are in good agreement with the results of simulations.

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Behavior of Global Bending Distortion of Hatch-cover in Container Carrier during Fabrication Process (컨테이너 운반선 해치-커버 제작시 전 굽힘 변형 거동에 관한 연구)

  • Lee, Dong-Ju;Kim, Gyung-Gyu;Shin, Sang-Beom
    • Journal of Welding and Joining
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    • v.28 no.4
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    • pp.41-48
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    • 2010
  • The purpose of this study is to establish the control method of the global bending distortion caused by fabrication process of hatch-cover in a container ship. In order to do it, the transitional behavior of global bending distortion in the deck of hatch-cover during fabrication process was measured by 3-dimensional measuring instrument. From the results, the principal factor controlling the global bending distortion was identified as the bending moment associated with the longitudinal shrinkage force and transverse shrinkage caused by welding and flame heating and the change of the centroid axis of hatch-cover in each fabrication process. Therefore, in this study, with the predictive equations of the longitudinal shrinkage force and transverse shrinkage caused by welding and flame heating and the simplified thermo elastic method, the predictive method for the global bending distortion was established and verified by comparing with the measured result. Based on the results, the amount of reverse bending distortion of main stiffeners was determined to prevent the global bending distortion of hatch-cover.

Hull Deflections Affecting on the Ship's Propulsion Shafting Alignment in 46K Oil/Chemical Carrier

  • Lee, Yong-Jin;Kim, Ue-Kan;Kim, Jong-Su
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.7
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    • pp.800-807
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    • 2006
  • This paper introduces the hull deflection analysis method by using the direct measurements. Accordingly, this paper demonstrates how the hull deflection data is obtained by the reverse calculations using the bending moments from the stain gauge and bearing reactions from jack-up method. Where the hull deflection data provided by this research is used for the shafting alignment calculations for identical or similar vessels, shafting failures due to hull deflections can be minimized. It will also save time and expenses associated finite element method to predict hull deflections.

An evaluation of load of the steel bar straightener using plastic moment (소성모멘트를 이용한 철근 직선화 장치의 하중 분석)

  • 이동호;박수진;손정현;유완석
    • Journal of the Korean Society for Railway
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    • v.5 no.3
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    • pp.196-200
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    • 2002
  • In this paper, the straightening process of a steel bar straightener is studied. The straightener carries out the bending and reverse bending process repeatedly. Plastic theory is employed for the analysis of roller-supporting-load, and the residual stress and the axial load of a steel bar are calculated by using the bending moment. The Bauschinger effect and plastic moment are calculated by using the residual stress and Swift's method respectively. It is verified from the experiments that the displacement calculated from theory makes it possible to straighten a steel bar.

Quantitative Analysis of Elastic Recovery Behavior after Bending of Ultra High Strength Steel Sheet: Spring-back or Spring-go (유한요소법을 이용한 초고강도 판재 굽힘에 따른 후변형의 정량적 분석: Spring-back or Spring-go)

  • Kwak, E.J.;Lee, K.;Suh, C.H.;Lim, Y.H.
    • Transactions of Materials Processing
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    • v.20 no.6
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    • pp.456-460
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    • 2011
  • A major source of difficulty in die design for high strength steel is the high level of elastic recovery during unloading. The degree of elastic recovery is affected by factors such as material strength, bending angle, punch's corner radius and sheet thickness. Finite Element Method was used in the present work to quantitatively analyze the elastic recovery for various combinations of these parameters. In some cases elastic recovery happened in reverse direction. This phenomenon, which we call spring-go, was explained via changes in stress distribution in the panel occurring in the forming process.

Properties of Alkali Hydrolyzed Polyester Fabric by Tank/Liquor-flow Method (Tank/liquor-flow 방식에 의한 폴리에스테르 직물의 감량특성)

  • 서말용;한선주;박상완;서수정;김삼수
    • Textile Coloration and Finishing
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    • v.10 no.2
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    • pp.1-7
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    • 1998
  • In this study, PET fabric was hydrolyzed with NaOH using the Tank m/c and Liquor-flow m/c to determine the alkali hydrolysis properties of PET fabrics. The results were as follows : The weft density and tensile strength of PET fabrics hydrolyzed with Liquor-flow m/c were higher than those hydrolyzed with Tank m/c in case of less than 10% of weight loss. However, above 10% of weight loss, reverse phenomenon was showed. K/S value of hydrolyzed PET with Liquor-flow m/c was higher than that with Tank m/c above 10% of weight loss. It was observed that the micropores of PET surface were collapsed due to physical force(abrasion and collision) during hydrolysis. Bending rigidity of hydrolyzed PET fabric was about 32% and 40% of bending rigidity of warp and weft direction of untreated fabric at 7% of weight loss, respectively. Above 7% of weight loss, decrease rate was decreased.

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Complex Modal Testing for Rotating Disks with Support Motion (지지부의 운동을 가진 회전원판의 복소모드시험)

  • Ham, Jong-Seok;Lee, Chong-Won
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.1513-1520
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    • 2000
  • Complex modal testing method for rotating disks with support motion is introduced which handles the pairs of two point excitation and responses of the disk as complex input and output, respectively. This method utilizes the directivity information and the separation over the rotational speed of forward and backward traveling wave modes or bending coupled modes in the directional frequency response functions(dFRFs). This method synthesizes the normal/reverse dFRFs and complex wave dFRF, which were originally applied to rotating shaft and rotating disk, respectively, and is applied to complex system with dynamically coupled rotating disks and shaft. Experiments with a commercial hard disk drive spindle system demonstrate the validity of this method.

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