稀土超磁致伸缩材料应力与电磁耦合特性的实验研究

讨论了稀土超磁致伸缩棒特性实验的若干应力与电磁耦合问题，利用自己设计制作的实验装置建立了应力电磁耦合系统的物理模型，应用阻抗分析方法得到了相应的等效电路。测定了在电磁场与应力场共同作用下ＴｂｘＤｙ１－ｘＦｅ２－ｚ三元稀土合金超磁致伸缩棒的磁致伸缩系数，机电耦合系数等。针对磁通泄漏问题，专门设计制作了圆柱型硅钢密闭磁路，本的实验结果为稀土眼磁致伸缩材料应用器提供了重要而准确的数据。     

超磁致伸缩换能器耦合磁弹性模型与振动特性分析

针对应用于非圆车削加工的超磁致伸缩换能器,建立了其耦合磁弹性动力学模型与复系数动力学微分方程,基于实验建立的激励电流磁致伸缩材料轴向位移-磁场强度三者之间的关系式,得到了换能器磁力-位移关系的磁动方程的解析解,分析了系统的频响特性及不同频率下,激励电流与换能器输出位移之间的滞回关系,对现有磁场-电流公式进行了修正,讨论了偏置磁场对系统的影响,并与数值解进行了对比.结果表明:超磁致伸缩换能器的输出位移与输入激励电流之间的滞回环及其环方位与激励频率有关,且修正公式与实验所得结论完全一致.换能器的频响关系具有明显的共振和反共振特性,且频响曲线的正负向决定了滞回环的方位,换能器输出位移的绝对值决定了滞回环包围面积的大小换能器滞回环的面积、倾斜度随偏置磁场的增大而增大.本文的结果为换能器的控制与优化提供了理论基础.     

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。     

SOME PROBLEMS IN ELECTROSTRICTIVE AND MAGNETOSTRICTIVE MATERIALS

Some of the previous theories in the electrostrictive and magnetostrictive materials and their differences are discussed in this paper.A variational principle in the general thermody- namic sense is given and the governing equations can be derived from this principle.Illustrational examples are given.     

界面及热残余应力对超磁致伸缩复合材料有效性能的影响

论文基于Mori-Tanaka理论,考虑了界面相对超磁致伸缩复合材料的有效性能的影响,得到了具有界面相的超磁致伸缩复合材料的有效性能的一般解析表达.考虑到固化过程中热残余应力对超磁致伸缩复合材料有效性能的影响,通过数值计算,给出超磁致伸缩复合材料有效弹性模量、有效磁致伸缩应变及有效热膨胀系数随夹杂物长径比、体分比、界面参数和固化热残余应力的变化特征曲线,数值结果表明:界面和固化热残余应力对于超磁致复合材料有效性能的影响是显著的.     

VIBRATION SUPPRESSION OF CANTILEVER LAMINATED COMPOSITE PLATE WITH NONLINEAR GIANT MAGNETOSTRICTIVE MATERIAL LAYERS

In this paper, a nonlinear and coupled constitutive model for giant magnetostrictive materials(GMM) is employed to predict the active vibration suppression process of cantilever laminated composite plate with GMM layers. The nonlinear and coupled constitutive model has great advantages in demonstrating the inherent and complicated nonlinearities of GMM in response to applied magnetic field under variable bias conditions(pre-stress and bias magnetic field).The Hamilton principle is used to derive the nonlinear and coupled governing differential equation for a cantilever laminated composite plate with GMM layers. The derived equation is handled by the finite element method(FEM) in space domain, and solved with Newmark method and an iteration process in time domain. The numerical simulation results indicate that the proposed active control system by embedding GMM layers in cantilever laminated composite plate can efficiently suppress vibrations under variable bias conditions. The effects of embedded placement of GMM layers and control gain on vibration suppression are discussed respectively in detail.     

分子动力学方法在研究材料力学行为中的应用进展

报道近年来分子动力学方法应用于研究位错、裂纹、晶界及其相互作用方面的进展．主要包括:裂纹尖端的位错发射,位错发射的不稳定堆垛能,晶体与裂纹’几何关系对位错发射的影响,温度对位错发射的影响以及由裂纹尖端发射的位错列与不对称倾侧晶界的相互作用．报道主要以我们的工作为主,重点讨论裂纹尖端位错发射的研究结果      

铁磁材料单向应力无损检测实验研究

传统的四磁极磁测应力传感器不仅存在结构对称性差异,而且其难以保障检测输出信号零点值为零.引入标准补偿试件平衡待测试件的工况误差,实现环境变量的自动补偿;采取检测线圈同相串联接法,以线圈连接中间接点与电位器滑动点间的电压信号作输出,使零点值可调.实验结果表明,该方法实现了对电路零点值的准确调节,而且传感器的输出特性与理论推导结果呈线性吻合.因此,该传感器可以实现铁磁材料单向应力测试.     

MULTISCALE MECHANICAL BEHAVIORS IN DISCRETE MATERIALS:A REVIEW

The discrete material,which belongs to the category of soft materials,is one of the most prevalent forms of matter in nature and engineering fields.These materials often exhibit abundant and complex mechanical properties which are still far from being perfectly understood.From the view of multi-scale framework concentrated on the ‘bridge’ role in the macro-micro relation,this review mainly introduces some theoretical investigations of mechanical behaviors in discrete materials,including the continuum constitutive model based on the macroscopic phe-nomenological approach and coupled micro-macro approach,the statistical analysis of some micro-scopic physical quantities involved contacted forces between particles and its transmission within the whole system,and the statistical analysis for some microscopic processes in aeolian landform systems involving the grain-bed impact,the transportation and sedimentation of wind-blown sand flux,et al.Finally,some further worthwhile challenges in these fields are suggested.     

高温结构材料的蠕变和疲劳研究的一些新进展

高温部件长期在高温严酷环境和载荷作用下,蠕变和疲劳是制约其使用寿命的重要因素,成为高温结构强度领域的关键问题,近年来日益受到研究者们的高度关注.本文回顾了实际高温结构部件和材料的失效机制、损伤评估以及寿命预测等方面的研究进展,着重介绍了本课题组在高温蠕变和疲劳领域的最新研究成果,并对该领域今后的发展方向进行了展望.     

磁致伸缩薄膜力学行为的有限元仿真研究

建立了一种磁致伸缩薄膜力学行为的有限元计算方法.该方法将磁致伸缩薄膜在磁场中的形变行为等效为薄膜在热场中的各向异性热膨胀形变行为,基于该等效模型,利用有限元软件计算了磁致伸缩薄膜悬臂梁的力学行为与外加磁场的关系.结果表明,该方法可有效模拟磁致伸缩薄膜在外磁场下的力学行为.     

THE NONLINEAR MAGNETOELASTIC PROPERTIES OF 〈 110 〉 ORIENTED TBo.27DYo.73FE1.95 POLYCRYSTALLINE ALLOYS UNDER COUPLED MAGNETOMECHANICAL LOADING

In the paper, the nonlinear magnetoelastic properties of composition Tb0.27Dy0.73 Fel.95 〈 110 〉 oriented polycrystalline alloys are investigated under coupled loads of high mag- netic field and compressive stress. The magnetization and magnetostriction are measured simul- taneously under applied magnetic field from -800 to 800 kA/m and compressive stress from 0 to 25 MPa at room temperature. The strain coefficient and relative permeability are obtained by differential calculation from the experimental curves. The results show that the values of satura- tion magnetization （M~） under different compressive stresses remain invariably constant in the region of the high magnetic field. The saturation magnetostriction （As） increases with increasing compressive stress and reaches 1680 ~ 10-6 under 25 MPa. According to the increase of the com- pressive stress, the hysteretic loop area of magnetization and magnetostriction increases, while the maximum relative permeability and strain coefficient decrease. Additionally, the influence of the bias magnetic field on the mechanical property is taken into account. The stress-strain relation- ship is nonlinear and sensitive to the applied external magnetic fields along the axis of rod. The results obtained are a useful complement to the existing experiments for theoretical approaches and engineering applications.     

Effective magnetoelastic properties of laminated composites

Effective physical parameters of a fine-layered medium whose layers exhibit linearized magnetostriction as ferrites are determined. Ferromagnetic materials of cubic system with ferromagnetic resonance are considered __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 8, pp. 36–43, August 2006.     

沉管隧道接头非线性力学性能模拟方法

沉管隧道柔性接头的力学性能是其抗震设计的关键准则. 用有限元方法模拟接头的非线性力学性能需要解决接头处材料非线性和接触非线性两个问题. 为简化分析计算,该文采用分段线性化的方法表征接头的材料非线性问题,引进调整因子改进接触算法中的判断条件,处理接头的边界非线性问题. 通过沉管隧道接头的三维精细化建模,研究了沉管隧道接头在拟静力载荷下的响应,获得了接头的轴向等效刚度曲线、抗弯刚度曲线和非线性耦合的剪切特性曲线,进而分析了不同轴向压力对接头剪切特性的影响.     

电感式磨粒传感器中铁磁质磨粒的磁特性研究

在电感式磨粒传感器中,铁磁质磨粒主要通过磁化作用改变传感器线圈的磁场分布,进而改变线圈的等效电感.建立了线圈中含有铁磁质磨粒时的磁场模型,得出了磨粒磁化场关于退磁因子的磁感应强度表达式.以球磨粒为例,通过计算球磨粒磁化场,得到球磨粒引起线圈电感变化率的解析式,并用有限元法计算了线圈的磁场,分析后发现:理论计算解与数值分析解相符,所建模型可以反映客观实际;磨粒的磁化强度由其磁导率和退磁因子共同决定,球磨粒的磁化强度可近似认为与磁导率无关;球磨粒引起的传感器线圈电感变化率随线圈单位长度上匝数的增加而减小,并趋向于一极限值;传感器线圈的电感变化率与球磨粒半径的三次方成正比,球磨粒半径在100μm以内,电感变化率在10-7数量级.本研究结论可为电感式磨粒传感器的设计提供理论指导.     

时间无关不可逆过程及不可逆系统的稳定性

在不可逆热力学框架内引入了四条基本假设，建立了宏观本构关系的新的逻辑系统．在假设3中通过引入一种新的运算，把内变量演化方程定义在时间的点集上．结合讨论C1ausius-Dubem不等式，得到了假设4，它把时间点集的性质与系统状态联起来．以此为基础，证明了一致性条件成立的判别准则和加卸载准则，并成功地解释了实验现象存在有一个应变速率的临界值，当加载应变速率低于该值时，材料的应力—应变关系基本上与速率无关；当高于该值时，则明显与速率相关、更富有力学含义地给出了不可逆系统稳定性的一种定义，并证明了判别稳定性的一个准则．此外，还得出系统稳定是不可逆行为与时间无关的前提条件．     

SELF-INSTABILITY AND BENDING BEHAVIORS OF NANO PLATES

This paper aims at investigating the size-dependent self-buckling and bending behaviors of nano plates through incorporating surface elasticity into the elasticity with residual stress fields. In the absence of external loading, positive surface tension induces a compressive residual stress field in the bulk of the nano plate and there may be self-equilibrium states corresponding to the plate self-buckling. The self-instability of nano plates is investigated and the critical self-instability size of simply supported rectangular nano plates is determined. In addition, the residual stress field in the bulk of the nano plate is usually neglected in the existing literatures, where the elastic response of the bulk is often described by the classical Hooke＇s law. The present paper considered the effect of the residual stress in the bulk induced by surface tension and adopted the elasticity with residual stress fields to study the bending behaviors of nano plates without buckling. The present results show that the surface effects only modify the coefficients in corresponding equations of the classical Kirchhoff plate theory.     

Linear stability of triple-diffusive convection in micropolar ferromagnetic fluid saturating porous medium

The triple-diffusive convection in a micropolar ferromagnetic fluid layer heated and soluted from below is considered in the presence of a transverse uniform magnetic field. An exact solution is obtained for a flat fluid layer contained between two free boundaries. A linear stability analysis and a normal mode analysis method are carried out to study the onset convection. For stationary convection, various parameters such as the medium permeability, the solute gradients, the non-buoyancy magnetization, and the micropolar parameters (i.e., the coupling parameter, the spin diffusion parameter, and the micropolar heat conduction parameter) are analyzed. The critical magnetic thermal Rayleigh number for the onset of instability is determined numerically for a sufficiently large value of the buoyancy magnetization parameter M ₁. The principle of exchange of stabilities is found to be true for the micropolar fluid heated from below in the absence of the micropolar viscous effect, the microinertia, and the solute gradients. The micropolar viscous effect, the microinertia, and the solute gradient introduce oscillatory modes, which are non-existent in their absence. Sufficient conditions for the non-existence of overstability are also obtained.     

复合材料的蠕变行为

本文着重介绍了粘弹性力学对复合材料蠕变问题的处理,蠕变的经验公式以及延迟破坏的一些研究成果,还涉及了蠕变的机理和试验方法。最后对含裂纹复合材料的蠕变行为提出了一些看法。