PSI - Issue 14

Ilyin A.V. et al. / Procedia Structural Integrity 14 (2019) 964–977 Ilyin A.V., Filin V.Yu. / Structural Integrity Procedia 00 (2018) 000 – 000

977

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K Ires is found from formulae similar to (8) received by FEM procedure mentioned above. One of the key problems is a choice of the upper limit in the integral (10). An admissibility of a large crack in a welded structure always remains disputable even in availability of reliable data on static fracture toughness in air and in a corrosion medium. Partly for this reason the suggested ideology includes such a calculation in a “virtual” manner. Existing failure assessment procedures, as a rule, demand for structural integrity in presence of a crack of the depth up to 0.25 S . Figure 8 represents the integration results of (10) in the limits from 3 mm up to 0.25 S . Within this limitation a crack extends in a field of tensile residual stress, therefore no significant influence of cyclic asymmetry on N c is observed at low stress levels, this value mainly depends on the single stress range. One of specific features for welded joints (in contrast to base metal specimens) is an increasing difference of cyclic life at tension and compression with at a growing cyclic stress range. The suggested procedures of fatigue assessment for welded joints made of high strength steel include a long list of parameters that could essentially vary for a certain structure. An account of peculiarities for these materials may be in general reduced to the check of their probable tendency to stress corrosion cracking: if such a propensity is observed, it is necessary to adjust the limiting state to avoid uncertainties in prediction of corrosion-fatigue damage kinetics. Here the matter is that such assessments have to be carried out not only for base and weld metal, but also for the metal of heat-affected zone accounting for an expected range of specific heat input at welding (maximum and minimum ones for an accepted welding procedure) and well as for a probability of non-optimal corrosion protection. A much higher amount of methodical corrections arises in the need to consider the peculiarities of technological procedures applied for welding and assembling. The list of factors for the detailed analysis includes  Weld toe micro geometry for a particular welding procedure that determines the stress/strain concentration,  Weld beads allocation and interpass temperatures that may result in essential changes of residual stress fields,  Sequence of welding and assembling operations, application of elastic deformation to fit the parts of a structure being assembled, as they could result in appearance of long-distance acting reactive stress. Conclusion

Acknowledgements

Long-term cyclic tests giving the essential experimental results have been carried out by T.A.Fedorova, M.A.Gusev, K.E.Sadkin, A.A.Lavrentyev and O.P.Vinogradov on equipment maintained by E.A.Belkov. Numerical simulation and FEM analysis were done by A.V.Mizetsky and D.M.Artemiev.

References

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