超磁致伸缩换能器的磁滞非线性动力学仿真

在超磁致伸缩材料输出端位移假设的基础上,建立了以输出顶杆为研究对 象、考虑材料内部磁滞非线性及预压弹簧特性的超磁致伸缩换能器非线性动力学模 型; 并将Simulink仿真系统应用到超磁致伸缩换能器系统动力学仿真中. 仿真结果表 明: 换能器模型系统为稳定周期运动系统,并具有滞回非线性特性;弹簧非线性项中的平方 项是影响换能器模型系统的主要因素. 经验证,数值计算结果与文献给出的试验测试结果吻 合较好.     

磁致伸缩材料的非线性本构关系

给出了磁致伸缩材料的两个非线性本构关系,即标准平方型和双曲正切型。在确定一维问题的本构系数时,基于已有的实验结果,引进一个材料函数,用来描述磁致伸缩材料的压磁系数随预应力变化的关系。将非 线性本构关系的理论模型计算结果与实验曲线对比,结果表明标准平方型本构关系在中低磁场下能精确地模拟实验曲线,而双曲正切型本构关系在高磁场时能反映材料的磁致应变饱和现象。讨论了在标准平方型本构的一般三维情形,给出了确定本构系数的方法。     

超磁致伸缩材料执行器非线性动力学行为分析

考虑了超磁致伸缩棒的对称有间隙滞回特性,建立了相应的超磁致伸缩材料执行器的动力学模型。通过渐进法分析,得到超磁致伸缩材料执行器运动相应的近似解析式。通过数值模拟,发现对称有间隙滞回非线性振动系统具有复杂的分叉和混沌行为。     

超磁致伸缩材料的擦除特性和同余特性实验研究

超磁致伸缩材料在力磁耦合作用下具有复杂的迟滞响应。Preisach模型可有效描述物理过程中的滞后现象,它具有两个重要特性,即擦除特性和同余特性。擦除特性是指输入局部极大值擦除了加载过程中小于该值的所有极大值,或输入局部极小值擦除了加载过程中大于该值的所有极小值,同时,与这些历史极值相应的加载历史也被擦除,不再影响之后的输出。同余特性是指输入极大值与极小值相同的所有闭合曲线一致。本文通过实验系统地研究了超磁致伸缩材料在多轴力磁耦合场作用下的磁致伸缩曲线、磁滞回线和应力应变的迟滞行为,发现其在力磁耦合下的非线性滞后行为具有擦除特性和同余特性。这满足了Preisach模型描述滞后现象的两个基本要求,验证了利用Preisach模型描述超磁致伸缩材料迟滞行为的可行性,为超磁致伸缩材料的非线性理论和器件设计提供了依据。     

超磁致伸缩换能器系统动力学特性分析

根据第一压磁理论建立超磁致伸缩换能器系统含有平方、立方项非线性动力学模型,利用非线性振动近似解析方法对换能器系统进行分析,揭示了换能器系统非线性特性。利用基于MAT-LAB/Simulink的系统仿真理论,建立换能器系统动态仿真模型,发现换能器系统在一定参数下存在着混沌现象。通过数值模拟的方法对换能器系统做深入的理论分析,得出系统在不同参数下存在着倍周期、倒倍周期分岔等复杂非线性现象。本文的分析结果表明,超磁致伸缩材料的弹性模量、压磁系数、相对磁导率和系统阻尼系数等参数是超磁致伸缩换能器系统动力学特性的主要影响因素。     

超磁致伸缩材料多场耦合非线性力学行为的理论研究

超磁致伸缩材料由于具有位移大、响应快、驱动简单等性能优势,在智能系统中具有广阔的应用前景。对于其力学行为的研究,在理论上涉及的关键科学问题是多场耦合问题的理论建模与定量模拟,而其应用需求则涉及对超磁致伸缩器件性能的定量预测及优化。目前超磁致伸缩材料在工业上最广泛的应用是作为换能器的核心制动元件,其磁学、力学行为与工况密切相关。应力、外磁场、环境温度都会改变材料的磁化强度和应变状态,在交变磁场作用下磁致伸缩棒截面上产生涡电流,该损耗使材料的磁化和应变曲线出现洄滞。针对这些问题已有很多学者[1]-[4]进行了研究,这些工作揭示了外部条件对超磁致伸缩材料磁学、力学性质的单向联合作用,如图1中虚线所示。然而对于超磁致伸缩材料力学行为的准确刻画还需要考虑更深层次的多物理场耦合关系（图1中实线所示）：由于超磁致伸缩材料被外场磁化而产生磁致应变的同时,被磁化的介质也可以充当一种源而改变其周围的磁场,改变的程度依赖于介质的变形,因此需要考虑介质对周围磁场的反作用;棒截面上的涡电流除了会带来磁滞损耗外还会产生大量的热,改变周围温度,进而因为热膨胀、热磁效应等改变超磁致伸缩棒的磁学、力学输出,所以涡电流的热效应也不可忽略;此外,超磁致伸缩棒在交变磁场下的振动响应使其应力状态发生改变,在建模时不能只考虑所施加的预应力,材料的实时应力状态必须加以考虑。图1中虚线和实线所指向的过程共同构筑了超磁致伸缩材料的多物理场耦合框架,综合考虑这些因素才能准确描述超磁致伸缩材料多场耦合非线性力学行为。本文围绕上述内容逐步深入,针对这一在理论和应用上具有重要意义的问题,开展了理论建模和数值模拟研究。     

磁致伸缩作动器的电-磁-机耦合动力特性

基于磁致伸缩材料的本构关系模型,结合磁致伸缩作动器结构动力学模型建立了可描述磁致伸缩作动器的电-磁-机耦合动力特性的运动方程.方程中考虑了作动器工作时磁致伸缩材料的弹性模量随着应力和磁场的改变而发生的变化,磁致伸缩材料的这种特性使得作动器系统表现出具有时变刚度的参数振动特性.通过对此参数振动方程进行数值求解,得到磁致伸缩作动器的参数频响特性,并研究了激励电流幅值以及作动器负载质量对作动器频响特性的影响.     

磁致伸缩主被动隔振装置中的磁机耦合效应研究

磁致伸缩材料和柔顺位移放大机构组成的主动驱动装置具有精度高、驱动力大等特点.将其与被动隔振装置并联,形成主被动隔振装置,可以弥补纯被动隔振在低频和微幅扰动工况下的不足.本文针对这类磁致伸缩主被动隔振装置进行磁机耦合效应研究.基于Jiles-Atherton模型,分析了磁致伸缩材料所受应力对有效磁场、磁化强度、磁致伸缩系数和材料杨氏模量的影响,表征了材料磁机耦合效应.在此基础上,建立了主被动隔振装置的动力学模型,分析了主动驱动装置与被动隔振装置间的耦合作用.在耦合作用影响下,若被动隔振装置刚度不同,即使输入磁场相同,驱动器产生的驱动位移和驱动力也不相同.磁致伸缩材料的变刚度效应使隔振装置整体等效刚度不再为定值,从而影响被动隔振效果.本文提出了通过柔顺机构参数设计减小前述两种耦合影响的方法.数值仿真结果表明,磁致伸缩主被动隔振装置在低于、接近和高于谐振频率三类扰动下,都能达到比被动隔振更好的振动抑制效果.此外,仿真结果验证了考虑磁机耦合效应的数值模型具有更高精度.      

磁致伸缩主被动隔振装置中的磁机耦合效应研究

磁致伸缩材料和柔顺位移放大机构组成的主动驱动装置具有精度高、驱动力大等特点.将其与被动隔振装置并联,形成主被动隔振装置,可以弥补纯被动隔振在低频和微幅扰动工况下的不足.本文针对这类磁致伸缩主被动隔振装置进行磁机耦合效应研究.基于Jiles-Atherton模型,分析了磁致伸缩材料所受应力对有效磁场、磁化强度、磁致伸缩系数和材料杨氏模量的影响,表征了材料磁机耦合效应.在此基础上,建立了主被动隔振装置的动力学模型,分析了主动驱动装置与被动隔振装置间的耦合作用.在耦合作用影响下,若被动隔振装置刚度不同,即使输入磁场相同,驱动器产生的驱动位移和驱动力也不相同.磁致伸缩材料的变刚度效应使隔振装置整体等效刚度不再为定值,从而影响被动隔振效果.本文提出了通过柔顺机构参数设计减小前述两种耦合影响的方法.数值仿真结果表明,磁致伸缩主被动隔振装置在低于、接近和高于谐振频率三类扰动下,都能达到比被动隔振更好的振动抑制效果.此外,仿真结果验证了考虑磁机耦合效应的数值模型具有更高精度.     

考虑膜厚影响薄膜磁致伸缩系数、泊松比和杨氏模量的同时测量

基于经典层合板理论,建立了一个能同时测量薄膜-基底系统中薄膜的磁致伸缩系数、杨氏模量和泊松比的板模型.以前的研究计算薄膜磁致伸缩系数时,大多假设薄膜的弹性属性与相应的块材一致,由此导致的磁致伸缩系数计算是不准确的.在目前大多数方法中仅仅在使用一个单一的弹性各向同性基底中能够避免这个问题.该文模型在各向异性基底下同样适用,并且不要求薄膜的厚度远远小于基底厚度,因此也能够用来计算磁致伸缩应变和设计微电机械系统和生物微电机械系统.对已有的铁基非晶薄膜的实验数据,在不同磁场强度下,磁致伸缩系数的计算结果与已有模型进行了比较,它们之间的差异得到了解释.同时,还可以得到薄膜的弹性常数.     

Hysteretic deteriorating model for quasi-brittle materials based on micromechanical damage approach

A damage model, which is based on the stochastic modeling of the microstructures, is developed for the quasi-brittle materials subjected to repeated loading. According to this model, the overall response of the material is represented with a series of micro-elements joined in parallel. A combined model is proposed for the micro-element considering the fracture as well as the hysteretic energy dissipation. To account for the progressive failure, the random fracture strains are assigned to the micro-elements. Therefore the overall parallel bundle is considered as a stationary random field. Then by averaging the microscopic random field, the overall loading, unloading and reloading curves are derived analytically. Two hysteretic rules are derived from the proposed model, and the overall hysteretic deteriorating behaviors could be well reproduced. To demonstrate the validity of the present model, the numerical results are shown against the stochastic simulated curves as well as the experimental data. The present model provides an alternative approach for the efficient modeling of the hysteretic deteriorating behaviors for the quasi-brittle materials.     

滞后细观模型在岩石力学中的应用

对以砂岩为代表的所谓``NME材料'的力学行为研究方面的一些新的概念和模型进行了评介.首先介绍了一种基于所谓``滞后单元'的描述滞后现象的物理模型------Preisach-Mayergoyz(P-M)模型,然后详细阐述了P-M模型应用于模拟岩石的非线性滞后应力应变关系的过程和结果.这种唯象模型很好地描述了宏观上的滞后表现和``离散记忆'效应.接着本文对应变能耗散的力学机制进行了简单分析. 最后,介绍了一种描述弹性波在``NME材料'中传播规律的数学方法, 该方法从一般的弹性波传播规律出发,分析了``NME材料'特殊的力学性质给弹性波传播带来的影响,揭示了产生特殊的弹性波传播规律的原因.      

Stochastic damage hysteretic model for concrete based on micromechanical approach

In the present paper, a kind of stochastic damage hysteretic model is proposed to describe the damage and hysteretic behaviors of concrete material. According to the model, a parallel system made up of micro-elements, which are developed based on the micro-tensile and shear damage mechanism respectively, is adopted to obtain the overall responses of concrete. The influence of plastic strain and hysteretic energy dissipation of the material are also considered in the model. To reflect the stochastic properties of concrete, the fracture strain of the micro-element is set as a random variable. Then the monotonic, loading and unloading curves of the parallel system are derived analytically by averaging the stochastic micro-elements and two hysteretic rules are combined to the proposed model to account for complicated loading conditions. Furthermore, a nonlocal process is introduced to the model to overcome the mesh dependence issues of softening materials. Finally, several numerical examples are conducted, demonstrating that the proposed model can provide reliable results reflecting the damage, plasticity and hysteretic behaviors of concrete material.     

A real-space phase field model for the domain evolution of ferromagnetic materials

A real-space phase field model based on the time-dependent Ginzburg–Landau (TDGL) equation is developed to predict the domain evolution of ferromagnetic materials. The phase field model stems from a thermodynamic theory of ferromagnetic materials which employs the strain and magnetization as independent variables. The phase field equations are shown to reduce to the common micromagnetic model when the magnetostriction is absent and the magnitude of magnetization is constant. The strain and magnetization in the equilibrium state are obtained simultaneously by solving the phase field equations via a nonlinear finite element method. The finite-element based phase field model is applicable for the domain evolution of ferromagnetic materials with arbitrary geometries and boundary conditions. The evolution of magnetization domains in ferromagnetic thin film subjected to external stresses and magnetic fields are simulated and the magnetoelastic coupling behavior is investigated. Phase field simulations show that the magnetization vectors form a single magnetic vortex in ferromagnetic disks and rings. The configuration and size of the simulated magnetization vortex are in agreement with the experimental observation, suggesting that the phase field model is a powerful tool for the domain evolution of ferromagnetic materials.     

2-dof non-linear dynamics of a rotor suspended in the magneto-hydrodynamic field in the case of soft and rigid magnetic materials

Non-linear dynamics of a high-speed rotor symmetrically supported on the magneto-hydrodynamic bearing is analyzed. In the case of soft magnetic materials the method of multiple scales [1] is applied. Non-resonant and primary resonance cases with and without internal resonance are illustrated and discussed. In the case of rigid magnetic materials the hysteretic properties are taken into consideration by means of the Bouc-Wen hysteretic model. In order to characterize the hysteretic close-loop control of the rotor motion, instability regions as well as the amplitude level contours of vertical and horizontal vibrations of the rotor are obtained in the form suitable for engineering applications, i.e. in the ‘frequency-amplitude’ parametric plane.     

微磁检测应力和塑性区的磁弹塑耦合理论

金属磁记忆微磁检测方法, 利用铁磁材料局部磁性状态的变化, 进行应力集中或塑性区域位置及程度的检测与评价. 面向微磁信号的定量理论分析可对其工程领域应用提供重要指导. 本文介绍铁磁材料微弱环境磁场下的磁弹塑性本构进展, 及其在微磁信号分析方面的应用. 力磁本构关系方面, 针对微磁检测弱磁化条件, 基于有效场理论构建了受弹塑性载荷铁磁材料的理想磁化本构的显式解析式, 并结合接近原理分析了恒定外加微弱磁场下应力-应变对材料磁化强度的影响. 检测信号分析方面, 基于弹性力学理论、静磁学理论和新建立的磁弹塑性本构关系, 建立并求解了微弱磁场下铁磁试件中弹性应力或塑性区诱导的表面磁信号的二维分析模型. 结合实验结果证实其在刻画弹塑性因素对微磁信号影响规律方面的能力, 并详细分析了微磁信号的特征量与局部弹性应力或塑性区的尺寸间的相关关系. 相比已有力磁本构关系, 本文建立的显式解析形式的理想磁化更加简洁, 有助于提升对力磁耦合效应的定量化理解和应用.      

基于等效阻尼理论的金属橡胶弹性迟滞力学模型及实验研究

针对弹性多孔金属橡胶非线性迟滞特性力学行为,将迟滞恢复力-位移曲线分解为非线性单值曲线和椭圆,并将等效阻尼理论用于动态力学性能参数识别,从而建立了一种新型的适用于黏弹性阻尼材料的宏观唯象力学模型。采用不同相对密度的环形金属橡胶进行动态实验测试,以验证理论模型的准确性,结果表明该模型可将具有非线性特性的金属橡胶系统进行降阶处理,提高金属橡胶力学模型的预测效率,并能很好地描述金属橡胶的迟滞力学行为。另外,研究了在不同激励频率条件下金属橡胶的阻尼耗能特性。实验结果表明:在高频加载的条件下,黏性阻尼系数对动态加载频率不敏感,阻尼耗能与加载幅值之间呈线性正相关。基于等效阻尼理论的弹性迟滞力学模型具有一定的普适性,可进一步推广应用于类似弹性多孔材料的力学性能表征,为其工程应用提供理论基础。     

Nonlinear modeling of hysteretic systems with double hysteretic loops using position and acceleration information

This paper presents two new dynamic hysteresis models obtained from the Bouc–Wen model by incorporating position and acceleration information. On the one hand, the model employing position information is rate-independent and it is able to reproduce some kind of double hysteretic loops unable to be reproduced with the original Bouc–Wen model. On the other hand, the model employing acceleration information is insensitive to linear time-scale variations. Moreover, a classification of the BIBO-stable models has been derived for both position and acceleration cases. Double hysteretic loops have been experimentally reported in shape-memory alloys, reinforced concrete structures, wood structures and lightweight steel shear wall structures. The proposed hysteretic models represent a prominent use in the field of structural dynamics and earthquake engineering because they can capture the nonlinear dynamics of the materials and structures presented earlier when they are subjected to dynamic loads as earthquake excitations.     

铁磁纳米结构磁化状态及其磁-力耦合效应的相场模拟

基于随时间变化的Ginzburg-Landau(TDGL)方程,建立了模拟铁磁材料磁-力耦合效应的相场模型。从弱解形式出发,推导出了相关控制方程的有限元格式,然后编制程序进行数值求解。由于有限元对复杂边界有良好的适用性,该模型可用于不同形状铁磁材料的畴结构模拟。通过相场模拟,发现铁磁纳米结构中的磁化会形成涡旋结构,与实验观察到的磁化涡旋结构符合较好。由非均匀磁化引起的结构的变形、应力等力学参量都可以通过模拟一并得到。本文结果表明,改变结构形状可以有效控制磁畴结构的形态,适当的外应力可以改变磁畴结构及其对外磁性的大小。     

An isotropic unilateral damage model coupled with frictional sliding for quasi-brittle materials

In this paper, we present an original extension of an isotropic damage model for quasi-brittle materials and assess its predictive capabilities. The proposed model accounts not only for unilateral behavior related to the opening and closure of microcracks but also for inelastic strains reflecting the frictional sliding along closed microcracks. More importantly, owing to its careful mathematical formulation with a particular attention paid to the continuous differentiability of the underlined thermodynamic potential, the model ensures the continuity of the inelastic stress–strain response. First applications show that it is able to predict the asymmetric behavior and hysteretic response of microcracked materials such as concrete and some rocks