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.     

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分析了拉索-并联弹簧-阻尼器系统的自由振动特性,由系统的运动方程及边界条件 得到其复特征值方程。进一步研究了系统的极限解,由此讨论了拉索-并联弹簧-阻尼器系统的模态变化分区现象。以拉索-并联弹簧-阻尼器系统的二阶模态解为例,给出了模态频率和阻尼比的变化分布区间及其对应振型的变化情况。讨论了系统分区中存在的模态交叉现象;同时也讨论了斜拉索垂度对于一阶振动模态变化规律的影响。研究表明拉索-并联弹簧-阻尼器系统的振动模态演化因并联弹簧-阻尼器的位置不同而存在的明确的分区现象;安装并联弹簧和阻尼器后拉索的模态阻尼比和模态频率均可明显提高。     

滚筒式洗衣机减隔振系统刚度阵的计算

本文针对滚筒式洗衣机弹簧减隔振系统的刚度阵的计算，提出了一种方便而概念清晰的方法。该法根据弹簧的主刚度方向，引入一个方向余弦矩阵和一个座标变换矩阵，通过两次矩阵变换，即可得到所求矩阵。     

橡胶弹簧非线性刚度的有限元解

本文探讨了用双重非线性有限元手段，求解橡胶弹簧的非线性刚度。橡胶的本构关系采用了广义虎克定律和基于应变能的超弹性材料的本构关系联合使用的方案，用单元内的静水压力ｐ，来修正广义虎克定律的弹性常数Ｅ和Ｇ。还提出了带刚性域的超单元和波前凝聚法两种新的办法，获得橡胶弹簧的刚度，使内存用量和ＣＰＵ时间大幅度下降。因而几何、物理双重非线性橡胶弹簧的计算，能在微机上实现。文内选用英国ＤＵＮＬＯＰ橡胶公司橡胶元件     

带弹簧-质量系统的车-桥耦合演变随机振动

提取悬挂有弹簧-质量系统桥梁的模态函数,将车辆简化为一个两自由度的移动系统,以桥面不平度功率谱密度为输入,建立车辆与带弹簧-质量系统的桥梁的耦合系统力学模型. 结合状态空间理论和演变随机过程的一般理论,研究车-桥耦合演变随机振动的弹簧-质量系统控制. 通过数值算例可知:弹簧-质量系统对车辆的随机响应没有影响,而可以降低桥梁的随机响应. 最后,探讨了弹簧-质量系统与桥梁质量比、弹簧--质量系统个数对桥梁随机响应的影响.     

自由振动中弹簧质量分支系统的系统矩阵确定准则

本文审定了弹簧质量分支系统作自由振动时的系统矩阵构成准则,对准则进行了调整,更便于应用.此外在文字叙述上更明确肯定.文中又将此准则扩大应用于直连通型弹簧质量系统,使准则适用于自由振动中的一切弹簧质量系统.     

螺旋压缩弹簧应力松弛特性试验分析及其应用

本文通过应力松弛试验、理论推导及数值模拟研究了高温下螺旋压缩弹簧的应力松弛规律,并利用加速模型对工况下弹簧应力松弛服役寿命做出预测。首先,根据螺旋压缩弹簧的结构特点搭建了弹簧应力松弛连续动态测试装置,该装置不仅避免了传统测试方法存在的缺陷,而且能够保证试验过程中位移载荷恒定,并实时监测载荷变化。本文以某飞机舱门单锁机构中的螺旋压缩弹簧为试验对象进行了不同温度条件下的应力松弛试验,得到其松弛动力学曲线,并基于Arrhenius模型建立了弹簧在工况下的应力松弛服役寿命预测模型;其次,基于应力松弛和蠕变在本质上的一致性,结合金属材料蠕变规律并根据试验弹簧的受力特点,推导出用于描述试验材料松弛行为的蠕变本构方程,由试验结果获得该本构方程的材料常数;最后,通过该本构方程及材料常数,在ANSYS软件中对试验弹簧的松弛过程进行模拟,结果表明,模拟结果与试验结果误差不大于4%。因此,通过本文方法所建立的蠕变方程对弹簧在不同载荷条件下的应力松弛规律进行仿真分析具有一定的可行性与准确性。     

静态等效质量法求振动系统的基频

在弹簧质量系统中,当弹簧与振体的质量比非常小时,可略去弹簧质量简化为单自由度系统.在不能略去弹簧质量的情况下或需求出较为精确的基频值时,必须考虑弹簧质量对系统基频的影响,此时,系统具有无穷多自由度.瑞利法运用能量原理,把一分布质量系统简化 ...     

引力波探测中的被动隔振系统

介绍了引力波探测实验中的被动隔振系统的基本原理和研究现状,讨论其性能及特点.低频被动隔振系统,如七级气体弹簧隔振系统,多级隔振堆,四级悬臂弹簧隔振系统以及三级弯曲弹簧隔振系统在10Hz以上,都具有好的隔振性能;倒摆、折叠摆、 X摆和锥摆等超低频水平隔振系统实现了几十秒的共振周期;建立在对称扭杆弹簧系统基础上,构思新颖的被动垂直隔振系统克服了传统被动垂直隔振系统无法解决的困难,实现了超低频被动垂直隔振.      

有限元—传递矩阵法求解链式结构非线性系统的动力响应

本文提出一分析多自由度非线性振动系统时域响应的数值计算法,并就一三自由度非线性系统,分别计算了此系统具有一个非线性弹簧、两个非线性弹簧和三个非线性弹簧三种情况下的动态响应;通过与对应的线性系统响应结果的比较,验证了此法的有效性、可靠性和多种优点.     

Fracturing of Clay During Drying: Modelling and Numerical Simulation

Non-uniform distribution of moisture contents inside of the porous materials during drying results in compressional stresses inside of the material and tensional ones close to the surface. The tensional stresses together with brittleness of dry material are the reasons of fracturing of the material. The proposed model consists of two parts. The mass transfer is described by simple diffusion equation. The mechanical behaviour of the material is modelled with the network model in which the material is modelled as the set of small particles interconnected elastically via springs. The spring constants and strengths depend on Young modulus and the material tensional strength. The dependences of these material parameters on the moisture content are determined. Then two 2D initial-boundary problems are solved. The results show possible way of cracks initiation and generation by drying.     

Coupled shear-torsional motion of a rubber support system

The finite amplitude, coupled shear-torsional motion of a circular disk supported between identical rubber spring cylinders is studied. The material of the springs is assumed to be an incompressible elastic material. The oscillatory motion oscillatory of the disk is studied for two different cases. In the first case, the material of the spring is assumed to be an incompressible elastic material whose response functions are constants. Typical examples include the Mooney-Rivlin model. The motion of the disk in this case is governed by two independent equations whose closed form solutions are noted. For the second case, the material of the spring is assumed to be an incompressible quadratic material. The motion oscillatory of the disk in this case is governed by two coupled nonlinear differential equations. The stability properties of small shearing oscillation superimposed on finite torsion and small torsional oscillation superimposed on finite shearing are studied.     

The effect of a spherical inclusion in an anisotropic solid

Summary A spherical domain within an anisotropic crystalline material is considered to have elastic constants differing from those of the remainder of the material; the particular case where the constants vanish within the sphere represents a cavity. The elastic fields inside and immediately outside the spherical domain, together with the interaction energy, are calculated for the case of a uniform stress applied at infinity. Specific examples are given for aluminum, copper, and pyrite, and numerical results are compared with those for isotropic material. The tensile stress concentration is larger for aluminum than for isotropic material while the opposite is true for pyrite. Similarly, the interaction energy of the inhomogeneity is larger for an anisotropic material than an isotropic material, but in pyrite the reverse is found.     

On Material Equations in Second Gradient Electroelasticity

The concern of this work is the derivation of material conservation and balance laws for second gradient electroelasticity. The conservation laws of material momentum, material angular momentum and scalar moment of momentum on the material manifold are derived using Noether's theorem and the exact conditions under which they hold are rigorously studied. The corresponding balance laws are also presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

Neural network optimization of material composition of a functionally graded material plate at arbitrary temperature range and temperature rise

Summary A neural network model is applied to optimization problems of material compositions for a functionally graded material plate with arbitrarily distributed and continuously varied material properties in the thickness direction. Unsteady temperature distribution is evaluated by taking into account the bounds of the number of the layers. Thermal stress components for an infinite functionally graded material plate are formulated under traction-free mechanical conditions. As a numerical example, a plate composed of zirconium oxide and titanium alloy is considered. In the optimization problem of minimizing the thermal stress distribution, the numerical calculations are carried out making use of the neural network. The optimum material composition is determined by taking into account the effect of temperature-dependence of material properties. The results obtained by neural network and ordinary nonlinear programming method are compared. Received 3 March 1998; accepted for publication 22 May 1998     

钢纤维对陶瓷基摩擦材料摩擦学性能的影响

以钢纤维为增强材料,采用氮气保护烧结方法制备出了钢纤维增强陶瓷基摩擦材料,用XD-MSM型定速摩擦磨损试验机对比研究了不同钢纤维含量对陶瓷基摩擦材料的热衰退性能、恢复性能以及磨损性能的影响,利用扫描电子显微镜(SEM)观察磨损表面形貌,并探讨了其磨损机理.研究结果表明:钢纤维的添加量(质量百分数)为24%时,钢纤维同陶瓷基体界面结合良好,陶瓷基摩擦材料的耐磨性能有所提高,热衰退率仅为5.8%,恢复率达到了107.8%,表明此配方陶瓷基摩擦材料具有较高的抗热衰退性能和恢复性能;钢纤维的含量影响陶瓷基摩擦材料的磨损形式,当含钢纤维含量较少时,陶瓷基摩擦材料以脆性脱落和疲劳磨损混合磨损形式为主;而随添加钢纤维含量的增多,其磨损形式转变为磨粒磨损;钢纤维过量加入时,则主要磨损形式为脆性脱落和疲劳磨损,并伴有黏着磨损.     

Mathematical characterization and identification of remodeling,growth, aging and morphogenesis

A clear demarcation between various processes of material evolution is established and the implications of the symmetry type on our ability to distinguish between them are investigated. The general features of the various types of material evolution are emphasized by establishing a spatio-temporal analogy between material uniformity and processes of material evolution.     

An improved Jones-Nelson nonlinear material model and rubber composite lamina analysis

A Jones-Nelson model has been applied to depict nonlinear stress-strain relations of composite laminae, where mechanical properties were expressed by strain energy density. The nonlinear material matrix is only a function of the strain energy density. Then a material model could be conveniently applied under complex stress condition. In this paper, by introducing large displacement stress-strain measurement and varying-Poisson's ratio idea, an improved Jones-Nelson material model is presented, where the expanding problem of material properties and convergence problems are overcome. Meanwhile a discuss of the reorientation of fiber and a material nonlinear analysis of rubber composite lamina under super large deformation conditions are made. The prediction results of improved material model are in fairly good agreement with those of the experiments.     

A thick anisotropic plate element in the framework of an absolute nodal coordinate formulation

In this research, the incorporation of material anisotropy is proposed for the large-deformation analyses of highly flexible dynamical systems. The anisotropic effects are studied in terms of a generalized elastic forces (GEFs) derivation for a continuum-based, thick, and fully parameterized absolute nodal coordinate formulation plate element, of which the membrane and bending deformation effects are coupled. The GEFs are first derived for a fully anisotropic, linearly elastic material, characterized by 21 independent material parameters. Using the same approach, the GEFs are obtained for an orthotropic material, characterized by nine material parameters. Furthermore, the analysis is extended to the case of nonlinear elasticity; the GEFs are introduced for a nonlinear Cauchy-elastic material, characterized by four in-plane orthotropic material parameters. Numerical simulations are performed to validate the theory for statics and dynamics and to observe the anisotropic responses in terms of displacements, stresses, and strains. The presented formulations are suitable for studying the nonlinear dynamical behavior of advanced elastic materials of an arbitrary degree of anisotropy.