Improving Creep-Fatigue Design Methodology for Advanced Ferritic-Martensitic Steels

2014 ◽  
Author(s):  
Meimei Li ◽  
William K. Soppet ◽  
Saurin Majumdar ◽  
Ken Natesan
Keyword(s):  
Design Methodology ◽  
Laboratory Data ◽  
Constitutive Models ◽  
Fatigue Loading ◽  
Cyclic Softening ◽  
Advanced Materials ◽  
Critical Element ◽  
Martensitic Steels ◽  
Fast Reactors ◽  
Creep Fatigue

Advanced materials are a critical element in the development of advanced sodium-cooled fast reactors. High temperature design methodology of advanced materials is an enabling reactor technology. Removal of unnecessary conservatism in design rules could lead to more flexibility in construction and operation of advanced sodium-cooled fast reactors. Developing mechanistic understanding and predictive models for long-term degradation phenomena such as creep-fatigue are essential to the extrapolation of accelerated laboratory data to reactor environments with high confidence, and to improve the American Society of Mechanical Engineers (ASME) code rules. This paper examines the cyclic softening and stress relaxation responses and associated plastic damage accumulation for Grade 91 ferritic-martensitic steel. Creep-fatigue experiments were conducted at 550°C in strain-controlled mode under various types of creep-fatigue loading conditions. Constitutive models were developed to describe the creep-fatigue interaction in G91.

Damage Assessment of Similar Martensitic Welds Under Creep, Fatigue and Creep-Fatigue Loading

2020 ◽  
Author(s):  
Thorben Bender ◽  
Andreas Klenk ◽  
Stefan Weihe
Keyword(s):  
Base Metal ◽  
Fatigue Behavior ◽  
Base Material ◽  
Fatigue Loading ◽  
Design Guidelines ◽  
Failure Behavior ◽  
Martensitic Steels ◽  
Viscoplastic Material ◽  
Local Strains ◽  
Creep Fatigue

Abstract For the assessment of welds under high-temperature conditions in the creep or creep-fatigue regimes, the knowledge on the damage location and its temporal evolution are of high importance. The failure behavior of similar welds of ferritic-martensitic steels in the creep regime is well known. For creep-fatigue loading, the behavior of welds is still subject to research but it seems that the heat affected zone (HAZ) limits the lifetime of welded components as well. This local failure behavior is not reflected in design guidelines using weld reduction factors or in typical assessment approaches. The evaluation of local strains and stresses in the HAZ is unavoidable. For the improvement of design and inspection guidelines, a more detailed consideration of weld behavior is of interest. In this paper, an overview of current developments in the assessment of welds under creep, fatigue, and creep-fatigue loading conditions is given. An assessment approach for creep damage and failure, including the prediction of rupture time and location, is presented. The assessment is based on numerical analyses considering the different behavior of base material and HAZ represented by three different subzones. The approach is validated with the simulation of a uniaxial cross weld, creep crack, and component tests. Whereas the creep behavior of the HAZ compared to base metal is quite well known, there is only little knowledge of their fatigue behavior. Using a set of fatigue tests on HAZ, base metal specimens and cross weld specimens, the influence of fatigue and creep-fatigue loading on the lifetime and failure location of a weld will be discussed. For the numerical simulations, a viscoplastic material law of Chaboche type is used and an evaluation of the local strains in the HAZ allows an attempt to explain the observed failure locations.

High Temperature Creep-Fatigue Design and Service Experience

2008 ◽  
Vol 1125 ◽  
Author(s):  
A-A. F. Tavassoli ◽  
B. Fournier ◽  
M. Sauzay
Keyword(s):  
High Temperature ◽  
Austenitic Stainless Steels ◽  
Oxide Dispersion Strengthened ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Oxide Dispersion ◽  
Martensitic Steels ◽  
Fatigue Design ◽  
Creep Fatigue

ABSTRACTGeneration IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances under creep-fatigue hold the key to success. This paper presents extended experimental results obtained from creep, fatigue and creep-fatigue tests on the main structural materials retained for these concepts, namely: stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and its low activation derivatives such as Eurofer steel, and their more advanced grades strengthened by oxide dispersion. It shows that the existing recommendations made in design codes adequately cover individual damage due to creep or fatigue but often fall short under combined creep-fatigue interaction. This is partly due to the difficulties of reproducing service conditions in laboratory. In this paper, results from tests performed on components removed from reactor, after long service, are used to refine code recommendations.Using the above combined assessment, it is concluded that there is good confidence in predicting creep-fatigue damage for austenitic stainless steels. For the martensitic steels the effects of cyclic softening and microstructure coarsening throughout the fatigue life need more consideration in creep-fatigue recommendation. In the long-term development of ferritic/martensitic oxide dispersion strengthened grades with stable microstructure and no cyclic softening, appears promising provided problems associated with their fabrication and embrittlement are resolved.

Methods for Determining Creep Damage and Creep-Fatigue Crack Growth Incubation in Austenitic Stainless Steel

2009 ◽  
Author(s):  
George A. Webster ◽  
David W. Dean ◽  
Michael W. Spindler ◽  
N. Godfrey Smith
Keyword(s):  
Structural Integrity ◽  
Laboratory Data ◽  
Creep Damage ◽  
Fatigue Loading ◽  
Operating Conditions ◽  
Advisory Group ◽  
Creep Fatigue ◽  
Creep Fatigue Crack ◽  
The Uk ◽  
Life Fraction

Most design and safety assessment procedures for estimating the accumulation of creep damage under plant operating conditions adopt either stress-based time (life) fraction or strain-based ductility exhaustion criteria for making component lifetime predictions. The UK Technical Advisory Group on Structural Integrity of Nuclear Plant (TAGSI) has reviewed new stress modified ductility exhaustion methods proposed for calculating the creep contribution to damage in components that are subjected to creep-fatigue loading. The new procedures have been found to give more reliable and less pessimistic predictions of creep damage for the isothermal laboratory data analysed than current methods in the British Energy R5 procedure. TAGSI has also reviewed the σd method in R5 for determining incubation periods for pre-existing and postulated defects and considers that it can be used with both stress (using the life fraction rule) and strain (using ductility exhaustion) based approaches. This paper gives the background to the reviews by TAGSI of these creep damage approaches and discusses the implications for data requirements and assessment methods.

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.

Aspects of Creep Fatigue Lifetime Assessment for High Temperature Components With Accumulative Model

2019 ◽  
Author(s):  
Stefan Linn ◽  
Christian Kontermann ◽  
Matthias Oechsner
Keyword(s):  
Power Plants ◽  
Response Times ◽  
Constitutive Models ◽  
Hysteresis Loops ◽  
Creep Damage ◽  
Cyclic Softening ◽  
Operating Conditions ◽  
Transition Time ◽  
Safety Margins ◽  
Creep Fatigue

Abstract Alternating temperatures induce thermomechanical stresses in thick-walled components such as turbine rotors or housings, which can lead to fatigue and superimposed creep. Subsequently, damage can occur at their heated surfaces. Under the nowadays prevailing operating conditions of power plants with multiple cold, warm and hot starts as reaction to the high volatility of electric demand from fossil fired power plants for ensuring grid stability, methods for lifetime assessment are coming more into the focus of investigations and research. Engineers are trying to estimate the residual lifetimes of in-service components and operators of power plants ask for strategies to minimize the calculative material damage while simultaneously providing a maximum flexibility with shortest response times on altered demands. Among constitutive models, which are not subject of this paper, accumulative models for lifetime assessment were introduced several decades ago and are partially considered in applicable standards. Such models based on a damage accumulation are easy to apply but they are considered to be either very imprecise or very conservative, while the conservatism reflects the necessity of large safety margins. This paper summarize a few measures, which are suitable to improve the predictive quality of models based on a simple time-fraction rule. The proposed model is based on a synthesis of hysteresis loops for isothermal and non-isothermal conditions, concepts for consideration of cyclic softening or hardening during lifetime, concepts for dealing with internal back stresses, mean strains or stresses, and for accounting of creep-fatigue interaction. The latter is based on a so-called transition time concept, where the creep damage during dwell times partially attributes to the portion of fatigue damage, which in turn is determined from fatigue life curves for dwell time experiments. In addition, the model comprises a concept for the post-processing of transient FEM calculations and dealing with multiaxial loading conditions. Since the essentials of the proposed method with the transition time concept were published more than 10 years ago, the listed modifications improve the benefit for daily engineering usage. Validation experiments provide evidence of the models predicting capabilities with acceptable uncertainty.

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.

Lifetime prediction of 9–12%Cr martensitic steels subjected to creep–fatigue at high temperature

2010 ◽  
Vol 32 (6) ◽  
pp. 971-978 ◽  
Author(s):  
B. Fournier ◽  
M. Salvi ◽  
F. Dalle ◽  
Y. De Carlan ◽  
C. Caës ◽  
...  
Keyword(s):  
High Temperature ◽  
Lifetime Prediction ◽  
Martensitic Steels ◽  
Creep Fatigue

Contrasting supply chain traceability and supply chain visibility: are they interchangeable?

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Vivek Roy
Keyword(s):  
Supply Chain ◽  
Supply Chain Management ◽  
Information Sharing ◽  
Design Methodology ◽  
Relevant Literature ◽  
Future Research ◽  
Critical Element ◽  
Effective Management ◽  
Chain Management ◽  
Content Type

PurposeSupply chain traceability and supply chain visibility have become a critical element for the effective management of contemporary complex supply chains. At their core is information sharing, which has been acknowledged as a key prerequisite for logistics and supply chain performance, but whose notional underpinnings have not been delineated fully, leading to interchangeable deployment of these terms. Addressing the shortcoming, this paper aims to establish a contrast between the two notions.Design/methodology/approachDrawing from systematic review protocols, a multi-disciplinary review scope is constructed wherein the synthesis is strategized to primarily channel implications for the scholarship of logistics and supply chain management. The review is aimed at addressing two research objectives: (1) how the notions of traceability and visibility in supply chain management develop contrast in terms of their thematic emphasis and (2) to attain an integrative understanding of the notional convergence and divergence between supply chain traceability and visibility for raising strategic recommendations.FindingsThe review outcomes help contrast both the convergence and the divergence between traceability and visibility in the supply chain environment, and the differentiated but fundamental role that information sharing plays within these notions to outline why they are not interchangeable.Originality/valueThe originality of the findings lies in the conceptual synthesis of the relevant literature from both technological and non-technological perspectives to ultimately draw logistics and supply chain management implications. The review also points out key strategic considerations to demarcate the notional boundaries of traceability and visibility in future research.

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