Recent investigations have shown that with varying the amplitude of the external force, the deterministic ratchets exhibit multiple current reversals, which are undesirable in certain circumstances. To control the mul...Recent investigations have shown that with varying the amplitude of the external force, the deterministic ratchets exhibit multiple current reversals, which are undesirable in certain circumstances. To control the multiple reverse current to unidirectional current, an adaptive control law is presented inspired from the relation between multiple reversaJs current and the chaos-periodic/quasiperiodic transition of the transport velocity. The designed controller can stabilize the transport velocity of ratchets to steady state and suppress any chaos-periodic/quasiperiodic transition, namely, the stable transport in ratchets is achieved, which makes the current sign unchanged.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
Achieving well-controlled directional steering of liquids is of great significance for both fundamental study and practical applications, such as microfluidics, biomedicine, and heat management. Recent advances allow ...Achieving well-controlled directional steering of liquids is of great significance for both fundamental study and practical applications, such as microfluidics, biomedicine, and heat management. Recent advances allow liquids with different surface tensions to select their spreading directions on a same surface composed of macro ratchets with dual reentrant curvatures. Nevertheless, such intriguing directional steering function relies on 3D printed sophisticated structures and additional polishing process to eliminate the inevitable microgrooves-like surface deficiency generated from printing process, which increases the manufacturing complexity and severally hinders practical applications. Herein, we developed a simplified dual-scale structure that enables directional liquid steering via a straightforward 3D printing process without the need of any physical and chemical post-treatment. The dual-scale structure consists of macroscale tilt ratchet equipped with a reentrant tip and microscale grooves that decorated on the whole surface along a specific orientation. Distinct from conventional design requiring the elimination of microgrooves-like surface deficiency, we demonstrated that the microgrooves of dual-scale structure play a key role in delaying or promoting the local flow of liquids, tuning of which could even enable liquids select different spreading pathways. This study provides a new insight for developing surfaces with tunable multi-scale structures, and also advances our fundamental understanding of the interaction between liquid spreading dynamics and surface topography.展开更多
A time-delayed feedback ratchet consisting of two Brownian particles interacting through the elastic spring is consid ered. The model describes the directed transport of coupled Brownian particles in an asymmetric two...A time-delayed feedback ratchet consisting of two Brownian particles interacting through the elastic spring is consid ered. The model describes the directed transport of coupled Brownian particles in an asymmetric two-well ratchet potential which can be calculated theoretically and implemented experimentally. We explore how the centre-of-mass velocity is af fected by the time delay, natural length of the spring, amplitude strength, angular frequency, external force, and the structure of the potential. It is found that the enhancement of the current can be obtained by varying the coupling strength of the delayed feedback system. When the thermal fluctuation and the harmonic potential match appropriately, directed current evolves periodically with the natural length of the spring and can achieve a higher transport coherence. Moreover, the external force and the amplitude strength can enhance the directed transport of coupled Brownian particles under certain conditions. It is expected that the polymer of large biological molecules may demonstrate a variety of novel cooperative effects in real propelling devices.展开更多
This paper describes the CVT （continuously variable transmission）. Generally, CVTs are classified as belt-type or toroidal CVTs, and each CVT is basically composed of two parts such as the V-belt and pulley, or fric...This paper describes the CVT （continuously variable transmission）. Generally, CVTs are classified as belt-type or toroidal CVTs, and each CVT is basically composed of two parts such as the V-belt and pulley, or friction wheels. In the belt-type CVT, the pulley is driven by a belt placed between two （left and right） circle boards, while in the toroidal CVT, two rollers rotate under the condition being pushed by strong compression power. Since these conventional CVTs use friction force, their energy transfer efficiency might be inferior. Furthermore, although these CVTs require precise structures and processing, they make noise, and are not durable. Consequently, we propose a new structural CVT in this paper.展开更多
The stochastic transport driven by flashing multi-noise sources in a ratchet is studied. The stationary current versus the noise strength and the colored noise correlated time T is obtained . At a fixed flip rate and ...The stochastic transport driven by flashing multi-noise sources in a ratchet is studied. The stationary current versus the noise strength and the colored noise correlated time T is obtained . At a fixed flip rate and strength of the colored noises, the novel phenomenon of the current reversal occurs as T reaches a certain value. More than one reversal point exists when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
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
We employed molecular dynamics simulations to investigate the directed transport of a double-stranded oligonucleotide(ds DNA)through a single-walled carbon nanotube(SWNT)powered by external mechanical vibrations.It is...We employed molecular dynamics simulations to investigate the directed transport of a double-stranded oligonucleotide(ds DNA)through a single-walled carbon nanotube(SWNT)powered by external mechanical vibrations.It is thermodynamically favorable for ds DNA to adsorb inside the SWNT,and its transport through the nanotube is challenging due to the high energy barrier.However,we demonstrate that mechanical vibrations at specific frequencies can effectively drive the ds DNA through the nanotube based on a ratchet effect.The system is driven away from thermal equilibrium,and the spatial inversion symmetry is broken by mechanical vibrations.This study provides valuable insights into the mechanisms of mechanically activated DNA transport and highlights the potential of using SWNTs as nanoscale conduits for ds DNA delivery in nanobiotechnology and biomedicine.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 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
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
The uniaxial time-dependent strain cyclic behaviors and ratcheting of SS304 stainless steel were studied at high temperatures （350 ℃ and 700 ℃）. The effects of straining and stressing rates, holding time at the pe...The uniaxial time-dependent strain cyclic behaviors and ratcheting of SS304 stainless steel were studied at high temperatures （350 ℃ and 700 ℃）. The effects of straining and stressing rates, holding time at the peak and/or valley of each cycle in addition to ambient temperature on the cyclic softening/hardening behavior and ratcheting of the material were discussed. It can be seen from experimental results that the material presents remarkable time dependence at 700 ℃, and the ratcheting strain depends greatly on the stressing rate, holding time and ambient temperature. Some significant conclusions are obtained, which are useful to build a constitutive model describiog the time-dependent cyclic deformation of the material.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos. 10862001 and 10947011the Construction of Key Laboratories in Universities of Guangxi under Grant No. 200912
文摘Recent investigations have shown that with varying the amplitude of the external force, the deterministic ratchets exhibit multiple current reversals, which are undesirable in certain circumstances. To control the multiple reverse current to unidirectional current, an adaptive control law is presented inspired from the relation between multiple reversaJs current and the chaos-periodic/quasiperiodic transition of the transport velocity. The designed controller can stabilize the transport velocity of ratchets to steady state and suppress any chaos-periodic/quasiperiodic transition, namely, the stable transport in ratchets is achieved, which makes the current sign unchanged.
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financial support from the ITF(GHP/021/19SZ)Shenzhen Science and Technology Innovation Council (9240061 and JCYJ20200109143206663)+3 种基金National Natural Science Foundation of China (No.51975502)Research Grants Council of Hong Kong(No. C1006-20WF, No. 11213320)Science and Technology Planning Project of Guangdong Province (No.2021A0505110002)Shenzhen-Hong Kong Joint Innovation Project (No. SGDX2019091716460172)。
文摘Achieving well-controlled directional steering of liquids is of great significance for both fundamental study and practical applications, such as microfluidics, biomedicine, and heat management. Recent advances allow liquids with different surface tensions to select their spreading directions on a same surface composed of macro ratchets with dual reentrant curvatures. Nevertheless, such intriguing directional steering function relies on 3D printed sophisticated structures and additional polishing process to eliminate the inevitable microgrooves-like surface deficiency generated from printing process, which increases the manufacturing complexity and severally hinders practical applications. Herein, we developed a simplified dual-scale structure that enables directional liquid steering via a straightforward 3D printing process without the need of any physical and chemical post-treatment. The dual-scale structure consists of macroscale tilt ratchet equipped with a reentrant tip and microscale grooves that decorated on the whole surface along a specific orientation. Distinct from conventional design requiring the elimination of microgrooves-like surface deficiency, we demonstrated that the microgrooves of dual-scale structure play a key role in delaying or promoting the local flow of liquids, tuning of which could even enable liquids select different spreading pathways. This study provides a new insight for developing surfaces with tunable multi-scale structures, and also advances our fundamental understanding of the interaction between liquid spreading dynamics and surface topography.
基金supported by the National Natural Science Foundation of China(Grant No.11075016)the Fundamental Research Funds for the Central Universities,China(Grant No.201001)+1 种基金the Research Fund for the Doctoral Program of Higher Education,China(Grant No.20100003110007)the Science Foundation of the Educational Department of Liaoning Province,China(Grant No.L2012386)
文摘A time-delayed feedback ratchet consisting of two Brownian particles interacting through the elastic spring is consid ered. The model describes the directed transport of coupled Brownian particles in an asymmetric two-well ratchet potential which can be calculated theoretically and implemented experimentally. We explore how the centre-of-mass velocity is af fected by the time delay, natural length of the spring, amplitude strength, angular frequency, external force, and the structure of the potential. It is found that the enhancement of the current can be obtained by varying the coupling strength of the delayed feedback system. When the thermal fluctuation and the harmonic potential match appropriately, directed current evolves periodically with the natural length of the spring and can achieve a higher transport coherence. Moreover, the external force and the amplitude strength can enhance the directed transport of coupled Brownian particles under certain conditions. It is expected that the polymer of large biological molecules may demonstrate a variety of novel cooperative effects in real propelling devices.
文摘This paper describes the CVT （continuously variable transmission）. Generally, CVTs are classified as belt-type or toroidal CVTs, and each CVT is basically composed of two parts such as the V-belt and pulley, or friction wheels. In the belt-type CVT, the pulley is driven by a belt placed between two （left and right） circle boards, while in the toroidal CVT, two rollers rotate under the condition being pushed by strong compression power. Since these conventional CVTs use friction force, their energy transfer efficiency might be inferior. Furthermore, although these CVTs require precise structures and processing, they make noise, and are not durable. Consequently, we propose a new structural CVT in this paper.
文摘The stochastic transport driven by flashing multi-noise sources in a ratchet is studied. The stationary current versus the noise strength and the colored noise correlated time T is obtained . At a fixed flip rate and strength of the colored noises, the novel phenomenon of the current reversal occurs as T reaches a certain value. More than one reversal point exists when
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 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(Grant No.11875237)。
文摘We employed molecular dynamics simulations to investigate the directed transport of a double-stranded oligonucleotide(ds DNA)through a single-walled carbon nanotube(SWNT)powered by external mechanical vibrations.It is thermodynamically favorable for ds DNA to adsorb inside the SWNT,and its transport through the nanotube is challenging due to the high energy barrier.However,we demonstrate that mechanical vibrations at specific frequencies can effectively drive the ds DNA through the nanotube based on a ratchet effect.The system is driven away from thermal equilibrium,and the spatial inversion symmetry is broken by mechanical vibrations.This study provides valuable insights into the mechanisms of mechanically activated DNA transport and highlights the potential of using SWNTs as nanoscale conduits for ds DNA delivery in nanobiotechnology and biomedicine.
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.
基金Item Sponsored by National Natural Science Foundation of China (NSFC10402037) Theoretical Research Fund of SouthwestJiaotong University (2005XJB23)
文摘The uniaxial time-dependent strain cyclic behaviors and ratcheting of SS304 stainless steel were studied at high temperatures （350 ℃ and 700 ℃）. The effects of straining and stressing rates, holding time at the peak and/or valley of each cycle in addition to ambient temperature on the cyclic softening/hardening behavior and ratcheting of the material were discussed. It can be seen from experimental results that the material presents remarkable time dependence at 700 ℃, and the ratcheting strain depends greatly on the stressing rate, holding time and ambient temperature. Some significant conclusions are obtained, which are useful to build a constitutive model describiog the time-dependent cyclic deformation of the material.
