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A K Vasudevan - One of the best experts on this subject based on the ideXlab platform.
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analysis of pit to crack transition under corrosion fatigue the safe life Approach using the modified kitagawa takahashi diagram
International Journal of Fatigue, 2020Co-Authors: K Sadananda, A K VasudevanAbstract:Abstract A detailed analysis of pit to crack transition during corrosion fatigue is presented considering corrosion pits as ellipsoidal notches with the associated stress concentration factors, Kt. For the analysis, the experimental data are collected from various publications in the open literature. Both S-N and fatigue crack growth (FCG) data are analyzed in this paper using our Unified Approach that considers the R-ratio effects are intrinsic to fatigue. The Kitagawa-Takahashi (KT or K-T) diagram, as modified by the authors, is used to connect the fatigue life of a smooth specimen to that of a fracture mechanics specimen. Internal stress and Safe-Life regimes are identified using the KT diagram.
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Analysis of pit to crack transition under corrosion fatigue & the Safe-Life Approach using the modified Kitagawa-Takahashi diagram
International Journal of Fatigue, 2020Co-Authors: K Sadananda, A K VasudevanAbstract:Abstract A detailed analysis of pit to crack transition during corrosion fatigue is presented considering corrosion pits as ellipsoidal notches with the associated stress concentration factors, Kt. For the analysis, the experimental data are collected from various publications in the open literature. Both S-N and fatigue crack growth (FCG) data are analyzed in this paper using our Unified Approach that considers the R-ratio effects are intrinsic to fatigue. The Kitagawa-Takahashi (KT or K-T) diagram, as modified by the authors, is used to connect the fatigue life of a smooth specimen to that of a fracture mechanics specimen. Internal stress and Safe-Life regimes are identified using the KT diagram.
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A two-parameter analysis of S-N fatigue life using Δσ and σmax
International Journal of Fatigue, 2009Co-Authors: K Sadananda, S. Sarkar, Daniel Kujawski, A K VasudevanAbstract:Abstract The effect of the load ratio, R, or the mean-stress on fatigue life has been recognized for more than a hundred years. In considering the mean-stress effects in the stress-life (S–N) Approach, research efforts have been mostly concentrated in establishing correlating functions in terms of the flow stress or yield stress or the ultimate tensile stress, etc., by taking, say, R = −1 test results as a reference. Very little effort has been made towards understanding the role of stress range Δσ and the maximum stress σmax, (or σmean) in the fatigue crack nucleation and propagation and also how to relate this to both the stress-life and the fracture-mechanics descriptions. In this paper we first examine crack nucleation based on the stress-life Approach using a two-parameter requirement in terms of Δσ and σmax, and then connect it to crack propagation using the Kitagawa diagram as the incipient crack grows to become a long crack. Since stress-life data include both nucleation and propagation, the connection of the Safe-Life Approach to the fracture-mechanics analysis is pertinent. Comparison of the present analysis with experimental data taken from the literature demonstrates that a two-parameter Approach in terms of Δσ and σmax forms a basis for the S–N analysis.
K Sadananda - One of the best experts on this subject based on the ideXlab platform.
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analysis of pit to crack transition under corrosion fatigue the safe life Approach using the modified kitagawa takahashi diagram
International Journal of Fatigue, 2020Co-Authors: K Sadananda, A K VasudevanAbstract:Abstract A detailed analysis of pit to crack transition during corrosion fatigue is presented considering corrosion pits as ellipsoidal notches with the associated stress concentration factors, Kt. For the analysis, the experimental data are collected from various publications in the open literature. Both S-N and fatigue crack growth (FCG) data are analyzed in this paper using our Unified Approach that considers the R-ratio effects are intrinsic to fatigue. The Kitagawa-Takahashi (KT or K-T) diagram, as modified by the authors, is used to connect the fatigue life of a smooth specimen to that of a fracture mechanics specimen. Internal stress and Safe-Life regimes are identified using the KT diagram.
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Analysis of pit to crack transition under corrosion fatigue & the Safe-Life Approach using the modified Kitagawa-Takahashi diagram
International Journal of Fatigue, 2020Co-Authors: K Sadananda, A K VasudevanAbstract:Abstract A detailed analysis of pit to crack transition during corrosion fatigue is presented considering corrosion pits as ellipsoidal notches with the associated stress concentration factors, Kt. For the analysis, the experimental data are collected from various publications in the open literature. Both S-N and fatigue crack growth (FCG) data are analyzed in this paper using our Unified Approach that considers the R-ratio effects are intrinsic to fatigue. The Kitagawa-Takahashi (KT or K-T) diagram, as modified by the authors, is used to connect the fatigue life of a smooth specimen to that of a fracture mechanics specimen. Internal stress and Safe-Life regimes are identified using the KT diagram.
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A two-parameter analysis of S-N fatigue life using Δσ and σmax
International Journal of Fatigue, 2009Co-Authors: K Sadananda, S. Sarkar, Daniel Kujawski, A K VasudevanAbstract:Abstract The effect of the load ratio, R, or the mean-stress on fatigue life has been recognized for more than a hundred years. In considering the mean-stress effects in the stress-life (S–N) Approach, research efforts have been mostly concentrated in establishing correlating functions in terms of the flow stress or yield stress or the ultimate tensile stress, etc., by taking, say, R = −1 test results as a reference. Very little effort has been made towards understanding the role of stress range Δσ and the maximum stress σmax, (or σmean) in the fatigue crack nucleation and propagation and also how to relate this to both the stress-life and the fracture-mechanics descriptions. In this paper we first examine crack nucleation based on the stress-life Approach using a two-parameter requirement in terms of Δσ and σmax, and then connect it to crack propagation using the Kitagawa diagram as the incipient crack grows to become a long crack. Since stress-life data include both nucleation and propagation, the connection of the Safe-Life Approach to the fracture-mechanics analysis is pertinent. Comparison of the present analysis with experimental data taken from the literature demonstrates that a two-parameter Approach in terms of Δσ and σmax forms a basis for the S–N analysis.
Stefano Beretta - One of the best experts on this subject based on the ideXlab platform.
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A log-normal format for failure probability under LCF: Concept, validation and definition of design curve
International Journal of Fatigue, 2016Co-Authors: Stefano Beretta, Stefano Foletti, E. Rusconi, Andrea Riva, Darrell F. SocieAbstract:Abstract Turbine components are usually designed onto Safe-Life Approach, where the low-cycle fatigue analysis is based on design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion for the case of components subjected to LCF. In this paper, we firstly propose a log-normal format for calculating reliability for an assessment point ( ∊ , N ^ ) based on a first order approximation. The validity of the Approach is then proved for two different materials with a series of Monte Carlo simulations, where the material cyclic response is coupled to its ∊ - N diagram. The format is then used for estimating failure probability and for defining the design point which corresponds to a target failure probability. A safety factor is then proposed and its application to a series of steels for power generation is shown.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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A Simple Format for the Definition of Safety Factors for LCF
Volume 7B: Structures and Dynamics, 2014Co-Authors: Stefano Beretta, Stefano Foletti, Andrea SanguinetiAbstract:Turbine components are heavy duty mechanical parts that are usually designed onto Safe-Life Approach, where the lowcycle fatigue analysis is based onto design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion of the case of LCF. In this paper, we firstly define a simple lognormal format for calculation of reliability for a given fatigue life under LCF conditions. Then, the partial safety factor to be applied to e N f curve are then obtained for different COV’s of the applied load. The so defined design e N f curve for a rotor steel is then adopted for a complex analysis of a notched component under LCF, whose life has been estimated by an elasto-plastic analysis.
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Probabilistic integrity assessment of turbine disks in presence of potential defects
MATEC Web of Conferences, 2014Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor disks for gas turbines are heavy components and are usually designed following a Safe-Life Approach, where the low-cycle fatigue analysis is carried out referring to design life curves with suitable probabilistic margins. However, in the case of such a heavy component there is the possibility of rare occurrence of undetected defects or, better, the need to identify the defect acceptability for the different rotor regions (considering stress, temperature, mission profile). In order to carry out such calculations for a turbine rotor disk a software named {AStrID} (Assessment of the Str uctural I ntegrity of D isks) has been developed in close cooperation between Politecnico di Milano and Ansaldo Energia (AEN). This paper summarizes its background and some of the relevant features.
Stefano Foletti - One of the best experts on this subject based on the ideXlab platform.
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A log-normal format for failure probability under LCF: Concept, validation and definition of design curve
International Journal of Fatigue, 2016Co-Authors: Stefano Beretta, Stefano Foletti, E. Rusconi, Andrea Riva, Darrell F. SocieAbstract:Abstract Turbine components are usually designed onto Safe-Life Approach, where the low-cycle fatigue analysis is based on design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion for the case of components subjected to LCF. In this paper, we firstly propose a log-normal format for calculating reliability for an assessment point ( ∊ , N ^ ) based on a first order approximation. The validity of the Approach is then proved for two different materials with a series of Monte Carlo simulations, where the material cyclic response is coupled to its ∊ - N diagram. The format is then used for estimating failure probability and for defining the design point which corresponds to a target failure probability. A safety factor is then proposed and its application to a series of steels for power generation is shown.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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A Simple Format for the Definition of Safety Factors for LCF
Volume 7B: Structures and Dynamics, 2014Co-Authors: Stefano Beretta, Stefano Foletti, Andrea SanguinetiAbstract:Turbine components are heavy duty mechanical parts that are usually designed onto Safe-Life Approach, where the lowcycle fatigue analysis is based onto design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion of the case of LCF. In this paper, we firstly define a simple lognormal format for calculation of reliability for a given fatigue life under LCF conditions. Then, the partial safety factor to be applied to e N f curve are then obtained for different COV’s of the applied load. The so defined design e N f curve for a rotor steel is then adopted for a complex analysis of a notched component under LCF, whose life has been estimated by an elasto-plastic analysis.
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Probabilistic integrity assessment of turbine disks in presence of potential defects
MATEC Web of Conferences, 2014Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor disks for gas turbines are heavy components and are usually designed following a Safe-Life Approach, where the low-cycle fatigue analysis is carried out referring to design life curves with suitable probabilistic margins. However, in the case of such a heavy component there is the possibility of rare occurrence of undetected defects or, better, the need to identify the defect acceptability for the different rotor regions (considering stress, temperature, mission profile). In order to carry out such calculations for a turbine rotor disk a software named {AStrID} (Assessment of the Str uctural I ntegrity of D isks) has been developed in close cooperation between Politecnico di Milano and Ansaldo Energia (AEN). This paper summarizes its background and some of the relevant features.
Emanuela Cavalleri - One of the best experts on this subject based on the ideXlab platform.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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Structural integrity assessment of turbine discs in presence of potential defects: probabilistic analysis and implementation
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor discs for gas turbines are heavy components usually designed following a Safe-Life Approach, where the low-cycle fatigue design is based on life curves with suitable probabilistic margins. However, in such a component, there is the possible occurrence of undetected defects that can propagate at each startup–shutdown cycle, and therefore, defect acceptance criteria have to be defined for the different rotor regions (considering stress distribution and temperature). Moreover, the failure risk should be evaluated considering static fracture at overspeed as a potential failure mode. In order to make such an assessment for a turbine rotor disc, a semi-probabilistic Approach for the integrity assessment-based current standards has been developed. The Approach has then been implemented into a code able to process axis-symmetric Finite Element (FE) analyses of the disc and to produce maps for the expected life (for a given defect size) and for the acceptable defect (for a target life). The probabilistic assessment of turbine rotor discs is first discussed together with a sensitivity study about the most significant calculation assumptions. Then, details of the semi-probabilistic code are shown together with application to a turbine disc.
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Probabilistic integrity assessment of turbine disks in presence of potential defects
MATEC Web of Conferences, 2014Co-Authors: Stefano Beretta, Stefano Foletti, Mauro Madia, Emanuela CavalleriAbstract:Rotor disks for gas turbines are heavy components and are usually designed following a Safe-Life Approach, where the low-cycle fatigue analysis is carried out referring to design life curves with suitable probabilistic margins. However, in the case of such a heavy component there is the possibility of rare occurrence of undetected defects or, better, the need to identify the defect acceptability for the different rotor regions (considering stress, temperature, mission profile). In order to carry out such calculations for a turbine rotor disk a software named {AStrID} (Assessment of the Str uctural I ntegrity of D isks) has been developed in close cooperation between Politecnico di Milano and Ansaldo Energia (AEN). This paper summarizes its background and some of the relevant features.
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A Tool for the Structural Integrity Assessment of Turbine Disks: Probabilistic and Numerical Background
Volume 7A: Structures and Dynamics, 2013Co-Authors: Mauro Madia, Stefano Foletti, Stefano Beretta, Emanuela CavalleriAbstract:Rotor disks for gas turbines are heavy components and are usually designed following a Safe-Life Approach, where the low-cycle fatigue analysis is carried out referring to design life curves with suitable probabilistic margins. However, in the case of such a heavy component there is the possibility of rare occurrence of undetected defects or, better, the need to identify the defect acceptability for the different rotor regions (considering stress, temperature, mission profile).In order to carry out such calculations for a turbine rotor disk a software named AStrID (Assessment of the Structural Integrity of Disks) has been developed in close cooperation between Politecnico di Milano and Ansaldo Energia (AEN). This paper summarizes its background and some of the relevant features.© 2013 ASME
