查看更多>>摘要：A theoretical model is developed to investigate the sliding electrical contact behavior with the consideration of the electrical-thermal-mechanical coupling effect.The interfacial electrical resistance and electrical constriction resistance are both involved.The Joule heating due to electrical contact resistance and the frictional energy dissipation are considered in the model for the assessment of the temperature rise at the contact interface.A singular integral equation for sliding electrical contact considering both frictional and Joule heat is developed and solved to obtain the contact pressure,current density,and temperature rise.Furthermore,a discrete fast Fourier transform-based boundary element method is applied to obtain the numerical solution of sliding electrical contact.Good agreement is achieved between theoretical and numerical results.After the validation,the effects of potential drop and sliding velocity on sliding electrical contact behavior are investigated.The results indicate that the proposed theoretical model can provide an exact prediction of multi-physics sliding electrical contact behavior.
查看更多>>摘要：Twisted and coiled polymer actuator(TCPA)is a type of artificial muscle that can be driven by heating due to its structure.A key issue with TCPA performance is the low driven frequency due to slow heat transfer in heating and cooling cycles,especially during cooling.We developed a numerical model of coating heating and nitrogen gas cooling that can effectively improve the driven forces and frequencies of the TCPA.Results indicate that natural cooling and electric fan cooling modes used in many experiments cannot restore the TCPA to its initial configuration when driven frequencies are high.Nitrogen gas cooling,at high driven frequencies,can fully restore the TCPA to its initial configuration,which is crucial for maintaining artificial muscle flexibility.In addition,as driven frequency increases,the corresponding driven force decreases.Systematic parametric studies were carried out to provide inspirations for optimizing TCPA design.The integrative computational study presented here provides a fundamental mechanistic understanding of the driven response in TCPA and sheds light on the rational design of TCPA through changing cooling modes.
查看更多>>摘要：A model of a sandwich magnetorheological elastomer(MRE)beam with a concentrated mass attached to one end is proposed to analyze the resonance characteristics of the cantilever beam-mass resonator.This model of sandwich MRE resonator consists of two types of components:the beam element with two nodes and four degrees of freedom and the beam element with concentrated mass.The effectiveness of this model is verified by comparing its results with existing results and finite element results.Through integrating the metamaterial beam with MRE resonators,a band-gap-adjustable metamaterial beam is proposed and low-frequency vibration suppression is achieved.The results suggest that the band gap of the structure can be effectively adjusted within a wide range by changing the external magnetic field applied to the presented MRE resonators.
查看更多>>摘要：In this work,a three-dimensional crystal-plasticity-based phase-field model considering three kinds of inelastic deformation mechanisms,i.e.,martensitic transformation,dislocation slip in austenite,and dislocation slip in martensite,is established to simulate the stress-assisted two-way shape memory effect(SATWSME)of NiTi single crystals and its cyclic degradation.The simulation results show that the ability of the SATWSME of NiTi single crystal increases as increasing the constant stress in the range discussed in this work(10-100 MPa),which is due to the increase of reoriented martensite formed in the cooling process due to the enhanced variant-selection capability of increased constant stress.The martensitic transformation and its reverse in the cyclic process reflecting the SATWSME show more and more obvious localization characteristics,resulting in the accumulation of significantly heterogeneous plastic deformation(mainly caused by the dislocation slip in austenite),which leads to the cyclic degradation of SATWSME.The simulation results and the conclusions drawn from this work are helpful for further understanding the mechanism of functional cyclic degradation of NiTi alloys.
查看更多>>摘要：This paper aims to seek expedited fatigue analysis methods using the infrared self-heating technique.The fatigue analysis of NiTi shape memory alloys is obtained through a hybrid approach:fatigue tests to failure yield relatively shorter fatigue lives,while determining the fatigue limit,normally involving extremely high cycles approaching 107 cycles,is directly achieved via self-heating tests.This methodology significantly reduces testing cycles,costing only a fraction of the several-thousand-cycle tests typically required.The validity of this approach is successfully demonstrated through fatigue testing of 18Ni steel:the entire S-N curve is examined using the traditional fatigue test until a life of up to 107 cycles,and the indicated fatigue limit agrees well with the one directly determined through the self-heating method.Subsequently,this developed approach is applied to the fatigue analysis of shape memory alloys under complex loading,enabling the concurrent estimation of the limits of phase transformation-dominated low-cycle fatigue and high-cycle fatigue in the elastic regime on a single specimen.The results obtained align well with other supporting evidence.
查看更多>>摘要：In order to enhance the fatigue properties of metallic materials,a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation.Based on this rationale,the study investigates the approach of improving the very high cycle fatigue properties of TC6 titanium alloys through near-β forging coupled with shot peening,conducted at 930 ℃ and ambient temperature,respectively.To unveil the associated mechanisms,microstructure,microhardness,residual stress,and fatigue properties are thoroughly analyzed after each process.Results indicate a considerable refinement in microstructure and significant mitigation of the initially existed strong texture post near-β forging and annealing,efficiently delaying crack initiation and propagation.As a result,the very high cycle fatigue property of TC6 achieves remarkable enhancement after forging.Compared to near-β forging,shot peening might not necessarily improve the very high cycle fatigue performance,particularly beyond 106 cycles.
查看更多>>摘要：The scattering of shear horizontal(SH)waves by a circular hole in an infinite piezomagnetic medium affected by magnetic field and compressive stress has been investigated theoretically in this study.The effective elastic,piezomagnetic,and magnetic permeability constants of the piezomagnetic material change with the external magnetic field and compressive stress.The governing differential equations for SH waves scattered by a circular hole are solved using the wave function expansion method.The effects of the magnetic field and compressive stress on mechanical displacement,dynamic stress,and magnetic potential of SH waves around a circular hole are discussed in detail.It has been found that the mechanical displacement around the circular hole increases with magnetic field and decreases with compressive stress.As the magnetic field increases,the maximum dynamic stress increases and structural resonance is strengthened.The findings presented in this study are beneficial for improving the performance of magnetoelastic acoustic wave devices.
查看更多>>摘要：Elastic beams resting on an elastic foundation are frequently encountered in civil,mechanical,aeronautical,and other engi-neering disciplines,and the analysis of static and dynamic deflections is one of the essential requirements related to various applications.The Galerkin method is a classical mathematical method for solving differential equations without a closed-form solution with a wide range of applications in engineering and scientific fields.In this study,a demonstration is presented to solve the nonlinear differential equation by transforming it into a series of nonlinear algebraic equations with the Galerkin method for asymptotic solutions in series,and the nonlinear deformation of beams resting on the nonlinear foundation is successfully solved as an example.The approximate solutions based on trigonometric functions are utilized,and the nonlinear algebraic equations are solved both numerically and iteratively.Although widely used in linear problems,it is worth reminding that the Galerkin method also provides an effective approach in dealing with increasingly complex nonlinear equations in practical applications with the aid of powerful tools for symbolic manipulation of nonlinear algebraic equations.
查看更多>>摘要：The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels.While existing studies are primarily focused on the adverse effects of hypoxia and oxygen supplementation strategies at high altitudes,there is a notable gap in understanding the fundamental mechanisms driving altitude hypoxia.In this context,we propose a sophisticated two-way fluid-structure interaction model that simulates respiratory processes with precisely structured and deformable upper airways.This model reveals that,under identical pressure differentials at the airway's inlet and outlet,the inspiratory air volume remains largely consistent and is minimally affected by specific pressure changes.However,an increase in the pressure differential enhances gas inhalation efficiency.Furthermore,airway morphology emerges as a pivotal factor influencing oxygen intake.Distorted airway shapes create areas of high flow velocity,where low wall pressure hampers effective airway opening,thus diminishing gas inhalation.These results may shed light on the effects of low-pressure conditions and upper airway structure on respiratory dynamics at high altitudes and inform the development of effective oxygen supply strategies.
查看更多>>摘要：Given the significant potential of multi-directional functionally graded materials(MFGMs)for customizable performance,it is crucial to develop versatile material models to enhance design optimization in engineering applications.This paper introduces a material model for an MFGM plate described by trigonometric functions,equipped with four parameters to control diverse material distributions effectively.The bending and vibration analysis of MFGM rectangular and cutout plates is carried out utilizing isogeometric analysis,which is based on a novel third-order shear deformation theory(TSDT)to account for transverse shear deformation.The present TSDT,founded on rigorous kinematics of displacements,is demonstrated to surpass other preceding theories.It is derived from an elasticity formulation,rather than relying on the hypothesis of displacements.The effectiveness of the proposed method is verified by comparing its numerical results with those of other methods reported in the relevant literature.Numerical results indicate that the structure,boundary conditions,and gradient parameters of the MFGM plate significantly influence its deflection,stress,and vibration frequency.As the periodic parameter exceeds four,the model complexity increases,causing result fluctuations.Additionally,MFGM cutout plates,when clamped on all sides,display almost identical first four vibration frequencies.
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