Friction systems are a kind of typical non-linear dynamical systems in the actual engineering and often generate abundant dynamics phenomena.Because of non-smooth characteristics,it is difficult to handle these system...Friction systems are a kind of typical non-linear dynamical systems in the actual engineering and often generate abundant dynamics phenomena.Because of non-smooth characteristics,it is difficult to handle these systems by conventional analysis methods directly.At the same time,random perturbation often affects friction systems and makes these systems more complicated.In this context,we investigate the steady-state stochastic responses and stochastic P-bifurcation of friction systems under random excitations in this paper.And in order to retain the non-smooth of friction system,the generalized cell mapping(GCM)method is first used to the original stochastic friction systems without any approximate transformation.To verify the accuracy and validate the applicability of the suggested approach,we present two classical nonlinear friction systems,i.e.,Coulomb force model and Dahl force model as examples.Meanwhile,this method is in good agreement with the Monte Carlo simulation method and the computation time is greatly reduced.In addition,further discussion finds that the adjustable parameters can induce the stochastic P-bifurcation in the two examples,respectively.The stochastic P-bifurcation phenomena indicate that the stability of the friction system changes very sensitively with the parameters.Research of responses analysis and stochastic P-bifurcation has certain significances for the reliability and stability analysis of practical engineering.展开更多
Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observ...Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observed that the average friction coefficient was increased after introducing film fragments into the friction system, where these film fragments can accelerate the breaking of the extreme thin oil film which could separate two friction surfaces when the system is under boundary lubrication conditions. The increasing friction load can accelerate the friction ehenfieal reaction on the friction interface and lead to the crushing effect on film fragments, which decreased the friction coefficient of friction system. It was also found that the wear width, depth, and volume of the film increased by introducing film fragments and applying great load.展开更多
Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately an...Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures.The state-of-the-art Multi-Harmonic Balance Method(MHBM)on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high.The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner;however,the efficiency and convergence are not guaranteed for large-scale models.In this paper,a semi-analytical MHBM on full-3D contact model is proposed.The original Trajectory Tracking Method(TTM)for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix(AJM)feasible.Based on the chain rule of derivation,the AJM which is the core to upgrade the performance is deduced.Through a shrouded blade finite element model,the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM.The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model.The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model.We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades.If one uses the quasi-3D model,the estimation relative error of damping can even reach 31.8%in some cases.In addition,the AJM also brings benefits for stability analysis.It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.展开更多
When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the l...When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the length of sliding trajectories of bridge superstructures during pulse-like near-fault earthquakes.As a result,a greater amount of energy will be dissipated due to the frictional sliding of the isolators.The GW-DFPS consists of a spherical surface and an outer surface described by a 1/x or logarithmic function to build gravity well.Full-scale isolators were fabricated and their response was characterized considering various parameters such as the friction material of slider,surface roughness of sliding surfaces,and applied vertical loads.Additionally,a finite element model of the isolator was created using the experimental test data.Numerical simulations were performed on a case-study bridge structure isolated using both a conventional DFPS system and the proposed GW-DFPS systems.The experimental results reveal that the proposed isolators exhibit stable response under vertical loads varying from 200 kN to 1000 kN with a negative stiffness response when the isolator slides at the outer sliding surface.The numerical simulations of the selected bridge structure demonstrate that the GW-DFPS significantly extends the sliding trajectory lengths of the superstructure during half of the earthquake pulses,resulting in increased energy dissipation during this interval.The kinetic energies of the bridge isolated by GW-DFPS are consistently lower than those of the bridge isolated by the other two kinds of isolators,resulting lower shear forces on the bridge.展开更多
Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing addit...Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.展开更多
Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling...Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.展开更多
The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance...The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.展开更多
Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to...Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to friction pain.The results showed that the primary brain activation evoked by friction pain was located in the Prefrontal Cortex(PFC).The activation area decreased,and the negative activation intensity in the PFC region increased with increasing intensity of pain.The inhibitory interactions between different brain regions,especially between the PFC and primary somatosensory cortex(SI)regions were enhanced,and excitatory-inhibitory connections between the medial and lateral pain pathways were balanced during pain perception.The percentage power spectral density of theαrhythm(Dα),dominant singularity strength(αpeak)and longest vertical line(Vmax)of EEG signals induced by pain significantly decreased,and the percent-age power spectral density of theβrhythm(Dβ)significantly increased.The combination of multiple features of Dα,Dβ,αpeak and Vmax could significantly improve the average recognition accuracy of different pain states.This study elucidated the neural processing mechanisms of friction-induced pain,and EEG features associated with friction pain were extracted and recognized.It was helpful to study the brain feedback mechanisms of pain and control signals of Brain-Computer Interface(BCI)system related to pain.展开更多
To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype wa...To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype was selected by Finite Element Method(FEM).In addition,the bionic parameters were optimized by Response Surface Method(RSM).Samples holding BNS were prepared by Laser Processing,tribological properties were tested by a Friction and Wear Tester and worn surface morphology was characterized by a Scanning Electron Microscope(SEM).The results showed that BNS on friction surface could regulate the stress distribution and alleviate the peak stress.Among all samples,the coupled texture of pit-hexagonal got the minimum peak stress.During braking,bionic texture could also collect wear debris or change the motion forms from sliding to rotation,which can reduce abnormal abrasion.The wear rate was reduced by 19.31%.The results in this paper can provide a new idea for enhancing the tribological properties of CBFMs,and can also lay the foundation for further research of bionic tribology.展开更多
In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is c...In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is considered dynamic.The contact condition on the normal plane is modeled by a unilateral constraint condition for a version of normal velocity in which the memory effect and the adhesion are considered.On the tangential plane a frictional contact condition is governed by the Clarke subdifferential of a locally Lipschitz function,and the evolution of the bonding field is governed by an ordinary differential equation.We formulate this problem as coupled system that consists of two ordinary differential equations and a variational-hemivariational inequality.Then,the existence,uniqueness and continuous dependence of the solution on the data results concerning the abstract system are established.Finally,we use the abstract results to show the existence and uniqueness of the solution to the contact problem.展开更多
5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conv...5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conventional melt-based AM methods often introduce defects such as pores,cracks and elemental evaporation.In the present study,a novel screw extrusion-plasticizing friction stir deposition(SEFSD)process,which enables the extrusion plasticization of 5183 particulate feedstocks via a three-stage tapered screw tool,was utilized to fabricate a 20-layer 5183 deposition wall through continuous linear reciprocating deposition in the solid state.The deposition wall exhibited a refined equiaxed microstructure.Due to the low stacking fault energy(SFE)of Al-Mg alloy,the influence of thermal cycles on microstructural evolution was minimal.Overall,the deposition wall demonstrated excellent mechanical properties,though strength and ductility in the deposition direction were reduced due to interlayer defects,which could be mitigated by incorporating stir pins or enhancing interlayer adhesive friction to intensify the material flow.This study confirms the applicability and significant potential of SEFSD for additive manufacturing 5xxx Al alloy components.展开更多
A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and...A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and mechanical properties of the fine-grained CS-HEA were characterized.The results showed that as-cast shrinkage cavities and elemental segregation were eliminated.The average grain size was refined from 121.1 to 5.4μm.The face-centered cubic phase fraction increased from 23%to 82%.During tensile deformation,dislocation slip dominated at strains ranging from 5%to 17%,followed by transformation induced plasticity(TRIP)from 17%to 26%,and twin induced plasticity(TWIP)from 26%to 37%.The yield strength,ultimate tensile strength,and elongation of the fine-grained CS-HEA were 503 MPa,1120 MPa,and 37%,respectively.The strength-ductility synergy of fine-grained CS-HEA was attributed to the combined effects of TRIP,TWIP,dislocation strengthening,and fine-grained strengthening.展开更多
Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically i...Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.展开更多
High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as not...High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.展开更多
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
Self-Centering Piston-Based Braced Frames(SC-PBBFs)are designed to curtail structural damage under severe ground motions.The self-centering mechanism in this bracing mitigates structural damage during an earthquake,th...Self-Centering Piston-Based Braced Frames(SC-PBBFs)are designed to curtail structural damage under severe ground motions.The self-centering mechanism in this bracing mitigates structural damage during an earthquake,thereby reducing post-earthquake repair costs and contributing to seismic resilience.However,non-structural components,particularly those sensitive to floor acceleration,remain vulnerable,resulting in prolonged func-tional recovery times.This paper aims to address this limitation by introducing a novel structural archetype,the Self-Centering Viscous-Based Braced Frame(SC-VBBF),which integrates superelastic shape memory alloy(SMA)bars,viscous dampers(VDs),and friction springs(FSs).A streamlined analytical approach relies on the strength decoupling of VD from other components using aλfactor to design SC-VBBFs.To evaluate the effectiveness of the hybrid brace,a set of 4-,8-,and 12-story archetypes equipped with SC-PBBs and SC-VBBFs are simulated in OpenSees and analyzed under various earthquake types,including crustal,subcrustal,and subduction events.The results demonstrate the superior performance of the SC-VBBF withλ≤0.5 system compared to SC-PBBFs in mitigating floor accelerations under design-level earthquakes and improving seismic resilience.展开更多
Friction stir processing(FSP) has emerged as a transformative solid-state technique for enhancing the mechanical performance and microstructural integrity of metallic materials,particularly in the context of additive ...Friction stir processing(FSP) has emerged as a transformative solid-state technique for enhancing the mechanical performance and microstructural integrity of metallic materials,particularly in the context of additive manufacturing(AM).This study demonstrates the effectiveness of FSP as a post-processing strategy for two distinct AM systems:wire arc additive manufacturing(WAAM) of low-carbon steel and selective laser melting(SLM) of Ti6Al4V alloy.In the case of WAAM fabricated steel,FSP significantly refined the coarse dendritic microstructure into ultrafine equiaxed grains,resulting in a 21 %-24 % increase in hardness and enhanced tensile properties at the overlapping regions.Similarly,for SLM fabricated Ti6Al4V,FSP eliminated the columnar prior-β grains and residual porosity,yielding a homogenous α+β structure with improved strengthductility balance and reduced anisotropy.These improvements were attributed to the dynamic recrystallization,conversion of low-angle to high-angle grain boundaries,and homogenization of phase constituents induced by FSP.Despite challenges such as tool wear and fixturing complexity,the study confirms that FSP can reliably bridge the performance gap in AM components by healing solidification defects,mitigating anisotropy,and tailoring the local microstructure.The findings position FSP as a versatile and scalable post-processing technique,crucial for advancing high-performance,application-ready components in aerospace,biomedical,and structural applications.展开更多
In light of the high nonlinearity of LuGre friction model, a novel method based on ant colony algorithm(ACA) for identifying the friction parameters of flight simulation servo system is proposed. ACA is a parallelized...In light of the high nonlinearity of LuGre friction model, a novel method based on ant colony algorithm(ACA) for identifying the friction parameters of flight simulation servo system is proposed. ACA is a parallelized bionic optimization algorithm inspired from the behavior of real ants, and a kind of positive feedback mechanism is adopted in ACA. On the basis of brief introduction of LuGre friction model, a method for identifying the static LuGre friction parameters and the dynamic LuGre friction parameters using ACA is derived. Finally, this new friction parameter identification scheme is applied to a electric-driven flight simulation servo system with high precision. Simulation and application results verify the feasibility and the effectiveness of the scheme. It provides a new way to identify the friction parameters of LuGre model.展开更多
A novel friction pendulum system （FPS） with dual rollers is studied based on the multibody dynamics theory. By analyzing kinematic characteristics of the system, it is reduced to a one degree-of-freedom system. Then...A novel friction pendulum system （FPS） with dual rollers is studied based on the multibody dynamics theory. By analyzing kinematic characteristics of the system, it is reduced to a one degree-of-freedom system. Then the equation of motion for the system is analytically derived by applying the theorem of the relative kinetic energy for a system of particles in differential form in the non-inertial reference system described as a nonlinear differential equation. In the case of the small angular displacement, the natural frequency of the corresponding undamped linear system is obtained, which is consistent with the experimental observation. The derived equation is useful for the study of dynamic characteristics of novel FPS, and its solution directly expedites the simulation of the system in a control loop, and further facilitates the semi-active control process including novel FPS.展开更多
Over the years,practical importance and interesting dynamical features have caused a growing interest in dry friction systems.Nevertheless,an effective approach to capture the non-smooth transition behavior of such sy...Over the years,practical importance and interesting dynamical features have caused a growing interest in dry friction systems.Nevertheless,an effective approach to capture the non-smooth transition behavior of such systems is still lacking.Accordingly,we propose a piecewise radial basis function neural network(RBFNN)strategy to solve the transient response of the randomly excited dry friction system.Within the established framework,the transient probability density function of the dry friction system is expressed in a piecewise form.Each segment of the solution is expressed by the sum of a series of Gaussian activation functions with time-dependent weights.These time dependent weights are solved by minimizing the loss function,which involves the residual of the Fokker-Planck-Kolmogorov equations and constraint conditions.To avoid the singularity of the initial condition being a Dirac delta function,a short-time Gaussian approximation strategy is presented to solve the initiating time-dependent weights.Based on some numerical results,the proposed scheme effectively performs.Moreover,a comparison with other existing methods reveals that the proposed scheme can completely capture the nonlinear characteristic of the dry friction system stochastic response more closely.Noteworthy,we can easily extend the proposed method to other types of non-smooth systems with piecewise response characteristics.Moreover,the semi-analytical solution provides a valuable reference for system optimization.展开更多
基金the National Science Foundation of China through the Grants(11872306,11772256)the Central University Fundamental Research Fund(3102018zy043).
文摘Friction systems are a kind of typical non-linear dynamical systems in the actual engineering and often generate abundant dynamics phenomena.Because of non-smooth characteristics,it is difficult to handle these systems by conventional analysis methods directly.At the same time,random perturbation often affects friction systems and makes these systems more complicated.In this context,we investigate the steady-state stochastic responses and stochastic P-bifurcation of friction systems under random excitations in this paper.And in order to retain the non-smooth of friction system,the generalized cell mapping(GCM)method is first used to the original stochastic friction systems without any approximate transformation.To verify the accuracy and validate the applicability of the suggested approach,we present two classical nonlinear friction systems,i.e.,Coulomb force model and Dahl force model as examples.Meanwhile,this method is in good agreement with the Monte Carlo simulation method and the computation time is greatly reduced.In addition,further discussion finds that the adjustable parameters can induce the stochastic P-bifurcation in the two examples,respectively.The stochastic P-bifurcation phenomena indicate that the stability of the friction system changes very sensitively with the parameters.Research of responses analysis and stochastic P-bifurcation has certain significances for the reliability and stability analysis of practical engineering.
基金supported by China National Machinery Industry Group(Grant No.SINOMACH 2017 246)
文摘Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observed that the average friction coefficient was increased after introducing film fragments into the friction system, where these film fragments can accelerate the breaking of the extreme thin oil film which could separate two friction surfaces when the system is under boundary lubrication conditions. The increasing friction load can accelerate the friction ehenfieal reaction on the friction interface and lead to the crushing effect on film fragments, which decreased the friction coefficient of friction system. It was also found that the wear width, depth, and volume of the film increased by introducing film fragments and applying great load.
基金financially supported by the National Natural Science Foundation of China(Nos.52175071,91860205)the Major Projects of Aero-engines and Gas turbines(No.J2019-IV-023-0091)。
文摘Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures.The state-of-the-art Multi-Harmonic Balance Method(MHBM)on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high.The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner;however,the efficiency and convergence are not guaranteed for large-scale models.In this paper,a semi-analytical MHBM on full-3D contact model is proposed.The original Trajectory Tracking Method(TTM)for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix(AJM)feasible.Based on the chain rule of derivation,the AJM which is the core to upgrade the performance is deduced.Through a shrouded blade finite element model,the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM.The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model.The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model.We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades.If one uses the quasi-3D model,the estimation relative error of damping can even reach 31.8%in some cases.In addition,the AJM also brings benefits for stability analysis.It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.
基金financially supported by the National Natural Science Foundation of China(Grants 52178124,52478151).
文摘When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the length of sliding trajectories of bridge superstructures during pulse-like near-fault earthquakes.As a result,a greater amount of energy will be dissipated due to the frictional sliding of the isolators.The GW-DFPS consists of a spherical surface and an outer surface described by a 1/x or logarithmic function to build gravity well.Full-scale isolators were fabricated and their response was characterized considering various parameters such as the friction material of slider,surface roughness of sliding surfaces,and applied vertical loads.Additionally,a finite element model of the isolator was created using the experimental test data.Numerical simulations were performed on a case-study bridge structure isolated using both a conventional DFPS system and the proposed GW-DFPS systems.The experimental results reveal that the proposed isolators exhibit stable response under vertical loads varying from 200 kN to 1000 kN with a negative stiffness response when the isolator slides at the outer sliding surface.The numerical simulations of the selected bridge structure demonstrate that the GW-DFPS significantly extends the sliding trajectory lengths of the superstructure during half of the earthquake pulses,resulting in increased energy dissipation during this interval.The kinetic energies of the bridge isolated by GW-DFPS are consistently lower than those of the bridge isolated by the other two kinds of isolators,resulting lower shear forces on the bridge.
基金National Key Research and Development Program of China(2022YFB4600902)Shandong Provincial Science Foundation for Outstanding Young Scholars(ZR2024YQ020)。
文摘Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.
文摘Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.
文摘The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.
基金National Natural Science Foundation of China(grant number:52375224)Natural Science Foundation of Jiangsu Province(grant number:BK20242086)+2 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions,a project supported by"the Fundamental Research Funds for the Central Universities"(grant number:202410976)Graduate Innovation Program of China University of Mining and Technology(grant number:2024WLKXJ075)Postgraduate Research&Practice Innovation Program of Jiangsu Province(grant number:KYCX24_2719).
文摘Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to friction pain.The results showed that the primary brain activation evoked by friction pain was located in the Prefrontal Cortex(PFC).The activation area decreased,and the negative activation intensity in the PFC region increased with increasing intensity of pain.The inhibitory interactions between different brain regions,especially between the PFC and primary somatosensory cortex(SI)regions were enhanced,and excitatory-inhibitory connections between the medial and lateral pain pathways were balanced during pain perception.The percentage power spectral density of theαrhythm(Dα),dominant singularity strength(αpeak)and longest vertical line(Vmax)of EEG signals induced by pain significantly decreased,and the percent-age power spectral density of theβrhythm(Dβ)significantly increased.The combination of multiple features of Dα,Dβ,αpeak and Vmax could significantly improve the average recognition accuracy of different pain states.This study elucidated the neural processing mechanisms of friction-induced pain,and EEG features associated with friction pain were extracted and recognized.It was helpful to study the brain feedback mechanisms of pain and control signals of Brain-Computer Interface(BCI)system related to pain.
基金Wuxi University Research Start-up Fund for Introduced Talents(Grant No:2024r031)Technology Development Contract(Contract Registration Number:2024320205000963)+1 种基金National Natural Science Foundation of China(Grant No.52275288)Ningbo Key Research and Development Plan(Grant No.2023Z022).
文摘To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype was selected by Finite Element Method(FEM).In addition,the bionic parameters were optimized by Response Surface Method(RSM).Samples holding BNS were prepared by Laser Processing,tribological properties were tested by a Friction and Wear Tester and worn surface morphology was characterized by a Scanning Electron Microscope(SEM).The results showed that BNS on friction surface could regulate the stress distribution and alleviate the peak stress.Among all samples,the coupled texture of pit-hexagonal got the minimum peak stress.During braking,bionic texture could also collect wear debris or change the motion forms from sliding to rotation,which can reduce abnormal abrasion.The wear rate was reduced by 19.31%.The results in this paper can provide a new idea for enhancing the tribological properties of CBFMs,and can also lay the foundation for further research of bionic tribology.
基金supported by the NSF of Shanxi(202303021221168)the Industry-university-research project of Shanxi Datong University(2022CXY10,2022CXY13).
文摘In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is considered dynamic.The contact condition on the normal plane is modeled by a unilateral constraint condition for a version of normal velocity in which the memory effect and the adhesion are considered.On the tangential plane a frictional contact condition is governed by the Clarke subdifferential of a locally Lipschitz function,and the evolution of the bonding field is governed by an ordinary differential equation.We formulate this problem as coupled system that consists of two ordinary differential equations and a variational-hemivariational inequality.Then,the existence,uniqueness and continuous dependence of the solution on the data results concerning the abstract system are established.Finally,we use the abstract results to show the existence and uniqueness of the solution to the contact problem.
基金the support received from the National Key Research and Development Program of China(Grant No.2023YFB3407400)the National Natural Science Foundation of China(Grant No.52475386,Grant No.52025058).
文摘5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conventional melt-based AM methods often introduce defects such as pores,cracks and elemental evaporation.In the present study,a novel screw extrusion-plasticizing friction stir deposition(SEFSD)process,which enables the extrusion plasticization of 5183 particulate feedstocks via a three-stage tapered screw tool,was utilized to fabricate a 20-layer 5183 deposition wall through continuous linear reciprocating deposition in the solid state.The deposition wall exhibited a refined equiaxed microstructure.Due to the low stacking fault energy(SFE)of Al-Mg alloy,the influence of thermal cycles on microstructural evolution was minimal.Overall,the deposition wall demonstrated excellent mechanical properties,though strength and ductility in the deposition direction were reduced due to interlayer defects,which could be mitigated by incorporating stir pins or enhancing interlayer adhesive friction to intensify the material flow.This study confirms the applicability and significant potential of SEFSD for additive manufacturing 5xxx Al alloy components.
基金the funds of the National Natural Science Fund for Excellent Young Scholars of China(No.52222410)Shaanxi Province National Science Fund for Distinguished Young Scholars,China(No.2022JC-24)the National Natural Science Foundation of China(Nos.52227807,52034005)。
文摘A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and mechanical properties of the fine-grained CS-HEA were characterized.The results showed that as-cast shrinkage cavities and elemental segregation were eliminated.The average grain size was refined from 121.1 to 5.4μm.The face-centered cubic phase fraction increased from 23%to 82%.During tensile deformation,dislocation slip dominated at strains ranging from 5%to 17%,followed by transformation induced plasticity(TRIP)from 17%to 26%,and twin induced plasticity(TWIP)from 26%to 37%.The yield strength,ultimate tensile strength,and elongation of the fine-grained CS-HEA were 503 MPa,1120 MPa,and 37%,respectively.The strength-ductility synergy of fine-grained CS-HEA was attributed to the combined effects of TRIP,TWIP,dislocation strengthening,and fine-grained strengthening.
基金financially supported by the National Natural Science Foundation of China(Nos.52034005,52227807,52104383,and 52222410)the Shaanxi Province National Science Fund for Distinguished Young Scholars,China(No.2022JC-24)+1 种基金the Key Research and Development Program of Shaanxi Province,China(No.2022JBGS2-01)the Central Guidance on Local Science and TechnologyDevelopment Fund of Shaanxi Province,China(No.2024ZY-JCYJ-04-09).
文摘Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.
基金supported by National Natural Science Foundation of China(Grant No.52171032)Hebei Natural Science Foundation(Grant No.E2023501002)Fundamental Research Funds for the Central Universities(Grant No.2024GFYD003)。
文摘High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
文摘Self-Centering Piston-Based Braced Frames(SC-PBBFs)are designed to curtail structural damage under severe ground motions.The self-centering mechanism in this bracing mitigates structural damage during an earthquake,thereby reducing post-earthquake repair costs and contributing to seismic resilience.However,non-structural components,particularly those sensitive to floor acceleration,remain vulnerable,resulting in prolonged func-tional recovery times.This paper aims to address this limitation by introducing a novel structural archetype,the Self-Centering Viscous-Based Braced Frame(SC-VBBF),which integrates superelastic shape memory alloy(SMA)bars,viscous dampers(VDs),and friction springs(FSs).A streamlined analytical approach relies on the strength decoupling of VD from other components using aλfactor to design SC-VBBFs.To evaluate the effectiveness of the hybrid brace,a set of 4-,8-,and 12-story archetypes equipped with SC-PBBs and SC-VBBFs are simulated in OpenSees and analyzed under various earthquake types,including crustal,subcrustal,and subduction events.The results demonstrate the superior performance of the SC-VBBF withλ≤0.5 system compared to SC-PBBFs in mitigating floor accelerations under design-level earthquakes and improving seismic resilience.
基金funded by the National Natural Science Foundation of China(Grant No.52322508)the R&D Program of Beijing Municipal Education Commission(Grant No.KZ20231000519).
文摘Friction stir processing(FSP) has emerged as a transformative solid-state technique for enhancing the mechanical performance and microstructural integrity of metallic materials,particularly in the context of additive manufacturing(AM).This study demonstrates the effectiveness of FSP as a post-processing strategy for two distinct AM systems:wire arc additive manufacturing(WAAM) of low-carbon steel and selective laser melting(SLM) of Ti6Al4V alloy.In the case of WAAM fabricated steel,FSP significantly refined the coarse dendritic microstructure into ultrafine equiaxed grains,resulting in a 21 %-24 % increase in hardness and enhanced tensile properties at the overlapping regions.Similarly,for SLM fabricated Ti6Al4V,FSP eliminated the columnar prior-β grains and residual porosity,yielding a homogenous α+β structure with improved strengthductility balance and reduced anisotropy.These improvements were attributed to the dynamic recrystallization,conversion of low-angle to high-angle grain boundaries,and homogenization of phase constituents induced by FSP.Despite challenges such as tool wear and fixturing complexity,the study confirms that FSP can reliably bridge the performance gap in AM components by healing solidification defects,mitigating anisotropy,and tailoring the local microstructure.The findings position FSP as a versatile and scalable post-processing technique,crucial for advancing high-performance,application-ready components in aerospace,biomedical,and structural applications.
文摘In light of the high nonlinearity of LuGre friction model, a novel method based on ant colony algorithm(ACA) for identifying the friction parameters of flight simulation servo system is proposed. ACA is a parallelized bionic optimization algorithm inspired from the behavior of real ants, and a kind of positive feedback mechanism is adopted in ACA. On the basis of brief introduction of LuGre friction model, a method for identifying the static LuGre friction parameters and the dynamic LuGre friction parameters using ACA is derived. Finally, this new friction parameter identification scheme is applied to a electric-driven flight simulation servo system with high precision. Simulation and application results verify the feasibility and the effectiveness of the scheme. It provides a new way to identify the friction parameters of LuGre model.
文摘A novel friction pendulum system （FPS） with dual rollers is studied based on the multibody dynamics theory. By analyzing kinematic characteristics of the system, it is reduced to a one degree-of-freedom system. Then the equation of motion for the system is analytically derived by applying the theorem of the relative kinetic energy for a system of particles in differential form in the non-inertial reference system described as a nonlinear differential equation. In the case of the small angular displacement, the natural frequency of the corresponding undamped linear system is obtained, which is consistent with the experimental observation. The derived equation is useful for the study of dynamic characteristics of novel FPS, and its solution directly expedites the simulation of the system in a control loop, and further facilitates the semi-active control process including novel FPS.
基金supported by the National Natural Science Foundation of China(Grant No.12072118)the Natural Science Funds for Distinguished Young Scholar of the Fujian Province of China(Grant No.2021J06024)the Project for Youth Innovation Fund of Xiamen(Grant No.3502Z20206005)。
文摘Over the years,practical importance and interesting dynamical features have caused a growing interest in dry friction systems.Nevertheless,an effective approach to capture the non-smooth transition behavior of such systems is still lacking.Accordingly,we propose a piecewise radial basis function neural network(RBFNN)strategy to solve the transient response of the randomly excited dry friction system.Within the established framework,the transient probability density function of the dry friction system is expressed in a piecewise form.Each segment of the solution is expressed by the sum of a series of Gaussian activation functions with time-dependent weights.These time dependent weights are solved by minimizing the loss function,which involves the residual of the Fokker-Planck-Kolmogorov equations and constraint conditions.To avoid the singularity of the initial condition being a Dirac delta function,a short-time Gaussian approximation strategy is presented to solve the initiating time-dependent weights.Based on some numerical results,the proposed scheme effectively performs.Moreover,a comparison with other existing methods reveals that the proposed scheme can completely capture the nonlinear characteristic of the dry friction system stochastic response more closely.Noteworthy,we can easily extend the proposed method to other types of non-smooth systems with piecewise response characteristics.Moreover,the semi-analytical solution provides a valuable reference for system optimization.
