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Journal of Theoretical and Applied Mechanics
Font Size. Journal of Theoretical and Applied Mechanics 56 , 3, pp. Regardless of the welding method, a new joint and the surrounding area are inevitably subjected to thermo-physical perturbation. The paper presents analyses of many different issues involved in welding and potential solutions including adoption of simplifying assumptions, application of numerical algorithms and development of reliable representative models. The Finite Element Method is used to determine residual stress distribution, using results from thermo-physical tests and widely known mechanical properties of metals subjected to welding processes.
This data reveals that it is necessary to precisely define location of the analyzed welded fragment to correctly determine thermal boundary conditions. Failure always initiated in the root of the weld. An overview of the fatigue tests is given in Table 2. From the results of the fatigue tests at constant amplitude loading S—N curves N?
In Eq. Geometry of? Some fracture mechanics tests were conducted under static and cyclic loading in order to investigate the behaviour of cracks in different welded CT-specimens.
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The details of these tests and their results are explained in Section 6. Results and numerical investigations with the nominal stress concept The nominal stress rn in the welded section can be easily calculated from: reference . The scatter of stress is Tr? The maximum likelihood method was used for analysis . All results were compared with the fatigue resistance curves in the IIW recommendation for fatigue design of welded joints and components . The section moduli, Wb and Wt for bending and torsion respectively are calculated from the dimension of the tube in the welded section.
Lifetime Estimation of Welded Joints | Tadeusz Lagoda | Springer
To simplify the calculation, the nominal stress at the outer diameter of the tube and not at the critical point in the root of the weld is used. For the? Together with the results from other concepts the values k, rak, ra2? The experimental results of the tube specimens show that conservative estimates of the fatigue strength are derived on the application of Ref.
Although the geometries of the welds are different and, therefore, the lifetime of the modi? The same results are achieved for laser welded?
Lifetime Estimation of Welded Joints
Only for TIG welds at lower stresses, does the modi? Fatigue strength is higher for laser welds in comparison to TIG welds. The different scatters of stress give an indication of the different welding qualities, Table 7. Results and numerical investigations with the structural hot spot stress concept The structural hot spot stress rhs in the welded section was determined by a linear elastic? Fatigue strength of MAG-welded tube specimens tested under rotating bending on the basis of nominal stresses and fatigue resistance curve according to .
Fatigue strength of MAG-welded tube specimens tested under torsion on the basis of nominal stresses and fatigue resistance curve according to . Fatigue strength of laser welded? A coarse or? The structural hot spot stress rhs was calculated by extrapolation of the principal stress r1 at the surface to the root of the weld and, for comparison, by linearisation through the plate thickness using the recommendations of , Fig. There is only a marginal difference between the results of these two calculations. It was observed that it is also possible to apply the structural hot spot stress concept when cracks start at the root of the weld even though to date this has been excluded in .
The difference between the structural hot spot stress and the nominal stress is described by a factor similar to a stress concentration factor with K ths;t? K ths;tc? K ths;b? The values of the experimentally determined S—N curves for the tube and? The results show that the structural hot spot stress is approximately equal for both geometries of weld. The high stress concentration in the conventional butt joint is only considered marginally in the factors Kths,t and Kths,tc. Fatigue strength of TIG-welded?
Detail of weld in FEA for determination of structural hot spot stress rhs in? Table 4 Stress concentration factors Kths,b for tube specimens tested under rotating bending, Kths,t for tube specimens tested under torsion and Kths,tc for? Tube specimen Rotating bending cbj MAG 1. Furthermore, the selection of an FAT-value for the particular case is dif?
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The use of the maximum value from  gives a conservative estimate. Results and numerical investigations with the elastic notch stress concept The elastic notch stress re in the root of the weld, as being the critical point, was determined by a linear elastic? The elastic notch stress can be either a principal stress r1 or a von-Mises stress rvM.
Probably local stiffness and stress distribution are too strongly in? For the latter, a reference curve was developed in  because it was also used in the other investigations in the reported study. The identical mesh was used in all cases in the joint project of the?
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In the? This excess penetration is more pronounced in the TIGwelded? Every specimen had a different excess penetration. Fatigue strength of MAG-welded tube specimens tested under rotating bending on the basis of structural hot spot stresses and fatigue resistance curve according to . Two reference radii had to be modeled. Calculation shows that stresses at radius 1 are always higher than at radius 2.
Failure also always occurred there. Therefore, only the stresses at radius 1 are considered in the following.