A Probabilistic Model for Forging Flaw Crack Nucleation Processes

2021 ◽  
Author(s):  
Francesco Radaelli ◽  
Christian Amann ◽  
Ali Aydin ◽  
Igor Varfolomeev ◽  
Peter Gumbsch ◽  
...  
Keyword(s):  
Probabilistic Model ◽  
Crack Nucleation ◽  
Low Cycle Fatigue ◽  
Renewable Energy Sources ◽  
Operating Conditions ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Heavy Duty ◽  
Risk Quantification ◽  
Nucleation Model

Abstract A probabilistic model for quantifying the number of load cycles for nucleation of forging flaws into a crack has been developed. The model correlates low cycle fatigue (LCF) data, ultrasonic testing (UT) indication data, flaw morphology and type with the nucleation process. The nucleation model is based on a probabilistic LCF model applied to finite element analyses (FEA) of flaw geometries. The model includes statistical size and notch effects. In order to calibrate the model, we conducted experiments involving specimens that include forging flaws. The specimens were machined out from heavy duty steel rotor disks for the energy sector. The large disks, including ultrasonic indications on the millimeter scale, were cut into smaller segments in order to efficiently machine specimens including manufacturing related forging flaws. We conducted cyclic loading experiments at a variety of temperatures and high stresses in order to capture realistic engine operating conditions for flaws as they occur in service. This newly developed model can be incorporated into an existing probabilistic fracture mechanics framework and enables a reliable risk quantification allowing to support customer needs for more flexible operational profiles due to the emergence of renewable energy sources.

A Probabilistic Model for Forging Flaw Crack Nucleation Processes

2020 ◽  
Author(s):  
Francesco Radaelli ◽  
Christian Amann ◽  
Ali Aydin ◽  
Igor Varfolomeev ◽  
Peter Gumbsch ◽  
...  
Keyword(s):  
Probabilistic Model ◽  
Crack Nucleation ◽  
Low Cycle Fatigue ◽  
Renewable Energy Sources ◽  
Operating Conditions ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Heavy Duty ◽  
Risk Quantification ◽  
Nucleation Model

Abstract A probabilistic model for quantifying the number of load cycles for nucleation of forging flaws into a crack has been developed. The model correlates low cycle fatigue (LCF) data, ultrasonic testing (UT) indication data, flaw morphology and type with the nucleation process. The nucleation model is based on a probabilistic LCF model applied to finite element analyses (FEA) of flaw geometries. The model includes statistical size and notch effects. In order to calibrate the model, we conducted experiments involving specimens that include forging flaws. The specimens were machined out from heavy duty steel rotor disks for the energy sector. The large disks, including ultrasonic indications on the millimeter scale, were cut into smaller segments in order to efficiently machine specimens including manufacturing related forging flaws. We conducted cyclic loading experiments at a variety of temperatures and high stresses in order to capture realistic engine operating conditions for flaws as they occur in service. This newly developed model can be incorporated into an existing probabilistic fracture mechanics framework and enables a reliable risk quantification allowing to support customer needs for more flexible operational profiles due to the emergence of renewable energy sources.

Failure Analysis of Thinned Wall Elbows Under Excessive Seismic Loading

2002 ◽  
Author(s):  
Masaki Shiratori ◽  
Yoji Ochi ◽  
Izumi Nakamura ◽  
Akihito Otani
Keyword(s):  
Finite Element ◽  
Fatigue Damage ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Local Buckling ◽  
Seismic Loading ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Residual Thickness ◽  
Limited Period

A series of finite element analyses has been carried out in order to investigate the failure behaviors of degraded bent pipes with local thinning against seismic loading. The sensitivity of such parameters as the residual thickness, locations and width of the local thinning to the failure modes such as ovaling and local buckling and to the low cycle fatigue damage has been studied. It has been found that this approach is useful to make a reasonable experimental plan, which has to be carried out under the condition of limited cost and limited period.

Verification of Specimens for Low-Cycle Fatigue and Cyclic Plasticity Testing

1979 ◽  
Vol 101 (4) ◽  
pp. 321-327
Author(s):  
C. C. Schultz ◽  
H. M. Zien
Keyword(s):  
Finite Element ◽  
Low Cycle Fatigue ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Stress Strain ◽  
Inelastic Analysis ◽  
Analysis Methods ◽  
Strain Data

The results of inelastic finite element analyses of several uniaxial specimens used for low-cycle fatigue and cyclic plasticity testing are presented. The test specimens studied include both hourglass and uniform gage-type geometries. These results indicate that normally used hourglass specimens may significantly underestimate the strain for a given stress. Uniform gage specimens with commonly used length-to-diameter ratios are shown to provide adequate stress-strain data. Two extensively strain-gaged uniform gage specimens were tested to provide data to confirm the acceptability of the inelastic analysis methods.

Pipe Elbows Under Strong Cyclic Loading

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
George E. Varelis ◽  
Spyros A. Karamanos ◽  
Arnold M. Gresnigt
Keyword(s):  
Cyclic Loading ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Fatigue Curve ◽  
Design Codes ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Fatigue Design ◽  
Process Piping

Motivated by the response of industrial piping under seismic loading conditions, the present study examines the behavior of steel process piping elbows, subjected to strong cyclic loading conditions. A set of experiments is conducted on elbow specimens subjected to constant amplitude in-plane cyclic bending, resulting into failure in the low-cycle-fatigue range. The experimental results are used to develop a low-cycle-fatigue curve within the strain-based fatigue design framework. The experimental work is supported by finite element analyses, which account for geometrical and material nonlinearities. Using advanced plasticity models to describe the behavior of elbow material, the analysis focuses on localized deformations at the critical positions where cracking occurs. Finally, the relevant provisions of design codes (ASME B31.3 and EN 13480) for elbow design are discussed and assessed, with respect to the experimental and numerical findings.

3D Crack Growth Analysis and Its Correlation With Experiments for Critical Turbine Components Under an International Collaborative Program

2008 ◽  
Author(s):  
J. Hou ◽  
J. Dubke ◽  
K. Barlow ◽  
S. Slater ◽  
L. Harris ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Cycle Fatigue ◽  
3D Crack Growth ◽  
International Collaborative ◽  
2D And 3D ◽  
Growth Analyses ◽  
Stress Analyses

Following a reanalysis of the original material data plus supplementary Low Cycle Fatigue (LCF) specimen testing, an Original Equipment Manufacturer (OEM) reduced the low cycle fatigue life limits for a number of turbine components. To ascertain the validity of the new life limits, an international collaborative spin rig test program was initiated to provide more accurate low cycle fatigue life limits. The program covered a broad range of activities including, Finite Element (FE) stress analyses, cyclic spin rig testing, fractographic assessment and fatigue crack growth (FCG) analyses. This paper describes the 2D and 3D crack growth analyses of critical turbine components in a turboprop gas turbine engine, comparison of predicted results obtained using different software and also correlations with spin test results from the program. First, FE stress analyses of selected turbine components were carried out under both engine operating conditions and spin-rig test configurations in order to determine the maximum and minimum operating speeds required to match the stress ranges at the critical location specified by the OEM under engine operating conditions. Second, 2D and 3D crack growth analyses were performed independently by three organisations for a disk bolthole using the state-of-the-art software. Third, the predictions from different software were compared, and the relative technical merits of each software were evaluated. Finally, the predicted results were correlated against the striation counts determined by the OEM from the results of spin rig tests.

HCF Component Tests on Full-Scale Low Pressure Steam Turbine End Stage Blades

2016 ◽  
Author(s):  
Shilun Sheng ◽  
Johan Flegler ◽  
Balazs Janos Becs ◽  
Michael Dankert
Keyword(s):  
Steam Turbine ◽  
Low Cycle Fatigue ◽  
Renewable Energy Sources ◽  
Low Pressure ◽  
Full Scale ◽  
Test Facility ◽  
Future Market ◽  
Cycle Fatigue ◽  
Component Test ◽  
End Stage

The design of steam turbine components is driven by high efficiency demands and also requirements for increased operational flexibility due to more renewable energy sources being added to the grid. Therefore, fossil power plants which operate reliably under these conditions must be designed. Robust low pressure (LP) end stage blades are one key factor for modern steam turbine design to meet current and future market requirements. In operation, LP end stage blades of steam turbines are exposed to complex mechanical load, resulting in stresses mainly due to blade vibration and high centrifugal forces. Design methods accounting for high cycle fatigue (HCF) and low cycle fatigue (LCF) are required for fatigue lifetime calculation. To determine the HCF component strength and to validate the calculation procedure, an HCF component test facility for full-scale LP end stage blades has recently been established at Siemens. Besides the validation of the calculation procedures, the full-scale component tests serve as part of upfront validation to minimize risk for first time implementation of newly developed as well as next generation blades, and to demonstrate operational robustness of the existing fleet. This paper describes the development and setup of the HCF component test facility for full-scale LP end stage blades at Siemens, the successful execution of HCF component tests with blades of different sizes, surface conditions and materials, and the evaluation of the results. In addition, crack growth and threshold behavior has been investigated in detail. Based on the test results, validation of the corresponding calculation methods has been performed. An outlook on further development of test facilities is provided.

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