The nonproportional multiaxial ratchetting of cast AZ91 magnesium (Mg) alloy was examined by performing a sequence of axial-torsional cyclic tests controlled by stress with various loading paths at room temperature (R...The nonproportional multiaxial ratchetting of cast AZ91 magnesium (Mg) alloy was examined by performing a sequence of axial-torsional cyclic tests controlled by stress with various loading paths at room temperature (RT).The evolutionary characteristics and path dependence of multiaxial ratchetting were discussed.Results illustrate that the cast AZ91 Mg alloy exhibits considerable nonproportional additional softening during cyclic loading with multiple nonproportional multiaxial loading paths;multiaxial ratchetting presents strong path dependence,and axial ratchetting strains are larger under nonproportional loading paths than under uniaxial and proportional45°linear loading paths;multiaxial ratchetting becomes increasingly pronounced as the applied stress amplitude and axial mean stress increase.Moreover,stress-strain curves show a convex and symmetrical shape in axial/torsional directions.Multiaxial ratchetting exhibits quasi-shakedown after certain loading cycles.The abundant experimental data obtained in this work can be used to develop a cyclic plasticity model of cast Mg alloys.展开更多
A new superposed rule of Mroz's kinematic hardening rule and Ziegler's kinematic hardening rule based on two-surface model is proposed in the paper. Some experimental results on ratchetting of 2014-T6 aluminum...A new superposed rule of Mroz's kinematic hardening rule and Ziegler's kinematic hardening rule based on two-surface model is proposed in the paper. Some experimental results on ratchetting of 2014-T6 aluminum alloy are predicted very well under multiaxial loading. In addition the conformability of the model is discussed for transient cyclic hardening under two kinds of nonproportional cyclic loading paths., i.e. square and rhombic path.展开更多
A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislo...A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislocations in the cell interiors and in the cell walls,is proposed based on the existing microscopic and macroscopic experimental results.The multiplication,annihilation,rearrangement and immobilization of dislocations on each slip system are taken as the basic evolutionary mechanism of the three dislocation categories,and the cross-slip of screw dislocations is viewed as the dynamic recovery mechanism at room temperature.The slip resistance associated with the isotropic hardening rule results from the interactions of dislocations on the slip systems.Meanwhile,a modified nonlinear kinematic hardening rule and a rate-dependent flow rule at the slip system level are employed to improve the predictive capability of the model for ratchetting deformation.The predictive ability of the developed model to uniaxial and mul-tiaxial ratchetting in macroscopic scale is verified by comparing with the experimental results of polycrystalline 316L stainless steel.The ratchetting in intra-granular scale which is obviously dependent on the crystallographic orientation and stress levels can be reasonably predicted by the proposed model.展开更多
The uniaxial ratchetting-fatigue interaction of extruded AZ31 magnesium(Mg)alloy is investigated by uniaxial stress-controlled cyclic tests at room temperature and with addressing the roles of different plastic deform...The uniaxial ratchetting-fatigue interaction of extruded AZ31 magnesium(Mg)alloy is investigated by uniaxial stress-controlled cyclic tests at room temperature and with addressing the roles of different plastic deformation mechanisms.Different stress levels are prescribed to reflect the cyclic plasticity of the alloy controlled by diverse deformation mechanisms(i.e.,dislocation slipping,deformation twinning and detwinning ones),and then the influences of stress level and stress rate on the ratchetting and fatigue life are discussed.The experimental results demonstrate that different evolution characteristics of whole-life ratchetting and fatigue life presented during cyclic tests with various mean stresses,stress amplitudes and stress rates are determined by the dominated plastic deformation mechanisms.It’s worth noting that the ratchetting can occur in the compressive direction even in the cyclic tests with a positive(tensile)mean stress,and the fatigue life increases first and then decreases with the increase of mean stress on account of the interaction between dislocation slipping and twinning/detwinning mechanisms.Comparing the fatigue lives obtained in the asymmetric stress-controlled and symmetrical strain-controlled cycle tests,it is seen that the ratchetting deformation causes an additional damage,and then leads to a shortening of fatigue life.展开更多
In the framework of elastoplastic theory,by introducing dissipative plastic energy(instead of cumulative plastic strain)and dissipative plastic energy rate(instead of cumulative plastic strain rate)into the ratchettin...In the framework of elastoplastic theory,by introducing dissipative plastic energy(instead of cumulative plastic strain)and dissipative plastic energy rate(instead of cumulative plastic strain rate)into the ratchetting parameter evolution equation and isotropic evolution rules respectively,a cyclic elastoplastic constitutive model based on dissipative plastic energy is established.This model,termed the WDP model,describes the physical meaning and evolution rule of the unclosed stress–strain hysteresis loop using an energy method.A comparison of numerical implementation results with experimental data demonstrates the capability of the WDP model to predict the cyclic deformation of EA4T steel,effectively capturing the cyclic softening characteristics and ratchetting behaviors of axle steel EA4T.展开更多
The silicon-graphite(Si-C)composite electrode is considered a promising candidate for next-generation commercial electrodes due to its high capacity.However,lithium-ion batteries with silicon electrodes often experien...The silicon-graphite(Si-C)composite electrode is considered a promising candidate for next-generation commercial electrodes due to its high capacity.However,lithium-ion batteries with silicon electrodes often experience capacity fading and poor cyclic performance,primarily due to the mechanical degradation of the solid-electrolyte interphase(SEI).In this work,we present a homogenized constitutive model for Si-C composite electrodes under finite deformation,incorporating lithium-ion concentration-dependent properties.We perform a wrinkling analysis and systematically examine the influence of key parameters,such as modulus and thickness ratios,on the critical conditions for instability.Additionally,we investigate the ratcheting effect across varying silicon contents.Our findings reveal that maintaining the silicon content within an optimal range effectively reduces plastic accumulation during charge–discharge cycles.These insights provide crucial guidance for optimizing the design and fabrication of Si–C electrode systems,enhancing their durability and performance.展开更多
This paper investigates the effect of hydrogen on the transformation ratcheting of NiTi shape memory alloy(SMA)wires in the experimental and theoretical aspects.In the aspect of experiments,the NiTi SMA orthodontic wi...This paper investigates the effect of hydrogen on the transformation ratcheting of NiTi shape memory alloy(SMA)wires in the experimental and theoretical aspects.In the aspect of experiments,the NiTi SMA orthodontic wires are hydrogen charged by the electrochemical charging method at room temperature with varying charging durations and charging lengths.After that,the ex-situ cyclic tension-unloading experiments are performed for the charged and non-charged wires.Experimental results reveal that the two transformation platforms(two-step MT)occur during the forward MT at the beginning and end of cyclic deformation for hydrogen-charged wires,which can be regarded as a global response of the non-charged and charged regions.Furthermore,this two-step MT and transformation ratcheting aggravate with the increase of the charging duration.In the aspect of the theoretical model,a diffusional-mechanically coupled constitutive model is developed.In this constitutive model,the strain is considered as four components:elasticity,transformation(MT),hydrogen expansion and transformation-induced plasticity(TRIP).Combining Helmholtz free energy and Clausius–Duhem inequality,the thermodynamic driving forces of MT and TRIP are obtained.Fick’s law and the mass conservation equation are incorporated to derive the evolution of hydrogen concentration.A transition from material points to the whole wire is employed to extend the model from a material point to the entire wire,and the overall response with a heterogeneous hydrogen concentration field is obtained.The proposed model's ability to predict the transformation ratcheting of the non-charged and charged NiTi SMA wires is verified by contrasting predictions and experimental results.展开更多
The Feynman ratchet has the ability to convert random fluctuations into directional particle transport.The transport velocity of particles is highly dependent on their size,leading to directional transport and subsequ...The Feynman ratchet has the ability to convert random fluctuations into directional particle transport.The transport velocity of particles is highly dependent on their size,leading to directional transport and subsequent particle separation under suitable parameter conditions.Here,exploiting the distinct responses of particles with different sizes to the system,the separation of bi-dispersed dust particles is achieved experimentally in air at 35 Pa using a dusty plasma ratchet.To reveal the underlying mechanisms,we construct a plasma model and perform Langevin simulations for the particle separation.Our numerical results reveal that charged dust particles experience an asymmetric ratchet potential,which dictates their directional transport.Crucially,bi-dispersed dust particles are suspended at different heights and are subject to ratchet potentials with opposing asymmetries,resulting in their separation.These findings may offer new perspectives for related fields,including microfluidics,nanotechnology,and micrometer-scale particle manipulation.展开更多
Under the framework of the small deformation crystal plasticity theory,a crystal plastic cyclic constitutive model for body-centered cubic(BCC)cyclic softening polycrystalline metals is established.The constitutive mo...Under the framework of the small deformation crystal plasticity theory,a crystal plastic cyclic constitutive model for body-centered cubic(BCC)cyclic softening polycrystalline metals is established.The constitutive model introduces the isotropic softening rule that includes two different mechanisms:namely softening under monotonic deformation and softening under cyclic deformation on each slip system.Meanwhile,a modified Armstrong-Frederick nonlinear kinematic hardening rule is adopted.The appropriate explicit scale transition rule is selected to extend the single crystal constitutive model to the polycrystalline constitutive model.Then the model is used to predict the uniaxial and multiaxial ratcheting deformation of BCC axle steel EA4T to verify the rationality of the proposed model.The simulation results indicate that the newly established crystal plasticity model can not only describe the cyclic softening characteristics of BCC axle steel EA4T well,but also reasonably describe the evolution laws of uniaxial ratcheting and nonproportional multiaxial ratcheting deformation.Moreover,the established crystal plastic cyclic constitutive model can reasonably predict the ratcheting behavior of BCC single crystal as well.展开更多
This investigation focuses on the under-damped Brownian transport of a dimer characterized by two harmonically interacting components.The friction coefficients between the dimer components are different;thus the dynam...This investigation focuses on the under-damped Brownian transport of a dimer characterized by two harmonically interacting components.The friction coefficients between the dimer components are different;thus the dynamic symmetry of the system is broken.In addition,the inertial ratchets are synchronously modulated by the feedback control protocol in time.Here,we analyze the transport performance by studying the average velocity and energy conversion efficiency of the dimer induced by friction symmetry breaking and external forces.Furthermore,we can also identify the enhancement of the centre-of-mass mean velocity and energy conversion efficiency of inertial frictional ratchets for intermediate values of the driving amplitude,coupling strength and damping force.Remarkably,in the weak bias case,the directed transport of inertial Brownian particles can be reversed twice by modulating the suitable friction of the dimer.In particular,the frictional ratchets can acquire a series of resonant steps under the influence of harmonic force.These conclusions of reliable transport in noisy environments are expected to provide insights into the performance of natural molecular motors.展开更多
The railway pantograph-catenary system employs a ratchet compensation device to sustain the tension of the contact wire.However,the excessive weight associated with the ratchet structure adversely affects the performa...The railway pantograph-catenary system employs a ratchet compensation device to sustain the tension of the contact wire.However,the excessive weight associated with the ratchet structure adversely affects the performance of the compensation device.An optimization design aimed at lightweight optimization of the ratchet wheel structure can enhance the system’s agility,improve material utilization,and reduce costs.This study uses a finite element model to establish an equivalent load model for the ratchet under service conditions and analyzes its load-bearing state.An optimization model was created and solved using ANSYS Workbench.The topological optimization configurations were compared under unconstrained conditions and four different periodic constraint scenarios.Following this,the structure was redesigned based on the topological optimization results,and a simulation analysis was conducted to compare the reconstructed model with the original model.The comparison results indicate that the masses of all four optimized models have been reduced by more than 10%.Additionally,under conditions of a fully wound compensation rope,the maximum stress has decreased by over 20%,leading to a more uniform stress distribution and improved overall performance.The topology optimization and redesign method based on periodic constraints offers a viable engineering solution for the lightweight design of the ratchet structure.展开更多
In the previous paper, in order to express steadystate ratchetting, the present s extended the cyclic plasticity model proposed by Ohno and Wang (1993), and the validity of the extended model was discussed on the ba...In the previous paper, in order to express steadystate ratchetting, the present s extended the cyclic plasticity model proposed by Ohno and Wang (1993), and the validity of the extended model was discussed on the basis of uniaxial ratchetting experiments of 316FR steel at room temperature. In the present paper, the validity of the extended model is discussed further on the basis of nonproportional experiments of IN738LC at 850 such as multiaxial ratchetting, multiaxial cyclic stress relaxation, circular cyclic straining with strain hold, and so on. Predictions based on the OhnoWang model as well as the ArmstrongFrederick model are also given for the sake of comparison. It is shown that the extended model is capable of simulating the nonproportional experiments accurately, and especially that the extended model can predict much less steadystate ratchetting than the ArmstrongFrederick model. It is also shown that the extended model provides almost the same predictions as the OhnoWang and th展开更多
The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratche...The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratchetting) and its physical nature were revealed. The experimental results demonstrate that the cast AZ91 Mg alloy behaviors tension-compression symmetry, because the dislocation slipping and twinning occur during both the tensile and compressive deformations;although the cast AZ91 alloy presents a certain pseudo-elastic behavior during unloading due to the detwinning, there is no obvious S-shaped asymmetric hysteresis loop like that of wrought Mg alloy in the cyclic tensile-compressive tests, and an obvious cyclic hardening is observed;moreover, the ratchetting of the cast AZ91 alloy presented in the cyclic stressing tests depends remarkably on the prescribed mean stress and stress amplitude, but slightly changes with the stress rate, and the evolution of responding peak/valley strain greatly differs from that of wrought Mg alloys and stainless steels. This work provides rich experimental data for establishing the constitutive model of cast Mg alloys.展开更多
An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading. The strain cyclic characteristics were researched ...An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled circular load path. The ratcheting was investigated for the stress-controlled multiaxial circular, elliptical and rhombic load paths with different mean stresses, stress amplitudes and their histories. The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history. However, the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude, but also on their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting. The ratcheting changes with the different loading paths.展开更多
This paper proposes a novel unified visco-plastic constitutive model for uniaxial ratcheting behaviors. The cyclic deformation of the material presents remarkable time-dependence and history memory phenomena. The frac...This paper proposes a novel unified visco-plastic constitutive model for uniaxial ratcheting behaviors. The cyclic deformation of the material presents remarkable time-dependence and history memory phenomena. The fractional(fractional-order)derivative is an efficient tool for modeling these phenomena. Therefore, we develop a cyclic fractional-order unified visco-plastic(FVP) constitutive model. Specifically, within the framework of the cyclic elasto-plastic theory, the fractional derivative is used to describe the accumulated plastic strain rate and nonlinear kinematic hardening rule based on the Ohno-Abdel-Karim model. Moreover, a new radial return method for the back stress is developed to describe the unclosed hysteresis loops of the stress-strain properly.The capacity of the FVP model used to predict the cyclic deformation of the SS304 stainless steel is verified through a comparison with the corresponding experimental data found in the literature(KANG, G. Z., KAN, Q. H., ZHANG, J., and SUN, Y. F. Timedependent ratcheting experiments of SS304 stainless steel. International Journal of Plasticity, 22(5), 858–894(2006)). The FVP model is shown to be successful in predicting the rate-dependent ratcheting behaviors of the SS304 stainless steel.展开更多
In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into...In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.展开更多
The accumulation of inelastic deformation occurring in NiTi shape memory alloy under the stress-controlled cyclic loading condition is named transformation ratcheting, since it is mainly caused by the solid-solid tran...The accumulation of inelastic deformation occurring in NiTi shape memory alloy under the stress-controlled cyclic loading condition is named transformation ratcheting, since it is mainly caused by the solid-solid transformation from austenite to martensite phase and vice versa. The transformation ratcheting and its effect on the fatigue life （i.e., transformation-fatigue interaction） are key issues that should be addressed in order to assess the fatigue of NiTi shape memory alloy more accurately. In this paper, the advances in the studies on the transformation ratcheting and rateheting-fatigue interaction of super-elastic NiTi shape memory alloy in recent years are reviewed： First, experimental observation of the uniaxial transformation ratcheting and ratcheting-fatigue interaction of super-elastic NiTi alloy under the stress-controlled cyclic loading conditions is treated, and the detrimental effect of transformation ratcheting on the fatigue life is addressed; Secondly, two types of cyclic constitutive models （i.e., a macroscopic phenomeno- logical model and a micromechanical one based on crystal plasticity） constructed to describe the transformation ratcheting of super-elastic NiTi alloy are discussed; Furthermore, an energy-based failure model is provided and dealt with by comparing its predicted fatigue lives with experimental ones; Finally, some suggestions about future work are made.展开更多
Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room a...Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room and elevated temperatures within the framework of unified visco-plasticity. In the model, the temperature dependence of the ratcheting was emphasized, and the dynamic strain aging occurred in the temperature range of 4 00-600℃ for the material was taken into account particularly. Finally, the prediction capability of the developed model was checked by comparing to the corresponding experimental results.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.12192210 and12192214)the Independent Project of State Key Laboratory of Traction Power(No.2022TPL-T05)。
文摘The nonproportional multiaxial ratchetting of cast AZ91 magnesium (Mg) alloy was examined by performing a sequence of axial-torsional cyclic tests controlled by stress with various loading paths at room temperature (RT).The evolutionary characteristics and path dependence of multiaxial ratchetting were discussed.Results illustrate that the cast AZ91 Mg alloy exhibits considerable nonproportional additional softening during cyclic loading with multiple nonproportional multiaxial loading paths;multiaxial ratchetting presents strong path dependence,and axial ratchetting strains are larger under nonproportional loading paths than under uniaxial and proportional45°linear loading paths;multiaxial ratchetting becomes increasingly pronounced as the applied stress amplitude and axial mean stress increase.Moreover,stress-strain curves show a convex and symmetrical shape in axial/torsional directions.Multiaxial ratchetting exhibits quasi-shakedown after certain loading cycles.The abundant experimental data obtained in this work can be used to develop a cyclic plasticity model of cast Mg alloys.
基金The project supported by the National Natural Science Foundation of China
文摘A new superposed rule of Mroz's kinematic hardening rule and Ziegler's kinematic hardening rule based on two-surface model is proposed in the paper. Some experimental results on ratchetting of 2014-T6 aluminum alloy are predicted very well under multiaxial loading. In addition the conformability of the model is discussed for transient cyclic hardening under two kinds of nonproportional cyclic loading paths., i.e. square and rhombic path.
基金This research is supported by the National Natural Science Foundation of China(11790282,U1534204,11472179)the Natural Science Foundation of Hebei Province(A2016210099).
文摘A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislocations in the cell interiors and in the cell walls,is proposed based on the existing microscopic and macroscopic experimental results.The multiplication,annihilation,rearrangement and immobilization of dislocations on each slip system are taken as the basic evolutionary mechanism of the three dislocation categories,and the cross-slip of screw dislocations is viewed as the dynamic recovery mechanism at room temperature.The slip resistance associated with the isotropic hardening rule results from the interactions of dislocations on the slip systems.Meanwhile,a modified nonlinear kinematic hardening rule and a rate-dependent flow rule at the slip system level are employed to improve the predictive capability of the model for ratchetting deformation.The predictive ability of the developed model to uniaxial and mul-tiaxial ratchetting in macroscopic scale is verified by comparing with the experimental results of polycrystalline 316L stainless steel.The ratchetting in intra-granular scale which is obviously dependent on the crystallographic orientation and stress levels can be reasonably predicted by the proposed model.
基金Financial support from National Natural Science Foundation of China(11532010)。
文摘The uniaxial ratchetting-fatigue interaction of extruded AZ31 magnesium(Mg)alloy is investigated by uniaxial stress-controlled cyclic tests at room temperature and with addressing the roles of different plastic deformation mechanisms.Different stress levels are prescribed to reflect the cyclic plasticity of the alloy controlled by diverse deformation mechanisms(i.e.,dislocation slipping,deformation twinning and detwinning ones),and then the influences of stress level and stress rate on the ratchetting and fatigue life are discussed.The experimental results demonstrate that different evolution characteristics of whole-life ratchetting and fatigue life presented during cyclic tests with various mean stresses,stress amplitudes and stress rates are determined by the dominated plastic deformation mechanisms.It’s worth noting that the ratchetting can occur in the compressive direction even in the cyclic tests with a positive(tensile)mean stress,and the fatigue life increases first and then decreases with the increase of mean stress on account of the interaction between dislocation slipping and twinning/detwinning mechanisms.Comparing the fatigue lives obtained in the asymmetric stress-controlled and symmetrical strain-controlled cycle tests,it is seen that the ratchetting deformation causes an additional damage,and then leads to a shortening of fatigue life.
基金supported by the Science&Technology Development Fund of Tianjin Education Commission for Higher Education(No.2023KJ250).
文摘In the framework of elastoplastic theory,by introducing dissipative plastic energy(instead of cumulative plastic strain)and dissipative plastic energy rate(instead of cumulative plastic strain rate)into the ratchetting parameter evolution equation and isotropic evolution rules respectively,a cyclic elastoplastic constitutive model based on dissipative plastic energy is established.This model,termed the WDP model,describes the physical meaning and evolution rule of the unclosed stress–strain hysteresis loop using an energy method.A comparison of numerical implementation results with experimental data demonstrates the capability of the WDP model to predict the cyclic deformation of EA4T steel,effectively capturing the cyclic softening characteristics and ratchetting behaviors of axle steel EA4T.
基金supported by the National Natural Science Foundation of China(Grants Nos.12172102 and 12372097)the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022013).
文摘The silicon-graphite(Si-C)composite electrode is considered a promising candidate for next-generation commercial electrodes due to its high capacity.However,lithium-ion batteries with silicon electrodes often experience capacity fading and poor cyclic performance,primarily due to the mechanical degradation of the solid-electrolyte interphase(SEI).In this work,we present a homogenized constitutive model for Si-C composite electrodes under finite deformation,incorporating lithium-ion concentration-dependent properties.We perform a wrinkling analysis and systematically examine the influence of key parameters,such as modulus and thickness ratios,on the critical conditions for instability.Additionally,we investigate the ratcheting effect across varying silicon contents.Our findings reveal that maintaining the silicon content within an optimal range effectively reduces plastic accumulation during charge–discharge cycles.These insights provide crucial guidance for optimizing the design and fabrication of Si–C electrode systems,enhancing their durability and performance.
基金Financial supports from the National Natural Science Foundation of China NSFC(No.12322203,12072296)are greatly appreciated.
文摘This paper investigates the effect of hydrogen on the transformation ratcheting of NiTi shape memory alloy(SMA)wires in the experimental and theoretical aspects.In the aspect of experiments,the NiTi SMA orthodontic wires are hydrogen charged by the electrochemical charging method at room temperature with varying charging durations and charging lengths.After that,the ex-situ cyclic tension-unloading experiments are performed for the charged and non-charged wires.Experimental results reveal that the two transformation platforms(two-step MT)occur during the forward MT at the beginning and end of cyclic deformation for hydrogen-charged wires,which can be regarded as a global response of the non-charged and charged regions.Furthermore,this two-step MT and transformation ratcheting aggravate with the increase of the charging duration.In the aspect of the theoretical model,a diffusional-mechanically coupled constitutive model is developed.In this constitutive model,the strain is considered as four components:elasticity,transformation(MT),hydrogen expansion and transformation-induced plasticity(TRIP).Combining Helmholtz free energy and Clausius–Duhem inequality,the thermodynamic driving forces of MT and TRIP are obtained.Fick’s law and the mass conservation equation are incorporated to derive the evolution of hydrogen concentration.A transition from material points to the whole wire is employed to extend the model from a material point to the entire wire,and the overall response with a heterogeneous hydrogen concentration field is obtained.The proposed model's ability to predict the transformation ratcheting of the non-charged and charged NiTi SMA wires is verified by contrasting predictions and experimental results.
基金supported by National Natural Science Foundation of China(Nos.12275064 and 12475203)the Hebei Natural Science Fund(No.A2024201020)+1 种基金Hebei University Natural Science Research Innovation Team Project(No.IT2023B03)the Post-graduate’s Innovation Fund Project of Hebei University(No.HBU2024BS007)。
文摘The Feynman ratchet has the ability to convert random fluctuations into directional particle transport.The transport velocity of particles is highly dependent on their size,leading to directional transport and subsequent particle separation under suitable parameter conditions.Here,exploiting the distinct responses of particles with different sizes to the system,the separation of bi-dispersed dust particles is achieved experimentally in air at 35 Pa using a dusty plasma ratchet.To reveal the underlying mechanisms,we construct a plasma model and perform Langevin simulations for the particle separation.Our numerical results reveal that charged dust particles experience an asymmetric ratchet potential,which dictates their directional transport.Crucially,bi-dispersed dust particles are suspended at different heights and are subject to ratchet potentials with opposing asymmetries,resulting in their separation.These findings may offer new perspectives for related fields,including microfluidics,nanotechnology,and micrometer-scale particle manipulation.
基金supported by the National Natural Science Foundation of China(Nos.12032017,11790282).
文摘Under the framework of the small deformation crystal plasticity theory,a crystal plastic cyclic constitutive model for body-centered cubic(BCC)cyclic softening polycrystalline metals is established.The constitutive model introduces the isotropic softening rule that includes two different mechanisms:namely softening under monotonic deformation and softening under cyclic deformation on each slip system.Meanwhile,a modified Armstrong-Frederick nonlinear kinematic hardening rule is adopted.The appropriate explicit scale transition rule is selected to extend the single crystal constitutive model to the polycrystalline constitutive model.Then the model is used to predict the uniaxial and multiaxial ratcheting deformation of BCC axle steel EA4T to verify the rationality of the proposed model.The simulation results indicate that the newly established crystal plasticity model can not only describe the cyclic softening characteristics of BCC axle steel EA4T well,but also reasonably describe the evolution laws of uniaxial ratcheting and nonproportional multiaxial ratcheting deformation.Moreover,the established crystal plastic cyclic constitutive model can reasonably predict the ratcheting behavior of BCC single crystal as well.
基金partially supported by the National Natural Science Foundation of China(Grant No.12375031)the Basic Scientific Research Project of Colleges in Liaoning Province,China(Grant No.LJKMZ20221478)Shenyang Normal University Doctoral Program(Grant No.BS202214)。
文摘This investigation focuses on the under-damped Brownian transport of a dimer characterized by two harmonically interacting components.The friction coefficients between the dimer components are different;thus the dynamic symmetry of the system is broken.In addition,the inertial ratchets are synchronously modulated by the feedback control protocol in time.Here,we analyze the transport performance by studying the average velocity and energy conversion efficiency of the dimer induced by friction symmetry breaking and external forces.Furthermore,we can also identify the enhancement of the centre-of-mass mean velocity and energy conversion efficiency of inertial frictional ratchets for intermediate values of the driving amplitude,coupling strength and damping force.Remarkably,in the weak bias case,the directed transport of inertial Brownian particles can be reversed twice by modulating the suitable friction of the dimer.In particular,the frictional ratchets can acquire a series of resonant steps under the influence of harmonic force.These conclusions of reliable transport in noisy environments are expected to provide insights into the performance of natural molecular motors.
基金supported by the National Natural Science Foundation of China(Grant No.52075033)Research and Development Plan of REG(Grant No.2023-20)。
文摘The railway pantograph-catenary system employs a ratchet compensation device to sustain the tension of the contact wire.However,the excessive weight associated with the ratchet structure adversely affects the performance of the compensation device.An optimization design aimed at lightweight optimization of the ratchet wheel structure can enhance the system’s agility,improve material utilization,and reduce costs.This study uses a finite element model to establish an equivalent load model for the ratchet under service conditions and analyzes its load-bearing state.An optimization model was created and solved using ANSYS Workbench.The topological optimization configurations were compared under unconstrained conditions and four different periodic constraint scenarios.Following this,the structure was redesigned based on the topological optimization results,and a simulation analysis was conducted to compare the reconstructed model with the original model.The comparison results indicate that the masses of all four optimized models have been reduced by more than 10%.Additionally,under conditions of a fully wound compensation rope,the maximum stress has decreased by over 20%,leading to a more uniform stress distribution and improved overall performance.The topology optimization and redesign method based on periodic constraints offers a viable engineering solution for the lightweight design of the ratchet structure.
文摘In the previous paper, in order to express steadystate ratchetting, the present s extended the cyclic plasticity model proposed by Ohno and Wang (1993), and the validity of the extended model was discussed on the basis of uniaxial ratchetting experiments of 316FR steel at room temperature. In the present paper, the validity of the extended model is discussed further on the basis of nonproportional experiments of IN738LC at 850 such as multiaxial ratchetting, multiaxial cyclic stress relaxation, circular cyclic straining with strain hold, and so on. Predictions based on the OhnoWang model as well as the ArmstrongFrederick model are also given for the sake of comparison. It is shown that the extended model is capable of simulating the nonproportional experiments accurately, and especially that the extended model can predict much less steadystate ratchetting than the ArmstrongFrederick model. It is also shown that the extended model provides almost the same predictions as the OhnoWang and th
基金Financial support from National Natural Science Foundation of China (11532010)。
文摘The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratchetting) and its physical nature were revealed. The experimental results demonstrate that the cast AZ91 Mg alloy behaviors tension-compression symmetry, because the dislocation slipping and twinning occur during both the tensile and compressive deformations;although the cast AZ91 alloy presents a certain pseudo-elastic behavior during unloading due to the detwinning, there is no obvious S-shaped asymmetric hysteresis loop like that of wrought Mg alloy in the cyclic tensile-compressive tests, and an obvious cyclic hardening is observed;moreover, the ratchetting of the cast AZ91 alloy presented in the cyclic stressing tests depends remarkably on the prescribed mean stress and stress amplitude, but slightly changes with the stress rate, and the evolution of responding peak/valley strain greatly differs from that of wrought Mg alloys and stainless steels. This work provides rich experimental data for establishing the constitutive model of cast Mg alloys.
基金Financially supported by the National Natural Science Foundation of China(197T2041)the Excellent Youth Fund of Sichuan Province.
文摘An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled circular load path. The ratcheting was investigated for the stress-controlled multiaxial circular, elliptical and rhombic load paths with different mean stresses, stress amplitudes and their histories. The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history. However, the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude, but also on their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting. The ratcheting changes with the different loading paths.
基金Project supported by the National Natural Science Foundation of China(Nos.11790282,U1534204,and 11472179)the Natural Science Foundation of Hebei Province of China(No.A2016210099)
文摘This paper proposes a novel unified visco-plastic constitutive model for uniaxial ratcheting behaviors. The cyclic deformation of the material presents remarkable time-dependence and history memory phenomena. The fractional(fractional-order)derivative is an efficient tool for modeling these phenomena. Therefore, we develop a cyclic fractional-order unified visco-plastic(FVP) constitutive model. Specifically, within the framework of the cyclic elasto-plastic theory, the fractional derivative is used to describe the accumulated plastic strain rate and nonlinear kinematic hardening rule based on the Ohno-Abdel-Karim model. Moreover, a new radial return method for the back stress is developed to describe the unclosed hysteresis loops of the stress-strain properly.The capacity of the FVP model used to predict the cyclic deformation of the SS304 stainless steel is verified through a comparison with the corresponding experimental data found in the literature(KANG, G. Z., KAN, Q. H., ZHANG, J., and SUN, Y. F. Timedependent ratcheting experiments of SS304 stainless steel. International Journal of Plasticity, 22(5), 858–894(2006)). The FVP model is shown to be successful in predicting the rate-dependent ratcheting behaviors of the SS304 stainless steel.
文摘In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.
基金Project supported by the National Natural Science Foundation of China (No. 11025210)Sichuan Provincial Youth Science and Technology Innovation Team, China (2013)
文摘The accumulation of inelastic deformation occurring in NiTi shape memory alloy under the stress-controlled cyclic loading condition is named transformation ratcheting, since it is mainly caused by the solid-solid transformation from austenite to martensite phase and vice versa. The transformation ratcheting and its effect on the fatigue life （i.e., transformation-fatigue interaction） are key issues that should be addressed in order to assess the fatigue of NiTi shape memory alloy more accurately. In this paper, the advances in the studies on the transformation ratcheting and rateheting-fatigue interaction of super-elastic NiTi shape memory alloy in recent years are reviewed： First, experimental observation of the uniaxial transformation ratcheting and ratcheting-fatigue interaction of super-elastic NiTi alloy under the stress-controlled cyclic loading conditions is treated, and the detrimental effect of transformation ratcheting on the fatigue life is addressed; Secondly, two types of cyclic constitutive models （i.e., a macroscopic phenomeno- logical model and a micromechanical one based on crystal plasticity） constructed to describe the transformation ratcheting of super-elastic NiTi alloy are discussed; Furthermore, an energy-based failure model is provided and dealt with by comparing its predicted fatigue lives with experimental ones; Finally, some suggestions about future work are made.
基金supported by the Theoretical Research Fund of Sichuan Province(No.03JY029-062-2)the Scientific Research Foundation for the Returned Overseas Chinese Scholars(SRF-ROCS),State Education Ministry of China(No.2003-406-01).
文摘Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room and elevated temperatures within the framework of unified visco-plasticity. In the model, the temperature dependence of the ratcheting was emphasized, and the dynamic strain aging occurred in the temperature range of 4 00-600℃ for the material was taken into account particularly. Finally, the prediction capability of the developed model was checked by comparing to the corresponding experimental results.
