• Title/Summary/Keyword: thermal residual stress

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Analysis of residual thermal stress in an aluminosilicate core and silica cladding optical fiber preform

  • Shin, Woo-Jin;K. Oh
    • Proceedings of the Optical Society of Korea Conference
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    • 2000.02a
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    • pp.214-215
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    • 2000
  • As silica based optical fibers and preforms are processed at a high temperature, residual stresses are bulit in the strucure when cooled down to the room temperature. The magnitude of the residual stress depends on the difference in the thermal expansion coefficients between core and cladding glass as well as on the temperature difference. Residual stress distribution determines the intrinsic strength and could affect the long term reliability of optical fibers. And furthermore, stress can introduces anisotropy into optical fibers by photoelastic effects. The analysis of thermal stress has been intensively studied for multimode fibers$^{(1)}$ and the authors and co-wokers recently reported the stress distribution in a depressed inner cladding structure$^{(2)}$ . The compositions of the glass in the previous studies, however, have been restricted to conventional glass formers, such as GeO2, B2O3, P2O5, Fluorine. (omitted)

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Analysis of Residual Stress Relaxation in Welded Joints due to External Loads (외부하중에 의한 용접 체결부의 잔류응력 이완 특성 해석에 관한 연구)

  • Jang, Chang-Doo;Song, Ha-Cheol;Jo, Young-Chun
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2003.10a
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    • pp.167-170
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    • 2003
  • Thermal elastic-plastic analysis was performed to assess the initial residual stress distribution of welded joints considering temperature dependent material properties. The test model was the idealized boxing fillet specimen, frequently appeared in the joints of longitudinal and transverse members of ship structure. Residual stress relaxations due to external loads were analyzed by subsequent elastic-plastic analysis considering loading and unloading steps, and the characteristics of residual stress relaxations were discussed with the levels of external loads. Additionally, to define the fatigue life of crack initiation and propagation, the S-N data for each crack length were appraised.

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Residual Stress of the Lower Control Arm Subjected to Cyclic Loading (변동하중을 받는 Lower Control Arm의 잔류응력 변화)

  • Kim Gi-Hoon;Kang Woo-Jong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.5 s.248
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    • pp.602-608
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    • 2006
  • Vehicle components such as lower control arm are usually affected by heat during the welding process. As a result, residual stress is generated, which has much effect on mechanical performances such as crashworthiness and durability. In this study, the residual stress in lower control arm has been measured by the x-ray diffraction method and been analyzed by finite element methods. Heat transfer during seam weld process has been calculated and used in calculating thermal deformation with temperature dependent material properties. High residual stress has been found at vertical wall both by measurement and simulation. The simulation also showed the residual stress re-distribution when the component is subjected to cyclic loading condition.

Fatigue Life Prediction of Weldment with Damage Mechanics (손상역학을 이용한 용접부의 피로수명예측)

  • Chung, Heung-Jin;Yoo, Byoung-Chan
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2008.04a
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    • pp.60-64
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    • 2008
  • According to previous research, welding-induced stress in steel structures can significantly affect the fatigue behaviour; it produces initial damage of weldiug part of structure locally and residual stresses reduce the fatigue strength after welding precess. In this study, through continuum damage mechanics, we can estimate the weldiug damage using the stress and strain history during welding process and the effect of welding residual stress for assessment of fatigue life. The variation of welding-induced stresses and strains need be traced precisely in advance for a reliable weldiug damage assessment. In this study, a damage and fatigue analysis techniques for steel structures with welding-induced residual stress are presented. First, We calculate the history of temperature according with welding process. And residual stress with a welding thermal history was evaluated by non-linear thermal stress analysis. Secondly, welding damage and fatigue life are estimated with kinetic damage law.

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Numerical analysis of post welding heat treatment base on the thermal creep elastic-plastic theory (점열탄소성 이론에 의한 용접후열처리에 대한 수치해석)

  • 방한서;차용훈;오율권;노찬승;김종명
    • Journal of Ocean Engineering and Technology
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    • v.11 no.1
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    • pp.113-123
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    • 1997
  • The welding residual stresses produced by welding frequently cause a crack and promote stress corrosion etc. in heat affected zone contained with external load and weakness of material. For the purpose pof relaxation of welding residual stress, post welding heat teratment(PWHT) is widely used. In this paper, the computer program which is based on Thermal-Elasto-plastic-creep theory for plane deformation on developed by finite element method (F.E.M) and verified its propriety by experimental measurement and also by using the developed computer program. The mechanical behavior of butt welding joint is clairfied during PWHT.

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Numerical Analysis of Welding Residual Stress Using Heat Source Models for the Multi-Pass Weldment

  • Bae, Dong-Ho;Kim, Chul-Han;Cho, Seon-Young;Hong, Jung-Kyun;Tsai, Chon-Liang
    • Journal of Mechanical Science and Technology
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    • v.16 no.9
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    • pp.1054-1064
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    • 2002
  • Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.

Numerical Analysis and Experimental Verification of Relaxation and Redistribution of Welding Residual Stresses (용접잔류응력의 이완과 재분포 해석 및 실험적 검증)

  • Song, Ha-Cheol;Jo, Young-Chun;Jang, Chang-Doo
    • Journal of the Society of Naval Architects of Korea
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    • v.41 no.6
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    • pp.84-90
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    • 2004
  • For the precise assessment of the effect of welding residual stresses on structural strength and fatigue crack growth behavior, new FE analysis algorithms for the estimation of residual stress relaxation due to external load and redistribution due to fatigue crack propagation were proposed in this paper. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis In the analysis of fatigue crack propagation, the applied SIF(Stress Intensity Factor) range was evaluated by $\frac{1}{4}$-point displacement extrapolation method, and the effect of welding residual stresses on crack propagation was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

The effect of initial stress induced during the steel manufacturing process on the welding residual stress in multi-pass butt welding

  • Park, Jeong-ung;An, Gyubaek;Woo, Wanchuck
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.2
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    • pp.129-140
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    • 2018
  • A residual stress generated in the steel structure is broadly categorized into initial residual stress during manufacturing steel material, welding residual stress caused by welding, and heat treatment residual stress by heat treatment. Initial residual stresses induced during the manufacturing process is combined with welding residual stress or heat treatment residual stress, and remained as a final residual stress. Because such final residual stress affects the safety and strength of the structure, it is of utmost importance to measure or predict the magnitude of residual stress, and to apply this point on the design of the structure. In this study, the initial residual stress of steel structures having thicknesses of 25 mm and 70 mm during manufacturing was measured in order to investigate initial residual stress (hereinafter, referred to as initial stress). In addition, thermal elastic plastic FEM analysis was performed with this initial condition, and the effect of initial stress on the welding residual stress was investigated. Further, the reliability of the FE analysis result, considering the initial stress and welding residual stress for the steel structures having two thicknesses, was validated by comparing it with the measured results. In the vicinity of the weld joint, the initial stress is released and finally controlled by the weld residual stress. On the other hand, the farther away from the weld joint, the greater the influence of the initial stress. The range in which the initial stress affects the weld residual stress was not changed by the initial stress. However, in the region where the initial stress occurs in the compressive stress, the magnitude of the weld residual compressive stress varies with the compression or tension of the initial stress. The effect of initial stress on the maximum compression residual stress was far larger when initial stress was considered in case of a thickness of 25 mm with a value of 180 MPa, while in case of thickness at 70 mm, it was 200 MPa. The increase in compressive residual stress is almost the same as the initial stress. However, if initial stress was tensile, there was no significant change in the maximum compression residual stress.

A Study on the Production Mechanisms of Residual Stress in Welded T-joint of Steel Pipe Member (T형 강관 용접 이음부의 잔류응력 생성기구에 관한 연구)

  • 장경호;장갑철;경장현;이은택
    • Journal of Welding and Joining
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    • v.21 no.6
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    • pp.40-45
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    • 2003
  • Steel members have advantages of resisting torsion and axial compression. In design, residual stresses at the welded joint of T-shape steel pipes are one of the most important points to be considered. In this paper, characteristics of residual stresses of welded joints are clarified by carrying out 3D non-steady heat conduction analysis and 3D thermal elastic-plastic FE-analysis. According to the results, the production mechanism of residual stresses at the welded joint of T-shape steel pipe is clarified. In this paper, circumferential stresses depended on thermal histories but axial and radial stresses were more dependent on geometrical shape than thermal histories. Residual stresses in the axial direction on the lower part of pipe member were tensile, controlled by geometrical shape. However, in case of middle part, residual stresses in all the directions were controlled by thermal histories.