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Erwan Verron - One of the best experts on this subject based on the ideXlab platform.
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Fatigue damage in carbon black filled natural rubber under uni- and Multiaxial Loading conditions
International Journal of Fatigue, 2013Co-Authors: Jean-benoit Le Cam, Bertrand Huneau, Erwan VerronAbstract:This paper deals with fatigue damage in carbon black filled natural rubber under uni- and Multiaxial Loading conditions. Fatigue damage is described at both the macroscopic (mechanical) scale and the microscopic (material) scale. The different fatigue damages observed at the macroscopic scale are presented according to the prescribed Loading conditions. At this scale, five elementary fatigue damage patterns are defined, three correspond to external macroscopic cracks and two correspond to internal macroscopic cracks. These elementary fatigue damage patterns are investigated at the microscopic scale by distinguishing crack initiation and crack growth. Results show that the cracks initiate from microstructural defects, whose mean diameter does not exceed 400 mu m and that crack initiation at the macroscopic scale corresponds to crack growth at the microscopic scale, which validates recent energetic approaches adopted to predict fatigue crack initiation in rubbers. The morphology of fracture surfaces exhibits two types of features: wrenchings and fatigue striations. In particular, results highlight that several shapes of fatigue striations can form, depending on the Loading conditions, and that several mechanisms of fatigue striation formation could come into play.
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energy release rate of small cracks in hyperelastic materials
International Journal of Non-linear Mechanics, 2012Co-Authors: Malik Aitbachir, W V Mars, Erwan VerronAbstract:Abstract The energy release rate of a small crack in an infinite hyperelastic medium, and subjected to large strain Multiaxial Loading conditions, is derived by considering the balance of configurational stresses acting on two planes: one cutting the center of the crack face, and the other at an infinite distance in front of the crack tip. The analysis establishes that the energy release rate of a small crack is always proportional to the size of the crack, irrespective of the Loading conditions and the crack orientation. The balance of configurational stresses is illustrated for several benchmark cases including simple extension, pure shear and equibiaxial extension, and for perpendicular and inclined cracks.
Weiwei Wang - One of the best experts on this subject based on the ideXlab platform.
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crack initiation life prediction for solid cylinders with transverse circular holes under in phase and out of phase Multiaxial Loading
International Journal of Fatigue, 2005Co-Authors: Weiwei WangAbstract:Abstract This work investigates crack initiation life for AISI 316 stainless steel solid cylinders with transverse circular holes under in-phase and out-of-phase Multiaxial Loading. Elastic–plastic finite element analysis is applied to determine the local stress/strain state. Four critical plane approaches and four combined energy and critical plane approaches are employed to predict the crack initiation life by correlating the predictive parameters with smooth specimen data. The critical plane model proposed by Fatemi and Socie and the energy-critical plane prediction model for shear failure-type material proposed by Chen, Xu and Han in 1999 are found to yield better predictions than other models. The location of crack initiation is also investigated herein and compared with the experimentally obtained results.
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crack initiation life prediction for solid cylinders with transverse circular holes under in phase and out of phase Multiaxial Loading
International Journal of Fatigue, 2005Co-Authors: Weiwei WangAbstract:Abstract This work investigates crack initiation life for AISI 316 stainless steel solid cylinders with transverse circular holes under in-phase and out-of-phase Multiaxial Loading. Elastic–plastic finite element analysis is applied to determine the local stress/strain state. Four critical plane approaches and four combined energy and critical plane approaches are employed to predict the crack initiation life by correlating the predictive parameters with smooth specimen data. The critical plane model proposed by Fatemi and Socie and the energy-critical plane prediction model for shear failure-type material proposed by Chen, Xu and Han in 1999 are found to yield better predictions than other models. The location of crack initiation is also investigated herein and compared with the experimentally obtained results.
A Varvanifarahani - One of the best experts on this subject based on the ideXlab platform.
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fatigue life assessment of steel samples under various irregular Multiaxial Loading spectra by means of two energy based critical plane damage models
International Journal of Fatigue, 2016Co-Authors: G R Ahmadzadeh, A VarvanifarahaniAbstract:Abstract Fatigue life of different steel alloys undergoing Multiaxial irregular Loading spectra was evaluated based on two energy-based models of Łagoda–Macha (LM) and Varvani-Farahani. The LM damage model evaluated the life of samples from calculation of the equivalent strain energy densities over counted reversals of the applied stress and strain histories on the critical plane. The Varvani damage approach assessed fatigue life through integration of the normal and shear energy ranges calculated on the critical plane at which the largest stress and strain Mohr’s circles over the counted Loading and unLoading reversals were determined. Based on the equivalent relative strain method of the Wang–Brown, peaks and valleys (reversals) were counted over irregular Multiaxial Loading spectra. Damage values were calculated and then accumulated over peak–valley events of a block Loading spectrum. The overall damage over block histories was then related to fatigue life Nf in the right hand side of the damage models. The predicted lives based on these damage models were compared with those of reported experimental data. The choice of damage assessment models and how to determine the fatigue life of components under irregular Loading spectra were discussed.
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ratcheting assessment of steel samples under various non proportional Loading paths by means of kinematic hardening rules
Materials & Design, 2015Co-Authors: S. M. Hamidinejad, A VarvanifarahaniAbstract:Abstract The present study predicts ratcheting response of 1045 and 1Cr18Ni9Ti tubular steel samples using nonlinear kinematic hardening rules of Ohno-Wang (O–W), Jiang–Sehitoglu (J–S), McDowell, Chen–Jiao–Kim (C–J–K) and newly modified model based on the hardening rule of Ahmadzadeh–Varvani (A–V) under various Multiaxial Loading histories. The modified hardening rule with less complexity holds components of backstress unity vector a ¯ / a ¯ and the normal vector to the yield surface n ¯ in its dynamic recovery to encounter non-proportionality. The components in the Macaulay brackets d e ¯ p ⋅ a ¯ / a ¯ possessing different directions enable the hardening rule to track different directions under Multiaxial stress cycles. Coefficient γ2 controls the ratcheting rate and is regulated by term 2 − n ¯ . a ¯ / a ¯ to further lower the ratcheting strain curve. Term n ¯ . a ¯ / a ¯ 1 / 2 in the dynamic recovery prevents ratcheting plastic shakedown as stress cycles progress. The O–W, J–S and McDowell models persistently overestimated ratcheting curves in 1045 and 1Cr18Ni9Ti steel alloys for various Multiaxial Loading paths. Chen–Jiao–Kim modified the O–W model and possessed lower ratcheting results as compared with those predicted by other hardening rules. The predicted ratcheting curves through the modified model closely agreed with experimental data obtained under various Multiaxial Loading paths.
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fatigue ratcheting damage assessment of steel samples under asymmetric Multiaxial stress cycles
Theoretical and Applied Fracture Mechanics, 2014Co-Authors: A VarvanifarahaniAbstract:Abstract The present study develops a model to assess fatigue–ratcheting damage in 1025 and 42CrMo steel samples undergoing various biaxial and Multiaxial Loading histories. Damage indices in fatigue and ratcheting phenomena were respectively defined by the upper and lower curves at which the upper curve is constructed under fully reversed Multiaxial fatigue cycles by means of an earlier developed critical plane-energy model by the author. The lower curve is developed on the basis of an energy-based ratcheting model in consistent with fatigue damage model to merely present damage values due to ratcheting phenomenon. Equations developed to address overall damage due to fatigue and ratcheting hold both axial and shear stress and strain components for data falling between the upper and the lower bounds. Weight factor ξ is used to partition the overall damage to damage values due to fatigue and ratcheting. The predicted life values based on the overall damage and the upper and lower damage bounds well agreed with those of experimentally obtained for steel samples under biaxial and Multiaxial Loading histories.
Filippo Berto - One of the best experts on this subject based on the ideXlab platform.
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Multiaxial fatigue life assessment in notched components based on the effective strain energy density
Procedia Structural Integrity, 2020Co-Authors: Ricardo Branco, Filippo Berto, José Costa, L.p. Borrego, Javad Razavi, Wojciech MacekAbstract:Abstract This paper presents a methodology to predict the fatigue lifetime in notched geometries subjected to Multiaxial Loading based on the effective strain energy density concept. The modus operandi consists of defining a fatigue master curve that relates the strain energy density with the number of cycles to failure from standard cylindrical specimens tested under low-cycle fatigue conditions. After that, the Multiaxial Loading history at the geometric discontinuity is reduced to an equivalent uniaxial Loading scenario via the calculation of an averaged value of the strain energy, which is done by combining the equivalent strain energy density concept along with the theory of critical distances. Then, this energy is inserted into the fatigue master curve to estimate the fatigue lifetime. The method is tested in solid round bars with lateral notches subjected to in-phase bending-torsion Loading. Overall, the comparison between the experimental and predicted fatigue lives shows a very good agreement. Additionally, the proposed approach enables the determination of the most likely initiation sites as well as the crack angles at the early stage of crack growth.
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rapid assessment of Multiaxial fatigue lifetime in notched components using an averaged strain energy density approach
International Journal of Fatigue, 2019Co-Authors: Ricardo Branco, Filippo Berto, L.p. Borrego, Jd Costa, P A Prates, Andrei Kotousov, F V AntunesAbstract:Abstract This paper proposes a rapid fatigue lifetime assessment approach to deal with notched components undergoing Multiaxial Loading. The modus operandi consists of calculating an effective quantity of the strain energy density nearby the crack initiation site of the notched component using an elastic-plastic numerical model. This quantity is then inserted into a fatigue master curve connecting the strain energy density with the number of cycles to failure to estimate the number of cycles to fatigue crack initiation. The proposed approach is applied to lateral U-shaped notched round bars subjected to Multiaxial in-phase Loading histories. Both the experimental results and the numerical predictions are in good agreement.
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generalized probabilistic model allowing for various fatigue damage variables
International Journal of Fatigue, 2017Co-Authors: Jose A F O Correia, Filippo Berto, Abilio M P De Jesus, Nicole Apetre, Attilio Arcari, Miguel Munizcalvente, Rui Calcada, Alfonso FernandezcanteliAbstract:Abstract This paper proposes a generalization of the Castillo and Fernandez-Canteli probabilistic fatigue model and shows how most fatigue models can be obtained as particular cases. Models that include mean-stress effects and Multiaxial Loading conditions are considered as examples of this general framework. Several fatigue damage parameters such as the Smith-Watson-Topper, the Walker-like strain, energy-based parameter in uniaxial and Multiaxial Loading conditions, and Multiaxial critical plane parameters are proposed as reference parameters for the probabilistic model. It is shown that the Castillo & Fernandez-Canteli probabilistic approach can be successfully extended to these advanced fatigue models.
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Fatigue strength of notched specimens made of 40CrMoV13.9 under Multiaxial Loading
Materials & Design (1980-2015), 2014Co-Authors: Filippo Berto, Paolo Lazzarin, C. MarangonAbstract:Abstract The work deals with Multiaxial fatigue strength of notched round bars made of 40CrMoV13.9 steel and tested under combined tension and torsion Loading, both in-phase and out-of-phase. The axis-symmetric V-notches present a constant notch root radius, 1 mm, and a notch opening angle of 90°; the notch root radius is equal to 4 mm in the semi-circular notches where the strength in the high cycle fatigue regime is usually controlled by the theoretical stress concentration factor, being the notch root radius large enough to result in a notch sensitivity index equals to unity. In both geometries the diameter of the net transverse area is 12 mm. The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion Loading from notched specimens with the same geometry. Altogether more than 120 new fatigue data are summarised in the present work, corresponding to a one-year of testing programme. All fatigue data are presented first in terms of nominal stress amplitudes referred to the net area and then re-analysed in terms of the mean value of the strain energy density evaluated over a given, crescent shape volume embracing the stress concentration region. For the specific steel, the radius of the control volume is found to be independent of the Loading mode.
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local strain energy density and fatigue strength of welded joints under uniaxial and Multiaxial Loading
Engineering Fracture Mechanics, 2008Co-Authors: Paolo Lazzarin, Filippo Berto, Paolo Livieri, Michele ZappalortoAbstract:Abstract In the notch stress intensity approach to the fatigue assessment of welded joints, the weld toe is modelled as a sharp V-notch and the local stress distributions in plane problems are given on the basis of the relevant mode I and mode II notch stress intensity factors (N-SIFs). These factors quantify the magnitude of asymptotic stress distribution obeying Williams’ solution. If the V-notch opening angle at the weld toe is constant and the mode II is not singular, the mode I N-SIF can be directly used to summarize the fatigue behaviour of welded joints. In all the other cases, varying the V-notch angle or including Multiaxial Loading conditions (where typically both Mode I and Mode III stress distributions are singular), the synthesis can be carried out on the basis of the mean value of the strain energy density over a well-defined volume surrounding the weld toe or the weld root. By using this scalar quantity, two fatigue scatterbands are obtained for structural steels and aluminium alloys, respectively. The material-dependent radius RC of the control volume (area) is carefully identified with reference to conventional arc welding processes. Sometimes the weld toe radius is found to be very different from zero. The local strain energy approach can be extended as it stands also to these cases, providing a gradual transition from a N-SIF-based approach to a Kt-based approach.
Luis Reis - One of the best experts on this subject based on the ideXlab platform.
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Fatigue damage assessment under random and variable amplitude Multiaxial Loading conditions in structural steels
International Journal of Fatigue, 2017Co-Authors: Vitor Anes, J. Caxias, Manuel Freitas, Luis ReisAbstract:Abstract Fatigue damage assessment of Multiaxial random Loadings is a complex issue and a subject of actual interest in mechanical design. In this work, the performance of the stress scale factor (SSF) criterion is evaluated under variable amplitude Loading conditions, and damage accumulation approaches. This evaluation is performed by taking into account two types of Loading spectra, namely the Loading block spectra (where the Loading pattern is well identified and repeated until rupture), and the random Loading spectra (where the stochastic behaviour of the axial and shear Loading components do not allow a direct identification of the Loading pattern). Moreover, the validity of the hypothesis in which the SSF damage map remains valid for any high strength steel under variable amplitude Loading conditions is also inspected by analysing fatigue life correlation of the 1050 QT steel and the 304L stainless steel under a Multiaxial Loading block.
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crack initiation and growth path under Multiaxial fatigue Loading in structural steels
International Journal of Fatigue, 2009Co-Authors: Luis Reis, Manuel FreitasAbstract:Abstract In real engineering components and structures many accidental failures occur due to unexpected or additional Loadings, such as additional bending or torsion. There are many factors influencing the fatigue crack paths, such as the material type (microstructure), structural geometry and Loading path. It is widely believed that fatigue crack nucleation and early crack growth are caused by cyclic plasticity. This paper studies the effects of Multiaxial Loading paths on the cyclic deformation behaviour, crack initiation and crack path. Three types of structural steels are studied: Ck45, medium carbon steel, 42CrMo4, low alloy steel and the AISI 303 stainless steel. Four biaxial Loading paths were applied in the tests to observe the effects of Multiaxial Loading paths on the additional hardening, fatigue crack initiation and crack propagation orientation. Fractographic analyses of the plane orientations of crack initiation and propagation were carried out by optical microscope and SEM approaches. It is shown that these materials have different crack orientations under the same Loading path, due to their different cyclic plasticity behaviour and different sensitivity to non-proportional Loading. Theoretical predictions of the damage plane were conducted using the critical plane approaches, either based on stress analysis or strain analysis (Findley, Smith–Watson–Topper, Fatemi–Socie, Wang–Brown–Miller, etc). Comparisons of the predicted crack orientation based on the critical plane approaches with the experimental observations for the wide range of Loading paths and the three structural materials are shown and discussed. Results show the applicability of the critical plane approaches to predict the fatigue life and crack initial orientation in structural steels.
