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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 30 Nov 2022 04:39:38 GMT2022-11-30T04:39:38ZA volumetric energy based high cycle multiaxial fatigue citerion
http://hdl.handle.net/10985/11218
A volumetric energy based high cycle multiaxial fatigue citerion
BANVILLET, ALexis; PALIN-LUC, Thierry; LASSERRE, Serge
A reliable design of industrial parts against high-cycle multiaxial fatigue requires a fatigue criterion capable of predicting both the stress gradient and the load-type effects. These effects are very important in the transfer of fatigue data from specimen to component. By using the concept of volume influencing fatigue crack initiation proposed by Palin-Luc and Lasserre with an energy based approach, a new criterion is presented. Based on the strain-work density given to the material, this proposal is usable whatever the constant amplitude loading is: in and out-of-phase combined loadings, with or without mean stress. Its predictions are compared both with a total of 38 experiments on four materials (a mild steel, two high strength steels and a spheroidal graphite cast iron) and with the predictions of local criteria (Crossland, Dang Van, Papadopoulos and Morel). The comparison shows that the predictions of the volumetric proposal are very good and less scattered than those of the local approaches, especially for loadings with mean stresses or under non-proportional loadings.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10985/112182003-01-01T00:00:00ZBANVILLET, ALexisPALIN-LUC, ThierryLASSERRE, SergeA reliable design of industrial parts against high-cycle multiaxial fatigue requires a fatigue criterion capable of predicting both the stress gradient and the load-type effects. These effects are very important in the transfer of fatigue data from specimen to component. By using the concept of volume influencing fatigue crack initiation proposed by Palin-Luc and Lasserre with an energy based approach, a new criterion is presented. Based on the strain-work density given to the material, this proposal is usable whatever the constant amplitude loading is: in and out-of-phase combined loadings, with or without mean stress. Its predictions are compared both with a total of 38 experiments on four materials (a mild steel, two high strength steels and a spheroidal graphite cast iron) and with the predictions of local criteria (Crossland, Dang Van, Papadopoulos and Morel). The comparison shows that the predictions of the volumetric proposal are very good and less scattered than those of the local approaches, especially for loadings with mean stresses or under non-proportional loadings.Experimental Investigation on the Significance of the Conventional Endurance Limit of a Spheroidal Graphite Cast Iron
http://hdl.handle.net/10985/11235
Experimental Investigation on the Significance of the Conventional Endurance Limit of a Spheroidal Graphite Cast Iron
PALIN-LUC, Thierry; LASSERRE, Serge; BERARD, J-Y.
Fatigue tests were performed on a spheroidal graphite cast iron in four point plane bending under constant stress amplitude and block loading conditions. The microstructure of this material has a ‘bull’s eyes’ appearance, i.e. the spheroids of graphite are surrounded by ferrite and these nodules and ferrite zones are included in a pearlitic matrix. Scanning electronic microscope observations were carried out at different fractions of life for constant stress amplitude loadings above and below the conventional endurance limit. Non-propagating micro-cracks were observed at a stress level equal to the conventional endurance limit. These observations showed that another limit can be defined below the conventional endurance one, i.e. one below which micro-cracks were not observed to initiate in the matrix. These cracks were found to arrest at the ferrite/pearlite interface when the material was tested below this new limit. This concept was used to rationalize fatigue results from tests with loading in blocks above and below the conventional endurance limit.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10985/112351998-01-01T00:00:00ZPALIN-LUC, ThierryLASSERRE, SergeBERARD, J-Y.Fatigue tests were performed on a spheroidal graphite cast iron in four point plane bending under constant stress amplitude and block loading conditions. The microstructure of this material has a ‘bull’s eyes’ appearance, i.e. the spheroids of graphite are surrounded by ferrite and these nodules and ferrite zones are included in a pearlitic matrix. Scanning electronic microscope observations were carried out at different fractions of life for constant stress amplitude loadings above and below the conventional endurance limit. Non-propagating micro-cracks were observed at a stress level equal to the conventional endurance limit. These observations showed that another limit can be defined below the conventional endurance one, i.e. one below which micro-cracks were not observed to initiate in the matrix. These cracks were found to arrest at the ferrite/pearlite interface when the material was tested below this new limit. This concept was used to rationalize fatigue results from tests with loading in blocks above and below the conventional endurance limit.Comparative study and link between mesoscopic and energetic approaches in high cycle multiaxial fatigue
http://hdl.handle.net/10985/11221
Comparative study and link between mesoscopic and energetic approaches in high cycle multiaxial fatigue
MOREL, Franck; PALIN-LUC, Thierry; FROUSTEY, Catherine
Multiaxial fatigue analysis can be categorized into several viewpoints, i.e. empirical formulae, methods based on stress invariants, critical plane approaches, models using averages of stress quantities and energetic considerations. The aim of this paper is not to survey the current state of knowledge concerning multiaxial fatigue but to critically examine two endurance criteria so as to prove that a direct link can be established between them. The first of the two methods, proposed by Papadopoulos, has been built by exploring the fatigue of metals from the mesoscopic scale, that is from the scale of the metal grains of a metallic aggregate. The localized plastic strains developping in some less favourably oriented crystals is considered to be the main cause of fatigue crack nucleation. According to relationships between macroscopic and mesoscopic quantities, this model is finally expressed in terms of the usual macroscopic stresses relative to an elementary material volume. The second approach proposed by Froustey and Lasserre is an energetic based criterion. It has been deduced from experimental observations concerning multiaxial endurance limit and states that crack initiation occurs as soon as the total strain energy density exceeds a critical value. This paper shows that the critical value of the accumulated mesoscopic plastic strain used by Papadopoulos to characterize the endurance limit can be estimated with the global strain energy density at the macroscopic scale. Indeed, it is demonstrated that when dealing with in-phase or out-of-phase synchronous sinusoidal constant amplitude loadings, a single analytical formulation of these criteria can be written either with stress quantities or with energetic ones describing thus the same physical phenomenon. The mean stress influence is discussed; the predictions of the two approaches are similar when the material remains quasi elastic. Another important result concerns the phase difference of the stress tensor components. Very few approaches are able to predict the independence of the fatigue strength on the phase difference between normal and shear stresses. The two proposed criteria reflect this phenomenon which has been experimentally observed for many metals subjected to combined bending-torsion loading. Nevertheless, this independence with regard to the phase shift is no more effective when dealing with some biaxial stress systems with two normal stresses. In this case the two models are consistent with the experimental results since they show a marked influence of the phase difference.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10985/112212001-01-01T00:00:00ZMOREL, FranckPALIN-LUC, ThierryFROUSTEY, CatherineMultiaxial fatigue analysis can be categorized into several viewpoints, i.e. empirical formulae, methods based on stress invariants, critical plane approaches, models using averages of stress quantities and energetic considerations. The aim of this paper is not to survey the current state of knowledge concerning multiaxial fatigue but to critically examine two endurance criteria so as to prove that a direct link can be established between them. The first of the two methods, proposed by Papadopoulos, has been built by exploring the fatigue of metals from the mesoscopic scale, that is from the scale of the metal grains of a metallic aggregate. The localized plastic strains developping in some less favourably oriented crystals is considered to be the main cause of fatigue crack nucleation. According to relationships between macroscopic and mesoscopic quantities, this model is finally expressed in terms of the usual macroscopic stresses relative to an elementary material volume. The second approach proposed by Froustey and Lasserre is an energetic based criterion. It has been deduced from experimental observations concerning multiaxial endurance limit and states that crack initiation occurs as soon as the total strain energy density exceeds a critical value. This paper shows that the critical value of the accumulated mesoscopic plastic strain used by Papadopoulos to characterize the endurance limit can be estimated with the global strain energy density at the macroscopic scale. Indeed, it is demonstrated that when dealing with in-phase or out-of-phase synchronous sinusoidal constant amplitude loadings, a single analytical formulation of these criteria can be written either with stress quantities or with energetic ones describing thus the same physical phenomenon. The mean stress influence is discussed; the predictions of the two approaches are similar when the material remains quasi elastic. Another important result concerns the phase difference of the stress tensor components. Very few approaches are able to predict the independence of the fatigue strength on the phase difference between normal and shear stresses. The two proposed criteria reflect this phenomenon which has been experimentally observed for many metals subjected to combined bending-torsion loading. Nevertheless, this independence with regard to the phase shift is no more effective when dealing with some biaxial stress systems with two normal stresses. In this case the two models are consistent with the experimental results since they show a marked influence of the phase difference.How to reduce the duration of multiaxial fatigue tests under proportional service loadings
http://hdl.handle.net/10985/11226
How to reduce the duration of multiaxial fatigue tests under proportional service loadings
PALIN-LUC, Thierry; BANVILLET, Alexis; VITTORI, Jean-François
This paper deals with a technique to transform a multiaxial stress and strain-time sequence (in service recorded) in a simplified sequence. This simplified sequence is shorter than the original one and equivalent in terms of damage and lifetime: the number of simplified sequences to crack initiation is equal to the number of original sequences. The proposal is based on an energy threshold, below which no micro-crack can initiate or grow in the material. This technique was validated with real loading sequences recorded by strain gauges pasted on a car suspension arm. Fatigue tests were carried out on smooth specimens made of spheroidal graphite cast iron loaded in bending, in torsion and in combined bending and torsion. Experimental fatigue lives under the original sequence and under the simplified one are in very good correlation. Fatigue test duration is reduced up to a factor of 10 for the severe stress–strain sequences tested in this study.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10985/112262006-01-01T00:00:00ZPALIN-LUC, ThierryBANVILLET, AlexisVITTORI, Jean-FrançoisThis paper deals with a technique to transform a multiaxial stress and strain-time sequence (in service recorded) in a simplified sequence. This simplified sequence is shorter than the original one and equivalent in terms of damage and lifetime: the number of simplified sequences to crack initiation is equal to the number of original sequences. The proposal is based on an energy threshold, below which no micro-crack can initiate or grow in the material. This technique was validated with real loading sequences recorded by strain gauges pasted on a car suspension arm. Fatigue tests were carried out on smooth specimens made of spheroidal graphite cast iron loaded in bending, in torsion and in combined bending and torsion. Experimental fatigue lives under the original sequence and under the simplified one are in very good correlation. Fatigue test duration is reduced up to a factor of 10 for the severe stress–strain sequences tested in this study.High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets
http://hdl.handle.net/10985/11225
High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets
DEHMANI, Helmi; BRUGGER, Charles; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel
Some parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/112252016-01-01T00:00:00ZDEHMANI, HelmiBRUGGER, CharlesPALIN-LUC, ThierryMAREAU, CharlesKOECHLIN, SamuelSome parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.High cycle multiaxial fatigue crack initiation : experimental observations and microstructure simulations
http://hdl.handle.net/10985/7497
High cycle multiaxial fatigue crack initiation : experimental observations and microstructure simulations
KOMLAN, AGBESSI; SAINTIER, Nicolas; PALIN-LUC, Thierry
This study provides an analysis of high cycle multiaxial fatigue crack initiation modes based on SEM observations.The statistical study of crack initiation preferential sites shows that grains with multiple slip have a high probability of crack initiation. The application of Dang Van criterion at the grain scale using finite element analysis (cubic elasticity with / or without crystal plasticity) on 3D synthetic semi-periodic microstructures shows a strong heterogeneity of both the hydrostatic stress and shear. The evolution of this heterogeneity introduced by the material behavior is discussed. Finally, a method based on the extreme values statistics is proposed and applied to the fatigue indicative parameter associated to the Dang Van criterion. The effects of free surface and constitutive material model were analyzed.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/74972013-01-01T00:00:00ZKOMLAN, AGBESSISAINTIER, NicolasPALIN-LUC, ThierryThis study provides an analysis of high cycle multiaxial fatigue crack initiation modes based on SEM observations.The statistical study of crack initiation preferential sites shows that grains with multiple slip have a high probability of crack initiation. The application of Dang Van criterion at the grain scale using finite element analysis (cubic elasticity with / or without crystal plasticity) on 3D synthetic semi-periodic microstructures shows a strong heterogeneity of both the hydrostatic stress and shear. The evolution of this heterogeneity introduced by the material behavior is discussed. Finally, a method based on the extreme values statistics is proposed and applied to the fatigue indicative parameter associated to the Dang Van criterion. The effects of free surface and constitutive material model were analyzed.Statistical assessment of multiaxial HCF criteria at the grain scale
http://hdl.handle.net/10985/8394
Statistical assessment of multiaxial HCF criteria at the grain scale
HOR, Anis; SAINTIER, Nicolas; ROBERT, Camille; PALIN-LUC, Thierry; MOREL, Franck
Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/83942014-01-01T00:00:00ZHOR, AnisSAINTIER, NicolasROBERT, CamillePALIN-LUC, ThierryMOREL, FranckMultiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed.High-Cycle Fatigue Behaviour of Pure Tantalum under Multiaxial and Variable Amplitude Loadings
http://hdl.handle.net/10985/8397
High-Cycle Fatigue Behaviour of Pure Tantalum under Multiaxial and Variable Amplitude Loadings
MARECHAL, David; SAINTIER, Nicolas; PALIN-LUC, Thierry; NADAL, François
Due to its specific mechanical properties, tantalum is often used in strength-demanding military applications. High-cycle fatigue (HCF) behaviour of pure tantalum, however, has been rarely reported and the mechanisms at stake to account for deformation under cyclic loadings are still badly understood. This paper aims at better understanding the fatigue behaviour of tantalum and at clarifying the mechanisms of damage formation encountered under such loadings. HCF experiments performed at room temperature on commercially-pure tantalum are presented. Mean stress effects were investigated in the aim of clarifying the interaction between fatigue and creep. Fracture mechanisms were observed to vary from intergranular to transgranular depending on applied stress amplitude and mean stress. Damage mechanisms were investigated under tension and torsion. Results are analyzed in the light of existing fatigue criteria, the limitations of which are discussed. Finally, complex sequential loadings, representative of in-service loadings, were applied to tantalum smooth specimens. The contribution of each loading sequence to the overall damage was quantified and analyzed in terms of linear or non-linear cumulative damage rule
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/83972014-01-01T00:00:00ZMARECHAL, DavidSAINTIER, NicolasPALIN-LUC, ThierryNADAL, FrançoisDue to its specific mechanical properties, tantalum is often used in strength-demanding military applications. High-cycle fatigue (HCF) behaviour of pure tantalum, however, has been rarely reported and the mechanisms at stake to account for deformation under cyclic loadings are still badly understood. This paper aims at better understanding the fatigue behaviour of tantalum and at clarifying the mechanisms of damage formation encountered under such loadings. HCF experiments performed at room temperature on commercially-pure tantalum are presented. Mean stress effects were investigated in the aim of clarifying the interaction between fatigue and creep. Fracture mechanisms were observed to vary from intergranular to transgranular depending on applied stress amplitude and mean stress. Damage mechanisms were investigated under tension and torsion. Results are analyzed in the light of existing fatigue criteria, the limitations of which are discussed. Finally, complex sequential loadings, representative of in-service loadings, were applied to tantalum smooth specimens. The contribution of each loading sequence to the overall damage was quantified and analyzed in terms of linear or non-linear cumulative damage ruleFatigue behaviour of two-phase titanium alloy in VHCF regime
http://hdl.handle.net/10985/12047
Fatigue behaviour of two-phase titanium alloy in VHCF regime
NIKITIN, Alexander; SHANYAVSKIY, Andrey; PALIN-LUC, Thierry
This paper is focused on fatigue crack initiation and early growth in two-phase titanium alloy VT3-1 (similar to Ti-6Al-4V) under VHCF loads. The material was produced by two different processes: forging and extrusion. Each kind of material was investigated under three different loading types (push-pull, pull-pull and fully reversed torsion). Fracture surfaces of the tested specimens were analyzed by scanning electron microscopy (SEM) for getting information on crack initiation sites and surrounded fracture surface zones. The results of such analysis were compared with microstructure of the titanium alloy for establishing a crack initiation and early crack growth mechanisms. It was found that crack initiation in this alloy is caused by single or an agglomeration (“cluster”) of alpha-platelets. Under fully reversed tension the fatigue life seems to depend on the geometry of alpha-platelets clusters whereas under tension tension loading such dependence was not observed. However, materials with larger alpha-platelets clusters (macro-zones) have a lower VHCF resistance. The comparison of tension and torsion VHCF test results show a higher slop of the S-N curve under torsion than under tension for both forged and extruded titanium alloys. Nonetheless, some similarities in crack initiation and propagation scenarios were outlined between tension and torsion loadings.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/120472017-01-01T00:00:00ZNIKITIN, AlexanderSHANYAVSKIY, AndreyPALIN-LUC, ThierryThis paper is focused on fatigue crack initiation and early growth in two-phase titanium alloy VT3-1 (similar to Ti-6Al-4V) under VHCF loads. The material was produced by two different processes: forging and extrusion. Each kind of material was investigated under three different loading types (push-pull, pull-pull and fully reversed torsion). Fracture surfaces of the tested specimens were analyzed by scanning electron microscopy (SEM) for getting information on crack initiation sites and surrounded fracture surface zones. The results of such analysis were compared with microstructure of the titanium alloy for establishing a crack initiation and early crack growth mechanisms. It was found that crack initiation in this alloy is caused by single or an agglomeration (“cluster”) of alpha-platelets. Under fully reversed tension the fatigue life seems to depend on the geometry of alpha-platelets clusters whereas under tension tension loading such dependence was not observed. However, materials with larger alpha-platelets clusters (macro-zones) have a lower VHCF resistance. The comparison of tension and torsion VHCF test results show a higher slop of the S-N curve under torsion than under tension for both forged and extruded titanium alloys. Nonetheless, some similarities in crack initiation and propagation scenarios were outlined between tension and torsion loadings.Effect of mean shear stress on the fatigue strength of notched components under multiaxial stress state
http://hdl.handle.net/10985/13395
Effect of mean shear stress on the fatigue strength of notched components under multiaxial stress state
BENNEBACH, Mohamed; PALIN-LUC, Thierry; MESSAGER, Alexandre
The effect of a static and intermittent shear stress on the HCF strength of two quenched and tempered steel grades used to produce shafts in crane industry was studied on notched specimens (Kt=1.7 and 2.7) for being representative of critical areas. Three main load cases were considered: C1=rotative bending (RB), C2=RB and static torsion and C3=RB and mean torsion fluctuating in blocks to simulated start and stop cycles. In this last case the first investigated mean shear stress, τm, was equal to the material yield stress in pure shear, τy. Additional C3 variants were investigated too where τm was equal to 0.3τy and 0.7τy. It has been shown that τm has little effect on the rotating bending HCF strength at 3×106 cycles. For both steel grades and notch geometries studied, the results of the fatigue tests confirm that the influence of a static torsion on the rotating bending HCF strength is negligible even when the static torsion level is equivalent to the yield strength of the material in torsion. However, in intermittent service conditions (C3), it has been shown that torsion cycles can affect significantly the HCF strength in RB, depending on the notch acuity and torsion level. Elastic-plastic cyclic FEA has been done for the two specimen geometries to assess the stabilized stress-strain state at the notch root and then to compute the fatigue life by using the multiaxial HCF life models proposed by: Fatemi-Socie, Smith-Watson-Topper, and Wang-Brown. The Palmgreen-Miner hypothesis was used to cumulate damage mainly because of its simplicity for design purposes. According to our simulations and with the chosen cumulative damage rule, none of the tested fatigue life calculation methods give good results for all the load cases. The efficiency of the tested methods is very dependent on both the material and the load cases. However, the Smith-Watson-Topper approach gives the best results whereas the Fatemi-Socie models leads to the more conservative ones except in one load case
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/133952018-01-01T00:00:00ZBENNEBACH, MohamedPALIN-LUC, ThierryMESSAGER, AlexandreThe effect of a static and intermittent shear stress on the HCF strength of two quenched and tempered steel grades used to produce shafts in crane industry was studied on notched specimens (Kt=1.7 and 2.7) for being representative of critical areas. Three main load cases were considered: C1=rotative bending (RB), C2=RB and static torsion and C3=RB and mean torsion fluctuating in blocks to simulated start and stop cycles. In this last case the first investigated mean shear stress, τm, was equal to the material yield stress in pure shear, τy. Additional C3 variants were investigated too where τm was equal to 0.3τy and 0.7τy. It has been shown that τm has little effect on the rotating bending HCF strength at 3×106 cycles. For both steel grades and notch geometries studied, the results of the fatigue tests confirm that the influence of a static torsion on the rotating bending HCF strength is negligible even when the static torsion level is equivalent to the yield strength of the material in torsion. However, in intermittent service conditions (C3), it has been shown that torsion cycles can affect significantly the HCF strength in RB, depending on the notch acuity and torsion level. Elastic-plastic cyclic FEA has been done for the two specimen geometries to assess the stabilized stress-strain state at the notch root and then to compute the fatigue life by using the multiaxial HCF life models proposed by: Fatemi-Socie, Smith-Watson-Topper, and Wang-Brown. The Palmgreen-Miner hypothesis was used to cumulate damage mainly because of its simplicity for design purposes. According to our simulations and with the chosen cumulative damage rule, none of the tested fatigue life calculation methods give good results for all the load cases. The efficiency of the tested methods is very dependent on both the material and the load cases. However, the Smith-Watson-Topper approach gives the best results whereas the Fatemi-Socie models leads to the more conservative ones except in one load case