Issue 38

M. Kepka et alii, Frattura ed Integrità Strutturale, 38 (2016) 82-91; DOI: 10.3221/IGF-ESIS.38.11 90 The largest damage is caused by the longitudinal component of the load (bending load acting on the articulated joint). Fig. 10 shows plots of the distribution function of the complex load capacity factor for three design lifetimes of the bus. These distributions indicate the following outcomes. The probability that a tot at the design lifetime of L = 1 mil. km will be less than 1 is lower than 30 %. There is a high probability of P = 97.5 % that the value a tot will be less than 1 only at the lifetime of L = 250 000 km. Figure 10 : Distribution functions of the complex loading factor for three values of design service life. C ONCLUSION he objective of this paper was to use an articulated joint of a bus for demonstrating the engineering approach for fatigue life assessment of welded parts operating under multiaxial loads, and expand this approach by incorporating the probabilistic perspective. The assessment of the resistance to fatigue damage is based on distribution functions of the complex load capacity factor which has been calculated from three load components acting on the welded joint by using a formula analogous to yield criteria calculations. This paper illustrates the following benefits of this approach. If this structural detail was examined using no other than the deterministic approach, taking into account only the normal stress component which is perpendicular to the welded joint, and the median S - N curve, the detail would be found to meet the design lifetime requirement (Fig. 9, component a x ). Even though the stress component perpendicular to the welded joint dominates in this case, the combined assessment of the weld shows that the probability of meeting the design lifetime is no more than 30 %. The variance of in-service loading conditions has a milder effect on the life than the variance of material properties, provided that the lifetime estimates are based on a sufficiently long record of the loading process (21 km in our case). At half running distance, the variance doubles, which would broaden the distribution functions plotted in Fig. 10. In the redesigned structural detail, the stresses in the welded joint were found to be substantially lower, as confirmed by repeated measurement. A CKNOWGLEMENTS his paper is a result of the collaboration between the Regional Technological Institute and Research and Testing Institute Pilsen under the project no. LO1502 entitled Development of the Regional Technological Institute funded from the National Sustainability Programme I (Ministry of Education of the Czech Republic). T T