Fatigue design of welded components of railway vehicles - influence of manufacturing conditions and weld quality

The weld quality has a significant influence on the fatigue strength of welded joints and components. In the industrial field, there are different manufacturing conditions and as a consequence of this, the weld quality can vary considerably. Therefore, fatigue tests of different joint types were performed, analysing the influence of manufacturing conditions and of weld quality on the fatigue strength of welded components of railway vehicles. For these fatigue tests, typical welded joints with the significantly different notch effect were selected, i.e. butt weld specimens with relatively low notch effect and cruciform joints with relatively high notch effect. These specimens were made under typical industrial conditions by three different companies from the railway industry (Bombardier, Siemens, and ALSTOM). Thus, they represented the weld quality level of this industrial field. Prior to the fatigue testing of these specimens, the weld quality was checked in accordance with the criteria of the DIN EN 15085, which is based upon the general weld quality standard DIN EN ISO 5817. On the basis of the result of this weld quality inspection, most specimens have the quality level B relating to DIN EN ISO 5817. The fatigue tests under axial loading show a significantly higher fatigue strength level for the nominal approach in comparison with IIW Recommendations. However, the determined fatigue stress range of both joint types investigated is conservative, in comparison with the allowable fatigue strength of the actual guidelines or standards applied in the railway industry. For both joint types investigated the relevant notch stress range was determined based on the results for nominal fatigue strength. The fatigue strength differences between the notch stress range of the test results and the notch fatigue resistance of the IIW Recommendations are significantly less than the differences in the nominal strength comparison. The determined nominal fatigue strength values of the investigated welded joints correspond to the weld quality level B, as defined by DIN EN ISO 5817, and additionally, to the requirement of angular distortion = 0.75 x plate thickness and to the root face length <= 0.75 x plate thickness. In summary, this investigation shows the fatigue strength potential for welded components in the field of the railway industry. The results provide useful information for the economical and safe fatigue design of welded components, depending on the manufacturing conditions and the real weld quality