scholarly journals Creep-fatigue criteria and inelastic behavior of modified 9Cr-1Mo steel at elevated temperatures. Final report

1994 ◽  
Author(s):  
M.B. Ruggles ◽  
T. Ogata
Keyword(s):  
Elevated Temperatures ◽  
Final Report ◽  
Inelastic Behavior ◽  
Creep Fatigue

scholarly journals SCALING OF ZIRCONIUM AT ELEVATED TEMPERATURES. Final Report

1959 ◽  
Author(s):  
H Probst ◽  
E Evans ◽  
W Baldwin, Jr
Keyword(s):  
Elevated Temperatures ◽  
Final Report

scholarly journals A Concise Binomial Model for Nonlinear Creep-Fatigue Crack Growth Behavior at Elevated Temperatures

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 651
Author(s):  
Jianxing Mao ◽  
Zhixing Xiao ◽  
Dianyin Hu ◽  
Xiaojun Guo ◽  
Rongqiao Wang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Dwell Time ◽  
Elevated Temperatures ◽  
Nonlinear Creep ◽  
Nickel Based Superalloy ◽  
Proposed Model ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

The creep-fatigue crack growth problem remains challenging since materials exhibit different linear and nonlinear behaviors depending on the environmental and loading conditions. In this paper, we systematically carried out a series of creep-fatigue crack growth experiments to evaluate the influence from temperature, stress ratio, and dwell time for the nickel-based superalloy GH4720Li. A transition from coupled fatigue-dominated fracture to creep-dominated fracture was observed with the increase of dwell time at 600 °C, while only the creep-dominated fracture existed at 700 °C, regardless of the dwell time. A concise binomial crack growth model was constructed on the basis of existing phenomenal models, where the linear terms are included to express the behavior under pure creep loading, and the nonlinear terms were introduced to represent the behavior near the fracture toughness and during the creep-fatigue interaction. Through the model implementation and validation of the proposed model, the correlation coefficient is higher than 0.9 on ten out of twelve sets of experimental data, revealing the accuracy of the proposed model. This work contributes to an enrichment of creep-fatigue crack growth data in the typical nickel-based superalloy at elevated temperatures and could be referable in the modeling for damage tolerance assessment of turbine disks.

Grain Boundary Cracking of Nickel-Based Alloy 625 Under Creep Loadings at Elevated Temperatures

2019 ◽  
Author(s):  
Yan Liang ◽  
Yifan Luo ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Power Plants ◽  
Elevated Temperatures ◽  
Thermal Power ◽  
Thermal Power Plants ◽  
Alloy 625 ◽  
Creep Fatigue ◽  
Creep Loading ◽  
Initial Cracks

Abstract Since the operating condition of thermal power plants has become harsher for minimizing the emission of CO2, Ni-based superalloys, such as Alloy 617 and 625, have been used in the plants to replace the conventional ferritic materials. Unfortunately, the increase of coefficient of thermal expansion compared with conventional steels is a concern. In addition, Ni-based superalloys have to suffer creep-fatigue random loading because thermal power plants have to compensate the random output of various renewable energies. It was found that the lifetime of Ni-based superalloys under creep-fatigue loading was much shorter than that under simple fatigue or creep loading. Thus, it has become very important to clarify the crack mechanism and establish the quantitative theory for estimating their lifetime under various loading conditions at elevated temperatures. Thus, the elucidation of the initial damage mechanism of Alloy 625 under various loading is indispensable. Hence, the initial cracking mechanism of Alloy 625 at grain boundaries under creep loading was investigated experimentally. The creep test was applied to small specimens in Argon atmosphere. The change of the micro texture during the creep test was observed by using SEM. It was confirmed that all the initial cracks appeared at certain grain boundaries. The change of the crystallinity was observed by EBSD (Electron Back-Scatter Diffraction) analysis quantitatively. It was found that the local accumulation of dislocations at the cracked grain boundaries caused the initial cracks at those grain boundaries. The initiation of cracks appeared clearly between two grains which had difference of KAM (Kernel Average Misorientation) values larger than 0.2. Therefore, dislocations were accumulated at one side of the grain boundary. By measuring the KAM values near grain boundaries, the appearance of initial cracks can be predicted approximately.

Sophisticated Creep-Fatigue Life Estimation Scheme for Pressure Vessel Components Based on Stress Redistribution Locus Concept

2004 ◽  
Author(s):  
Takashi Shimakawa ◽  
Kyotada Nakamura ◽  
Ken-Ichi Kobayashi
Keyword(s):  
Thermal Stress ◽  
Pressure Vessel ◽  
Inelastic Strain ◽  
Stress Redistribution ◽  
Inelastic Behavior ◽  
Strain Concentration ◽  
Strain Behavior ◽  
Creep Fatigue ◽  
Current Design ◽  
Estimation Scheme

High temperature components are operated under cyclic thermal transient. Creep-Fatigue is the most dominant failure mode to be considered in Elevated Temperature Design of these components. Design limit for computed thermal stress is allowed to exceed yielding, because thermal stress is generally regarded as a displacement controlled one. Since creep deformation is considered as additional inelastic behavior, methodology to estimate inelastic strain concentration should be prepared in a design standard. Though inelastic FEM analyses can be applied to calculate inelastic strain concentration magnitude, it is well known that prediction is affected by applied constitutive model. Current design codes recommend to apply elastic FEM and to estimate inelastic strain behavior by simplified method. This paper presents sophisticated technique to estimate inelastic strain behavior based on Stress Redistribution Locus (SRL) method. Applicability of SRL concept is discussed with a help of FEM results for representative components of pressure vessel components such as nozzle, skirt and tube sheet.

Study on the Stress-Strain Redistribution Caused by Inelastic Deformation in Perforated Plate

2012 ◽  
Author(s):  
Sho Ikeda ◽  
Masakazu Sato ◽  
Naoto Kasahara
Keyword(s):  
Design Method ◽  
Perforated Plate ◽  
Chemical Plants ◽  
Inelastic Behavior ◽  
Stress Strain ◽  
Elastic Plastic ◽  
Pipe Model ◽  
Elastic Core ◽  
Creep Fatigue ◽  
Breeder Reactors

Fast Breeder Reactors and chemical plants that is operated at elevated temperature must be designed considering creep deformation in addition to elastic-plastic deformation. Especially at structural discontinuities, strain concentration induced by stress-strain redistribution reduces creep-fatigue strength. For this reason, a design method is needed for appropriately evaluating inelastic behavior at a structural discontinuity. As one of simplified methods with elastic analysis, a rational method with Stress Redistribution Locus (SRL) has been studied during recent years. Previous studies have shown that SRL does not depend on constitutive equations or on the magnitude of loading. And through the elastic-plastic-creep analysis of a one-dimensional pipe model, it was revealed that there was a relation between stress-strain redistribution and the size of elastic core. The purpose of this study is to clarify the mechanism of stress-strain redistribution in complex structures like actual components. Multi-dimensional stress-strain distribution and multiaxial stress occur in those structures. For considering those effects, inelastic analyses on perforated plate were performed and the relation between the region of elastic cores and SRL was examined. Then, it was revealed that SRL could be divided into two parts. One half is affected by the region of elastic core and the other half depends on the loading type. Furthermore, this paper proposes the new SRL method based on the mechanism and validates the method.

A PC-Based Modeling Tool for Creep, Fatigue, and Creep-Fatigue Interactions Using a Viscoplasticity Theory

1991 ◽  
Vol 113 (2) ◽  
pp. 174-179 ◽  
Author(s):  
J. T. Fong ◽  
B. Bernstein
Keyword(s):  
Elevated Temperatures ◽  
Helmholtz Free Energy ◽  
Thermodynamic Theory ◽  
Rate Of Change ◽  
Free Energy Function ◽  
Explicit Dependence ◽  
Time Rate ◽  
Modeling Tools ◽  
One Dimensional ◽  
Creep Fatigue

Computational results for modeling one-dimensional stress relaxation, creep, fatigue, and creep-fatigue interaction phenomena of metals at elevated temperatures using a unifying thermodynamic theory of viscoplasticity are presented. The theory incorporates in a nonequilibrium formulation the idea of a “concealed” parameter α, originally due to Bridgman (1950), where the constitutive equations are governed by 1) a thermodynamic potential such as the Helmholtz free energy function F with an explicit dependence on α, and 2) a prescription for α˙, the time rate of change of α, such that α˙ is proportional to −Fα, the negative of the partial derivative of F with respect to α. Significance of the results and a comparison with other modeling tools in the literature are discussed.

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