Engineering models for softening and relaxation of Gr. 91 steel in creep-fatigue conditions

2017 ◽  
Vol 8 (6) ◽  
pp. 670-682 ◽  
Author(s):  
Stefan Holmström ◽  
Frits De Haan ◽  
Ulrich Führer ◽  
Rami Pohja ◽  
Jaromir Janousek
Keyword(s):  
Low Cycle Fatigue ◽  
Hold Time ◽  
Cyclic Softening ◽  
Relaxation Behavior ◽  
Cyclic Life ◽  
Content Type ◽  
Softening Curve ◽  
Creep Fatigue ◽  
Engineering Models ◽  
Arbitrary Location

Purpose There are a number of different approaches for calculating creep-fatigue (CF) damage for design, such as the French nuclear code RCC-MRx, the American ASME III NH and the British R5 assessment code. To acquire estimates for the CF damage, that are not overly conservative, both the cyclic material softening/hardening and the potential changes in relaxation behavior have to be considered. The data presented here and models are an initial glimpse of the ongoing European FP7 project MATISSE effort to model the softening and relaxation behavior of Grade 91 steel under CF loading. The resulting models are used for calculating the relaxed stress at arbitrary location in the material cyclic softening curve. The initial test results show that softening of the material is not always detrimental. The initial model development and the pre-assessment of the MATISSE data show that the relaxed stress can be robustly predicted with hold time, strain range and the cyclic life fraction as the main input parameters. The paper aims to discuss these issues. Design/methodology/approach Engineering models have been developed for predicting cyclic softening and relaxation for Gr. 91 steel at 550 and 600°C. Findings A simple engineering model can adequately predict the low cycle fatigue (LCF) and CF softening rates of Gr. 91 steel. Also a simple relaxation model was successfully defined for predicting relaxed stress of both virgin and cyclically softened material. Research limitations/implications The data are not yet complete and the models will be updated when the complete set of data in the MATISSE project is available. Practical implications The models described can be used for predicting P91 material softening in an arbitrary location (n/Nf0) of the LCF and CF cyclic life. Also the relaxed stress in the softened material can be estimated. Originality/value The models are simple in nature but are able to estimate both material softening and relaxation in arbitrary location of the softening curve. This is the first time the Wilshire methodology has been applied on cyclic relaxation data.

The Effect of Nitrogen Alloying on the Low Cycle Fatigue and Creep-Fatigue Interaction Behavior of 316LN Stainless Steel

2013 ◽  
Vol 794 ◽  
pp. 441-448 ◽  
Author(s):  
G.V. Prasad Reddy ◽  
R. Sandhya ◽  
M.D. Mathew ◽  
S. Sankaran
Keyword(s):  
Stainless Steel ◽  
Strain Rate ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Hold Time ◽  
Cyclic Plasticity ◽  
Dynamic Strain ◽  
Cycle Fatigue ◽  
Intergranular Cracking ◽  
Creep Fatigue

Low cycle fatigue (LCF) and Creep-fatigue interaction (CFI) behavior of 316LN austenitic stainless steel alloyed with 0.07, 0.11, 0.14, .22 wt.% nitrogen is briefly discussed in this paper. The strain-life fatigue behavior of these steels is found to be dictated by not only cyclic plasticity but also by dynamic strain aging (DSA) and secondary cyclic hardening (SCH). The influence of the above phenomenon on cyclic stress response and fatigue life is evaluated in the present study. The above mentioned steels exhibited both single-and dual-slope strain-life fatigue behavior depending on the test temperatures. Concomitant dislocation substructural evolution has revealed transition in substructures from planar to cell structures justifying the change in slope. The beneficial effect of nitrogen on LCF life is observed to be maximum for 316LN with nitrogen in the range 0.11 - 0.14 wt.%, for the tests conducted over a range of temperatures (773-873 K) and at ±0.4 and 0.6 % strain amplitudes at a strain rate of 3*10-3 s-1. A decrease in the applied strain rate from 3*10-3 s-1 to 3*10-5 s-1 or increase in the test temperature from 773 to 873 K led to a peak in the LCF life at a nitrogen content of 0.07 wt.%. Similar results are obtained in CFI tests conducted with tensile hold periods of 13 and 30 minutes. Fractography studies of low strain rate and hold time tested specimens revealed extensive intergranular cracking.

Study on Life Prediction Method for Creep-Fatigue Interaction at Elevated Temperature

2007 ◽  
Vol 353-358 ◽  
pp. 190-194
Author(s):  
Nian Jin Chen ◽  
Zeng Liang Gao ◽  
Wei Zhang ◽  
Yue Bao Le
Keyword(s):  
Elevated Temperature ◽  
Prediction Model ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Prediction Method ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Creep Fatigue ◽  
316L Austenitic Stainless Steel

The law of low-cycle fatigue with hold time at elevated temperature is investigated in this paper. A new life prediction model for the situation of fatigue and creep interaction is developed, based on the damage due to fatigue and creep. In order to verify the prediction model, strain-controlled low-cycle fatigue tests at temperature 693K, 823K and 873K and fatigue tests with various hold time at temperature 823K and 873K for 316L austenitic stainless steel were carried out. Good agreement is found between the predictions and experimental results.

scholarly journals Alloy 617 Creep–Fatigue Damage Evaluation Using Specimens With Strain Redistribution

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Yanli Wang ◽  
T.-L. Sham ◽  
Robert I. Jetter
Keyword(s):  
Hold Time ◽  
Damage Evaluation ◽  
Test Results ◽  
Structural Components ◽  
Cyclic Life ◽  
Alloy 617 ◽  
Creep Fatigue ◽  
Asme Code ◽  
Time Test

The simplified model test (SMT) method is an alternate approach to determine the cyclic life at elevated temperature. It is based on the use of creep–fatigue hold time test data from test specimens with elastic follow-up conservatively designed to bound the response of general structural components. In this paper, the previously documented development of the SMT approach and applicable restrictions are reviewed; the design of the Alloy 617 SMT specimen, measurement issues and constraints are presented; initial test results and their application to a prototypic design curve are presented; and further testing and analysis for ASME code incorporation are discussed.

Low-Cycle Fatigue Fracture Behavior of Superalloy GH4586 at Elevated Temperature

2004 ◽  
Vol 449-452 ◽  
pp. 337-340 ◽  
Author(s):  
Lei Wang ◽  
Tong Cui ◽  
Jun Ying Lü ◽  
Hong Cai Yang ◽  
Guang Pu Zhao
Keyword(s):  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Property ◽  
Plastic Strain Amplitude ◽  
Cycle Fatigue ◽  
Cyclic Life ◽  
Creep Fatigue ◽  
Fatigue Fracture Behavior ◽  
Higher Sensitivity

Low-cycle fatigue property of superalloy GH4586 was investigated using a stress amplitude-controlled mode at 1023K. Fracture surface was examined with a scanning electronic microscopy. It was found that the cyclic life can be illustrated by Manson-Coffin at all strain levels. The fatigue cracks initiate primarily on the surface of the specimen. The plastic strain amplitude responded to the cyclic loading shows higher sensitivity than that of the elastic strain amplitude. It was demonstrated that the failure of the present alloy is in a manner of creep-fatigue feature.

Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Celine Cabet ◽  
Laura Carroll ◽  
Richard Wright
Keyword(s):  
High Temperature ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Dominant Role ◽  
Hold Time ◽  
Outlet Temperature ◽  
Cycle Fatigue ◽  
Alloy 617 ◽  
Creep Fatigue

Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the very high temperature nuclear reactor (VHTR), expected to have an outlet temperature as high as 950 °C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanisms and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 °C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle fatigue specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens and the addition of a hold time at peak tensile strain degraded the cycle life. This suggests that creep-fatigue interaction occurs and that the environment may be partially responsible for accelerating failure.

Microstructural Effects in the Low-Cycle Fatigue of Fe-Ni-Cr Austenite

1977 ◽  
Vol 99 (1) ◽  
pp. 29-35 ◽  
Author(s):  
N. F. Fiore ◽  
D. R. Diercks
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Weight Percent ◽  
Fatigue Tests ◽  
304 Stainless Steel ◽  
Cycle Fatigue ◽  
Cyclic Life ◽  
Localized Deformation ◽  
Cast Alloys

A series of low-cycle fatigue tests was performed at 593 deg C on Fe-20 Cr-10 Ni and Fe-20 Cr-20 Ni (in weight percent) austenitic alloys in both the cast and wrought conditions. The as-cast alloys exhibited substantially longer cyclic lives than the wrought alloys or wrought Type 304 stainless steel. An effect of Ni content on fatigue life was noted for the cast alloys, but not for the wrought. Striation, measurements indicated that the majority of the cyclic life was spent in crack initiation and early growth in all cases, and the superiority of the cast alloys was almost entirely due to a greater resistance to crack initiation. Macroscopic crack-growth rates were found to be essentially independent of composition and microstructure. A 1-min tension hold time per cycle produced a significant reduction in cyclic life in all cases except for the as-cast high Ni alloy. The decrease in life appeared to be associated with the initiation of cracks from localized deformation at grain boundaries.

Low Cycle Fatigue Behavior of a Near-α Ti Alloy Containing Rare Earth Nd

2005 ◽  
Vol 475-479 ◽  
pp. 599-602
Author(s):  
Zhi Shou Zhu ◽  
Chun Xiao Cao ◽  
Ming Gao Yan
Keyword(s):  
Titanium Alloy ◽  
Rare Earth ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Range ◽  
Cyclic Softening ◽  
Propagation Model ◽  
Cyclic Behavior ◽  
Transgranular Fracture ◽  
Creep Fatigue

Low cyclic behavior of a new type near-α titanium alloy containing rare earth Nd (Ti60) with and without dwell time introduced at maximum tensile strain has been investigated at ambient temperature and 600°C. The results show that, Ti60 alloy exhibits a cyclic softening behavior at almost all strain levels being investigated. The cyclic processes show good agreement with predictions based on the fatigue crack propagation model. At 600°C, the LCF life of Nd-bearing near-α titanium alloy is superior to that at room temperature within the investigated strain range, which indicates that Ti60 alloy is a good candidate for high temperature component under complicated load and temperature conditions. The results also show that the creep-fatigue interaction is related to the strain range applied. The creep-fatigue fracture is characterized by transgranular fracture mode due to the formation of matrix voids induced by Nd-bearing particles.

Creep-Fatigue Behavior in Ferritic-Martensitic Steels

2011 ◽  
Author(s):  
Meimei Li ◽  
Saurin Majumdar ◽  
Ken Natesan
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Fatigue Behavior ◽  
Hold Time ◽  
Creep Damage ◽  
Cyclic Softening ◽  
Relaxation Response ◽  
Martensitic Steels ◽  
Softening Effect ◽  
Creep Fatigue

Ferritic-martensitic steels are the lead structural materials for next-generation nuclear energy systems. Due to increased operating temperatures required in advanced high-temperature reactor concepts, the high temperature performance of structural alloys and reliable high temperature structural design methodology have become increasingly urgent issues. Ferritic-martensitic steels experience significant cyclic softening at high temperatures, and this cyclic softening behavior affects consecutive stress relaxation response during hold time under creep-fatigue loading. It is found that the stress relaxation response during hold of the mod.9Cr-1Mo steel can be accurately described by a stress relaxation model. The creep damage associated with the stress relaxation during hold time can then be accurately calculated using the stress relaxation data and creep rupture data. It is shown that the unit creep damage per cycle in mod.9Cr-1Mo steel decreases considerably with increasing number of cycles due to cyclic softening, and the creep damage is sensitive to the initial stress of stress relaxation. Proper evaluation of the creep-fatigue damage in mod.9Cr-1Mo steel must consider the cyclic softening effect and its associated variations in creep damage from stress relaxation during the hold time.

A Study on the Notch Effect on the Low Cycle Fatigue of Metals in Creep-Fatigue Interacting Conditions at Elevated Temperature

1983 ◽  
Vol 105 (2) ◽  
pp. 75-80 ◽  
Author(s):  
M. Sakane ◽  
M. Ohnami
Keyword(s):  
Elastic Stress ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Cycle Fatigue ◽  
Time Effects ◽  
Notched Specimen ◽  
Notched Specimens ◽  
Creep Fatigue ◽  
Neuber's Rule ◽  
Modified Equation

Frequency and hold-time effects on fatigue lives of cylindrical notched specimens of SUS 316 stainless steel were studied at 600° C in air. From the tests, the following conclusions were obtained: Neuber’s rule, as used in the ASME N-47 Code, predicts very conservatively the life of notched specimens in tests without a hold-time. But it gives a nonconservative estimate for the reduction in the life of the material by the introduction of a hold-time. An empirical formula of a “frequency-elastic stress concentration factor modified equation” was obtained by analysing the experimental data. It predicts accurately the life of the notched specimen tested at different frequencies.

Fatigue Behavior of K447A Superalloy under Low Cycle Fatigue and Creep-Fatigue Interaction Conditions

2015 ◽  
Vol 750 ◽  
pp. 121-126 ◽  
Author(s):  
Hui Chen Yu ◽  
Cheng Li Dong ◽  
Ying Li
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Hold Time ◽  
Strain Ratio ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Creep Fatigue ◽  
Cyclic Damage ◽  
Mean Stresses

Strain-controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of K447A are conducted at 760oC in order to investigate the effects of different dwell times and strain ratios on the fatigue behavior and life. For the cases of stain ratio Rε=-1 with balanced hold time, the tensile and compressive mean stresses will generate. For the case of stain ratio Rε=-1 with compressive holding 60s, the tensile mean stress will produce. For the case of stain ratio Rε=-1 with tensile holding 60s, the compressive mean stress will produce. For the cases of stain ratio Rε=0.1 and Rε=-1with no hold time, the tensile mean stress will produce. The cyclic damage accumulation (CDA) method and modified CDA method were employed to predict the fatigue life for K447A, respectively. The fatigue life predicted by CDA method is within the scatter band of 18.2X. The fatigue life predicted by the modified CDA method agrees very well with the experimental life and the predicted life is well within the scatter band of 3.1X, which means that the modified CDA method is able to consider the influences of dwell time and strain ratio on the fatigue life of K447A.

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