Novel Test Facility for Investigation of the Impact of Thermally Induced Stress Gradients on Fatigue Life of Cooled Gas Turbine Components

2018 ◽  
Author(s):  
Marcus Thiele ◽  
Uwe Gampe ◽  
Kathrin A. Fischer
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Heat Fluxes ◽  
Test Facility ◽  
Test Results ◽  
Cycle Fatigue ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
The Impact

A novel test facility has been designed and set up for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients with respect to the damage evolution of cooled gas turbine components. Thermally induced stress gradients differ from geometrically induced stress gradients. From the point of view of stress mechanics, they are independent from external loads. From the perspective of material mechanics, their impact on service life is influenced by locally different material properties and strength. However, the impact of thermally induced stress gradients on the cyclic life of high loaded, cooled components is not precisely known. In order to increase knowledge surrounding these mechanisms, a research project was launched. To achieve high temperature gradients and extended mechanical stress gradients, large heat fluxes are required. The authors developed a test bench with a unique radiant heating to achieve very high heat fluxes of q̇ ≥ 1.6MW/m2 on cylindrical specimen. Special emphasis has been placed on homogenous temperature and loading conditions in order to achieve valid test results comparable to standard low cycle or thermo-mechanical fatigue tests. Different test concepts of the literature were reviewed and the superior performance of the new test rig concept was demonstrated. The austenitic stainless steel 316L was chosen as the model material for commissioning and validation of the test facility. The investigation of thermally induced stress gradients and, based on this analysis, low-cycle fatigue tests with superimposed temperature gradients were conducted. Linear elastic finite element studies were performed to calculate the local stress-strain field and the service life of the test specimens. The test results show a considerable influence of the temperature gradient on the low-cycle fatigue life of the investigated material. Both the temperature variation over the specimen wall and thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results increase the understanding of fatigue damage mechanisms under local unsteady conditions and can serve as a basis for improved lifetime calculation methods.

Experimental and Numerical Investigation on the Influence of Thermally Induced Stress Gradients on Fatigue Life of the Nickel-Base Alloy Mar-M247

2019 ◽  
Author(s):  
Marcus Thiele ◽  
Stefan Eckmann ◽  
Min Huang ◽  
Uwe Gampe ◽  
Kathrin A. Fischer ◽  
...  
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Heat Fluxes ◽  
Cycle Fatigue ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
Nickel Base

Abstract Today’s and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Thermally induced stress gradients differ from geometrically induced stress gradients with respect to stress mechanics by the independence from external loads and material mechanics by the influence of temperature on material properties and strength. Regarding the contribution and evaluation on damage, the latter characteristic feature in turbomachinery is currently not fully understood. Therefore, a test facility has been designed, set up, and reported in GT2018-76519 for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients, on the damage evolution of cooled high-temperature components. To achieve high temperature and thermally induced stress gradients, large heat fluxes are required. A unique radiation heating has been developed allowing very high heat fluxes of q̇ ≥ 1.5 MW/m2 for testing of hollow cylindrical specimens. The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. The low-cycle fatigue testing of the hollow cylindrical specimens has been conducted both with and without superimposed stationary temperature gradients. In addition, Complex Low-Cycle Fatigue (CLCF) tests with symmetric and nonsymmetric loading conditions have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress-strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanics-based lifetime model. The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results enhance the understanding of fatigue-damage mechanisms under local unsteady conditions and can be used as a basis for improved service life predictions.

Novel Test Facility for Investigation of the Impact of Thermally Induced Stress Gradients on Fatigue Life of Cooled Gas Turbine Components

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Marcus Thiele ◽  
Uwe Gampe ◽  
Kathrin A. Fischer
Keyword(s):  
Service Life ◽  
Gas Turbine ◽  
Heat Fluxes ◽  
Temperature Gradients ◽  
Test Facility ◽  
Test Results ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
The Impact

A novel test facility has been designed and setup for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients with respect to the damage evolution of cooled gas turbine components. Thermally induced stress gradients differ from geometrically induced stress gradients. From the point of view of stress mechanics, they are independent from external loads. From the perspective of material mechanics, their impact on service life is influenced by locally different material properties and strength. However, the impact of thermally induced stress gradients on the cyclic life of high loaded, cooled components is not precisely known. In order to increase knowledge surrounding these mechanisms, a research project was launched. To achieve high temperature gradients and extended mechanical stress gradients, large heat fluxes are required. The authors developed a test bench with a unique radiant heating to achieve very high heat fluxes of q˙ ≥ 1.6 MW/m2 on cylindrical specimen. Special emphasis has been placed on homogenous temperature and loading conditions in order to achieve valid test results comparable to standard low-cycle or thermo-mechanical fatigue tests. Different test concepts of the literature were reviewed and the superior performance of the new test rig concept was demonstrated. The austenitic stainless steel 316 L was chosen as the model material for commissioning and validation of the test facility. The investigation of thermally induced stress gradients and, based on this analysis, low-cycle fatigue (LCF) tests with superimposed temperature gradients were conducted. Linear elastic finite element studies were performed to calculate the local stress–strain field and the service life of the test specimens. The test results show a considerable influence of the temperature gradient on the LCF life of the investigated material. Both the temperature variation over the specimen wall and thermally induced stresses (TIS) are stated to be the main drivers for the change in LCF life. The test results increase the understanding of fatigue damage mechanisms under local unsteady conditions and can serve as a basis for improved lifetime calculation methods.

Experimental and Numerical Investigation on the Influence of Thermally Induced Stress Gradients on Fatigue Life of the Nickel-Base Alloy Mar-M247

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Marcus Thiele ◽  
Stefan Eckmann ◽  
Min Huang ◽  
Uwe Gampe ◽  
Kathrin A. Fischer ◽  
...  
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Heat Fluxes ◽  
Cycle Fatigue ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
Nickel Base

Abstract Today's and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Thermally induced stress gradients differ from geometrically induced stress gradients with respect to stress mechanics by the independence from external loads and material mechanics by the influence of temperature on material properties and strength. Regarding the contribution and evaluation on damage, the latter characteristic feature in turbomachinery is currently not fully understood. Therefore, a test facility has been designed, setup, and reported in GTP-18-1482 for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients, on the damage evolution of cooled high-temperature components. To achieve high temperature and thermally induced stress gradients, large heat fluxes are required. A unique radiation heating has been developed allowing very high heat fluxes of q˙ ≥ 1.5 MW/m2 for testing of hollow cylindrical specimens. The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. The low-cycle fatigue testing of the hollow cylindrical specimens has been conducted both with and without superimposed stationary temperature gradients. In addition, complex low-cycle fatigue (CLCF) tests with symmetric and nonsymmetric loading conditions have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress–strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanics-based lifetime model. The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results enhance the understanding of fatigue-damage mechanisms under local unsteady conditions and can be used as a basis for improved service life predictions.

Effects of Surface Finish and Loading Conditions on the Low Cycle Fatigue Behavior of Austenitic Stainless Steel in PWR Environment: Comparison of LCF Test Results With NUREG/CR-6909 Life Estimations

2008 ◽  
Author(s):  
Jean Alain Le Duff ◽  
Andre´ Lefranc¸ois ◽  
Jean Philippe Vernot
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Austenitic Stainless Steel ◽  
Environmental Effects ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Complex Signal ◽  
Loading Conditions ◽  
Test Results ◽  
Cycle Fatigue

During mid 2006, ANL issued a NUREG/CR-6909 [2] report that is now applicable in The US for evaluations of PWR environmental effects in the fatigue analysis of new reactor components. In order to assess the conservativeness of the application of this NUREG report, low cycle fatigue (LCF) tests were performed by AREVA NP on austenitic stainless steel specimens in a PWR environment. The selected material exhibits in an air environment a fatigue behavior consistent with the ANL reference “air” mean curve. Tests were performed for two various loading conditions: for fully reverse triangular signal (for comparison purpose with tests performed by other laboratories with same loading conditions) and complex signal, simulating strain variation for actual typical PWR thermal transients. Two surface finish conditions were tested: polished and ground. The paper presents on one side the comparison of environmental penalty factors (Fen = Nair,RT/Nwater) as observed experimentally with the ANL formulation (considering the strain integral method for complex loading), and, on the other hand, the actual fatigue life of the specimen with the fatigue life predicted through the NUREG/CR-6909 application. Low Cycle Fatigue test results obtained on austenitic stainless steel specimens in PWR environment with triangle waveforms at constant low strain rates gives Fen penalty factors close to those estimated using the ANL formulation (NUREG report 6909). On the contrary, it was observed that constant amplitude LCF test results obtained under complex signal reproducing an actual sequence of a cold and hot thermal shock exhibits significantly lower environmental effects when compared to the Fen penalty factor estimated on the basis of the ANL formulations. It appears that the application of the NUREG/CR-6909 [2] in conjunction with the Fen model proposed by ANL for austenitic stainless steel provides excessive margins whereas the current ASME approach seems sufficient to cover significant environmental effect for components.

scholarly journals Low Cycle Fatigue Failure of a Sitka Spruce Tree in Hurricane Winds

2014 ◽  
Vol 40 (5) ◽  
Author(s):  
Warren Leigh
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Wind Speed ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Failure Prediction ◽  
Picea Sitchensis ◽  
Cycle Fatigue ◽  
Hurricane Wind ◽  
The Impact

Pine plantations are prone to stem breakage due to high cyclic stress levels associated with hurricane force winds. Stress analytical and finite element simulation models were constructed of a representative profile of a (Sitka) Picea sitchensis tree. The profile surface stress (S) was determined due to the combined load of tree self-weight and hurricane wind speed. The results were complemented by reference to two other studies by other researchers that investigated the impact of fatigue cycles on failure (N) of pine wood and tree sway cycles to present a stem fatigue life prediction. The position of maximum surface profile stress and trunk fracture initiation location was ascertained from a non-uniform stress response. No stress uniformity along the trunk profile was observed for any wind-load case examined. The analytical model and finite element analysis of the P. sitchensis tree trunk profile revealed a statically adequate strength reserve factor of 1.4, which suggested another mode of failure was responsible. Fatigue life failure prediction was examined under cyclic and same-stress amplitude related to the hurricane wind speed of 33 m s-1. Predicted trunk fracture occurred in 2.6 hours, which dramatically reduced to two minutes with an increase in wind speed of only 1 m s-1. The calculated exposure time was similar to that recorded during Hurricane Hugo’s transit in 1989. The time-to-failure prediction obtained by the method of analysis provided in this study seemed plausible, and that the profile associated with the P. sitchensis tree would suffer trunk breakage by low cycle fatigue failure.

Analysis on Torsional Fatigue Life of Turbo-Generator Shafts

2011 ◽  
Vol 467-469 ◽  
pp. 1858-1863 ◽  
Author(s):  
Yu Jiong Gu ◽  
Tie Zheng Jin
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Circuit Simulation ◽  
Short Circuit ◽  
Cycle Fatigue ◽  
Two Phase ◽  
Torsional Fatigue ◽  
Turbo Generator ◽  
The Impact

Both low-cycle fatigue and high-cycle fatigue exist during torsional vibrations, but the impact of high-cycle fatigue has rarely been considered. In this paper, a torsional fatigue life analyzing method used for torsional vibration of turbo-generator shafts has been developed based on Manson-Coffin equation and high-cycle fatigue theory. The method has been used to estimate the torsional fatigue life in the most dangerous section of the shafts in a power plant. The cumulative torsional fatigue damage under two-phase short circuit simulation has been predicted.

scholarly journals Numerical modeling of the low cycle fatigue: effect of manufacturing imperfections caused by machining process

2021 ◽  
Vol 349 ◽  
pp. 02011
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Machining Process ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Maximum Shear Strain ◽  
Element Analysis ◽  
The Impact

The majority of mechanical components in nuclear power plants must be designed to withstand extreme cyclic loading conditions. In fact, when these components are subjected to low cycle fatigue, machining imperfections are considered one of the most significant factors limiting their service life. In the present work, using finite element analysis, a methodology has been suggested to predict the fatigue life of cylindrical parts made of 316 SS, at ambient temperature, under nominal strain amplitude ranging from ± 0.5 to ±1.2% with various surface roughness conditions. Two different multiaxial strain-life criteria have been considered to estimate the fatigue life, namely Brown-Miller and maximum shear strain. The comparison between the predicted and the experimental fatigue lifetimes has revealed that the adopted multiaxial strain life criteria can successfully estimate the fatigue life of 316 SS grade under uniaxial loading conditions. Furthermore, it has been found that the fatigue life decreases as the surface roughness average value increases, which indicates that surface regularities have a significant impact on low cycle fatigue life. Therefore, the proposed methodology is found to be capable of assessing the impact of surface roughness on the fatigue life of this specific steel in the low cycle fatigue regime.

scholarly journals INFLUENCE OF TEMPERATURE AND LOADING PROGRAM ON THE FATIGUE LIFE OF STEEL P91

2013 ◽  
Vol 7 (2) ◽  
pp. 93-98
Author(s):  
Stanisław Mroziński ◽  
Michał Piotrowski
Keyword(s):  
Fatigue Life ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Test Results ◽  
Influence Of Temperature ◽  
Program Type ◽  
Influence Of Temperature On ◽  
Two Temperatures ◽  
A Minor ◽  
The Impact

Abstract In this paper there are shown the results of low-cycle fatigue testing of steel P91 samples. During the testing there was conducted a fixed amplitude loading testing as well as programmed loading with various sequence degrees of the program. The testing was done in two temperatures: T=20°C and T=600°C. During the testing a cyclic steel weakening was observed without a clear period of stabilization. Greater changes of the cyclic properties were observed in temperature T=600°C. The influence of temperature on the fatigue life was determined in this paper. This influence is dependent on the degree of strain. It’s a minor one in the range of big strain and increases in the process of decreasing the degree of strain. Furthermore, the impact of the loading program type was determined on the test results and fatigue life calculations

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