• Structural Engineering and Mechanics
• /
• 제4권4호
• /
• pp.347-364
• /
• 1996

Presently welded components are designed using S/N curves which predict only the fatigue life of the component. In order to ascertain the condition of the weld at any intermediate period of its life inspection is carried out. If cracks are detected in a weld fracture mechanics is used to find their remaining life. A procedure for assessment is developed here that can be used to verify the condition of a weld before inspection is carried out to detect cracks. This simple method has been developed using linear fracture envelopes by combining S/N curves with linear elastic fracture mechanics.

• 대한조선학회 특별논문집
• /
• 대한조선학회 2015년도 특별논문집
• /
• pp.63-68
• /
• 2015

This paper presents fatigue analysis of helideck structures located in FPSO. After FPSO is moved to the target position where production of resource is performed, FPSO stays at the target position and performs production of resource, storage and off-loading during the design life. Helideck structure is located in FPSO essentially for the movement of personnel and life rescue at emergency situations by using helicopters. Because inertial load induced by FPSO motion and landing and taking-off load of helicopter occur at helideck structures cyclically, helideck structures should be designed to withstand fatigue loads. Therefore, The fatigue assessment of helideck structures should be performed with fatigue loads. Effect of stress concentration due to misalignment between welded plates is considered in fatigue assessment additionally.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2002년도 춘계학술대회 논문집
• /
• pp.125-129
• /
• 2002

Authors had developed the model for the fatigue life assessment of welded details considering residual stress and its relaxation. The model consists of three ingredients; a hot-spot stress approach, a residual stress relaxation, and an equivalent stress. The equivalent stress is induced by stress ranges and the ratios between the applied mean stresses and the ultimate stress of material. Once being tuned with two specific fatigue tests by using load carrying cruciform joint, this model can be applied to many kinds of welded details which structural stress concentration factors are different from each other. This paper reports the application of the proposed model for various welded details including cover plate, longitudinal stiffener, gusset and side attachment. From the investigation of predicted results by using the proposed model it was shown that the ambiguous fatigue characteristics of the various details influenced widely by the welding residual stress are clarified, and also the model could be applied to assess fatigue life of general welded structures.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1989년도 봄 학술발표회 논문집
• /
• pp.11-16
• /
• 1989

This paper presents a fatigue reliability model for the reliability-based evaluation of remaining fatigue life of existing rail-road bridges. It is demonstrated that the simple fatigue reliability model based on the Weibull distribution of fatigue life can be extended by incorporating various effects due to the rate of the train-traffic increase and in-service Inspections. The paper also suggests the system fatigue reliability analysis using an approximate formulation and 2nd-order bound solutions. The application of the proposed model to existing rail-road brdiges based on field load tests shows that it may be practically used for the assessment of fatigue reliability, remaining life, and in-service inspection scheduling of existing rail-road bridges.

• 한국생산제조학회지
• /
• 제19권1호
• /
• pp.71-79
• /
• 2010

One of methods that accomplish fuel-efficient vehicle is to reduce the overall vehicle weight by using aluminum structure typically for cross members, rails and panels in body and chassis. For aluminum structures, the use of Self Piercing Rivet(SPR) is a relatively new joining technique in automotive manufacture. To predict SPR fatigue life, fatigue behavior of SPR connections needs to be investigated experimentally and numerically. Tests and simulations on lap-shear specimen with various material combinations are performed to obtain the joining strength and the fatigue life of SPR connections. A Finite element model of the SPR specimen is developed by using a FEMFAT SPR pre-processor. The fatigue lives of SPR specimens with the curvature are predicted using a FEMFAT 4.4e based on the liner finite element analysis.

• 한국안전학회지
• /
• 제15권1호
• /
• pp.132-139
• /
• 2000

In this study, the fatigue life assessments of steel railway bridge in Japan National Railway were carried out. This railway bridge has been under in service from 1957, and fatigue damages were occurred at bead toe of upper part of vertical stiffeners of stringers, bead toes of scallop in lower part of vertical stiffeners in stringers and crossings of cross beams and stringers. From this study, a series of field tests were carried out by stress history measurement about above mentioned points. And as a results of stress histogram analysis, cummulative fatigue damage rate and fatigue life of these members should be calculate quantitatively. And from this estimation technique, cummulative fatigue damage rate and fatigue life of this railway bridge were strongly affected in passing tonage every year and the histories of live load.

• Journal of Welding and Joining
• /
• 제24권2호
• /
• pp.48-56
• /
• 2006

The fatigue strength of the welds is affected by such factors as the weld geometry, microstructures, tensile properties and residual stresses caused by fabrication. It is very important to evaluate the structural integrity of the welds in nuclear power plant because the weldment undergoes the most of damage and failure mechanisms. In this study, the fatigue assessments for a reactor vessel outlet nozzle with the weldment to the piping system are performed considering the welding residual stresses as well as the effect of local brittle zone in the vicinity of the weld fusion line. The analytical approaches employed are the microstructure and mechanical properties prediction by semi-analytical method, the thermal and stress analysis including the welding residual stress analysis by finite element method, the fatigue life assessment by following the ASME Code rules. The calculated results of cumulative usage factors(CUF) are compared for cases of the elastic and elasto-plastic analysis, and with or without residual stress and local brittle zone effects, respectively. Finally, the fatigue life of reactor vessel outlet nozzle weld is slightly affected by the local brittle zone and welding residual stresses.

• Nuclear Engineering and Technology
• /
• 제45권1호
• /
• pp.99-106
• /
• 2013

Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants. In particular, as operating plants become older and life time extension activities are initiated, operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee connections are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, in this study thermal fatigue evaluation of piping system Tee-connections is performed using the fluid-structure interaction (FSI) analysis. From the thermal hydraulic analysis, the temperature distributions are determined and their results are applied to the structural model of the piping system to determine the thermal stress. Using the rain-flow method the fatigue analysis is performed to generate fatigue usage factors. The procedure for improved load thermal fatigue assessment using FSI analysis shown in this study will supply valuable information for establishing a methodology on thermal fatigue.

• Journal of Welding and Joining
• /
• 제22권2호
• /
• pp.28-32
• /
• 2004

Fatigue life at seam weldment of thick plate was estimated using the finite element and FEM-FAT(an exclusive fatigue solver). Finite element meshing at toe and root of weldment was based oil Radaj's theory. Also, the results of FE analysis were compared with experimental results in the point of Miner's Rule. The results of FE and FEM-FAT analysis were in accord with experimental results within 60% confidence. This result reveals that above techniques is useful in assessment of seam weldment and to be an alternative method instead of an object experiment.

• 대한기계학회논문집A
• /
• 제28권8호
• /
• pp.1174-1182
• /
• 2004

Recently, Self Piercing Rivet(SPR) has been spotlighted in the automotive industry as a substitutive resort of spot welding and has also been watched by the designer as lightening a car body due to their superior assembly processes. Fatigue behavior of SPR joint needs to be investigated experimentally and numerically to predict its structural stiffness and fatigue life. Testing of lap-shear specimens with various material combinations is performed to obtain the joining strength and the fatigue life of SPR connections. The simulation of SPR lap-shear specimens is also conducted to obtain the structural stiffness of SPR connections under different material combinations. A Finite element model of the SPR lap-shear specimen is developed using a FEMFAT SPR pre-processor. The fatigue lift of SPR specimen is predicted using a FEMFAT 4.4e based on the liner finite element analysis.