Speaker
Description
Design codes are typically providing the Efthymiou stress concentration factors (SCF) for the fatigue life estimation of tubular joints. These are often assumed to be slightly biased to the safe side. Hence, many engineers seeking fatigue life optimization are using finite element analysis (FEA) or measurements direct from laboratory tests to obtain unbiased SCFs for tubular joints, both for design optimization and particularly for life extension of existing structures.
However, SCFs both based on FEA and measurements from laboratory experiments are associated with uncertainties. For laboratory experiments these uncertainties may be a result of the individual geometry of the weld profile, the placement of the strain gauges, the strain measurements and the SCF extrapolation methodology. For an FEA such uncertainties are related to modelling of the weld profile, element type, mesh density, SCF extrapolation methodology and other numerical inaccuracies. To understand these uncertainties, SCF values can be determined from a set of tests, or several SCF-values estimated from converged FEA. The challenge is to determine a recommended value for the SCF based on these tests or analysis, where the resulting SCF meets the code required 2.3% exceedance probability and are compatible with the way the SN-curve is determined.
In this paper, structural reliability analysis (SRA) methods are used to model the combined uncertainty of the parameters representing the SN-curve and the measured SCFs from the 4 quadrants of 4 experimental test joints. Based on this analysis, the SCF that, combined with the design SN-curve, provides the minimum fatigue life is established. Based on this analysis, a method to provide characteristic values of the SCF is suggested. Finally, different FEA analysis of the same detail is established (with and without weld, first and second order elements) and used to estimate the SCF by linear extrapolation and direct extraction and a suggested method to extract SCFs from FEA is provided.
| Conference Topic Areas | Track4: Structural Safety, Integrity Management and Life Extension of Structures |
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