The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
Theodore Nicholas - One of the best experts on this subject based on the ideXlab platform.
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Effect of sample thickness on local contact behavior in a flat-on-flat fretting Fatigue apparatus
International Journal of Fatigue, 2020Co-Authors: A. L. Hutson, Theodore Nicholas, Steven E. Olson, N.e. AshbaughAbstract:Abstract Thin plate samples of Ti–6Al–4V contacted on both sides with pads of the same material were used to simulate contact conditions in real structures subjected to fretting Fatigue. Laboratory tests on specimens of varying thicknesses were used to determine the Stresses that correspond to a Fatigue life of 107 cycles using a step-loading procedure. For the specific apparatus used in this study, changes in thickness produced changes in the ratio of shear load to clamping load for a specific fretting pad geometry. Specimen thicknesses of 1, 2, and 4 mm, and Stress ratios of R=0.1 and 0.5 were investigated for two different contact pad lengths. Fatigue Limit Stresses in the specimen were found to be relatively insensitive to the average clamping or shear Stress. Finite element analyses of the test geometry were used to provide details of the Stress distribution in the contact region for the flat-on-flat geometry with blending radius. Results show that Stress and displacement fields for a variety of test conditions corresponding to a Fatigue life of 107 cycles vary widely and do not provide any clear indication of the existence of a simple parameter equivalent to a uniaxial Fatigue Limit Stress. The Stress and displacement fields are also shown to be very sensitive to the coefficient of friction used in the analysis.
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Influence of residual Stresses on high cycle Fatigue strength of Ti–6Al–4V subjected to foreign object damage
International Journal of Fatigue, 2020Co-Authors: S. R. Thompson, John J. Ruschau, Theodore NicholasAbstract:Abstract The role of residual Stresses in the high cycle Fatigue (HCF) strength of Ti–6Al–4V subjected to foreign object damage (FOD) was evaluated on simulated airfoil and rectangular geometries. Both real and simulated impacts were conducted using spherical projectiles launched at 300 m/s and quasi-static chisel indentation, respectively. The spheres used were 1 mm diameter glass beads while the quasi-static indentor had a radius of 1 mm. The airfoil specimens had leading edge (LE) radii of either 0.13 or 0.38 mm and were indented at 30° to the airfoil LE. The rectangular plates were 1.25 mm thick and were indented quasi-statically at 0°. All specimens subjected to FOD were subsequently tested in uniaxial HCF at a frequency of 350 Hz using a step loading procedure to determine the Fatigue Limit corresponding to 107 cycles. Before the HCF testing, half of the specimens were Stress relief annealed to remove residual Stresses. Results indicate that Stress relief generally improves the Fatigue Limit Stress, indicating that tensile residual Stresses are present after both quasi-static or dynamic indentation. For the dynamic impacts, the craters formed have less influence on the Fatigue strengths than that predicted from conventional notch Fatigue analysis.
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In search of a parameter for fretting Fatigue
2013Co-Authors: Theodore Nicholas, A. L. Hutson, Steven E. Olson, N.e. AshbaughAbstract:Fretting Fatigue experiments were conducted to determine the Fatigue Limit Stress at 107 cycles for Ti-6Al4V. A step-loading procedure was used to determine the Fatigue Limit Stress that, in turn, was applied to the test geometry in numerical simulations using finite elements. Several fretting pad geometries and specimen thicknesses were used to obtain a range of normal and shear forces that produced the Stress and displacement fields in the specimen. An evaluation was made of the conditions near the edge of contact where peak Stresses occur to deduce parameters which lead to fretting Fatigue failures at 107 cycles. However, no simple combination of Stresses and slip displacements could be used to correlate all of the experimental data. A fracture mechanics methodology was also employed in order to determine the conditions for propagation or non-propagation of cracks that initiate in the edge of contact region. While no parameters were found which could uniquely predict the fretting Fatigue failure, adjustment of the coefficient of friction based on computed slip displacements was shown to have a substantial effect on the Stress and Stress intensity factors. A correlation of friction coefficient with slip displacement is proposed as a possible method for consolidating data from fretting Fatigue experiments conducted under different conditions.
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Staircase testing of a titanium alloy in the gigacycle regime
International Journal of Fatigue, 2006Co-Authors: Ryan J. Morrissey, Theodore NicholasAbstract:Abstract The objective of this research was to investigate the high cycle Fatigue behavior of a titanium alloy using an ultrasonic Fatigue system. Fatigue testing from 10 6 to 10 9 cycles under fully reversed cycling ( R = −1) was performed to determine the ultra-high cycle Fatigue behavior of Ti–6Al–4V. The staircase test method was employed to obtain accurate values of the mean Fatigue Limit Stress corresponding to fixed numbers of cycles up to 10 9 . These results were compared to similar data generated on conventional servohydraulic test systems and electromagnetic shaker systems to determine if there are any frequency effects. In addition, specimens were tested with and without cooling air to determine the effects of temperature on the Fatigue behavior. Results indicate that the Fatigue strength determined from ultrasonic testing was consistent with conventional testing. In addition, the temperature rise in this material during ultrasonic testing is insignificant and has no apparent effect on the endurance Limit.
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The effect of notch geometry on critical distance high cycle Fatigue predictions
International Journal of Fatigue, 2005Co-Authors: David B Lanning, Theodore Nicholas, Anthony N. PalazottoAbstract:Abstract A critical distance method for predicting the Fatigue Limit Stresses of notched specimens was implemented for notched specimens with a wide range of notch dimensions. Circumferentially notched cylindrical specimens (kt=1.97–4.07) taken from Ti–6Al–4V forged plate were cycled to failure (R=0.1 and 0.5) using a step loading method for estimating the 106 cycle Fatigue Limit Stresses. These experimental data were used in combination with finite element solutions for all specimen geometries to determine a ‘critical distance’, a quantity or parameter determined from the Stress distribution surrounding the notch in combination with Fatigue Limit Stress data from unnotched specimens. A unique parameter was not found for all of the specimen geometries. However, predictions for the Fatigue Limit Stresses of the larger notch geometries may be made with some amount of accuracy using a single value of the critical distance parameter, while reasonable predictions for the specimens with the smallest notch dimensions may be made upon the recognition of an apparent size effect.
George K. Haritos - One of the best experts on this subject based on the ideXlab platform.
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on the use of critical distance theories for the prediction of the high cycle Fatigue Limit Stress in notched ti 6al 4v
International Journal of Fatigue, 2005Co-Authors: David B Lanning, Theodore Nicholas, George K. HaritosAbstract:Abstract Methods are investigated for predicting the high cycle Fatigue (HCF) lives of notched cylindrical Ti–6Al–4V specimens using critical distance concepts that employ the Stress distribution in the vicinity of the notch. Cylindrical Fatigue specimens had circumferential V-notches with a range of elastic Stress concentration factors ( k t =1.97–4.07). Notched and unnotched specimens were cycled to failure using a step-loading technique to generate points on a Haigh (Goodman) diagram for a constant Fatigue life of 10 6 cycles. Finite element solutions were generated to provide Stress distributions for the notched gage sections. The Stress distributions were used in the search for a critical distance over which the quantities of mean Stress, Stress range, or elastic strain energy may contribute to the Fatigue process and can be correlated to similar quantities from smooth, unnotched specimens. If the decrease in the local Stress ratio at the notch root for high applied Stress ratio is accounted for in the analysis, trends independent of applied Stress ratio were found in the calculated critical distances. Predictions based upon the results gave accuracy to within 12% of the experimental Fatigue Limit Stresses and illustrate the method has promise for use in Fatigue design of Ti–6Al–4V components.
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Effect of Plastic Prestrain on High Cycle Fatigue of Ti–6Al–4V
Mechanics of Materials, 2002Co-Authors: David B Lanning, Theodore Nicholas, George K. HaritosAbstract:Abstract The effect of initial plastic strain on the high cycle Fatigue (HCF) lives of smooth cylindrical Ti–6Al–4V specimens is investigated. Specimens were monotonically, quasi-statically loaded under strain control in tension to produce plastic strains from 1% to 5% and under load control in compression to produce 9.5% plastic strain. A step-loading technique was then employed to establish the 106 or 107 cycle Fatigue Limit Stress under load control conditions for Stress ratios of R=0.1, 0.5 and 0.8 at frequencies of either f=50 or 400 Hz. Results are compared with baseline Fatigue Limit Stresses for Ti–6Al–4V without prior plastic strain. Initial plastic prestrain in both tension and compression resulted in a small reduction in the Fatigue Limit at R=0.1, while a lesser reduction was exhibited at higher Stress ratios in terms of maximum Stress.
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Low-cycle Fatigue/high-cycle Fatigue interactions in notched Ti-6Al-4V*
Fatigue & Fracture of Engineering Materials & Structures, 2001Co-Authors: David B Lanning, Theodore Nicholas, George K. Haritos, D. C. MaxwellAbstract:Combined low-cycle Fatigue/high-cycle Fatigue (LCF/HCF) loadings were investigated for smooth and circumferentially V-notched cylindrical Ti-6Al-4V Fatigue specimens. Smooth specimens were first cycled under LCF loading conditions for a fraction of the previously established Fatigue life. The HCF 10 7 cycle Fatigue Limit Stress after LCF cycling was established using a step loading technique. Specimens with two notch sizes, both having elastic Stress concentration factors of K t = 2.7, were cycled under LCF loading conditions at a nominal Stress ratio of R = 0.1. The subsequent 10 6 cycle HCF Fatigue Limit Stress at both R = 0.1 and 0.8 was determined. The combined loading LCF/HCF Fatigue Limit Stresses for all specimens were compared to the baseline HCF Fatigue Limit Stresses. After LCF cycling and prior to HCF cycling, the notched specimens were heat tinted, and final fracture surfaces examined for cracks formed during the initial LCF loading. Fatigue test results indicate that the LCF loading, applied for 75% of total LCF life for the smooth specimens and 25% for the notched specimens, resulted in only small reductions in the subsequent HCF Fatigue Limit Stress. Under certain loading conditions, plasticity-induced Stress redistribution at the notch root during LCF cycling appears responsible for an observed increase in HCF Fatigue Limit Stress, in terms of net section Stress.
David B Lanning - One of the best experts on this subject based on the ideXlab platform.
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The effect of notch geometry on critical distance high cycle Fatigue predictions
International Journal of Fatigue, 2005Co-Authors: David B Lanning, Theodore Nicholas, Anthony N. PalazottoAbstract:Abstract A critical distance method for predicting the Fatigue Limit Stresses of notched specimens was implemented for notched specimens with a wide range of notch dimensions. Circumferentially notched cylindrical specimens (kt=1.97–4.07) taken from Ti–6Al–4V forged plate were cycled to failure (R=0.1 and 0.5) using a step loading method for estimating the 106 cycle Fatigue Limit Stresses. These experimental data were used in combination with finite element solutions for all specimen geometries to determine a ‘critical distance’, a quantity or parameter determined from the Stress distribution surrounding the notch in combination with Fatigue Limit Stress data from unnotched specimens. A unique parameter was not found for all of the specimen geometries. However, predictions for the Fatigue Limit Stresses of the larger notch geometries may be made with some amount of accuracy using a single value of the critical distance parameter, while reasonable predictions for the specimens with the smallest notch dimensions may be made upon the recognition of an apparent size effect.
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on the use of critical distance theories for the prediction of the high cycle Fatigue Limit Stress in notched ti 6al 4v
International Journal of Fatigue, 2005Co-Authors: David B Lanning, Theodore Nicholas, George K. HaritosAbstract:Abstract Methods are investigated for predicting the high cycle Fatigue (HCF) lives of notched cylindrical Ti–6Al–4V specimens using critical distance concepts that employ the Stress distribution in the vicinity of the notch. Cylindrical Fatigue specimens had circumferential V-notches with a range of elastic Stress concentration factors ( k t =1.97–4.07). Notched and unnotched specimens were cycled to failure using a step-loading technique to generate points on a Haigh (Goodman) diagram for a constant Fatigue life of 10 6 cycles. Finite element solutions were generated to provide Stress distributions for the notched gage sections. The Stress distributions were used in the search for a critical distance over which the quantities of mean Stress, Stress range, or elastic strain energy may contribute to the Fatigue process and can be correlated to similar quantities from smooth, unnotched specimens. If the decrease in the local Stress ratio at the notch root for high applied Stress ratio is accounted for in the analysis, trends independent of applied Stress ratio were found in the calculated critical distances. Predictions based upon the results gave accuracy to within 12% of the experimental Fatigue Limit Stresses and illustrate the method has promise for use in Fatigue design of Ti–6Al–4V components.
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Effect of Plastic Prestrain on High Cycle Fatigue of Ti–6Al–4V
Mechanics of Materials, 2002Co-Authors: David B Lanning, Theodore Nicholas, George K. HaritosAbstract:Abstract The effect of initial plastic strain on the high cycle Fatigue (HCF) lives of smooth cylindrical Ti–6Al–4V specimens is investigated. Specimens were monotonically, quasi-statically loaded under strain control in tension to produce plastic strains from 1% to 5% and under load control in compression to produce 9.5% plastic strain. A step-loading technique was then employed to establish the 106 or 107 cycle Fatigue Limit Stress under load control conditions for Stress ratios of R=0.1, 0.5 and 0.8 at frequencies of either f=50 or 400 Hz. Results are compared with baseline Fatigue Limit Stresses for Ti–6Al–4V without prior plastic strain. Initial plastic prestrain in both tension and compression resulted in a small reduction in the Fatigue Limit at R=0.1, while a lesser reduction was exhibited at higher Stress ratios in terms of maximum Stress.
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Low-cycle Fatigue/high-cycle Fatigue interactions in notched Ti-6Al-4V*
Fatigue & Fracture of Engineering Materials & Structures, 2001Co-Authors: David B Lanning, Theodore Nicholas, George K. Haritos, D. C. MaxwellAbstract:Combined low-cycle Fatigue/high-cycle Fatigue (LCF/HCF) loadings were investigated for smooth and circumferentially V-notched cylindrical Ti-6Al-4V Fatigue specimens. Smooth specimens were first cycled under LCF loading conditions for a fraction of the previously established Fatigue life. The HCF 10 7 cycle Fatigue Limit Stress after LCF cycling was established using a step loading technique. Specimens with two notch sizes, both having elastic Stress concentration factors of K t = 2.7, were cycled under LCF loading conditions at a nominal Stress ratio of R = 0.1. The subsequent 10 6 cycle HCF Fatigue Limit Stress at both R = 0.1 and 0.8 was determined. The combined loading LCF/HCF Fatigue Limit Stresses for all specimens were compared to the baseline HCF Fatigue Limit Stresses. After LCF cycling and prior to HCF cycling, the notched specimens were heat tinted, and final fracture surfaces examined for cracks formed during the initial LCF loading. Fatigue test results indicate that the LCF loading, applied for 75% of total LCF life for the smooth specimens and 25% for the notched specimens, resulted in only small reductions in the subsequent HCF Fatigue Limit Stress. Under certain loading conditions, plasticity-induced Stress redistribution at the notch root during LCF cycling appears responsible for an observed increase in HCF Fatigue Limit Stress, in terms of net section Stress.
Guillermo E Moralesespejel - One of the best experts on this subject based on the ideXlab platform.
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the Fatigue Limit of bearing steels part ii characterization for life rating standards
International Journal of Fatigue, 2012Co-Authors: Antonio Gabelli, Thore Lund, Karin Ryden, Ingemar Strandell, Guillermo E MoralesespejelAbstract:Abstract The dynamic load ratings and life rating standard for rolling bearings, ISO 281:2007, makes use of a Fatigue Limit Stress of hardened bearing steels as a parameter in the estimation of the Fatigue life of rolling bearings. Part I of this paper series presented an analytical-probabilistic model that provides a unified prediction of Fatigue strength corresponding to various Fatigue regimes including the very high cycle Fatigue (VHCF) regime. Based on the Fatigue model, Monte Carlo simulation of rotating bending and push–pull tests of bearing steels indicates the existence of a horizontal asymptote in the S–N curve in excess of 1012 cycles, which corresponds to the Fatigue Limit. Prediction of Fatigue Limit associated with certain reliability can be realized using the developed model and methodology. In the present paper (Part II of the paper series), the application of a Fatigue Limit Stress in the standard Fatigue load ratings of rolling bearings is described. The up-to-date interpretations and standard definition of the Fatigue Limit Stress are discussed in relation to the very long Stress cycling. The recent developments and results in the area of VHCF testing of hardened AISI 52100, SUJ2, 100Cr6 bearing steels are also reviewed. The Fatigue Limits predicted using the model from Part I, are compared with the VHCF data of bearing steels available from both the in-house tests and those in the literature. Good correlation is observed between the Fatigue Limit model and the experimental results. Plotting the experimental data on top of the predicted Fatigue Limit shows that the S–N data approaches asymptotically the predicted Fatigue Limit in the VHCF regime. It is found that the predicted Fatigue Limits and the VHCF testing data correlate well with the Fatigue Limit value set in the ISO 281:2007 standard for life rating of rolling bearings.
Antonio Gabelli - One of the best experts on this subject based on the ideXlab platform.
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A model for gear life with surface and subsurface survival: Tribological effects
Wear, 2018Co-Authors: Guillermo E. Morales-espejel, Antonio GabelliAbstract:Abstract The paper describes a model for gear Fatigue life based on the well-established methods used in dynamic load capacity of machine components. The model applies the Weibull's weakest link of material strength and the Lundberg-Palmgren theory for bearing dynamic load ratings. Significant, of the present model, is the introduction of a well-defined separation between the risk of surface initiated failures and the traditional subsurface Fatigue of the gear contact. This opens new possibilities for the use of specialized endurance models to predict the surface life of the gear contact. A further advantage of the proposed model is the use of a statistical definition of the Fatigue life of gears. Current design practices for gears are condition based rules. Essentially it is required to satisfy a Fatigue Limit Stress which is further reduced using service penalty factors. Contrary to this approach, the proposed model makes use of a L10 life associated to a 90% reliability for the gear population. Comparison between the experimentally obtained gear endurances and L10 predicted life, using the present theory, indicates the ability of the model to account for the gear endurance and the contribution of the surface to the performance. This new approach is felt to be of advantage for future progress in gear design.
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the Fatigue Limit of bearing steels part ii characterization for life rating standards
International Journal of Fatigue, 2012Co-Authors: Antonio Gabelli, Thore Lund, Karin Ryden, Ingemar Strandell, Guillermo E MoralesespejelAbstract:Abstract The dynamic load ratings and life rating standard for rolling bearings, ISO 281:2007, makes use of a Fatigue Limit Stress of hardened bearing steels as a parameter in the estimation of the Fatigue life of rolling bearings. Part I of this paper series presented an analytical-probabilistic model that provides a unified prediction of Fatigue strength corresponding to various Fatigue regimes including the very high cycle Fatigue (VHCF) regime. Based on the Fatigue model, Monte Carlo simulation of rotating bending and push–pull tests of bearing steels indicates the existence of a horizontal asymptote in the S–N curve in excess of 1012 cycles, which corresponds to the Fatigue Limit. Prediction of Fatigue Limit associated with certain reliability can be realized using the developed model and methodology. In the present paper (Part II of the paper series), the application of a Fatigue Limit Stress in the standard Fatigue load ratings of rolling bearings is described. The up-to-date interpretations and standard definition of the Fatigue Limit Stress are discussed in relation to the very long Stress cycling. The recent developments and results in the area of VHCF testing of hardened AISI 52100, SUJ2, 100Cr6 bearing steels are also reviewed. The Fatigue Limits predicted using the model from Part I, are compared with the VHCF data of bearing steels available from both the in-house tests and those in the literature. Good correlation is observed between the Fatigue Limit model and the experimental results. Plotting the experimental data on top of the predicted Fatigue Limit shows that the S–N data approaches asymptotically the predicted Fatigue Limit in the VHCF regime. It is found that the predicted Fatigue Limits and the VHCF testing data correlate well with the Fatigue Limit value set in the ISO 281:2007 standard for life rating of rolling bearings.
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The Fatigue Limit of bearing steels – Part II: Characterization for life rating standards
International Journal of Fatigue, 2012Co-Authors: Antonio Gabelli, Thore Lund, Karin Ryden, Ingemar Strandell, Guillermo E. Morales-espejelAbstract:Abstract The dynamic load ratings and life rating standard for rolling bearings, ISO 281:2007, makes use of a Fatigue Limit Stress of hardened bearing steels as a parameter in the estimation of the Fatigue life of rolling bearings. Part I of this paper series presented an analytical-probabilistic model that provides a unified prediction of Fatigue strength corresponding to various Fatigue regimes including the very high cycle Fatigue (VHCF) regime. Based on the Fatigue model, Monte Carlo simulation of rotating bending and push–pull tests of bearing steels indicates the existence of a horizontal asymptote in the S–N curve in excess of 1012 cycles, which corresponds to the Fatigue Limit. Prediction of Fatigue Limit associated with certain reliability can be realized using the developed model and methodology. In the present paper (Part II of the paper series), the application of a Fatigue Limit Stress in the standard Fatigue load ratings of rolling bearings is described. The up-to-date interpretations and standard definition of the Fatigue Limit Stress are discussed in relation to the very long Stress cycling. The recent developments and results in the area of VHCF testing of hardened AISI 52100, SUJ2, 100Cr6 bearing steels are also reviewed. The Fatigue Limits predicted using the model from Part I, are compared with the VHCF data of bearing steels available from both the in-house tests and those in the literature. Good correlation is observed between the Fatigue Limit model and the experimental results. Plotting the experimental data on top of the predicted Fatigue Limit shows that the S–N data approaches asymptotically the predicted Fatigue Limit in the VHCF regime. It is found that the predicted Fatigue Limits and the VHCF testing data correlate well with the Fatigue Limit value set in the ISO 281:2007 standard for life rating of rolling bearings.
