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A 3D finite element study of fatigue life dispersion in rolling line contacts / Nick Weinzapfel in Transactions of the ASME . Journal of tribology, Vol. 133 N° 4 (Octobre 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 133 N° 4 (Octobre 2011) . - 10 p. Titre : A 3D finite element study of fatigue life dispersion in rolling line contacts Type de document : texte imprimé Auteurs : Nick Weinzapfel, Auteur ; Farshid Sadeghi, Auteur ; Alexander Liebel, Auteur Année de publication : 2012 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Fatigue  cracks  Fatigue  testing  Grain  boundaries  Rolling  bearings  Steel Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Rolling contact fatigue of rolling element bearings is a statistical phenomenon that is strongly affected by the heterogeneous nature of the material microstructure. Heterogeneity in the microstructure is accompanied by randomly distributed weak points in the material that lead to scatter in the fatigue lives of an otherwise identical lot of rolling element bearings. Many life models for rolling contact fatigue are empirical and rely upon correlation with fatigue test data to characterize the dispersion of fatigue lives. Recently developed computational models of rolling contact fatigue bypass this requirement by explicitly considering the microstructure as a source of the variability. This work utilizes a similar approach but extends the analysis into a 3D framework. The bearing steel microstructure is modeled as randomly generated Voronoi tessellations wherein each cell represents a material grain and the boundaries between them constitute the weak planes in the material. Fatigue cracks initiate on the weak planes where oscillating shear stresses are the strongest. Finite element analysis is performed to determine the magnitude of the critical shear stress range and the depth where it occurs. These quantities exhibit random variation due to the microstructure topology which in turn results in scatter in the predicted fatigue lives. The model is used to assess the influence of (1) topological randomness in the microstructure, (2) heterogeneity in the distribution of material properties, and (3) the presence of inherent material flaws on relative fatigue lives. Neither topological randomness nor heterogeneous material properties alone account for the dispersion seen in actual bearing fatigue tests. However, a combination of both or the consideration of material flaws brings the model's predictions within empirically observed bounds. Examination of the critical shear stress ranges with respect to the grain boundaries where they occur reveals the orientation of weak planes most prone to failure in a three-dimensional sense that was not possible with previous models. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] A 3D finite element study of fatigue life dispersion in rolling line contacts [texte imprimé] / Nick Weinzapfel, Auteur ; Farshid Sadeghi, Auteur ; Alexander Liebel, Auteur . - 2012 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 133 N° 4 (Octobre 2011) . - 10 p. Mots-clés : Fatigue  cracks  Fatigue  testing  Grain  boundaries  Rolling  bearings  Steel Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Rolling contact fatigue of rolling element bearings is a statistical phenomenon that is strongly affected by the heterogeneous nature of the material microstructure. Heterogeneity in the microstructure is accompanied by randomly distributed weak points in the material that lead to scatter in the fatigue lives of an otherwise identical lot of rolling element bearings. Many life models for rolling contact fatigue are empirical and rely upon correlation with fatigue test data to characterize the dispersion of fatigue lives. Recently developed computational models of rolling contact fatigue bypass this requirement by explicitly considering the microstructure as a source of the variability. This work utilizes a similar approach but extends the analysis into a 3D framework. The bearing steel microstructure is modeled as randomly generated Voronoi tessellations wherein each cell represents a material grain and the boundaries between them constitute the weak planes in the material. Fatigue cracks initiate on the weak planes where oscillating shear stresses are the strongest. Finite element analysis is performed to determine the magnitude of the critical shear stress range and the depth where it occurs. These quantities exhibit random variation due to the microstructure topology which in turn results in scatter in the predicted fatigue lives. The model is used to assess the influence of (1) topological randomness in the microstructure, (2) heterogeneity in the distribution of material properties, and (3) the presence of inherent material flaws on relative fatigue lives. Neither topological randomness nor heterogeneous material properties alone account for the dispersion seen in actual bearing fatigue tests. However, a combination of both or the consideration of material flaws brings the model's predictions within empirically observed bounds. Examination of the critical shear stress ranges with respect to the grain boundaries where they occur reveals the orientation of weak planes most prone to failure in a three-dimensional sense that was not possible with previous models. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

An approach for modeling material grain structure in investigations of hertzian subsurface stresses and rolling contact fatigue / Nick Weinzapfel in Transactions of the ASME . Journal of tribology, Vol. 132 N° 4 (Octobre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 12 p. Titre : An approach for modeling material grain structure in investigations of hertzian subsurface stresses and rolling contact fatigue Type de document : texte imprimé Auteurs : Nick Weinzapfel, Auteur ; Farshid Sadeghi, Auteur ; Vasilios Bakolas, Auteur Année de publication : 2011 Article en page(s) : 12 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Computational  geometry  Crystal  microstructure  Fatigue  Finite  element  analysis  Internal  stresses  Mechanical  contact  Rolling  bearings  Rolling  friction Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The continuum theory of elasticity and/or homogeneously discretized finite element models have been commonly used to investigate and analyze subsurface stresses in Hertzian contacts. These approaches, however, do not effectively capture the influence of the random microstructure topology on subsurface stress distributions in Hertzian contacts. In this paper, a finite element model for analyzing subsurface stresses in an elastic half-space subjected to a general Hertzian contact load with explicit consideration of the material microstructure topology is presented. The random internal geometry of polycrystalline microstructures is modeled using a 3D Voronoi tessellation, where each Voronoi cell represents a distinct material grain. The grains are then meshed using finite elements, and an algorithm was developed to eliminate poorly shaped elements resulting from “near degeneracy” in the Voronoi tessellations. Hertzian point and line contacts loads are applied as distributed surface loads, and the model's response is evaluated with commercial finite element software ABAQUS. Internal stress results obtained from the current model compare well with analytical solutions from theory of elasticity. The influence of the internal microstructure topology on the subsurface stresses is demonstrated by analyzing the model's response to an over rolling element using a critical plane approach. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] An approach for modeling material grain structure in investigations of hertzian subsurface stresses and rolling contact fatigue [texte imprimé] / Nick Weinzapfel, Auteur ; Farshid Sadeghi, Auteur ; Vasilios Bakolas, Auteur . - 2011 . - 12 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 12 p. Mots-clés : Computational  geometry  Crystal  microstructure  Fatigue  Finite  element  analysis  Internal  stresses  Mechanical  contact  Rolling  bearings  Rolling  friction Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The continuum theory of elasticity and/or homogeneously discretized finite element models have been commonly used to investigate and analyze subsurface stresses in Hertzian contacts. These approaches, however, do not effectively capture the influence of the random microstructure topology on subsurface stress distributions in Hertzian contacts. In this paper, a finite element model for analyzing subsurface stresses in an elastic half-space subjected to a general Hertzian contact load with explicit consideration of the material microstructure topology is presented. The random internal geometry of polycrystalline microstructures is modeled using a 3D Voronoi tessellation, where each Voronoi cell represents a distinct material grain. The grains are then meshed using finite elements, and an algorithm was developed to eliminate poorly shaped elements resulting from “near degeneracy” in the Voronoi tessellations. Hertzian point and line contacts loads are applied as distributed surface loads, and the model's response is evaluated with commercial finite element software ABAQUS. Internal stress results obtained from the current model compare well with analytical solutions from theory of elasticity. The influence of the internal microstructure topology on the subsurface stresses is demonstrated by analyzing the model's response to an over rolling element using a critical plane approach. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

A new approach for including cage flexibility in dynamic bearing models by using combined explicit finite and discrete element methods / Ankur Ashtekar in Transactions of the ASME . Journal of tribology, Vol. 134 N° 04 (Octobre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 134 N° 04 (Octobre 2012) . - 12 p. Titre : A new approach for including cage flexibility in dynamic bearing models by using combined explicit finite and discrete element methods Type de document : texte imprimé Auteurs : Ankur Ashtekar, Auteur ; Farshid Sadeghi, Auteur Année de publication : 2012 Article en page(s) : 12 p. Note générale : tribology Langues : Anglais (eng) Mots-clés : bearing  dynamics;  cage  flexibility;  finite  elements;  disrcere  elements Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In this investigation, a new approach was developed to study the influence of cage flexibility on the dynamics of inner and outer races and balls in a bearing. A 3D explicit finite element model (EFEM) of the cage was developed and combined with an existing discrete element dynamic bearing model (DBM) with six degrees of freedom. The EFEM was used to determine the cage dynamics, deformation, and resulting stresses in a ball bearing under various operating conditions. A novel algorithm was developed to determine the contact forces between the rigid balls and the flexible (deformable) cage. In this new flexible cage dynamic bearing model, the discrete and finite element models interact at each time step to determine the position, velocity, acceleration, and forces of all bearing components. The combined model was applied to investigate the influence of cage flexibility on ball-cage interactions and the resulting ball motion, cage whirl, and the effects of shaft misalignment. The model demonstrates that cage flexibility (deflection) has a significant influence on the ball-cage interaction. The results from this investigation demonstrate that the magnitude of ball-cage impacts and the ball sliding reduced in the presence of a flexible cage; however, as expected, the cage overall motion and angular velocity were largely unaffected by the cage flexibility. During high-speed operation, centrifugal forces contribute substantially to the total cage deformation and resulting stresses. When shaft misalignment is considered, stress cycles are experienced in the bridge and rail sections of the cage where fatigue failures have been observed in practice and in experimental studies. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE9000134000004 [...] [article] A new approach for including cage flexibility in dynamic bearing models by using combined explicit finite and discrete element methods [texte imprimé] / Ankur Ashtekar, Auteur ; Farshid Sadeghi, Auteur . - 2012 . - 12 p. tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 134 N° 04 (Octobre 2012) . - 12 p. Mots-clés : bearing  dynamics;  cage  flexibility;  finite  elements;  disrcere  elements Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In this investigation, a new approach was developed to study the influence of cage flexibility on the dynamics of inner and outer races and balls in a bearing. A 3D explicit finite element model (EFEM) of the cage was developed and combined with an existing discrete element dynamic bearing model (DBM) with six degrees of freedom. The EFEM was used to determine the cage dynamics, deformation, and resulting stresses in a ball bearing under various operating conditions. A novel algorithm was developed to determine the contact forces between the rigid balls and the flexible (deformable) cage. In this new flexible cage dynamic bearing model, the discrete and finite element models interact at each time step to determine the position, velocity, acceleration, and forces of all bearing components. The combined model was applied to investigate the influence of cage flexibility on ball-cage interactions and the resulting ball motion, cage whirl, and the effects of shaft misalignment. The model demonstrates that cage flexibility (deflection) has a significant influence on the ball-cage interaction. The results from this investigation demonstrate that the magnitude of ball-cage impacts and the ball sliding reduced in the presence of a flexible cage; however, as expected, the cage overall motion and angular velocity were largely unaffected by the cage flexibility. During high-speed operation, centrifugal forces contribute substantially to the total cage deformation and resulting stresses. When shaft misalignment is considered, stress cycles are experienced in the bridge and rail sections of the cage where fatigue failures have been observed in practice and in experimental studies. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE9000134000004 [...]

A new approach to modeling surface defects in bearing dynamics simulations / Ankur Ashtekar in Transactions of the ASME . Journal of tribology, Vol. 130 N° 4 (Octobre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 8 p. Titre : A new approach to modeling surface defects in bearing dynamics simulations Type de document : texte imprimé Auteurs : Ankur Ashtekar, Auteur ; Farshid Sadeghi, Auteur ; Lars-Erik Stacke, Auteur Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Product  quality  Bearings  Dynamics  (Mechanics)  Force  Deflection  Engineering  simulation  Modeling  Motion Résumé : A dynamic model for deep groove and angular contact ball bearings was developed to investigate the influence of race defects on the motions of bearing components (i.e., inner and outer races, cage, and balls). In order to determine the effects of dents on the bearing dynamics, a model was developed to determine the force-deflection relationship between an ellipsoid and a dented semi-infinite domain. The force-deflection relationship for dented surfaces was then incorporated in the bearing dynamic model by replacing the well-known Hertzian force-deflection relationship whenever a ball/dent interaction occurs. In this investigation, all bearing components have six degrees-of-freedom. Newton’s laws are used to determine the motions of all bearing elements, and an explicit fourth-order Runge–Kutta algorithm with a variable or constant step size was used to integrate the equations of motion. A model was used to study the effect of dent size, dent location, and inner race speed on bearing components. The results indicate that surface defects and irregularities like dent have a severe effect on bearing motion and forces. Furthermore, these effects are even more severe for high-speed applications. The results also demonstrate that a single dent can affect the forces and motion throughout the entire bearing and on all bearing components. However, the location of the dent dictates the magnitude of its influence on each bearing component. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468093#D [...] [article] A new approach to modeling surface defects in bearing dynamics simulations [texte imprimé] / Ankur Ashtekar, Auteur ; Farshid Sadeghi, Auteur ; Lars-Erik Stacke, Auteur . - 8 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 8 p. Mots-clés : Product  quality  Bearings  Dynamics  (Mechanics)  Force  Deflection  Engineering  simulation  Modeling  Motion Résumé : A dynamic model for deep groove and angular contact ball bearings was developed to investigate the influence of race defects on the motions of bearing components (i.e., inner and outer races, cage, and balls). In order to determine the effects of dents on the bearing dynamics, a model was developed to determine the force-deflection relationship between an ellipsoid and a dented semi-infinite domain. The force-deflection relationship for dented surfaces was then incorporated in the bearing dynamic model by replacing the well-known Hertzian force-deflection relationship whenever a ball/dent interaction occurs. In this investigation, all bearing components have six degrees-of-freedom. Newton’s laws are used to determine the motions of all bearing elements, and an explicit fourth-order Runge–Kutta algorithm with a variable or constant step size was used to integrate the equations of motion. A model was used to study the effect of dent size, dent location, and inner race speed on bearing components. The results indicate that surface defects and irregularities like dent have a severe effect on bearing motion and forces. Furthermore, these effects are even more severe for high-speed applications. The results also demonstrate that a single dent can affect the forces and motion throughout the entire bearing and on all bearing components. However, the location of the dent dictates the magnitude of its influence on each bearing component. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468093#D [...]

A numerical model for life scatter in rolling element bearings / Nihar Raje in Transactions of the ASME . Journal of tribology, Vol. 130 N°1 (Janvier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 10 p. Titre : A numerical model for life scatter in rolling element bearings Type de document : texte imprimé Auteurs : Nihar Raje, Auteur ; Farshid Sadeghi, Auteur ; Richard G. Rateick, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Computer  simulation  Stress  Shear  (Mechanics)  Electromagnetic  scattering  Fatigue  Bearings  Fatigue  cracks  Fatigue  life  Rolling  bearings  Weibull  distribution Résumé : Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the mechanisms responsible for the bearing failure process. Life models that account for this dispersion are empirical in nature and do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the inhomogeneous nature of the bearing material. Here, a new approach based on a discrete material representation is presented that simulates this inherent material randomness. In this investigation, two levels of randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress field in Hertzian line contacts is studied. Fatigue life is formulated as a function of a critical stress quantity and its corresponding depth, following a similar approach to the Lundberg–Palmgren theory. However, instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. A new critical stress quantity is introduced that considers shear stress acting along internal material planes of weakness. It is found that there is a scatter in the magnitude as well as depth of occurrence of this critical stress quantity, which leads to a scatter in computed fatigue lives. Further, the range of depths within which the critical stress quantity occurs is found to be consistent with experimental observations of fatigue cracks. The life distributions obtained from the numerical simulations are found to follow a two-parameter Weibull distribution closely. The L10 life and the Weibull slope decrease when a nonuniform distribution of elastic modulus is assumed throughout the material. The introduction of internal flaws in the material significantly reduces the L10 life and the Weibull slope. However, it is found that the Weibull slope reaches a limiting value beyond a certain concentration of flaws. This limiting value is close to that predicted by the Lundberg–Palmgren theory. Weibull slopes obtained through the numerical simulations range from 1.29 to 3.36 and are within experimentally observed values for bearing steels. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467974 [article] A numerical model for life scatter in rolling element bearings [texte imprimé] / Nihar Raje, Auteur ; Farshid Sadeghi, Auteur ; Richard G. Rateick, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 10 p. Mots-clés : Computer  simulation  Stress  Shear  (Mechanics)  Electromagnetic  scattering  Fatigue  Bearings  Fatigue  cracks  Fatigue  life  Rolling  bearings  Weibull  distribution Résumé : Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the mechanisms responsible for the bearing failure process. Life models that account for this dispersion are empirical in nature and do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the inhomogeneous nature of the bearing material. Here, a new approach based on a discrete material representation is presented that simulates this inherent material randomness. In this investigation, two levels of randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress field in Hertzian line contacts is studied. Fatigue life is formulated as a function of a critical stress quantity and its corresponding depth, following a similar approach to the Lundberg–Palmgren theory. However, instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. A new critical stress quantity is introduced that considers shear stress acting along internal material planes of weakness. It is found that there is a scatter in the magnitude as well as depth of occurrence of this critical stress quantity, which leads to a scatter in computed fatigue lives. Further, the range of depths within which the critical stress quantity occurs is found to be consistent with experimental observations of fatigue cracks. The life distributions obtained from the numerical simulations are found to follow a two-parameter Weibull distribution closely. The L10 life and the Weibull slope decrease when a nonuniform distribution of elastic modulus is assumed throughout the material. The introduction of internal flaws in the material significantly reduces the L10 life and the Weibull slope. However, it is found that the Weibull slope reaches a limiting value beyond a certain concentration of flaws. This limiting value is close to that predicted by the Lundberg–Palmgren theory. Weibull slopes obtained through the numerical simulations range from 1.29 to 3.36 and are within experimentally observed values for bearing steels. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467974

Numerical modeling of mixed lubrication and flash temperature in EHL elliptical contacts / Neelesh Deolalikar in Transactions of the ASME . Journal of tribology, Vol. 130 N°1 (Janvier 2008) 

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A statistical damage mechanics model for subsurface initiated spalling in rolling contacts / Nihar Raje in Transactions of the ASME . Journal of tribology, Vol. 130 N° 4 (Octobre 2008) 

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A voronoi FE fatigue damage model for life scatter in rolling contacts / Behrooz Jalalahmadi in Transactions of the ASME . Journal of tribology, Vol. 132 N° 2 (Avril 2010) 

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