Residual stresses in an offshore weld may affect the fatigue life of the structure, and should hence be included in calculations of fatigue crack propagation and fatigue lives. In the present investigation neutron diffraction is used as a non-destructive technique for the evaluation of through thickness variations of residual strains in welded test samples of steel plates. The neutron diffraction strain measurements show relatively high residual strains reaching 0.001 near the outer surfaces and - 0.0004 near the centre of the plates. A simplified strain/stress conversion indicates that the highest residual stress exceeds approximately 50 % of the material yield stress of sigmay is nearly equal to 400 MPa. The non-destructive neutron diffraction technique has been used successfully to investigate the residual strain state caused by welding in two test welds. The results show that for both samples the welding process has caused relatively high tensile residual strains near the surfaces where fatigue cracks are expected to initiate. The maximum residual stresses are found to reach approximately 50 % of the material yield stress. This is expected to have a pronounced effect on the fatigue crack propagation during stochastic loading and constant amplitude loadings. It is now the aim to incorporate the residual strains and stresses determinded in the investigation into the calculations of fatigue lives by modifying the load spectra for constant amplitude loading and stochastic loading. Subsequently the results of these calculations will be compared to actual fatigue tests of similar test samples.
Neutron diffraction measurements of residual strains in offshore welds
Messung der Eigenspannungen in Offshore-Schweißnähten durch Neutronenbeugung
1995
6 Seiten, 4 Bilder, 2 Tabellen, 24 Quellen
Article (Journal)
English
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