The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform
R. Tovo - One of the best experts on this subject based on the ideXlab platform.
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a Stress Invariant based spectral method to estimate fatigue life under multiaxial random loading
International Journal of Fatigue, 2011Co-Authors: Alessandro Cristofori, Denis Benasciutti, R. TovoAbstract:Abstract The present paper aims to propose a frequency-domain formulation of a Stress Invariant based multiaxial fatigue criterion, called “Projection by Projection” (PbP) approach, suitable for estimating fatigue life in presence of complex multiaxial loadings. The new proposed spectral method is first validated with experimental data from the literature, concerning bending-torsion random loading, showing a general accuracy. Numerical simulations are next used to generate a wide set of bending-torsion random loading with different correlation degrees, variance ratios and frequency content, in order to further validate the new proposed method. Simulations confirm a general quite good accuracy for PbP spectral method and also emphasize its better precision compared to another spectral method, namely the equivalent von Mises Stress approach, developed by Preumont and co-workers.
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Effective Stress parameters close to Stress singularities
2011Co-Authors: P. Livieri, R. TovoAbstract:The effective Stress values have been defined, in order to find a measurement of the Stress field directly related to the initiation of a failure mechanism, usually a fracture or fatigue crack initiation. This paper investigates several definitions of effective Stress values and applies them to different Stress parameters, as well as Stress Invariant or strain energy density components. In particular, this work examines the effective values not only at the tip of a Stress raiser, but also in the surrounding material. The final aim is to understand the relationship between the actual distribution of effective values and the real failure initiation point, i.e. to verify if the location of maximum values of effective Stress parameters is actually the position of the failure initiation.
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a Stress Invariant based criterion to estimate fatigue damage under multiaxial loading
International Journal of Fatigue, 2008Co-Authors: Alessandro Cristofori, Luca Susmel, R. TovoAbstract:This paper summarises an attempt to propose a novel Stress Invariant based approach suitable for estimating fatigue damage in the presence of complex multiaxial fatigue loadings. In more detail, according to the devised method, fatigue damage is evaluated by studying the components of the deviator path projected along the axes of a convenient frame of reference, whose orientation univocally depends on the profile of the applied loading path. The rainflow counting method used in conjunction with the so-called modified Wohler curve method is subsequently employed to estimate the number of cycles to failure in the medium-cycle fatigue regime. The accuracy of the proposed approach was systematically checked by means of several experimental data taken from the literature and generated by testing different metallic materials under both in-phase and out-of-phase biaxial fatigue loading. This exercise allowed us to prove that the systematic application of the proposed approach resulted in highly accurate predictions and it held true independently of degree of multiaxiality of the Stress field damaging the fatigue process zone.
Jonas Faleskog - One of the best experts on this subject based on the ideXlab platform.
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tension torsion fracture experiments part i experiments and a procedure to evaluate the equivalent plastic strain
International Journal of Solids and Structures, 2013Co-Authors: Jonas Faleskog, Imad BarsoumAbstract:Abstract Ductile failure experiments on a double notched tube (DNT) specimen subjected to a combination of tensile load and torque that was applied at a fixed ratio is presented. The experimental results extend those in Barsoum and Faleskog (2007a) down to zero Stress triaxiality. A new and robust evaluation procedure for such tests is proposed, and a simple relation for the equivalent plastic strain at failure for combined normal and shear deformation, respectively, is developed. Tests were carried out on the medium strength medium hardening steel Weldox 420, and the high strength low hardening steel Weldox 960. The experimental results unanimously show that ductile failure not only depends on Stress triaxiality, but is also strongly affected by the type of deviatoric Stress state that prevails, which can be quantified by a Stress Invariant that discriminates between axisymmetric Stressing and shear dominated Stressing, e.g., the Lode parameter. Additional experiments on round notch bar (RNB) specimens are recapitulated in order to give a comprehensive account on how ductile failure depends on Stress triaxiality, ranging from zero to more than 1.6, and the type of Stress state for the two materials tested. This provides an extensive experimental data base that will be used to explore an extension of the Gurson model that incorporates damage development in shear presented in Xue et al. (2013) (Part II).
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tension torsion fracture experiments part ii simulations with the extended gurson model and a ductile fracture criterion based on plastic strain
International Journal of Solids and Structures, 2013Co-Authors: Zhenyu Xue, Jonas Faleskog, J W HutchinsonAbstract:An extension of the Gurson model that incorporates damage development in shear is used to simulate the tension-torsion test fracture data presented in Faleskog and Barsoum (2012) (Part I) for two steels, Weldox 420 and 960. Two parameters characterize damage in the constitutive model: the effective void volume fraction and a shear damage coefficient. For each of the steels, the initial effective void volume fraction is calibrated against data for fracture of notched round tensile bars and the shear damage coefficient is calibrated against fracture in shear. The calibrated constitutive model reproduces the full range of data in the tension-torsion tests thereby providing a convincing demonstration of the effectiveness of the extended Gurson model. The model reinforces the experiments by highlighting that for ductile alloys the effective plastic strain at fracture cannot be based solely on Stress triaxiality. For nominally isotropic alloys, a ductile fracture criterion is proposed for engineering purposes that depends on Stress triaxiality and a second Stress Invariant that discriminates between axisymmetric Stressing and shear dominated Stressing.
Alessandro Cristofori - One of the best experts on this subject based on the ideXlab platform.
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a Stress Invariant based spectral method to estimate fatigue life under multiaxial random loading
International Journal of Fatigue, 2011Co-Authors: Alessandro Cristofori, Denis Benasciutti, R. TovoAbstract:Abstract The present paper aims to propose a frequency-domain formulation of a Stress Invariant based multiaxial fatigue criterion, called “Projection by Projection” (PbP) approach, suitable for estimating fatigue life in presence of complex multiaxial loadings. The new proposed spectral method is first validated with experimental data from the literature, concerning bending-torsion random loading, showing a general accuracy. Numerical simulations are next used to generate a wide set of bending-torsion random loading with different correlation degrees, variance ratios and frequency content, in order to further validate the new proposed method. Simulations confirm a general quite good accuracy for PbP spectral method and also emphasize its better precision compared to another spectral method, namely the equivalent von Mises Stress approach, developed by Preumont and co-workers.
-
a Stress Invariant based criterion to estimate fatigue damage under multiaxial loading
International Journal of Fatigue, 2008Co-Authors: Alessandro Cristofori, Luca Susmel, R. TovoAbstract:This paper summarises an attempt to propose a novel Stress Invariant based approach suitable for estimating fatigue damage in the presence of complex multiaxial fatigue loadings. In more detail, according to the devised method, fatigue damage is evaluated by studying the components of the deviator path projected along the axes of a convenient frame of reference, whose orientation univocally depends on the profile of the applied loading path. The rainflow counting method used in conjunction with the so-called modified Wohler curve method is subsequently employed to estimate the number of cycles to failure in the medium-cycle fatigue regime. The accuracy of the proposed approach was systematically checked by means of several experimental data taken from the literature and generated by testing different metallic materials under both in-phase and out-of-phase biaxial fatigue loading. This exercise allowed us to prove that the systematic application of the proposed approach resulted in highly accurate predictions and it held true independently of degree of multiaxiality of the Stress field damaging the fatigue process zone.
J W Hutchinson - One of the best experts on this subject based on the ideXlab platform.
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tension torsion fracture experiments part ii simulations with the extended gurson model and a ductile fracture criterion based on plastic strain
International Journal of Solids and Structures, 2013Co-Authors: Zhenyu Xue, Jonas Faleskog, J W HutchinsonAbstract:An extension of the Gurson model that incorporates damage development in shear is used to simulate the tension-torsion test fracture data presented in Faleskog and Barsoum (2012) (Part I) for two steels, Weldox 420 and 960. Two parameters characterize damage in the constitutive model: the effective void volume fraction and a shear damage coefficient. For each of the steels, the initial effective void volume fraction is calibrated against data for fracture of notched round tensile bars and the shear damage coefficient is calibrated against fracture in shear. The calibrated constitutive model reproduces the full range of data in the tension-torsion tests thereby providing a convincing demonstration of the effectiveness of the extended Gurson model. The model reinforces the experiments by highlighting that for ductile alloys the effective plastic strain at fracture cannot be based solely on Stress triaxiality. For nominally isotropic alloys, a ductile fracture criterion is proposed for engineering purposes that depends on Stress triaxiality and a second Stress Invariant that discriminates between axisymmetric Stressing and shear dominated Stressing.
Imad Barsoum - One of the best experts on this subject based on the ideXlab platform.
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tension torsion fracture experiments part i experiments and a procedure to evaluate the equivalent plastic strain
International Journal of Solids and Structures, 2013Co-Authors: Jonas Faleskog, Imad BarsoumAbstract:Abstract Ductile failure experiments on a double notched tube (DNT) specimen subjected to a combination of tensile load and torque that was applied at a fixed ratio is presented. The experimental results extend those in Barsoum and Faleskog (2007a) down to zero Stress triaxiality. A new and robust evaluation procedure for such tests is proposed, and a simple relation for the equivalent plastic strain at failure for combined normal and shear deformation, respectively, is developed. Tests were carried out on the medium strength medium hardening steel Weldox 420, and the high strength low hardening steel Weldox 960. The experimental results unanimously show that ductile failure not only depends on Stress triaxiality, but is also strongly affected by the type of deviatoric Stress state that prevails, which can be quantified by a Stress Invariant that discriminates between axisymmetric Stressing and shear dominated Stressing, e.g., the Lode parameter. Additional experiments on round notch bar (RNB) specimens are recapitulated in order to give a comprehensive account on how ductile failure depends on Stress triaxiality, ranging from zero to more than 1.6, and the type of Stress state for the two materials tested. This provides an extensive experimental data base that will be used to explore an extension of the Gurson model that incorporates damage development in shear presented in Xue et al. (2013) (Part II).
