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.

Prediction of the fracture life of a wrinkled steel pipe subject to low cycle fatigue load

2007 ◽  
Vol 34 (9) ◽  
pp. 1131-1139 ◽  
Author(s):  
Sreekanta Das ◽  
J J. Roger Cheng ◽  
David W Murray
Keyword(s):  
Plastic Strain ◽  
Oil And Gas ◽  
Pipe Wall ◽  
Low Cycle Fatigue ◽  
Local Buckling ◽  
Petroleum Products ◽  
Assessment Model ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Fatigue Load

The economy of Canada depends largely on the performance of the hydrocarbon-based energy industry (oil and gas), which in turn is dependent on the performance of steel pipelines that are used for transporting crude oil, natural gas, and petroleum products. Field observations of buried pipelines indicate that it is not uncommon for geotechnical movements to impose large displacements on the pipelines, resulting in localized curvature, deformations, and strain in the pipe wall. Often these local deformations result in local buckling (wrinkling) in the pipe wall, and in the post-buckling range of response such wrinkles develop rapidly. Subsequent cyclic load histories may produce cyclic plastic strain reversals leading to the formation of fractures in the wrinkle region. This paper presents the development and application of a simple fracture-life assessment model that can be used successfully by the pipeline industries to assess the remaining life before fracture of wrinkled pipelines subject to strain reversals due to low cycle fatigue loadings.Key words: wrinkled pipeline, low cycle fatigue load, plastic strain reversal, fracture, hysteresis loop energy, fracture-life assessment model.

An Energy-Based Approach to Determine the Fatigue Strength and Ductility Parameters for Life Assessment of Turbine Materials

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
M.-H. Shen ◽  
Sajedur R. Akanda
Keyword(s):  
Experimental Data ◽  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Turbine Rotor ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Strength Parameters ◽  
Strength And Ductility ◽  
Good Agreement

An energy-based framework is developed to determine the fatigue strength parameters of the Basquin equation and the fatigue ductility parameters of the Manson–Coffin equation to predict high cycle fatigue (HCF) and low cycle fatigue (LCF) life of a steam turbine rotor base and weld materials. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as the fatigue toughness. From the fatigue toughness and the experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg–Osgood constitutive equation that describes the hysteresis stress–strain loop of a cycle are determined. Next, the coefficients and the exponents of the Basquin and the Manson–Coffin equations are computed from the fatigue toughness and the cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework is found to be in a good agreement with the experimental data.

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