A synergistic creep fatigue failure model damage (case of the alloy Z5NCTA at 550 °C)

Creep–fatigue tests have been performed on nickel base alloy Z5NCTA 33-21 grade 1. Hold time varied from 0, 10, 30, 90, 300, 1440 and 10,080 min at two values of strain range. It was found that the number of cycles to failure N R decreases with holding time t m, according to a power law: N R = 1.88 × 10 3 · ( t m ) - 0.39 . Prediction of number of cycles to failure for these conditions were made using 3 models which consider the interaction between fatigue and creep damage: Chaboche cumulative damage model, Levaillant creep damage model, and a new proposed synergistic model. This new model has been introduced to significantly reduce the number of adjustable parameters; 12 and 13 that are used versions of Chaboche and Levaillant’s model to 3 in the proposed model. The new model uses a hybrid approach for damage (life fraction for fatigue, relative crack length for creep) and considers a multiplicative rather than an additive synergy of the damages. The two damage evolutions for fatigue and creep are strongly non-linear without incubation periods. The proposed model and the two previous models provide good correlation with experiments except for holding time less than 1000 min.