Welded specimens of closed section steel parts, as used in railway bogies, were investigated by fatigue tests and by calculation of nominal and notch stresses. The analysed square tubular specimen is geometrically similar to the dimensions of the section of interest in the railway bogie. Weld seam types analysed using the square section were fillet welds and single bevel butt welds. As single bevel groove welds are also used in bogies, but pose problems when welding square section tubes (backing run is not possible), these welds were analysed using flat specimens under tension loading. The cycles to crack initiation of all detail specimens amount to around 50% of the failure cycles. Square tubular specimens with fillet weld and without stress relief fail in the weld root notch as well as at the weld toe. The area of failure of these square tubular specimens with stress relief and blast cleaning after welding is always the weld root. The notch stress in the weld root is 15% higher than at the weld toe using a reference radius of 1 mm. The differing points of failure of the square tubular specimens with and without stress relief can be explained by the residual stress state. The residual stress measurements show relatively high tensile residual stresses at the weld toe after 100,000 cycles (transverse to weld direction: 100-200 MPa) for as-welded specimens. The blast cleaning process produces compressive residual stresses in the area of weld toe. Thus, the stress relieving and the blast cleaning operations increase the fatigue strength behaviour of weld toe. This could be one possible cause for the crack initiation at the weld root of stress relieved and blast cleaned specimens with fillet weld. The scatter range of SN-curves of the square tubular specimens is considerably smaller for the specimens with residual stresses relieved after welding, compared to the as-welded specimens. The line of 50% survival probability is however unchanged. The test results related to the nominal and notch stresses are significant higher than the relevant fatigue resistance in IIW recommendations. The notch stress evaluation of the test results has a higher difference between the experimental stress values and the fatigue strength of IIW-Recommendations than the nominal stress evaluation. Thus, the results confirm that the application of the notch stress method according to the IIW-Recommendations supplies a sufficiently conservative evaluation of welded joints.
Fatigue strength analysis of welded joints in closed steel sections in rail vehicles
Dauerschwingfestigkeitsanalyse von Schweißverbindungen in geschlossenen Stahlbereichen von Schienenfahrzeugen
International Journal of Fatigue ; 34 , 1 ; 112-121
2011
10 Seiten, 22 Bilder, 1 Tabelle, 23 Quellen
Article (Journal)
English
Welded joints for flat footed rail sections
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