Deformation and life assessment of high temperature materials under creep fatigue loading

The knowledge of mechanical long term behaviour under static and cyclic loading for high temperature components requires methodologies for life assessment in order to employ the full potential of materials. A phenomenological life time prediction concept which was developed for multi-stage creep fatigue loading demonstrates the applicability of rules for synthesis of stress strain path and relaxation including an internal stress concept, as well as mean stress effects. Further, a creep fatigue interaction concept which was also developed covers a wide range of creep dominant loading as well as fatigue dominant loading. Service-type experiments conducted at different strain rates and. hold times for verification purposes demonstrate the acceptability of life prediction method for variation of conventional 1 %Cr-steels as well as modem high chromium 9-10 %Cr-steels. Generally, the service life of components is influenced by multiaxial behaviour. Multi-axial experiments with e.g. notched specimens and with cruciform specimens accompanied by advanced methods for calculation of stress strain path and life time prediction stress conditions are of future interest.