Probabilistic Life Assessment Method of Low Cycle Fatigue for Power Plant Components

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1704-1710
Author(s):  
Myung Soo Kang
Keyword(s):  
Power Plant ◽  
Low Cycle Fatigue ◽  
Operating Time ◽  
Assessment Method ◽  
Life Assessment ◽  
Assessment Procedure ◽  
Cycle Fatigue ◽  
Inspection Planning ◽  
Structural Failure ◽  
Plant Components

This study focuses on the probabilistic analysis method to the determination of low cycle fatigue life for power plant components. The analysis incorporates standard life assessment modeling techniques used in the determination analysis of the low cycle fatigue. The probabilistic life assessment is developed to increase the reliability of life assessment. A probabilistic life assessment procedure can provide the engineer with the probability of structural failure as a function of operating time given the uncertainties in the input data. The probabilistic life assessment involves some uncertainties, for example, initial crack size, aspect ratio, crack initiation time, crack location, structural geometry, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure. This information can form the basis of inspection planning and retirement-for-cause decisions. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

Prediction of Stress Relaxation in Power Plant Components Based on a Constitutive Model

2017 ◽  
Author(s):  
Y. Kostenko ◽  
K. Naumenko
Keyword(s):  
Power Plant ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Evolution Equations ◽  
Material Behavior ◽  
Assessment Procedure ◽  
Reliable Prediction ◽  
Inelastic Material ◽  
Plant Components

Many power plant components and joint connections are subjected to complex thermo-mechanical loading paths under severe temperature environments over a long period. An important part in the lifetime assessment is the reliable prediction of stress relaxation using improved creep modeling to avoid possible integrity or functionality issues and malfunction in such components. The aim of this work is to analyze the proposed constitutive model for advanced high chromium steels with the goal of predicting stress relaxation over the long term. The evolution equations of the constitutive model for inelastic material behavior are introduced to account for hardening and softening phenomena. The material properties were identified for 9–12%CrMoV steels in the creep range. The model is applied to the stress relaxation analysis of power plant components. The results for long-term assessment, which are encouragingly close to reality, will be presented and discussed. An outlook on further developments of the model and assessment procedure is also provided.

A Revisit of Material and Structural Failures

2015 ◽  
Author(s):  
Sheldon Wang
Keyword(s):  
Low Cycle Fatigue ◽  
High Stress ◽  
Engineering Practice ◽  
Material Failure ◽  
Cycle Fatigue ◽  
Structural Failure ◽  
Column Buckling ◽  
Typical Material ◽  
Structural Failures ◽  
To Come

In this paper, we revisit the issues related to material and structural failures. In particular, we employ a similar bridging function between the typical structural failure, the so-called column buckling, and the typical material failure under compression, to link the low stress high cycle and the high stress low cycle fatigue. A part of the intention of this paper is to come up with simple formulas as guidelines in engineering practice for both material and structural failures in both static and dynamic situations.

Low-Cycle Fatigue, Fractography and Life Assessment of EN AW 2024-T351 under Various Loadings

2018 ◽  
Vol 43 (1) ◽  
pp. 41-56 ◽  
Author(s):  
M. Peč ◽  
J. Zapletal ◽  
F. Šebek ◽  
J. Petruška
Keyword(s):  
Low Cycle Fatigue ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Fatigue Fractography

Low-cycle fatigue test and life assessment of carbon structural steel GB Q235B butt joints and cruciform joints

2018 ◽  
Vol 22 (3) ◽  
pp. 581-596
Author(s):  
Zhao Fang ◽  
Aiqun Li ◽  
Sheng Shen ◽  
Wanrun Li
Keyword(s):  
Fatigue Test ◽  
Failure Mode ◽  
Stress Amplitude ◽  
Low Cycle Fatigue ◽  
Butt Joint ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Carbon Structural Steel ◽  
Cruciform Joint ◽  
Linear Slip Model

Axial low-cycle fatigue tests are conducted on transverse butt joint specimens and cruciform joint specimens made of carbon structural steel GB Q235B. The effect of slip between the specimens and the grips of the test machine is considered by the proposal of a linear slip model. The cyclic softening properties are studied by observing the variation of stress amplitude with cycles. The cyclic stress–strain curve and the strain–life curve for both kinds of specimens are obtained based on the fatigue test data, and the corresponding coefficients are fitted. In order to verify the fatigue test results, finite element models of specimens are established and the corresponding fatigue life assessment is conducted using the local stress–strain approach and the equivalent structural stress approach, respectively. The results show that the effect of slip is unneglectable and the established linear slip model is reasonable. The two kinds of specimens both show a strain softening property, but cruciform joint specimens experience sudden falls of stress amplitude during the test due to the damage of welded lines; cruciform joint specimens show an either one-side failure mode or two-side failure mode while butt joint specimens only show a one-side failure mode; the two-side failure mode tends to lead to shorter fatigue life, so in the design of cruciform joint, such failure mode should be avoided.

Improved Low Cycle Fatigue Analysis for Ni-Based Turbine Nozzles

2018 ◽  
Author(s):  
Gianluca Maggiani ◽  
Matthew J. Roy ◽  
Simone Colantoni ◽  
Philip J. Withers
Keyword(s):  
Gas Turbines ◽  
Mechanical Test ◽  
Low Cycle Fatigue ◽  
Computation Time ◽  
Cyclic Hardening ◽  
Life Assessment ◽  
Type Model ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Material Models

The requirements for cleaner energy have driven industrial gas turbines manufacturers to increase firing temperatures and improve cooling of nozzles. The application of high temperature alloys having adequate thermo-mechanical requirements is critical, as assessed by low cycle fatigue performance. The effect of higher firing temperatures combined with higher cooling efficiencies has lead to operating cycles where the level of plastic strain imparted define component life. The capability of material models to account for non-linear effects such as ratchetting or shakedown, cyclic hardening or softening as well as Bauschinger or relaxation effects have been highlighted in this context. Neglecting these effects can lead to over and under-conservative life assessment analysis, while accounting for them using standard multilinear material models lead to convergence issues in finite element analysis. In this paper, Chaboche viscoplastic model has been applied to a transient structural of a first stage gas turbine nozzle. Fitting of the model based on experimental mechanical test data on MAR-M-247 alloy will be described, followed by an overview of how the model may be implemented to a benchmark nozzle thermo-mechanical transient analysis. Finally the details how the Chaboche-type model has provided up to 50% decrease in computation time when compared to using a standard multi-linear material modelling approach.

Transition From Low Cycle to High Cycle in Uniaxial Fatigue

2013 ◽  
Author(s):  
Mohamed E. M. El-Sayed
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Uniaxial Stress ◽  
Life Assessment ◽  
Elastic Behavior ◽  
Cycle Fatigue ◽  
Fatigue Life Assessment ◽  
Component Development

Fatigue is the most critical failure mode of many mechanical component. Therefore, fatigue life assessment under fluctuating loads during component development is essential. The most important requirement for any fatigue life assessment is knowledge of the relationships between stresses, strains, and fatigue life for the material under consideration. These relationships, for any given material, are mostly unique and dependent on its fatigue behavior. Since the work of Wöhler in the 1850’s, the uniaxial stress versus cycles to fatigue failure, which is known as the S-N curve, is typically utilized for high-cycle fatigue. In general, high cycle fatigue implies linear elastic behavior and causes failure after more than 104 or 105 cycles. However. the transition from low cycle fatigue to high cycle fatigue, which is unique for each material based on its properties, has not been well examined. In this paper, this transition is studied and a material dependent number of cycles for the transition is derived based on the material properties. Some implications of this derivation, on assessing and approximating the crack initiation fatigue life, are also discussed.

Risk Based Optimization of the Life Assessment for Fossil Power Plant

2006 ◽  
Vol 321-323 ◽  
pp. 1572-1575
Author(s):  
Bum Shin Kim ◽  
Jung Soo Ha ◽  
Gee Wook Song ◽  
Jung Seob Hyun ◽  
Woo Sung Choi
Keyword(s):  
Risk Assessment ◽  
High Pressure ◽  
Power Plant ◽  
Power Plants ◽  
Life Assessment ◽  
Assessment Procedure ◽  
Operation Condition ◽  
High Pressure And Temperature ◽  
Fossil Power Plant

As a number of aged fossil power plants recently increased, the precise life assessment of critical equipments gets to be important more than ever. Despite of infrequent likelihood of failure, the equipments in high pressure and temperature operation condition have traditionally been considered as critical because of huge consequence of the equipments and hence life assessment of fossil power plant has been focused on all of the severe operated equipments for past decades. Nowadays, with Risk-Based Inspection technology being developed rapidly, most of the power plant utilities get a chance to reduce the scope of the inspection and test and to extend the interval for the life assessment. This paper provides methodology based on Risk-Based Inspection technology to optimize the life assessment work scope and interval and also demonstrates the enhanced life assessment procedure including risk assessment of equipments.

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