形状记忆合金在军事上的应用

 现代战争对兵器性能的要求越来越高。形状记忆合金作为一种新型功能材料,由于其独特的性能,在许多领域得到了广泛应用。本文简述了形状记忆合金在火炮、枪弹、战斗机等领域的应用情况。所谓形状记忆合金是指具有形状记忆效应的合金,而形状记忆效应指的是,将某些金属材料变形后加热到某一特定温度以上时,能恢复原来形状的一种效应。     

金属橡胶迟滞特性本构模型研究

金属橡胶作为一种新型阻尼材料, 其原材料及加工工艺具有一定特殊性. 基于材料的细观结构特征, 选取了金属丝螺旋卷作为金属橡胶的基本微元体结构, 并以圆柱压缩螺旋弹簧理论为基础, 分别建立了横向和纵向排列微元体结构的刚度. 鉴于库仑摩擦模型, 分别建立三种接触状态螺旋卷接触对的力学模型. 考虑整个加工工艺流程的特点, 分析了不同接触状态数目变化规律, 建立了金属橡胶迟滞特性本构模型. 从理论上解释了金属橡胶迟滞特性的特点, 以及刚度和阻尼非线性的产生机理. 最后, 通过对比不同相对密度金属橡胶试件的理论和试验结果, 验证了理论模型的适用性. 本模型从螺旋卷微元体结构上描述了金属橡胶迟滞特性, 为工程上预测和分析金属橡胶的刚度、阻尼特性和设计金属橡胶产品提供了有效的理论基础.     

敷设阻尼材料的双层圆柱壳声辐射性能分析

研究了外层壳上敷设粘弹性阻尼材料的双层壳体的振动和声辐射性能,采用经典Flugge微分算子描述壳体的运动,敷设粘弹性阻尼材料的双层壳体的粘弹性阻尼层的运动用三维Navier方程描述,将阻尼沿厚度方向的位移用泰勒展开表示,利用位移和应力的连续性边界条件建立振动方程。详细讨论了阻尼层厚度、弹性模量、损耗因子及静水压缩因子等参数对双层壳体振动和声辐射的影响,表明阻尼材料的弹性模量越高,阻尼层越薄,损耗因子越小,壳体的辐射声功率越高;对于较高频率的激励,必需考虑阻尼层质量的影响,选择密度低的阻尼材料对减振降噪有利。     

应用于高速转子系统的金属橡胶阻尼环动力特性分析

针对金属橡胶构件的非线性特性及结构不同时弹性阻尼力学性能不同的特点, 利用实验和理论相结合的方法建立了金属橡胶构件迟滞回线边界变形过程力学模型, 推导了不同相对密度金属橡胶构件非线性迟滞恢复力表达式. 分析了简谐激励载荷作用下金属橡胶阻尼环动力学特性, 对该阻尼环进行了实验研究, 研究了存在预变形情况下阻尼环的弹性阻尼性能, 实验和理论分析结果基本一致, 为该种阻尼环的实际应用奠定了理论基础. 关键词： 金属橡胶构件 力学模型 非线性迟滞恢复力     

黏弹性吸声材料复弹性模量优化研究

针对黏弹性材料吸声效率问题,利用分层介质声传播理论和数值算法优化了不同物理条件下材料的复弹性模量。采用参数等效的方法分析了含气泡黏弹性材料的声学特性,并给出了此种材料优化后的弹性模量曲线。根据物理模型计算了一定边界条件下材料复弹性模量等吸声系数曲线,得到了几种背衬条件下黏弹性材料吸声系数大于0.8的弹性模量和损耗因子范围。研究表明调节黏弹性材料的复弹性模量可以有效提高材料的吸声性能,吸声系数大于0.8时其弹性模量和损耗因子范围在不同背衬条件下差异较大,发现一定厚度的钢背衬会降低调控复弹性模量的难度,对含气泡黏弹性材料的计算也可得到类似结果。      

铁电马氏体中的电致形状记忆效应

与温度驱动形状记忆的缓慢响应及磁场驱动形状记忆的巨大体积相比较,电场驱动形状记忆具有响应快和体积小的优点.但是,基于传统反压电效应的电场驱动形状记忆由于变形量较小而收到限制.本研究表明,通过运用基于点缺陷短程序对称性遵循的普适性原理的可逆畴翻转机制,可以在铁电马氏体中获得巨大的电致形状记忆效应;其产生的变形量理论上是反压电效应所产生变形量的几十倍.采用原位畴观察实验给出了可逆畴翻转的直接证据.并且,在铁电多晶陶瓷中也获得了这种大的电致形状记忆效应.这种效应在很宽的频率范围内都很稳定,在疲劳测试中也显示了很好的可靠性.运用这一新的电致形状效应有望制备出新一代非线性驱动器材料.     

应用于精密振荡器的石英晶体温度特性研究

采用一种新型压电材料精确表征方法研究了不同环境温度条件下应用于振荡器的石英材料特性变化.测量了从室温至100℃不同稳定环境温度下AT切向石英晶体材料的电子阻抗共振特性,并采用基于模拟退火优化算法的压电材料精确表征方法对电子阻抗共振特性进行了准确的拟合,计算出了AT切向石英晶体材料在不同温度下包含损耗特性的复数形式材料参数.通过研究和分析温度变化对石英晶体材料参数及其损耗特性的影响,为具有稳定温度特性的精密振荡器设计提供了理论和技术支持.     

以修正WLF方程研究压力作用下丁腈橡胶的阻尼性能

时温等效原理表明固定频率下温度越高,模量越低,而相同温度下频率越低,模量越低,即升高温度与降低频率具有同等效应。根据这一规律,可将聚合物的力学性能随温度的变化转化为这些性能随频率的变化,从而可通过不同温度下的力学性能测试数据,换算成宽频率范围内的材料力学性能表现。为了研究压力作用下橡胶阻尼性能的基本变化规律,通过自由体积理论推导出加压后的修正WLF方程,采用动态热机械分析实验,测试得到丁腈橡胶在不同温度下的损耗因子tanδ对频率ω的曲线,根据计算得到不同压力下的测试温度至室温的平移因子,便可做出加压后的丁腈橡胶的损耗因子-频率谱的主拟合曲线,其曲线的频率跨度达10个数量级以上。结果表明,丁腈橡胶的tanδ测试段在高于参考温度以后出现,而随着压力的增加,玻璃化温度相应升高,峰值往高频移动达1.5个数量级。此结果为研究压力作用下橡胶材料阻尼性能的定量变化提供了理论依据。     

掩埋隧道结垂直面激光器速率方程参量提取

为了设计和优化高速激光二极管的高频特性,其速率方程模型参量的精确提取方法非常重要.本文针对新型长波长高带宽的掩埋隧道结垂直面激光器,给出一种速率方程模型参量提取方法.此方法是主要基于阈值电流、输出光功率、张弛振荡频率、阻尼因子和高偏置下增益压缩因子非线性效应等因素,根据已测量的不同偏置下芯片的小信号频率响应来拟合出方程中的张弛振荡频率和阻尼因子.通过考虑增益压缩因子,分别非线性拟合已提取的偏置光功率下的张弛振荡频率和阻尼因子,即可提取速率方程模型中的参量.     

均匀增黏剂在丁基橡胶阻尼复合材料中的应用

丁基橡胶阻尼复合材料是以丁基橡胶为基体材料，加入树脂硫化剂进行混炼、出片、模压硫化成型，制备出的适合不同频率不同使用温度范围要求的高性能橡胶阻尼功能复合材料。工艺中发现在混炼过程中混合体系分散不均匀，分析认为这是由于基体胶料自身的互黏性和自黏性差的特性所决定的，需要进一步改善工艺条件。向体系中加入少量的均匀增黏剂，可增加基体胶料的自黏性和互黏性；从改善胶料分子链间的作用机理出发来优化混炼工艺，也可以促进第二组分树脂硫化剂的分散性和混容效果，进而达到提高和优化产品的表观质量。     

Frequency power law of material damping

The experimental studies often show that the damping in various solid materials increases with frequency over a finite bandwidth, and the increase is weak if the damping is low. A frequency power law is suggested and discussed in this paper to describe this damping behaviour with special respect to the low loss resilient materials used for sound and vibration control. The dynamic modulus as a function of frequency is determined from the loss modulus through the Kramers-Kronig dispersion relations to satisfy the causality requirement. It is proved that the dynamic modulus obeys the frequency power law of the same type as the loss modulus. In addition, it is proved that the weak frequency dependences of damping properties are inevitably associated with the low loss factor. Examples of fitting the frequency power law to experimental data on some materials of acoustical purposes are presented.     

Alternate stresses and temperature variation as factors of influence of ultrasonic vibration on mechanical and functional properties of shape memory alloys

It is known that the main factors in a variation in the shape memory alloy properties under insonation are heating of the material and alternate stresses action. In the present work the experimental study of the mechanical behaviour and functional properties of shape memory alloy under the action of alternate stresses and varying temperature was carried out. The data obtained had demonstrated that an increase in temperature of the sample resulted in a decrease or increase in deformation stress depending on the structural state of the TiNi sample. It was shown that in the case of the alloy in the martensitic state, a decrease in stress was observed, and on the other hand, in the austenitic state an increase in stress took place. It was found that action of alternate stresses led to appearance of strain jumps on the strain–temperature curves during cooling and heating the sample through the temperature range of martensitic transformation under the constant stress. The value of the strain jumps depended on the amplitude of alternate stresses and the completeness of martensitic transformation. It was shown that the heat action of ultrasonic vibration to the mechanical behaviour of shape memory alloys was due to the non-monotonic dependence of yield stress on the temperature. The force action of ultrasonic vibration to the functional properties was caused by formation of additional oriented martensite.     

Elastic characterization of closed cell foams from impedance tube absorption tests

A method is presented to determine the bulk elastic properties of isotropic elastic closed-cell foams from impedance tube sound absorption tests. For such foams, a resonant sound absorption is generally observed, where acoustic energy is transformed into mechanical vibration, which in turn is dissipated into heat due to structural damping. This article shows how the bulk Young's modulus, Poisson's ratio, and damping loss factor can be deduced from the resonant absorption. Also, an optimal damping loss factor yielding 100% of absorption at the first resonance is defined from the developed theory. The method is introduced for a sliding edge condition which is an ideal condition. Then, the method is extended to a bonded edge condition which is more easily achievable and additionally enables the identification of the Poisson's ratio. The method is experimentally tested on expanding closed-cell foams to find their elastic properties in both cases. Using the found properties, sound absorption predictions using an equivalent solid model with and without surface absorption are compared to measurements. Good correlations are obtained when considering surface absorption.     

Passive-active vibration isolation systems to produce zero or infinite dynamic modulus: theoretical and conceptual design strategies

The application of mechanical springs connected in parallel and/or in series with active springs can produce dynamical systems characterised by infinite or zero value stiffness. This mathematical model is extended to more general cases by examining the dynamic modulus associated with damping, stiffness and mass effects. This produces a theoretical basis on which to design an isolation system with infinite or zero dynamic modulus, such that stiffness and damping may have infinite or zero values. Several theoretical designs using a mixture of passive and active systems connected in parallel and/or in series are proposed to overcome limitations of feedback gain experienced in practice to achieve an infinite or zero dynamic modulus. It is shown that such systems can be developed to reduce the weight supported by active actuators as demonstrated, for example, by examining suspension systems of very low natural frequency or with a very large supporting stiffness or with a viscous damper or a self-excited vibration oscillator. A more general system is created by combining these individual systems allowing adjustment of the supporting stiffness and damping using both displacement and velocity feedback controls. Frequency response curves show the effects of active feedback control on the dynamical behaviour of these systems. The theoretical design strategies presented can be applied to design feasible hybrid vibration control systems displaying increased control performance.     

Damping characteristics of a spray-deposited shape memory alloy beam

The damping characteristics of an Ni–Ti shape memory alloy (SMA) beam are theoretically and experimentally studied with interest in identifying an appropriate damping model for the material. The SMA beam is manufactured by a spray deposition method followed by heat treatment and found to have nanocrystalline structure in which damping capacity is high. The beam is then tested to obtain an impulse response and the frequency response function (FRF). By using the Hilbert transform technique it is shown that damping of the beam is almost amplitude independent in the tested range of displacement. It is also shown from the FRF that the damping of the spray-deposited shape memory alloy beam is well represented by a model including both linear viscous and hysteretic dampings.     

Active structural acoustics control of beams using active constrained layer damping through loss factor maximization

Vibration and acoustic control of beams with classical boundary conditions using active constrained layer damping is presented. The control input that maximizes the loss factor of the active constrained layer damping is determined through taking the first variation of the loss factor with respect to the control input. Although the loss factor is a positive definite quantity, the first variation yields control input that maximizes the factor. The resulting control input significantly reduces the vibration and acoustic response of the beams at their resonant frequencies.     

Aero-thermo-mechanical characteristics of imperfect shape memory alloy hybrid composite panels

A nonlinear finite element model is provided to predict the static aero-thermal deflection and the vibration behavior of geometrically imperfect shape memory alloy hybrid composite panels under the combined effect of thermal and aerodynamic loads. The nonlinear governing equations are obtained using Marguerre curved plate theory and the principle of virtual work taking into account the temperature-dependence of material properties. The effect of large deflection is included in the formulation through the von Karman nonlinear strain-displacement relations. The thermal load is assumed to be a steady-state constant-temperature distribution, whereas the aerodynamic pressure is modeled using the quasi-steady first-order piston theory. The Newton-Raphson iteration method is employed to obtain the nonlinear aero-thermal deflections, while an eigenvalue problem is solved at each temperature step and static aerodynamic load to predict the free vibration frequencies about the deflected equilibrium position. Finally, the nonlinear deflection and free vibration characteristics of a composite panel are presented, illustrating the effects of geometric imperfection, temperature rise, aerodynamic pressure, boundary conditions and shape memory alloy fiber embeddings on the panel response.     

一种机载光电设备减振系统设计及稳定精度试验研究

以光电设备减振系统为研究对象,从光电设备轻型化、小型化设计角度出发,针对现有内置橡胶减振系统的诸多不足,采用金属减振器,设计出一款适用于机载光电设备的外置型金属减振系统。通过对该减振系统的振动和冲击试验,测得固有频率、最大传递率及冲击最大位移值。通过对比光电设备在两种减振系统下的稳定精度, 得出以下结论:外置金属减振系统和内置橡胶减振系统均能使光电设备的稳定精度满足不大于25μrad的使用要求,但外置金属减振系统能提高光电设备内部有效空间,同时,外置金属减振系统作为整体可更换单元,降低了减振系统的维修难度,提高了光电设备整体维修性,为其他光电传感器的集成和实现机载光电设备轻型化、小型化提供了可能。