• Title/Summary/Keyword: Fatigue design curve

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FATIGUE DESIGN OF BUTT-WELDED TUBULAR JOINTS

  • Kim, D. S.;S. Nho;F. Kopp
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.127-132
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    • 2002
  • Recent deepwater offshore structures in Gulf of Mexico utilize butt welded tubular joints. Application of welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical because the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimating the fatigue behavior of these tubular members in the design stage is generally conducted by using S-N curves specified in the codes and standards. Applying the stress concentration factor of the welded structure to S-N approach often results in very conservative assessment because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fracture mechanics and fitness for service (FFS) technology have been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves to be used and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. An attempt was made to develop set of S-N curves based on fracture mechanics approach by considering non-uniform stress distribution and a threshold stress intensity factor. Series of S-N curves generated from this approach were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02"). Similar comparison with API X′ was made for tubular joint.. These initial crack depths are larger than the limits of inspection by current Non-destructive examination (NDE) means, such as Automatic Ultrasonic Inspection (AUT). Thus a safe approach can be taken by specifying acceptance criteria that are close to limits of sizing capability of the selected NDE method. The comparison illustrates conservatism built into the S-N design curve.

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Robust Design and Thermal Fatigue Life Prediction of Anisotropic Conductive Film Flip Chip Package (이방성 전도 필름을 이용한 플립칩 패키지의 열피로 수명 예측 및 강건 설계)

  • Nam, Hyun-Wook
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.9
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    • pp.1408-1414
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    • 2004
  • The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

A Study on Fatigue Characteristics of Domestic Low-Relaxation PS Strands (국산 저이완 PS 강연선의 피로특성에 관한 연구)

  • 변근주;송하원;박상순;노병철
    • Journal of the Korea Concrete Institute
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    • v.11 no.6
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    • pp.113-119
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    • 1999
  • Fatigue failure is a phenomenon such that structures under cyclic service load is failed by sudden brittle manner. Therefore, in order to obtain structures safety against the fatigue failure during their service lifes, fatigue characteristics should be considered for design and analysis of the structures. As stress range of prestressed (PS) tendons, which governs fatigus characteristic of prestressed concrete (PSC) structures, increases with increased use of partial prestressig, it is more necessary to consider fatigue characteristics of PS tendons. In this paper, direct-tension fatigue experiments with special specimen-setting devices are carried out to obtain fatigue characteristics of domestic low relaxation PS strands having different diameters and PS strands connected with coupler. Then, allowable stress range of fatigue for PSC beams using low relaxation strands are presented for the fatigue examination of prestressed concrete beams applied cyclic loading.

Fatigue Analysis of Welding Bogie Frames for Rolling Stocks Using The equilibrium-equivalent structural stress method (등가구조응력법을 이용한 철도차량 용접대차프레임의 피로해석)

  • Kim, Chul-Su;Ahn, Seung-Ho;Chung, Kwang-Woo;Cheon, Young-Suk;Park, Choon-Soo;Kim, Sang-Su;Jang, Cheon-Su
    • Proceedings of the KSR Conference
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    • 2010.06a
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    • pp.1243-1248
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    • 2010
  • Fatigue design and evaluation of welded joints are typically carried out by weld classification approach in which a family (theoretically infinite) of parallel nominal stress based S-N curves are used according to joint types and loading modes as well as extrapolation-based hot spot stress. Traditional finite element methods are not capable of consistently capturing the stress concentration effects on fatigue behavior due to their mesh-sensitivity in stress determination at welds resulted from notch stress singularity. The extrapolated hot spot stresses tend vary, depending on the element sizes, types, joint types, and loading mode. however, the equilibrium-equivalent structural stress method(E2S2) has been recently developed through several joint industry projects as a robust method to analyze welded components using finite element analysis. This method has been proven effective in correlating a large amount of published fatigue test results in the literature such as master S-N curve and has used for evaluating the fatigue life of welding components. In this study, fatigue analysis of the welding bogie frame is examined using E2S2 method with master S-N curve.

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A parametric study based on spectral fatigue analysis for 170k LNGC

  • Park, Tae-Yoon;Jang, Chang-Doo;Suh, Yong-Suk;Kim, Bong-Jae
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.3 no.2
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    • pp.116-121
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    • 2011
  • The Spectral Fatigue Analysis is representative fatigue life assessment method for vessels. This Analysis is performed generally for the whole vessel and many assessment sites. The spectral fatigue analysis is performed through the process of hydrodynamic response analysis, global structural analysis, local structural analysis and calculation of fatigue damage. In these processes, fatigue damage is affected by many variables. The representative variables are S-N curve data, wave scatter data, wave spectrum, bandwidth effect and etc. In this paper, the effects of these variables to the fatigue damage are analyzed through the spectral fatigue analysis for 170k LNGC.

Reliability analysis on fatigue Strength for Certification of Aircraft Composite Structures

  • Choi, Cheong Ho;Lee, Doo Jin;Jo, Jae Hyun;Bae, Sung Hwan;Lee, Myung Jik;Lee, Jong Ho
    • Journal of Aerospace System Engineering
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    • v.15 no.2
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    • pp.16-25
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    • 2021
  • Reliability of fatigue strength on Aircraft Composites(GFRP) Structures was assessed in this paper. Fatigue strength of GFRP was used through the existing fatigue test data with Monte Carlo method. The Sa-Nf curve of composites fatigue strength was assumed as normal distribution and reliability was analyzed using SSIT model. Fatigue stress was designed IAW ASTM F3114-15 with special safety factor of Ssf=1.2~2.0. Reliability was calculated by analytic method and FORM. Sensitivity for the effect of mean and standard deviation of fatigue strength as well as fatigue stability was evaluated. This result can be usefully applied to reliability and fatigue design for composite structures of light weight aircraft.

Evaluation of the Fatigue Strength and the Mechanical Properties for Cargo Containment System in LNG Ship (LNG선박용 내조시스템 소재의 기계적 특성 및 피로강도 평가)

  • Shim, Hee-Jin;Kim, Min-Tea;Yoon, In-Su;Kim, Yung-Kyun;Kim, Jung-Kyu
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1-6
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    • 2007
  • The membrane type LNG(Liquefied Natural Gas) cargo containment system is a special design structure for the large deformation behavior at LNG temperature$(-162^{\circ}C)$. The design of membrane is required great confidence so that membrane can plat role in the tightness of flammable fluid storing. LNG cargo containment is loaded and unloaded LNG between twice and five times in a week. During this process, the membrane has large deformation behavior due to the variation of temperature and pressure to the self weight. In this study, the evaluation of the fatigue strength of membrane is very important to determine the design life of LNG storage tank and to evaluate the mechanical properties at the LNG temperature. Also, in the view point of large deformation, the evaluation method is applied conservatively $\epsilon-N_f$ curve of SUS 304L.

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Fatigue Analysis of LNG Cargo Containment System Connections in Membrane LNG Carrier

  • Park, Jun-Bum
    • Journal of Advanced Research in Ocean Engineering
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    • v.3 no.3
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    • pp.112-124
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    • 2017
  • As an LNG carrier preserves and transports liquefied natural gas under minus $163^{\circ}C$, the cargo tank has to have sufficient hull strength against not only the wave loads but also against loads caused by loading and unloading and thermal expansion to keep the LNG safely. The main insulation types for a CCS are No.96 and Mark III from GTT for the membrane LNG carrier. Particularly, the invar membrane plate in No.96 is very thin and its connections could experience high local stresses owing to such dynamic loads. Therefore, it should be verified whether those connections have sufficient fatigue lives for the purpose of operation and maintenance. This research aims at performing fatigue analysis with 0.1 fatigue damage criteria for 40 years of design life to support new membrane CCS development using proper S-N curves and the associated finite element modeling technique for each connection and then propose a reasonable design methodology.

Shape Optimization Considering Fatigue Life of Pulley in Power-Steering Pulley (파워스티어링 오일펌프용 풀리의 피로수명을 고려한 형상최적화)

  • Shim, Hee-Jin;Kim, Jung-Kyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.9 s.252
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    • pp.1041-1048
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    • 2006
  • The pulley is one of core mechanical elements in the power steering system for vehicles. The pulley operates under both the compressive loading and the torque. Therefore, to assure the safety of the power steering system, it is very important to investigate the durability and the optimization of the pulley. In this study, the applied stress distribution of the pulley under high tension and torsion loads was obtained by using finite element analysis. Based on these results the fatigue life of the pulley with the variation of the fatigue strength was evaluated by a durability analysis simulator. The results at 50% and 1% for the failure probability were compared with respect to the fatigue life. In addition to the optimum design for the fatigue life is obtained by the response surface method. The response function utilizes the function of the life and weight factors. Within range for design life condition the minimization of the weight, one of the formulation, is obtained by the optimal design. Moreover the optimum design by considering its durability and validity is verified by the durability test.

An Experimental Study of fatigue Strength of Welded Structures Using Structural Stress and Hot Spot Stress (구조응력 및 핫스팟응력을 이용한 피로수명 평가에 관한 실험적 연구)

  • Kang, Sung-Won;Kim, Myung-Hyn;Kim, Seok-Hun;Ha, Woo-Il
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.2 s.140
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    • pp.129-135
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    • 2005
  • At present, fatigue design of welded structures is primarily based on a nominal stress or hot spot stress approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress based fatigue design approach is cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. The hot spot stress based fatigue design has a difficulty of finding a proper stress through the global model, the midium size model, and the detail model of ship structure. Also, it is difficult to link proper displacements within three different mesh size models. Recently, the structural stress is proposed as a mesh-size insensitive structural stress definition that gives a stress state at weld toe with relatively large mesh size. However, this method requires an experimental validation in obtaining the fatigue strength of weldments. Therefore, in this study, a series of experiment is performed for various sizes of weldments.