Citation: Ji, D.; Hu, X.; Zhao, Z.; Jia,
X.; Hu, X.; Song, Y. Stress Rupture
Life Prediction Method for Notched
Specimens Based on Minimum
Average Von Mises Equivalent Stress.
Metals 2022, 12, 68. https://doi.org/
10.3390/met12010068
Academic Editor: Marcello Cabibbo
Received: 28 November 2021
Accepted: 24 December 2021
Published: 30 December 2021
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Article
Stress Rupture Life Prediction Method for Notched Specimens
Based on Minimum Average Von Mises Equivalent Stress
Dawei Ji
1,2
, Xianming Hu
1,2
, Zuopeng Zhao
1,2
, Xu Jia
1,2
, Xuteng Hu
1,2,
* and Yingdong Song
1,2,3
1
College of Energy & Power Engineering, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China; jidawei@nuaa.edu.cn (D.J.); 15950537166@163.com (X.H.); zpzhao@nuaa.edu.cn (Z.Z.);
xujiacepe@nuaa.edu.cn (X.J.); ydsong@nuaa.edu.cn (Y.S.)
2
Key Laboratory of Aero Engine Thermal Environment and Thermal Structure, Ministry of Industry and
Information Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
3
State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics
and Astronautics, Nanjing 210016, China
* Correspondence: xthu@nuaa.edu.cn
Abstract:
Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169
with different stress concentration coefficients. It was found that the duration of the first stage of
the creep curve increases with the increase of stress concentration coefficient, while the fracture
ductility decreases with the increase of stress concentration coefficient. To predict the life of notched
plate specimens, four constitutive models were used to analyze the stress and strain of the notches.
It was
found that the average Von Mises equivalent stress (AVES) on the minimum notch section
first decreases and then increases with the creep time, resulting in a minimum value. The minimum
average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched
specimens in this paper. The creep life equation is fitted according to the results of creep tests of
smooth specimens, and then the predicted life of notched specimens is obtained by substituting the
minimum average Von Mises equivalent stress of notched specimens into the creep equation. The
prediction results of the four constitutive models are within 2 times the dispersion band, and the
three-stage model is within the 1.5 times dispersion band.
Keywords:
nickel-based superalloy; creep rupture; life prediction; notched specimens; average Von
Mises equivalent stress
1. Introduction
The hot section components of aero-engine often operate at relatively high tempera-
tures for a prolonged time. The complex loads and irregular shapes result in a multiaxial
state of stress in the components. To study the creep behavior of this kind of component
in the complex working environment and predict their life, the first step is to accurately
predict the stress rupture life of notched specimens under a laboratory environment.
The research on the rupture life of notched specimens at high temperatures has
gradually increased since the 1970s, among which the notched round bar specimens are
widely researched. The commonly used methods include the skeletal point method [
1
–
6
],
the multi-axial ductility exhaustion method [
7
–
11
], and the prediction method based on
AVES [
12
]. These methods cannot be operated without the finite element analysis of notched
specimens. Hayhurst [
6
] et al. used skeletal point stress for the prediction of rupture life.
They found that in the process of stress redistribution, there was a point at the minimum
cross-section where the stresses are nearly constant. The skeletal point stresses have been
used to characterize the deformation and failure behavior of the material under multiaxial
creep conditions. This model is suitable for notched round bar specimens to find the skeletal
point along the radius direction. While if the cross-section of the specimen is rectangular
or irregular like that in the real components, it is not easy to find the skeletal point. The
Metals 2022, 12, 68. https://doi.org/10.3390/met12010068 https://www.mdpi.com/journal/metals
