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2 Journal of Theoretical and Applied Mechanics

2 2023

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

Wu Dongquan, Li Yupeng, Liu Zixiang, Li Dinghe

Journal of Theoretical and Applied Mechanics

2023

Vol. 61 nr 3

481--494

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 α was revised by using an empirical fitting expression denoted as αWu, which exhibited a good agreement to analytical results of the stress-state parameter α and multiaxial cavities growth rates. Then, according to the re- lationship between uniaxial and multiaxial creep failure strain, a new empirical predicting model of multiaxial ductility factor MDFWu was established which involved the multiax- ial parameter αWu and uniaxial parameter α0. Besides, the theoretical model of multiaxial ductility factor MDF could also be established. By fitting the theoretical values of MDF, an- other predicting model MDFWM was proposed. The development of two multiaxial ductility factor predicting models could be achieved. Finally, predictions of these two novel multiax- ial 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.

Study on constraint effect and creep crack initiation of plate containing elliptical embedded cracks

Wu Dongquan, Liu Zixiang, Li Yupeng, Li Dinghe, Zhang Zhiqiang

Journal of Theoretical and Applied Mechanics

2023

Vol. 61 nr 3

545--557

In this study, a plate structure containing elliptical embedded cracks loaded under high temperature is studied. The constraint effect and creep crack initiation of the plate con- taining embedded cracks are discussed by using the finite element method based on the creep ductility exhaustion model. It is indicated that the highest constraint level or the load-independent parameter Q* is observed at the endpoint of the ellipse major axis of an elliptical embedded crack, and the constraint levels increase with crack length or depth, which represents a worse condition for the structure, such as higher stress concentration and greater danger of failure for a larger crack depth ratio a/t or crack length ratio a/c. Moreover, under the creep condition, the embedded crack with a larger a/t, a/c or loadings is accompanied with a higher crack driving force, which can accelerate creep damage, creep cracking initiation (CCI) and shorten the creep crack initiation (CCI) time. Additionally, an empirical prediction equation and engineering approach to the constraint parameter and the CCI time for elliptical embedded cracks are proposed, and the engineering approach to the CCI time is validated.