LIFE PREDICTION FOR THE TITANIUM-ALLOY IMI-834 UNDER HIGH-TEMPERATURECREEP-FATIGUE LOADINGS

In the present investigation the life behaviour of the titanium alloy IMI 834 under loading conditions which are close to real service was c onsidered. Different types of creep-fatigue loadings were applied at 6 00 degrees C, i.e. balanced and unbalanced cycles with different rampi ng rimes into tension and into compression and stress hold Strain Rang e Partitioning (SRP) cycles. The resting was performed in laboratory a ir. The results of the creep-fatigue tests showed that life was reduce d by the different types of creep-fatigue cycles. In the stress hold t ests the mean stresses had a pronounced influence on life. The observe d life of the stress hold SRP cycles could be predicted within a facto r of +/-2 of actual life by frequency-modified approaches. Ii mean str esses were considered in terms of maximum tensile stress or by a modif ied Morrow approach, life predictions remained within a factor of +/- 1.5 of the actual test results. A SRP approach which was frequency mod ified in the present study led to life predictions which fell within a band of a factor of +/- 1.35 of the actual test results.