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Gbadebo Owolabi - One of the best experts on this subject based on the ideXlab platform.
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a new approach to estimating the fatigue Notch factor of ti 6al 4v components
International Journal of Fatigue, 2016Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Adewale Olasumboye, Horace WhitworthAbstract:Abstract Titanium alloy is used for airframe components and compressor blades application because of its high strength and fracture toughness at low temperatures and high strength and creep resistance at elevated temperature. This paper extends a recently developed probabilistic mesomechanics based model to Notched titanium alloy components using simulation strategies that capture both the essence of Notch root stress gradient and the complexity of realistic microstructures. The Notch Size effects and Notch root and inelastic behavior are combined with probability distributions of microscale stress and small crack initiation to inform minimum life design methods. A new approach which can be applied using crystal plasticity finite element or closed form solution is also proposed as a more robust method for determining the fatigue Notch factor than the existing classical methods. The fatigue Notch factors predicted using the new probabilistic mesomechanics based model are in good agreements with experimental for Notched titanium alloy specimens subjected to cyclic loads with various stress ratios.
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The effects of Notch Size and material microstructure on the Notch sensitivity factor for Notched components
Engineering Fracture Mechanics, 2015Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Adewale Olasumboye, Horace WhitworthAbstract:Abstract Nickel base superalloys are used in hot sections of gas turbine engines due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. In this paper, a new probabilistic approach based on weakest-link theory that accounts for the effects of the microstructure, Notch Size and Notch acuity is described and applied to nickel base superalloy to determine the fatigue Notch factor, Notch sensitivity index and the probability of forming microstructurally small crack from the Notch root. The simulation results obtained from this framework are compared with experimental results and results obtained using existing classical methods for Notched polycrystalline nickel base superalloys for the different Notch root radii and acuities considered.
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extension of a probabilistic mesomechanics based model for fatigue Notch factor to titanium alloy components
Procedia Materials Science, 2014Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Horace WhitworthAbstract:Abstract This paper extends a recently developed probabilistic mesomechaniccs based model for fatigue Notch factor to titanium alloy components. The Notch Size effects and Notch root and inelastic behaviour are combined with probability distributions of microscale stress-strain gradient and small crack initiation to inform minimum life design methods. The fatigue Notch factors predicted using the new model are in good agreements with the experimental results for the Notched titanium alloy specimens.
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fatigue strength reduction factor for polycrystalline nickel base superalloy with and without non metallic inclusions
Procedia Engineering, 2014Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Horace WhitworthAbstract:Abstract Polycrystalline nickel base superalloy is popular for its wide applications; it is used in hot sections of power generation turbines, rocket engines and other challenging conditions due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. However, the presence of inclusions introduced into the superalloy during the fabrication processes can significantly degrade the fatigue life. This paper utilizes a new probabilistic method which captures both the essence of microstructure and Notch root stress gradient to determine the Notch Size and inclusions effects on the fatigue strength of Notched nickel base superalloy with and without non-metallic inclusions. Notched cylindrical specimens of nickel base superalloy of varying Notch root radii are modeled using microstructural-sensitive crystal plasticity finite element codes. The stresses extracted from the fatigue damage process zone around the Notch are used in determining the fatigue strength reduction factor and the associated probability of failure of the Notched specimens. The numerical results obtained are in direct correlation with the experimentally obtained value for the different Notch root radii.
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On Fatigue Strength Reduction Factor: State of the Art
Volume 8: Mechanics of Solids Structures and Fluids, 2012Co-Authors: Gbadebo Owolabi, Horace Whitworth, Benedict Egboiyi, Olanrewaju AlukoAbstract:Numerous theoretical models have been developed to predict the fatigue strength reduction factor (also known as fatigue Notch factor), an important parameter in fatigue life prediction of Notched components. These models include: the classical average stress method, the fracture mechanics method, the stress field intensity method, the strain energy method, and the weakest link method. However, most of these methods do not incorporate explicit sensitivity to materials microstructure. Accordingly, Notch sensitivity remains a highly empirical subject in spite of significant advances in microstructure-sensitive modeling. This paper gives a detailed literature review of these methods and addresses their limitations. It also discusses a recently developed probabilistic method for microstructure-sensitive fatigue Notch factor. The probabilistic method provides a very strong physical basis for fatigue strength reduction and associated Notch sensitivity; thus it can be used to determine the effect of Notches on reduction of fatigue resistance in a way that directly incorporates microstructure. The results obtained using the new probabilistic framework and other conventional methods are compared with experimental data for Notched components. The probabilistic framework gives better correlation with experimental results for the Notch sensitivity and Notch Size effect than the conventional approaches including the Neuber’s, the Peterson, and the fracture mechanics methods.Copyright © 2012 by ASME
Horace Whitworth - One of the best experts on this subject based on the ideXlab platform.
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a new approach to estimating the fatigue Notch factor of ti 6al 4v components
International Journal of Fatigue, 2016Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Adewale Olasumboye, Horace WhitworthAbstract:Abstract Titanium alloy is used for airframe components and compressor blades application because of its high strength and fracture toughness at low temperatures and high strength and creep resistance at elevated temperature. This paper extends a recently developed probabilistic mesomechanics based model to Notched titanium alloy components using simulation strategies that capture both the essence of Notch root stress gradient and the complexity of realistic microstructures. The Notch Size effects and Notch root and inelastic behavior are combined with probability distributions of microscale stress and small crack initiation to inform minimum life design methods. A new approach which can be applied using crystal plasticity finite element or closed form solution is also proposed as a more robust method for determining the fatigue Notch factor than the existing classical methods. The fatigue Notch factors predicted using the new probabilistic mesomechanics based model are in good agreements with experimental for Notched titanium alloy specimens subjected to cyclic loads with various stress ratios.
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The effects of Notch Size and material microstructure on the Notch sensitivity factor for Notched components
Engineering Fracture Mechanics, 2015Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Adewale Olasumboye, Horace WhitworthAbstract:Abstract Nickel base superalloys are used in hot sections of gas turbine engines due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. In this paper, a new probabilistic approach based on weakest-link theory that accounts for the effects of the microstructure, Notch Size and Notch acuity is described and applied to nickel base superalloy to determine the fatigue Notch factor, Notch sensitivity index and the probability of forming microstructurally small crack from the Notch root. The simulation results obtained from this framework are compared with experimental results and results obtained using existing classical methods for Notched polycrystalline nickel base superalloys for the different Notch root radii and acuities considered.
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extension of a probabilistic mesomechanics based model for fatigue Notch factor to titanium alloy components
Procedia Materials Science, 2014Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Horace WhitworthAbstract:Abstract This paper extends a recently developed probabilistic mesomechaniccs based model for fatigue Notch factor to titanium alloy components. The Notch Size effects and Notch root and inelastic behaviour are combined with probability distributions of microscale stress-strain gradient and small crack initiation to inform minimum life design methods. The fatigue Notch factors predicted using the new model are in good agreements with the experimental results for the Notched titanium alloy specimens.
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fatigue strength reduction factor for polycrystalline nickel base superalloy with and without non metallic inclusions
Procedia Engineering, 2014Co-Authors: Gbadebo Owolabi, Oluwamayowa Okeyoyin, Oluwakayode Bamiduro, Horace WhitworthAbstract:Abstract Polycrystalline nickel base superalloy is popular for its wide applications; it is used in hot sections of power generation turbines, rocket engines and other challenging conditions due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. However, the presence of inclusions introduced into the superalloy during the fabrication processes can significantly degrade the fatigue life. This paper utilizes a new probabilistic method which captures both the essence of microstructure and Notch root stress gradient to determine the Notch Size and inclusions effects on the fatigue strength of Notched nickel base superalloy with and without non-metallic inclusions. Notched cylindrical specimens of nickel base superalloy of varying Notch root radii are modeled using microstructural-sensitive crystal plasticity finite element codes. The stresses extracted from the fatigue damage process zone around the Notch are used in determining the fatigue strength reduction factor and the associated probability of failure of the Notched specimens. The numerical results obtained are in direct correlation with the experimentally obtained value for the different Notch root radii.
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On Fatigue Strength Reduction Factor: State of the Art
Volume 8: Mechanics of Solids Structures and Fluids, 2012Co-Authors: Gbadebo Owolabi, Horace Whitworth, Benedict Egboiyi, Olanrewaju AlukoAbstract:Numerous theoretical models have been developed to predict the fatigue strength reduction factor (also known as fatigue Notch factor), an important parameter in fatigue life prediction of Notched components. These models include: the classical average stress method, the fracture mechanics method, the stress field intensity method, the strain energy method, and the weakest link method. However, most of these methods do not incorporate explicit sensitivity to materials microstructure. Accordingly, Notch sensitivity remains a highly empirical subject in spite of significant advances in microstructure-sensitive modeling. This paper gives a detailed literature review of these methods and addresses their limitations. It also discusses a recently developed probabilistic method for microstructure-sensitive fatigue Notch factor. The probabilistic method provides a very strong physical basis for fatigue strength reduction and associated Notch sensitivity; thus it can be used to determine the effect of Notches on reduction of fatigue resistance in a way that directly incorporates microstructure. The results obtained using the new probabilistic framework and other conventional methods are compared with experimental data for Notched components. The probabilistic framework gives better correlation with experimental results for the Notch sensitivity and Notch Size effect than the conventional approaches including the Neuber’s, the Peterson, and the fracture mechanics methods.Copyright © 2012 by ASME
Theodore Nicholas - One of the best experts on this subject based on the ideXlab platform.
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a critical plane gradient approach for the prediction of Notched hcf life
International Journal of Fatigue, 2005Co-Authors: Rajiv A Naik, David B Lanning, Theodore Nicholas, Alan R KallmeyerAbstract:Abstract A new approach, which uses the Findley critical plane damage parameter along with the stress gradient at the Notch, was developed for predicting Notched HCF life. The proposed approach and methodology for HCF Notch analysis accounts for: (i) the multiaxial stress state at the Notch, (ii) the Notch Size effect, and (iii) the effect of fatigue stress ratio. Two fatigue failure criteria based on the critical distance method were used to define a Notch gradient parameter, GF. It was shown that GF is invariant with Notch geometry and fatigue stress ratio. This invariance of GF was used to successfully and consistently analyze and predict Notched HCF life of the titanium alloy Ti–6Al–4V for: (i) different Notch geometries, and (ii) different fatigue stress ratios. For a Notch under a general 2-dimensional stress state subjected to constant amplitude fatigue loading, the current approach can be performed in closed-form. Closed-form equations were developed for the fatigue Notch factor Kf, and the Findley gradient factor, GF, as a function of the critical distance, ac, the Notch radius, ρ, the stress concentration factor Kt, and the stress ratio, R. The proposed approach can be applied equally well using either finite element analysis or the closed-form analysis. A relationship was also established between GF and the Notch sensitivity of a material. A new Findley Notch sensitivity parameter, QF, given by (2-GF) was proposed as a convenient and a more robust measure of the Notch sensitivity than the classical Notch sensitivity parameter, q, which can vary with the applied fatigue stress ratio.
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Notch Size effects on high cycle fatigue limit stress of udimet 720
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Theodore NicholasAbstract:Abstract Notch Size effects on the high cycle fatigue (HCF) limit stress of Ni-base superalloy Udimet 720 were investigated on cylindrical specimens with three Notch Sizes of the same stress concentration factor Kt=2.74. The HCF limit stress corresponding to a life of 106 cycles was experimentally determined at a stress ratio of 0.1 and a frequency of 25 Hz at room temperature. The stresses were calculated using finite element analysis (FEA) and the specimens analyzed using scanning electron microscopy (SEM). Test results show that at the same Kt value, Notch Size can slightly affect the HCF limit stress of U720 when Notch root plasticity occurs. FEA and SEM results reveal that the Notch Size effects are influenced by a complicated combination of the stress and plastic strain fields at the Notch tip, the nominal stress, and the effects of prior plastic deformation on fatigue crack initiation.
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Notch Size effects in HCF behavior of Ti–6Al–4V☆
International Journal of Fatigue, 1999Co-Authors: George K. Haritos, Theodore Nicholas, David B LanningAbstract:Abstract The high cycle fatigue (HCF) behavior of Ti–6Al–4V is investigated for cylindrical specimens having three Sizes of geometrically similar circumferential V-Notches, each with an elastic stress concentration factor, K t , of approximately 2.78. A step loading technique for obtaining a point on a constant life (10 6 cycles) Haigh diagram from a single test specimen was implemented. Tests were performed at stress ratios of R =0.1, 0.5, and 0.8 for specimens machined from two different product forms of Ti–6Al–4V, bar and plate forgings. Results indicate that while there is a definite Notch Size effect in the Ti–6Al–4V bar within the range of Notch Sizes tested, little or no such effect exists in the plate.
David B Lanning - One of the best experts on this subject based on the ideXlab platform.
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a critical plane gradient approach for the prediction of Notched hcf life
International Journal of Fatigue, 2005Co-Authors: Rajiv A Naik, David B Lanning, Theodore Nicholas, Alan R KallmeyerAbstract:Abstract A new approach, which uses the Findley critical plane damage parameter along with the stress gradient at the Notch, was developed for predicting Notched HCF life. The proposed approach and methodology for HCF Notch analysis accounts for: (i) the multiaxial stress state at the Notch, (ii) the Notch Size effect, and (iii) the effect of fatigue stress ratio. Two fatigue failure criteria based on the critical distance method were used to define a Notch gradient parameter, GF. It was shown that GF is invariant with Notch geometry and fatigue stress ratio. This invariance of GF was used to successfully and consistently analyze and predict Notched HCF life of the titanium alloy Ti–6Al–4V for: (i) different Notch geometries, and (ii) different fatigue stress ratios. For a Notch under a general 2-dimensional stress state subjected to constant amplitude fatigue loading, the current approach can be performed in closed-form. Closed-form equations were developed for the fatigue Notch factor Kf, and the Findley gradient factor, GF, as a function of the critical distance, ac, the Notch radius, ρ, the stress concentration factor Kt, and the stress ratio, R. The proposed approach can be applied equally well using either finite element analysis or the closed-form analysis. A relationship was also established between GF and the Notch sensitivity of a material. A new Findley Notch sensitivity parameter, QF, given by (2-GF) was proposed as a convenient and a more robust measure of the Notch sensitivity than the classical Notch sensitivity parameter, q, which can vary with the applied fatigue stress ratio.
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Notch Size effects in HCF behavior of Ti–6Al–4V☆
International Journal of Fatigue, 1999Co-Authors: George K. Haritos, Theodore Nicholas, David B LanningAbstract:Abstract The high cycle fatigue (HCF) behavior of Ti–6Al–4V is investigated for cylindrical specimens having three Sizes of geometrically similar circumferential V-Notches, each with an elastic stress concentration factor, K t , of approximately 2.78. A step loading technique for obtaining a point on a constant life (10 6 cycles) Haigh diagram from a single test specimen was implemented. Tests were performed at stress ratios of R =0.1, 0.5, and 0.8 for specimens machined from two different product forms of Ti–6Al–4V, bar and plate forgings. Results indicate that while there is a definite Notch Size effect in the Ti–6Al–4V bar within the range of Notch Sizes tested, little or no such effect exists in the plate.
Tandy R Freeman - One of the best experts on this subject based on the ideXlab platform.
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intercondylar Notch Size and anterior cruciate ligament injuries in athletes a prospective study
American Journal of Sports Medicine, 1993Co-Authors: Tarek O Souryal, Tandy R FreemanAbstract:Published reports agree that there is a strong association between intercondylar Notch stenosis and anterior cruciate ligament injuries. In a previously published retrospective study on bilateral anterior cruciate ligament injuries and associated intercondylar Notch stenosis, we formulated the Notch width index to measure and compare intercondylar Notch width. The purpose of this prospective study was to establish a normal range for the Notch width index and to correlate intercondylar Notch Size and anterior cruciate ligament injuries. We gathered data on 902 high school athletes, including range of motion, thigh girth, ligament stability and intercondylar Notch width using the Notch width index. The population was then followed prospectively and anterior cruciate ligament injuries were recorded and correlated with Notch width index in a blind manner. Two-year results showed that the overall anterior cruciate ligament injury rate was 3%. The normal intercondylar Notch ratio was 0.231 +/- 0.044. Intercondylar Notch width index for men was larger than that for women. Athletes sustaining noncontact anterior cruciate ligament tears have statistically significant intercondylar Notch stenosis (Notch width index, 0.189). Ten of 14 athletes with noncontact anterior cruciate ligament injuries had a Notch width index that was at least 1 SD below the mean. Athletes with contact anterior cruciate ligament injuries had a mean of 0.233. We conclude that athletes with a stenotic intercondylar Notch are at significantly greater risk for sustaining noncontact anterior cruciate ligament injury.
