粘接层对各向异性层合阻尼结构内耗特性的影响

借助动态机械分析仪(DMA Q800) 考察了两种粘接层材料和两个位置的不同粘接层厚度对7 层各向异性交替层合阻尼结构内耗特性的影响。结果表明, 在低于阻尼层材料玻璃化转变温度附近, 用压敏胶做粘接层材料, 其结构内耗的温度特性优于用环氧树脂; 在不同位置不同厚度对结构内耗的温频特性的影响不同, 结构内耗的频率特性与粘接层材料及其厚度密切相关, 刮涂越薄, 结构内耗的温度特性越好。      

不同边界条件下泡沫铝硅合金的内耗特征

为了获得不同边界条件下泡沫金属的内耗特征,通过采用动态机械分析仪在不同弯曲模式下对泡沫铝硅合金的内耗进行实验研究.结果表明:泡沫铝硅合金在不同边界条件下的内耗峰出现情况不同,且温度对三点弯曲模式时内耗的频率特性影响最大;三种边界条件下泡沫铝硅合金的内耗的振幅效应基本相似;温度对该材料在三点弯曲模式比单双悬臂梁振动模式下内耗的影响更大.     

含宏观孔开孔泡沫铝的阻尼机制研究

采用空气加压渗流技术制备了含宏观孔的开孔泡沫铝材料,通过多功能内耗仪采用内耗技术测试了泡沫铝在不同温度、不同频率和不同振幅下的内耗谱特征,研究表明与致密工业纯铝的阻尼能力相比,泡沫铝的阻尼能力得到很大的提高,泡沫铝的内耗随着测量频率的增加而增大,同时,内耗也随着应变振幅的增加而增大。经透射电子显微镜观察发现在晶界附近存在大量的位错亚结构。根据内耗测量和微观观察提出了泡沫铝中可能的阻尼机制:孔周围的应力集中和模式转换,孔洞/金属基体界面处由于动力学模量相差很大而使机械能转化为热能,孔洞发生不均匀的膨胀或畸变使外加应变能耗散为热能。     

复相型Zn—Al基减震合金阻尼特性的研究

采用声频法和低频扭摆法及粘弹仪对复相型Zn-Al减震合金的内耗温度谱(Q~(-1)-T)、内耗频率谱(Q~(-1)-f)和内耗应力应变振幅谱(Q~(-1)-Am)的依存性特征进行了研究.表明Zn-Al减震合金的内耗(阻尼性能)与温度和频率具有显著的依存性。内耗随温度的上升呈单调增大,随频率的下降而提高。Zn-Al基减震合金的阻尼性能几乎无应变振幅效应,在低应力应变振幅条件下就具备高阻尼特性。文中将Zn-Al减震合金的上述性能与普通铸铝ZL104和铸铁HT200进行了对比.     

连续纤维增韧碳化硅基复合材料内耗特征及机制

采用强迫振动法研究了不同应变振幅下C/SiC和SiC/SiC复合材料从室温到600℃的内耗特征,并讨论了其内耗产生机制.结果表明,C/SiC复合材料内耗随温度升高先减小, 后增加,并在120℃附近达到最小值;SiC/SiC复合材料内耗随温度升高一直增加;C/SiC 复合材料具有比SiC/SiC复合材料更高的内耗水平和更低的动态模量;C/SiC和SiC/SiC复合材料内耗随应变振幅增加而减小,但动态模量和应变振幅无关.     

扭摆法和振簧法测量内耗振幅效应的修正公式

传统的内耗测量规范多采用扭摆法和振簧法,并没有涉及内耗随应变振幅变化的情况。为更加准确测量材料在不同应变振幅下的内耗和模量值,该文根据不同内耗测量方法中试样的应力分布情况,从内耗基本定义出发,考虑内耗随应变振幅变化的情况,重新推演扭摆法和振簧法测量内耗和模量的基本方程,获得采用扭摆法和振簧法测量内耗(模量)-振幅曲线的修正公式,为准确测量大应变振幅激发情形下高阻尼材料的内耗和模量提供参考。     

纤维增强复合材料动力学固有特性及阻尼特性分析

基于模态应变能原理,推导了复合材料层合梁阻尼计算式,进行复合材料模态应变能Abaqus有限元验证;采用手糊和真空工艺制作了3种不同复合材料层合梁试件,并开展了动力学试验,得到了复合材料层合梁固有频率和面内各向异性阻尼系数;分析了不同角度铺层对层合梁固有频率和结构阻尼比的影响规律.结果表明:复合材料面内损耗系数以剪切损耗最大;手糊制作的层合试件材料主方向损耗因子均较真空制作的要大;两种常用的正交布材料主方向损耗因子存在下列关系:高强正交布(手糊)＞无碱正交布(手糊)＞高强正交布(真空)＞无碱正交布(真空).     

交替层合阻尼结构主控各向异性层参数对结构阻尼的影响

借助动态热机械分析仪(DMA Q800) 对交替层合各向异性阻尼结构阻尼性能的影响权重最大层的各参数进行优化实验研究。探讨了该主控约束层的不同铺设角度、不同厚度和不同多子层替代对层合阻尼结构刚度、阻尼的温频特性的影响规律。实验结果表明, 结构阻尼性能的影响权重最大层纤维铺设角度越接近90°(包括两个90°约束层层合) 时, 结构阻尼性能越好; 结构不同, 影响权重最大层较优厚度有所差异, 当阻尼层总厚度与结构阻尼性能影响最大层厚度比约为10 时, 结构阻尼性能较好。      

Fe-Cr、Fe-Cr-Al铁磁性合金的阻尼特性研究

本文研究了热处理工艺、合金成份、磁场、温度及不同应力振幅等对Fe-Cr、Fe-Cr-Al铁磁性合金阻尼(内耗)特性的影响。内耗和阻尼特性是用弯曲共振法(共振频率1500～1700Hz)和大应力扭摆仪(倒摆,振动频率20Hz左右)测得的。研究结果表明: 1. Fe-Cr、Fe-Cr-Al合金在磁场40～50Oe区间出现内耗峰。内耗峰的位置及峰值同合金成分及退火温度有关。磁场超过40～50Oe,合金的内耗明显下降,直至最低值,此时合金已磁化饱和,即其磁机械滞后效应完全消失。 2. 温升从20～350℃时,合金由于磁机械滞后效应引起的内耗略有下降趋势,高于350℃时,合金的内耗开始明显下降,并急剧降到最低值。 3. 阻尼比(内耗)随应力振幅(τ_(max))增加而明显增高,并达到最大值;应力振幅继续增加,合金阻尼比开始下降或在一定应力范围内维持不变,随后又缓慢降低。合金的成份和热处理工艺对内耗-应力(Q~(-1)～τ_(max))曲线特性影响尤为明显。 4. Fe-Cr-Al合金内耗-应力曲线出现的峰值随外磁场增加而下降,当合金磁化饱和时,内耗-应力曲线的内耗峰完全消失,即合金由于磁机械滞后效应所引起内耗已不存在,此时合金的阻尼性能最低。     

泡沫金属——高分子聚合物的复合体机械阻尼性能研究

本文研究了泡沫金属和同分子聚合物形成的复合体机械阻尼性能，结果表明它是一种内耗值Ｑ＾－１极高的阻尼材料，其阻尼特征表现为与应变振幅密切相关而与频率无显著关系的非线性内耗。同时研究了泡沫金属孔隙结构对复合体内耗值的影响关系，并对实验结果进行了讨论。     

A three-dimensional shape memory alloy/elastomer actuator

This paper presents a mathematical model for analysis of a thermally-driven shape memory alloy (SMA)/elastomer actuator under arbitrary loading and boundary conditions. The actuator is a three-dimensional laminated composite box beam that consists of SMA and elastomer layers with a uniform rectangular cross section. The thermomechanical behavior of SMA layers is modeled utilizing Tanaka and Nagaki's constitutive equation and linear phase transformation kinetics. The behavior of the elastomer layers is assumed to be thermoelastic, in which the elastic modulus is considered to be temperature dependent. The classical laminated beam theory is employed to obtain the force-deformation relationships. The analysis provides explicit solutions to the structural response of the actuator, including strain and curvature of actuator's midplane. A numerical example for a cantilever box beam with uniform square cross-section subjected to a transverse concentrated load is presented. Results demonstrate that significant changes occur in the actuator's responses during phase transformation due to the strain recovery.     

Vibration characteristics of laminated composite plates with embedded shape memory alloys

Shape memory alloy (SMA) is commercially available for a variety of actuator and damping materials. Recently, SMA wires have also become commercially available for the design of smart composite structures because SMA wires with a small diameter can be easily produced. In this work, two types of SMA-based composites are presented for investigating the vibration characteristics. First, laminated composite plates containing unidirectional fine SMA wires are fabricated. By measuring the vibration mode of a clamped cantilever, the influence of both SMA arrangement and temperature on the vibration characteristics is made clear. Next, laminated composite plates with embedded woven SMA layer are fabricated. The stiffness tuning capability is evaluated by impact vibration tests with different temperatures. It is found that the stiffness tuning capability may be improved by increasing the volume fraction of SMAs and by controlling accurately the internal stress according to the phase transformation temperature of SMAs from martensite to austenite. The theoretical prediction on the natural frequency considering the SMAs behavior and laminated structures is proposed and their results agree reasonably with experimental ones.     

Similitude study for a laminated cylindrical tube under tensile, torsion, bending, internal and external pressure. Part I: governing equations

A general analytical model is developed for the stresses and displacements of an assembly of several coaxial laminated hollow circular cylinders made of orthotropic layers, and subjected to internal and external pressure, tensile, torsion and bending loads. Slip and friction conditions at the interfaces are not considered in lieu of perfect bonding. The model results are compared to the experimental tensile test of a composite tube. Displacements and stresses are evaluated for different angle-ply layers and radius-tothickness ratios.     

Dynamic analysis and damping of composite structures embedded with viscoelastic layers

In recent years, it has been found that composites co-cured with viscoelastic materials can enhance the damping capacity of a composite structural system with little reduction in stiffness and strength. Because of the anisotropy of the constraining layers, the damping mechanism of co-cured composites is quite different from that of conventional structures with metal constraining layers. This paper presents an analysis of the dynamic properties of multiple damping layer, laminated composite beams with anisotropic stiffness layers, by means of the finite element-based modal strain energy method. ANSYS 4.4A finite element software has been used for this study. The variation of resonance frequencies and modal loss factors of various beam samples with temperature is studied. Some of these results are compared with the closed-form theoretical results of an earlier published work. For obtaining optimium dynamic properties, the effects of different parameters, such as layer orientation angle and compliant layering, are studied. Also, the effect of using a combination of different damping materials in the system for obtaining stable damping properties over a wide temperature range is studied.     

泡沫铝室温声频内耗特征

采用声频内耗仪测定了泡沫铝在室温下不同振幅、频率的内耗，研究了泡沫铝的室温声频内耗特征，并讨论了泡沫铝内耗产生的机理。     

The change of grain boundary internal friction peak during high temperature deformation at different modes

The change of grain boundary internal friction peak during high temperature deformation at different modes (i.e., static tensile creep, cyclic tensile creep, and cyclic reverse torsion) in high purity aluminum was studied in conjunction with microstructure examinations. It was observed that the internal friction peak decreased with increasing plastic strain for all the modes, indicating that grain boundary sliding was degraded by the deformation. Nevertheless, at the same strain the decrement of internal friction was different for different modes, in particular smallest for reverse torsion. The origin of the decrease of internal friction and the difference among different modes is interpreted in the light of microstructure observations.     

Damping behavior of Al/SiCP multilayer composite manufactured by roll bonding

High damping materials comprising good mechanical properties as structural materials and high damping capacity for vibration loading are the best solutions for vibration problem. In current study, functionally graded material from composite sheets with different percentages of reinforcement was manufactured by hot rolling process. The damping behavior of base alloy composite including different percentages of SiC particles and Al/SiC_P multilayer composite sheets was studied at room temperature conditions. The Al/SiC_P composites were found to exhibit higher damping capacity compared to Al alloy. The damping capacity increased by increase in the percentage of reinforcement. Furthermore, Al/SiC_P multilayer composite sheet provided higher damping capacity in comparison to Al alloy. Therefore, damping capacity enhanced by increasing the number of layers. The main source for damping behavior in composite materials is dislocation damping whereas in stepwise multilayer composite sheets, it comes from boundary conditions between layers.     

功能梯度形状记忆合金复合梁的力学行为

功能梯度形状记忆合金（Functionally graded shape memory alloy,FGSMA）兼具功能梯度材料和形状记忆合金材料的双重特性,广泛应用于微机电、航空航天等工程领域。为研究FGSMA复合梁的弯曲行为,本文对形状记忆合金（SMA）力学本构方程进行简化处理,并根据复合材料层合板理论建立了FGSMA复合梁的力学模型,据此研究了SMA体积分数沿厚度方向呈线性变化的FGSMA悬臂梁内SMA纤维铺设角度对悬臂梁横截面应变、中面轴向位移、中性面高度和相变层高度的影响以及悬臂梁中面应变、曲率、SMA马氏体相变临界层高度和中性面高度随弯矩载荷的变化规律。研究结果表明:在弯矩载荷作用下,悬臂梁中性面位置与中面位置不重合,且悬臂梁上下层SMA马氏体相变临界层位置不对称;截面轴向应变绝对值随铺设角度增大而增大,截面纵向应变绝对值随铺设角度增大先增大后减小,中面轴向位移随铺设角度增大先增大后减小;随着铺设角度增大,悬臂梁中性面高度逐渐增大,拉伸状态下相变结束临界层高度先减小后增大,压缩状态的趋势相反;随着弯矩载荷绝对值逐渐增大,中性面位置高度表现出先稳定后减小然后逐渐增大的趋势,相变临界层逐渐向中性面位置靠拢;中面正应变和挠曲率随着弯矩载荷绝对值逐渐增大而发生变化,且变化率先增大后减缓。