The development of two multiaxial ductility factor predicting models based on creep cavity growth theory

In this study, the multiaxial ductility factor was analyzed based on the power-law creep grain-boundary cavities growth theory under multiaxial stress states. Based on this theory, the theoretical cavities growth rates under a multiaxial stress state were discussed and the predicting model of a stress-state parameter & alpha; was revised by using an empirical fitting expression denoted as & alpha;Wu, which exhibited a good agreement to analytical results of the stress-state parameter & alpha; and multiaxial cavities growth rates. Then, according to the relationship between uniaxial and multiaxial creep failure strain, a new empirical predicting model of multiaxial ductility factor MDFWu was established which involved the multiaxial parameter & alpha;Wu and uniaxial parameter & alpha;0. Besides, the theoretical model of multiaxial ductility factor MDF could also be established. By fitting the theoretical values of MDF, another predicting model MDFWM was proposed. The development of two multiaxial ductility factor predicting models could be achieved. Finally, predictions of these two novel multiaxial ductility factor models and the Cocks-Ashby as well as Wen-Tu model were compared with experimental data, and the prediction accuracy of MDFWu and MDFWM models was significantly improved, especially for the latter one.