The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
A. Varvani-farahani - One of the best experts on this subject based on the ideXlab platform.
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A comparative study in descriptions of coupled kinematic hardening rules and ratcheting assessment over asymmetric Stress Cycles
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: A. Varvani-farahaniAbstract:The present study evaluates coupled kinematic hardening rules at which the calculation of plastic moduli is coupled with these models through the consistency condition of yield surfaces. The frameworks of the Ohno–Wang (O–W), McDowell, Jiang–Sehitoglu (J–S), Chen–Jiao–Kim (C–J–K) and Ahmadzadeh–Varvani (A–V) hardening rules and their incorporated dynamic recovery terms/coefficients were discussed for steel samples undergoing asymmetric Stress Cycles. Different hardening rules offered distinct procedures to determine terms/coefficients and to generalize hardening rule descriptions applicable for different materials and loading spectra. The progressive evolution of backStress over plastic deformation was attributed to the interaction of dislocations controlled by the dynamic recovery of the models. The predicted ratcheting curves through the C–J–K and A–V hardening rules closely agreed with ratcheting data of 1045 and 304 steel samples tested at different loading paths. The O–W, J–S and McDowell hardening rules showed some overprediction in ratcheting as compared with experimental data.
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Ratcheting Prediction of 1070 and 16MnR Steel Alloys Under Uniaxial Asymmetric Stress Cycles By Means of Ohno–Wang and Ahmadzadeh–Varvani Kinematic Hardening Rules
Journal of Pressure Vessel Technology, 2015Co-Authors: G. R. Ahmadzadeh, S. M. Hamidinejad, A. Varvani-farahaniAbstract:The present study predicts ratcheting response of 1070 and 16MnR steel samples using nonlinear kinematic hardening rules of Ohno–Wang (O–W) and Ahmadzadeh–Varvani (A–V) under uniaxial Stress Cycles. The ratcheting values predicted based on the O–W model were noticeably influenced by the magnitude of exponents and the number of backStress components. Taking into account both material and cyclic Stress level dependent coefficients, the A–V hardening rule offered a simple framework to predict ratcheting strain over loading Cycles. A comparative study of these hardening rules to assess ratcheting of 1070 and 16MnR steel samples undergoing uniaxial loading conditions resulted in a close agreement of the A–V and O–W models. The choice of hardening rules in the assessment of materials ratcheting was further discussed based on the complexity of the hardening rule, number of constants/coefficients required to characterize ratcheting response, and central processing unit (CPU) time required to run the models.
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Ratcheting Assessment of GFRP Composites in Low-Cycle Fatigue Domain
Applied Composite Materials, 2014Co-Authors: G. R. Ahmadzadeh, A. Varvani-farahaniAbstract:The present study intends to examine ratcheting response of Glass Fiber Reinforced Polymer (GFRP) composites over fatigue Cycles by means of parametric variables. Stages of ratcheting deformation were related to Stress Cycles, lifespan, mechanical properties and cyclic Stress levels by means of linear and non-linear functions. The coefficients B and C in the proposed ratcheting formulation calibrated ratcheting equation by means of material properties over ratcheting stages. Coefficients A and C calibrated the stages I and II of ratcheting strain curve over Stress Cycles. The ratcheting curve over initial and final stages was affected as composite modulus of elasticity ( E _ c ) increased. An increase in E _ c -dependent coefficients A and B increased the magnitude of ratcheting strains over Stress Cycles. Ratcheting data for continuous and short fiber GFRP composites with various volume fractions were employed to evaluate the proposed ratcheting formulation. Interaction of ratcheting and fatigue phenomena was further assumed when the proposed parametric ratcheting equation was coupled with a fatigue damage model developed earlier by present authors. Overall damage is achieved from accumulation of ratcheting and fatigue over Stress Cycles.
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Ratcheting assessment of steel alloys under uniaxial loading: a parametric model versus hardening rule of Bower
Fatigue & Fracture of Engineering Materials & Structures, 2012Co-Authors: G. R. Ahmadzadeh, A. Varvani-farahaniAbstract:This study intends to compare ratcheting response of 42CrMo, 1020, SA333 and SS304 steel alloys over uniaxial Stress Cycles evaluated by a parametric ratcheting model and Bower's hardening rule. The parametric ratcheting equation was formulated to describe triphasic stages of ratcheting deformation over Stress Cycles. Mechanistic parameters of mean Stress, Stress amplitude, material properties and cyclic softening/hardening response of materials were employed to calibrate parametric equation. Based on the framework of cyclic plasticity theory, the modified Armstrong–Frederick nonlinear hardening rule of Bower was employed to assess ratcheting response of steel alloys under uniaxial Stress Cycles. Bower's model was chosen mainly due to simplicity of the model and its lower number of constants required to predict ratcheting strain over Stress Cycles as compared with other hardening rules. Ratcheting strain values predicted by Bower's model showed good agreements over stage I of Stress Cycles as compared with experimental values of ratcheting strain. Beyond of stage I Stress Cycles, Bower ratcheting strain rate stayed constant resulting in an arrest in ratcheting process. The predicted ratcheting strains based on the parametric equation were found in good agreements over three stages of ratcheting as compared with those of experimentally obtained.
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Triphasic ratcheting strain prediction of materials over Stress Cycles
Fatigue & Fracture of Engineering Materials & Structures, 2012Co-Authors: G. R. Ahmadzadeh, A. Varvani-farahaniAbstract:This study intends to formulate ratcheting strain evolution in steel alloys of 42CrMo, 20CS, SA333 Gr. 6 C-Mn and OFHC copper over uniaxial Stress Cycles. Stages of ratcheting deformation were related to Stress Cycles, lifespan, mechanical properties and amplitude and mean Stress components by means of linear and nonlinear functions. Terms of mechanical properties in the ratcheting formulation enabled to characterize ratcheting response of various materials over life Cycles. These terms were further employed to interpret the influence of softening/hardening response of materials on ratcheting deformation. Ratcheting data for 42CrMo, 20CS, SA333 steels and OFHC copper reported in the literature were employed to evaluate the proposed ratcheting formulation. The predicted ratcheting strain values based on the proposed equation were found in good agreements as compared with the experimental data.
Kentaro Yamada - One of the best experts on this subject based on the ideXlab platform.
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fatigue life evaluation of welded joints under combined normal and shear Stress Cycles
International Journal of Fatigue, 2005Co-Authors: Intae Kim, Kentaro YamadaAbstract:This paper discusses methods for evaluating the fatigue life when combined normal and shear Stresses are applied in phase simultaneously. The conventional fatigue design procedures based on maximum principal or normal Stress ranges are reviewed using published data. This indicates that the fatigue life may be under- or overestimated by the procedures, when the shear-to-normal-Stress ratio range is close to 1.0. A proposed alternative procedure, based on the equivalent Stress range and the fatigue life for a normal Stress range, produces a much more appropriate evaluation of the fatigue life for combined Stress ranges, independent of the ratio.
Keli Han - One of the best experts on this subject based on the ideXlab platform.
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a fluorescent probe for rapid detection of thiols and imaging of thiols reducing repair and h2o2 oxidative Stress Cycles in living cells
Chemical Communications, 2013Co-Authors: Zhangrong Lou, Xiaofei Sun, Songqiu Yang, Bingshuai Wang, Keli HanAbstract:A diselenide containing fluorescent probe based on a fluorescein scaffold for thiols was developed. The fluorescent probe exhibited rapid response, high selectivity and reversibility. Confocal fluorescence microscopy was used to visualize the redox changes mediated by thiols and reactive oxygen species in living HeLa cells.
G. R. Ahmadzadeh - One of the best experts on this subject based on the ideXlab platform.
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ratcheting prediction of al 6061 sicp composite samples under asymmetric Stress Cycles by means of the ahmadzadeh varvani hardening rule
Journal of Composite Materials, 2016Co-Authors: G. R. Ahmadzadeh, A VarvanifarahaniAbstract:The present study intends to examine ratcheting response of SiCP particle-reinforced Al 6061 matrix (Al 6061/SiCP) composite samples over asymmetric load Cycles based on the kinematic hardening rul...
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Ratcheting Prediction of 1070 and 16MnR Steel Alloys Under Uniaxial Asymmetric Stress Cycles By Means of Ohno–Wang and Ahmadzadeh–Varvani Kinematic Hardening Rules
Journal of Pressure Vessel Technology, 2015Co-Authors: G. R. Ahmadzadeh, S. M. Hamidinejad, A. Varvani-farahaniAbstract:The present study predicts ratcheting response of 1070 and 16MnR steel samples using nonlinear kinematic hardening rules of Ohno–Wang (O–W) and Ahmadzadeh–Varvani (A–V) under uniaxial Stress Cycles. The ratcheting values predicted based on the O–W model were noticeably influenced by the magnitude of exponents and the number of backStress components. Taking into account both material and cyclic Stress level dependent coefficients, the A–V hardening rule offered a simple framework to predict ratcheting strain over loading Cycles. A comparative study of these hardening rules to assess ratcheting of 1070 and 16MnR steel samples undergoing uniaxial loading conditions resulted in a close agreement of the A–V and O–W models. The choice of hardening rules in the assessment of materials ratcheting was further discussed based on the complexity of the hardening rule, number of constants/coefficients required to characterize ratcheting response, and central processing unit (CPU) time required to run the models.
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ratcheting prediction of 1070 and 16mnr steel alloys under uniaxial asymmetric Stress Cycles by means of ohno wang and ahmadzadeh varvani kinematic hardening rules
Journal of Pressure Vessel Technology-transactions of The Asme, 2015Co-Authors: G. R. Ahmadzadeh, S. M. Hamidinejad, A VarvanifarahaniAbstract:The present study predicts ratcheting response of 1070 and 16MnR steel samples using nonlinear kinematic hardening rules of Ohno–Wang (O–W) and Ahmadzadeh–Varvani (A–V) under uniaxial Stress Cycles. The ratcheting values predicted based on the O–W model were noticeably influenced by the magnitude of exponents and the number of backStress components. Taking into account both material and cyclic Stress level dependent coefficients, the A–V hardening rule offered a simple framework to predict ratcheting strain over loading Cycles. A comparative study of these hardening rules to assess ratcheting of 1070 and 16MnR steel samples undergoing uniaxial loading conditions resulted in a close agreement of the A–V and O–W models. The choice of hardening rules in the assessment of materials ratcheting was further discussed based on the complexity of the hardening rule, number of constants/coefficients required to characterize ratcheting response, and central processing unit (CPU) time required to run the models.
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Ratcheting Assessment of GFRP Composites in Low-Cycle Fatigue Domain
Applied Composite Materials, 2014Co-Authors: G. R. Ahmadzadeh, A. Varvani-farahaniAbstract:The present study intends to examine ratcheting response of Glass Fiber Reinforced Polymer (GFRP) composites over fatigue Cycles by means of parametric variables. Stages of ratcheting deformation were related to Stress Cycles, lifespan, mechanical properties and cyclic Stress levels by means of linear and non-linear functions. The coefficients B and C in the proposed ratcheting formulation calibrated ratcheting equation by means of material properties over ratcheting stages. Coefficients A and C calibrated the stages I and II of ratcheting strain curve over Stress Cycles. The ratcheting curve over initial and final stages was affected as composite modulus of elasticity ( E _ c ) increased. An increase in E _ c -dependent coefficients A and B increased the magnitude of ratcheting strains over Stress Cycles. Ratcheting data for continuous and short fiber GFRP composites with various volume fractions were employed to evaluate the proposed ratcheting formulation. Interaction of ratcheting and fatigue phenomena was further assumed when the proposed parametric ratcheting equation was coupled with a fatigue damage model developed earlier by present authors. Overall damage is achieved from accumulation of ratcheting and fatigue over Stress Cycles.
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Ratcheting assessment of steel alloys under uniaxial loading: a parametric model versus hardening rule of Bower
Fatigue & Fracture of Engineering Materials & Structures, 2012Co-Authors: G. R. Ahmadzadeh, A. Varvani-farahaniAbstract:This study intends to compare ratcheting response of 42CrMo, 1020, SA333 and SS304 steel alloys over uniaxial Stress Cycles evaluated by a parametric ratcheting model and Bower's hardening rule. The parametric ratcheting equation was formulated to describe triphasic stages of ratcheting deformation over Stress Cycles. Mechanistic parameters of mean Stress, Stress amplitude, material properties and cyclic softening/hardening response of materials were employed to calibrate parametric equation. Based on the framework of cyclic plasticity theory, the modified Armstrong–Frederick nonlinear hardening rule of Bower was employed to assess ratcheting response of steel alloys under uniaxial Stress Cycles. Bower's model was chosen mainly due to simplicity of the model and its lower number of constants required to predict ratcheting strain over Stress Cycles as compared with other hardening rules. Ratcheting strain values predicted by Bower's model showed good agreements over stage I of Stress Cycles as compared with experimental values of ratcheting strain. Beyond of stage I Stress Cycles, Bower ratcheting strain rate stayed constant resulting in an arrest in ratcheting process. The predicted ratcheting strains based on the parametric equation were found in good agreements over three stages of ratcheting as compared with those of experimentally obtained.
Srđan Podrug - One of the best experts on this subject based on the ideXlab platform.
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Numerical Modelling of Gear Tooth Root Fatigue Behaviour
2013Co-Authors: Damir Jelaska, Janez Kramberger, Srečko Glodež, Srđan PodrugAbstract:A computational model for determination of service life of gears in regardto bending fatigue in a gear tooth root is presented. The Coffin-Manson relationship isused to determine the number of Stress Cycles Ni required for the fatigue crackinitiation, where it is assumed that the initial crack is located at the point of the largestStresses in a gear tooth root. The simple Paris equation is then used for the furthersimulation of the fatigue crack growth, where required material parameters have beendetermined previously by the appropriate test specimens. The functional relationshipbetween the Stress intensity factor and crack length K=f(a), which is needed fordetermination of the required number of loading Cycles Np for a crack propagation fromthe initial to the critical length, is obtained numerically in the framework of the FiniteElement Method. The total number of Stress Cycles N for the final failure to occur isthen a sum N = Ni +Np.
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Gear Tooth Root Crack Path and Fatigue Life
2006Co-Authors: Damir Jelaska, Srđan PodrugAbstract:A numerical model for determination of the gear tooth root fatigue behaviour is presented. Two cases are being explored, first in which gear tooth was loaded with normal pulsating force acting at the highest point of single tooth contact, and second in which the fact that in actual gear operation the magnitude as well as the position of the force changes as the gear rotates through the mesh is taken into account. The critical plane damage model has been used to determine the number of Stress Cycles required for the fatigue crack initiation. The critical plane methods predict not only fatigue crack initiation life, but also the initiated crack direction, which makes a good starting point for further fatigue crack propagation studies. Finite element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth under a moving load.
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Numerical Modelling of Gear Tooth Root Fatigue Behaviour
2003Co-Authors: Damir Jelaska, Janez Kramberger, Srečko Glodež, Srđan PodrugAbstract:The Coffin-Manson relationship is used to determine the number of Stress Cycles required for the fatigue crack initiation, where it is assumed that the initial crack is located at the point of the largest Stresses in a gear tooth root. The simple Paris equation is then used for the further simulation of the fatigue crack growth, where required material parameters have been determined previously by the appropriate test specimens. The functional relationship between the Stress intensity factor and crack length, which is needed for determination of the required number of loading Cycles for a crack propagation from the initial to the critical length, is obtained numerically in the framework of the Finite Element Method. The total number of Stress Cycles for the final failure to occure is then sum of the number of Stress Cycles required for the fatigue crack initiation and the number of Stress Cycless for a crack propagation.
