scholarly journals Modelling of Cavity Nucleation, Early-stage Growth and Sintering in Polycrystal under Creep-fatigue Interaction

2021 ◽  
Author(s):  
J.-D. Hu ◽  
C.-J. Liu ◽  
Fuzhen Xuan ◽  
Bo Chen
Keyword(s):  
Early Stage ◽  
Hold Time ◽  
Fatigue Loading ◽  
Initial Tension ◽  
Stress Variation ◽  
Compression Phase ◽  
Cavity Nucleation ◽  
Sliding Mechanism ◽  
Creep Fatigue ◽  
Variation Rate

A mechanistic based cavitation model that considers nucleation, early-stage growth and sintering under creep-fatigue interaction is proposed. The number density of cavities ρ and their evolution during multi-cycle creep-fatigue loading are predicted. Both the cavity nucleation and early-stage growth rates, controlled by grain boundary (GB) sliding mechanism during the tension phase, are formulised as a function of local normal stress σ. The cavity sintering that occurs during the compression phase is described as a function of σ, but the mechanism switches to the unconstrained GB diffusion. By examining various load waveform parameters, results provide important insights into experimental design of studying the creep-dominated cavitation process under creep-fatigue interaction. First, creep-fatigue test with initial compression will promote higher ρ value compared to that with initial tension, if the unbalanced stress hold time in favour of tension is satisfied. Second, the ρ value does not have a monotonic dependence on either the compressive hold time or stress level, because of their competing effect on nucleation and sintering. Third, the optimum value of stress variation rate exists in terms of obtaining the highest ρ value due to sintering effect.

Evaluation of Damage Evolution in Nickel-Base Heat-Resistant Alloy Under Creep-Fatigue Loading Conditions

2017 ◽  
Author(s):  
Ken Suzuki ◽  
Takuya Murakoshi ◽  
Hiroki Sasaki ◽  
Hideo Miura
Keyword(s):  
Grain Boundaries ◽  
Fatigue Test ◽  
Damage Evolution ◽  
Power Plants ◽  
Hold Time ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Electron Back Scatter Diffraction ◽  
Heat Resistant Alloy ◽  
Creep Fatigue

In this study, interrupted creep and creep-fatigue tests of Alloy 617, which is a candidate alloy for boiler tubes and pipes of A-USC (advanced ultra-supercritical) power plants of the 700°C-class, were conducted to investigate damage evolution process. Also, the change of the micro texture of the alloy was continuously observed at a fixed area to elucidate the mechanism of damage evolution under creep and creep-fatigue loading from the viewpoint of the change of the order of atom arrangement using EBSD (Electron Back-Scatter Diffraction) analysis. The conditions of the creep test were a temperature of 800°C and the stress of 150 MPa in inert gas (99.9999% Ar). The stress-controlled creep-fatigue tests were carried out at 800°C in Ar using stress ratio R = −1 and hold time of 10 minutes at peak tension. IQ (Image Quality) values, which are the average sharpness of the obtained diffraction pattern, were used for evaluating the change of the micro texture during the tests. In both creep and creep-fatigue test, intergranular cracks appeared. The IQ value decreased monotonically in the vicinity of grain boundaries with the decrease of fracture life, indicating that the crystallinity of grain boundaries degraded faster than that of grains. This localized damage around grain boundaries was attributed to the intergranular crack propagation in the creep and creep-fatigue test. In addition, all the grain boundaries with IQ value lower than 85% of IQ value in as-received specimen were found to be cracked during both creep and creep-fatigue test. Therefore, there was the critical IQ value around grain boundaries at which intergranular cracks occurred under creep or creep-fatigue loading condition.

Considerations to the An-Isothermal Creep-Fatigue Assessment of Steam Turbine Rotor Steels

2007 ◽  
Author(s):  
Martin Reigl ◽  
Harish N. Dave
Keyword(s):  
Steady State ◽  
Creep Damage ◽  
Fatigue Loading ◽  
Turbine Rotor ◽  
Steam Turbines ◽  
Compression Phase ◽  
Warm Start ◽  
Steady State Operation ◽  
Creep Fatigue ◽  
Isothermal Creep

The high creep-fatigue loading of fast starting steam turbines is investigated. Based on real turbine operation, but assuming worse conditions like increased notch factors, typical stress-strain cycles of the rotor are calculated. These an-isothermal cycles consists of phases of different start-types (cold start, warm start and hot start), of steady-state operation, shut-down and stand-still. Experiments, performed with these cycles, are evaluated with different methods. For the LCF fraction of the lifetime consumption, several reference temperatures are compared, whereby the so-called ‘corner temperature’ is preferably incorporated, which is the temperature at the end of the compression phase. The creep fraction of the lifetime consumption is firstly assessed with the time fraction rule, either considering the midlife cycles only or considering each individual cycle, either considering all phases of the cycles or the steady state operation phase only. Then, the ductility exhaustion method for the creep damage is applied, after defining the ductility for several experiments.

High Temperature Crack Growth Behavior of 304 Stainless Steel under Creep and Fatigue Loading

2005 ◽  
Vol 297-300 ◽  
pp. 452-457
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Growth Rates ◽  
Hold Time ◽  
Fatigue Loading ◽  
Growth Behavior ◽  
304 Stainless Steel ◽  
Crack Growth Behavior ◽  
Creep Fatigue ◽  
Crack Growth Rates

The crack growth behavior in a 304 stainless steel has been investigated at 538°C in air environment. Compact tension specimens were subjected to fatigue, creep and creep-fatigue loading. The combined effects on crack growth rates of load level and hold time have been examined. Stress intensity factors are found to correlate crack growth rates reasonably well for fatigue crack growth. Creep crack growth rates are found to correlate with stress intensity factor and C*(t). Crack growth rates under hold time cycles are successfully correlated with C*(t)avg under various load levels and hold times. Crack growth under creep-fatigue loading has been simulated by elastic-plastic-steady state creep finite element analyses. The results of analysis show that fatigue loading interrupts stress relaxation around the crack tip during hold time and causes stress reinstatement, thereby giving rise to accelerated crack growth compared with crack growth under static loading. Analysis of hold time crack growth based on the cyclic stress-strain response yields crack closure during unloading, and creep deformation during hold time tends to lower the closure load.

An Analysis of the Fatigue/Creep Behavior of 304 Stainless Steel Using a Continuous Damage Approach

1986 ◽  
Vol 108 (3) ◽  
pp. 280-288 ◽  
Author(s):  
R. Gomuc ◽  
T. Bui-Quoc
Keyword(s):  
Stainless Steel ◽  
Hold Time ◽  
Fatigue Loading ◽  
304 Stainless Steel ◽  
Damage Functions ◽  
Hold Period ◽  
Creep Fatigue ◽  
Relaxation Stress ◽  
Type 304 ◽  
Type 304 Stainless Steel

A recently suggested procedure for estimating the life of a material subjected to fatigue-creep loading is applied to analyze the behavior of Type 304 stainless steel on the basis of the experimental data already available in the literature. The predictive technique is based on a combination of the two separate damage functions for fatigue and for creep. The effect of the tension hold time in interspersed creep-fatigue loading on the material life is taken into account by considering the relaxation stress characteristics during the hold period. The technique also permits the evaluation of damage (or healing) due to a compression hold time. The correlation between predictions and available experimental results obtained on Type 304 SS from 538 to 649° C under various loading conditions is discussed.

Effect of Strain Rate and Hold Time in Creep-Fatigue Test

2013 ◽  
Author(s):  
Masakazu Kojima ◽  
Madoka Funai ◽  
Takashi Dozaki ◽  
Osamu Watanabe ◽  
Akihiro Matsuda
Keyword(s):  
Strain Rate ◽  
Tensile Strain ◽  
Compressive Strain ◽  
Hold Time ◽  
Perforated Plate ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Holding Time ◽  
Loading History ◽  
Creep Fatigue

The present paper shows the two experimental results for creep-fatigue interaction effects of perforated plate at elevated temperature. (1) The loading history is assumed to be triangle form in fatigue tests, and that in creep-fatigue loading history, the loading rate from compressive strain to tensile strain is assumed to be constant, which vary from fast rate to slow rate in 5 types of strain rate. The slow strain rate loading includes the creep effects to reduce the life span, which is shown to be predicted if the constant loading assumption is assumed. (2) The holding time effect is also investigated. The tensile strain is held to be constant, and holding time is elongated in the present experiments, which is investigated by the fracture analysis.

Crack Growth in Stainless Steel 304 under Creep-Fatigue Loading

2007 ◽  
Vol 353-358 ◽  
pp. 485-490 ◽  
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Static Loading ◽  
Fatigue Loading ◽  
Creep Fatigue ◽  
Crack Growth Rates

Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.

On the Evaluation and Consideration of Fracture Mechanical Notch Support Within a Creep Fatigue Lifetime Assessment

2018 ◽  
Author(s):  
Christian Kontermann ◽  
Henning Almstedt ◽  
Falk Müller ◽  
Matthias Oechsner
Keyword(s):  
Fatigue Loading ◽  
Experimental Program ◽  
Energy Market ◽  
Steam Turbines ◽  
Fatigue Lifetime ◽  
Global Strain ◽  
Creep Fatigue ◽  
Main Components ◽  
Flexible Operation ◽  
The Impact

Changes within the global energy market and a demand for a more flexible operation of gas- and steam-turbines leads to higher utilization of main components and raises the question how to deal with this challenge. One strategy to encounter this is to increase the accuracy of the lifetime assessment by quantifying and reducing conservatisms. At first the impact of considering a fracture mechanical notch support under creep-fatigue loading is studied by discussing the results of an extensive experimental program performed on notched round-bars under global strain control. A proposal how to consider this fracture mechanical notch support within a lifetime assessment is part of the discussion of the second part. Here, a theoretical FEM-based concept is introduced and validated by comparing the theoretical prediction with the results of the previously mentioned experimental study. Finally, the applicability of the developed and validated FEM-based procedure is demonstrated.

scholarly journals Life Prediction Method Under Creep-Fatigue Loading for Gas Turbine Combustion Transition Piece of Ni-Based Superalloy N263

1997 ◽  
Author(s):  
J. Kusumoto ◽  
H. Watanabe ◽  
A. Kanaya ◽  
K. Ichikawa ◽  
S. Sakurai
Keyword(s):  
Crack Length ◽  
Surface Crack ◽  
Life Prediction ◽  
Prediction Method ◽  
Fatigue Loading ◽  
Maximum Surface ◽  
Creep Fatigue ◽  
Loading Tests ◽  
Transition Piece ◽  
Life Fraction

In order to develop the life prediction method under creep-fatigue loading for gas turbine combustion transition piece, creep-fatigue tests were carried out on both as-received and aged Ni-based superalloy Nimonic 263. Crack initiation and propagation behaviors for the smooth specimen were observed. An unique relationship was obtained between life fraction and the maximum surface crack length under triangular wave shape loading tests, except the results for the trapezoidal wave loading tests. The latter results were due to the over estimation of the surface crack length at the crack initiation. These were caused from an oxide film break during straining. In the case of removing the oxide film before the measurement of surface crack, the relationship between life fraction and the maximum surface crack length obtained as unique relationship regardless of triangular and trapezoidal strain wave shapes. Using the life prediction method proposed, which is based on maximum surface crack length, the damage of combustion transition piece materials in service was evaluated.

Sign in / Sign up

Export Citation Format

Share Document