复合材料夹杂双层粘弹性材料的应变能和阻尼性能分析

分析了复合材料夹杂双层粘弹性阻尼材料组成的对称夹层板的线性弯曲,其中夹杂的粘弹性阻尼材料作为各向同性材料处理。既考虑面内应变能又考虑横向切应力应变能,用Ritz法研究各应力分量的应变能。以四边夹紧为边界条件的方板为例,计算并分析了复合材料层和粘弹性层的应变能以及复合结构的损耗因子。结果表明:复合材料层中的面内应变能占主要地位;粘弹性层中的xz方向和yz方向的切应力应变能较大;芯层的应变能很小。     

黏弹性复合材料结构的多目标优化设计

黏弹性复合材料具有良好的阻尼性能,但黏弹性层的存在对黏弹性复合材料结构的强度性能会有所影响,黏弹性复合材料结构只有同时兼备良好的阻尼和强度才能满足工程要求。该文在经典层合板及小挠度弯曲理论基础上,运用Ritz法建立黏弹性复合材料结构应变能损耗因子和横向均布荷载作用下初始破坏强度计算模型。提出新的遗传算法适应度函数构造办法,克服了多目标优化问题中优化结果的偏移现象,对黏弹性复合材料结构进行单目标和双目标优化设计。优化结果表明:改进的遗传算法适用于黏弹性复合材料结构阻尼和强度性能的优化设计,而且多目标优化设计可以权衡复合结构的阻尼性能和强度性能,有利于发挥黏弹性复合材料结构良好的整体性能。     

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).     

基于温频效应的约束型垫高阻尼结构抗振性研究

考虑黏弹性阻尼材料的温度依赖性和频率依赖性,基于黏弹性阻尼材料的本构模型,利用ANSYS和MATLAB协同仿真的模态应变能迭代法,对约束型垫高阻尼结构的抗振性进行研究。分别考察温度、厚度对约束型垫高阻尼结构振动特性指标的影响,结果表明:存在最佳温域使约束型垫高阻尼结构的抗振性最好,因此,在减振降噪工程中尽量保证工作温度和最佳温域相匹配;随着垫高层、约束层厚度的递增,存在最佳厚度使结构的模态损耗因子达到峰值,而随着阻尼层厚度的递增,结构模态损耗因子增加的幅值由大变小,因此,后续有必要开展结构的优化设计。     

黏弹阻尼层共固化复合材料不同温度下的阻尼性能

采用共固化工艺制备了以丁腈橡胶为黏弹性阻尼层的复合材料 , 应用动态机械分析仪(DMA)测定了该材料损耗因子的温度谱 , 并对不同温度环境下该材料的阻尼性能和阻尼机制进行了分析。结果表明 : 当温度处于阻尼层玻璃态和高弹态区时 , 共固化复合材料损耗因子较小且随温度变化不大 ; 当温度处于阻尼层黏流态区时 ,共固化复合材料的损耗因子迅速增加到最大值后变小 , 最大损耗因子为 19. 2 % , 约为未插入黏弹阻尼层复合材料的 13倍; 共固化过程中阻尼层损耗因子的减小 , 使共固化复合材料的阻尼性能降低 , 并在阻尼层的黏流态区其损耗因子明显小于预报结果 ; 界面阻尼的影响提高了共固化复合材料的阻尼性能 , 并在阻尼层的玻璃态区其损耗因子大于预报结果。      

具有约束层阻尼旋转复合材料轴的动态特性研究

复合材料驱动轴在高速旋转下的振动抑制,是先进直升机和汽车传动系统结构设计需要考虑的重要问题。约束层阻尼技术是工程领域内普遍采用的实用有效的阻尼减振设计方法;然而通过采用约束层阻尼处置方式增加复合材料传动轴的阻尼能力的研究报道,目前国内外很少见到。从应力-应变关系、应变-位移关系出发,推导出复合材料Timoshenko轴、约束层与黏弹性层的动能及势能的数学表达式,采用Hamilton原理建立具有约束层阻尼的旋转复合材料轴的运动学方程。采用广义Galerkin法对动力学方程进行了离散化,建立了广义坐标表示的自由振动方程组,通过特征值求解得到系统的固有频率和阻尼比;基于比例阻尼假设和四阶Runge-Kutta数值积分方法求解上述方程,得到系统的自由振动响应曲线。通过数值分析揭示了约束层材料、黏弹性层材料、铺层方式、长径比和转速对具有约束层阻尼的旋转复合材料轴的固有振动特性以及自由振动响应特性的影响。     

嵌入式低温共固化高阻尼纤维/树脂基复合材料

通过正交试验新研制出一种可以与玻璃纤维/BA9913环氧树脂预浸料低温共固化的高阻尼黏弹性材料,提出使用四氢呋喃（THF）作为溶剂,将该高阻尼材料制成黏弹性材料溶液。采用双面刷涂工艺,将玻璃纤维/BA9913环氧树脂复合材料制成带阻尼薄膜的预浸料,按照设计的铺层根据热压罐固化工艺制成嵌入式低温共固化高阻尼复合材料试件。模态试验和层间剪切试验验证了本文所提出制作工艺和黏弹性材料组分的有效性,试件一阶模态损耗因子可达7.2%。为嵌入式低温共固化高阻尼复合材料的广泛使用奠定了基础。      

基于有效三维损耗矩阵的复合材料层合板模态阻尼预测

为了在复合材料层合板阻尼分析中既考虑层合板厚度方向应力、应变对结构阻尼的贡献,又不增加厚度方向的单元数量,基于复合材料的有效三维阻尼矩阵预报理论,建立了新的高效复合材料结构模态阻尼的三维有限元预测方法。沿层合板厚度方向将原结构分成若干亚层,每一亚层包含若干单层。根据合成理论计算每一亚层的刚度矩阵、柔度矩阵和有效三维阻尼损耗矩阵。对亚层划分单元,进行结构的有限元模态分析。根据模态分析结果,利用有效三维阻尼矩阵求出各个模态对应的模态阻尼。利用该理论,分别计算了单向层合板、对称层合板以及厚板的结构模态阻尼。数值计算结果表明,该方法具有很好的适用性,其优点在于既考虑了板厚方向的阻尼贡献,又减少了厚度方向的单元数,提高了计算的准确性和效率。      

直接诺模图—描述粘弹性阻尼材料性能的新方法

将粘弹性阻尼材料涂刷、粘贴于薄板或壳体表面上组成复合阻尼结构,来增加机械结构的损耗因子.在设计粘弹性阻尼结构、预估其损耗因子时,材料的损耗因子和弹性模量是两个最主要参数。粘弹性材料是一种高分子材料,其应力、应变通常用复模量的关系来表示,即:     

纤维增强粘弹性复合材料层合板的自由振动和应力分析

基于Reddy分层理论推导出纤维增强粘弹性复合材料层合板的动力学方程,得到了其自由振动频率和损耗因子;分析了自由振动时,纤维体积含量和纤维增强层厚度对自然频率和损耗因子的影响;且计算出了协调的横向应力,数值结果分析表明:结构频率和损耗因子随纤维体积含量的增加而增加;阻尼材料参数对结构损耗因子和横向应力影响较大,且阻尼材料模量存在最佳值;高阶模态下,较高的横向正应力是层合板脱层的主要因素。     

多翼型粘弹性阻尼层叶片的动态特性数值分析

采用有限元软件建立2MW风力机复合材料单翼型和多翼型叶片模型,将粘弹性阻尼层加入多翼型叶片中并进行额定风速载荷作用下的谐响应分析,探索单翼型和多翼型叶片的动态特性区别,并揭示粘弹性阻尼层层数和厚度变化对多翼型叶片动态特性的影响规律。研究结果表明,在高阶频率多翼型叶片的挥舞方向位移和应变能均远小于单翼型叶片的;粘弹性阻尼层对多翼型叶片的低阶频率的挥舞方向位移和应变能有很好的抑制效果。     

复合材料粘弹性本构关系与热应力松弛规律研究Ⅰ:理论分析

基于均匀化理论研究了复合材料粘弹性分析的多尺度方法, 以及复合材料等效热应力松弛规律。引入了等效粘弹性热应力系数张量和等效时变热膨胀系数的概念, 建立了含温度变化的复合材料热粘弹性本构关系, 并给出了基于均匀化理论的复合材料粘弹性松弛模量、等效热应力松弛系数和等效时变热膨胀系数的预测方法。对特殊复合材料的粘弹性性质进行了分析, 结果表明: (1) 复合材料的粘弹性本构关系具有与常规材料的本构关系类似的形式, 但一般复合材料的热应力松弛规律与常规材料不同, 其热膨胀不能瞬时完成, 而具有明显的时变性质;(2) 空心材料的热膨胀具有瞬时性质, 其等效时变热膨胀系数与基体材料的热膨胀系数相同, 其热应力松弛规律与基体材料的松弛规律相同;(3) 当各组分材料的松弛模量的各分量可分解成不同的系数与相同的时间函数的乘积时, 复合材料的等效时变热膨胀系数与时间无关, 其松弛规律与常规材料的松弛规律完全相同。     

聚合物梯度材料黏弹性断裂的双控制参数

针对组分材料体积分数任意分布的聚合物功能梯度材料,研究其在蠕变加载条件下Ⅰ型裂纹应力强度因子（SIFs）和应变能释放率的时间相依特征。由Mori-Tanaka方法预测等效松弛模量,在Laplace变换域中采用梯度有限元法和虚拟裂纹闭合方法计算断裂参数,由数值逆变换得到物理空间的对应量。分析边裂纹平行于梯度方向的聚合物功能梯度板条,分别考虑均匀拉伸和三点弯曲蠕变加载。结果表明,聚合物梯度材料应变能释放率随时间增加,其增大的程度与黏弹性组分材料体积分数正相关;材料的非均匀黏弹性性质产生应力重新分布,导致裂纹尖端应力场强度随时间变化,当裂纹位于黏弹性材料含量较低的一边时,应力强度因子随时间增加,反之,随时间减小。而且,材料的应力强度因子与时间相依的变化范围和体积分数分布以及加载方式有关,当体积分数接近线性分布时,变化最明显,三点弯曲比均匀拉伸的变化大。SIFs随时间的延长增加或减小、加剧或减轻裂纹尖端部位的“衰坏”,表明黏弹性功能梯度裂纹体的延迟失稳需要联合采用应力强度因子与应变能释放率作为双控制参数。     

The use of stress sweep tests for asphalt mixtures nonlinear viscoelastic and fatigue damage responses identification

Asphaltic materials are known to present a behavior that can be approximated by the theory of viscoelasticity. For these materials it is essential to characterize fatigue damage. An important aspect therein is the separation between nonlinear viscoelastic and fatigue damage responses. This is a complex issue, since both nonlinearity and damage have a similar effect on the overall material mechanical behavior, i.e. decrease in the stiffness and increase in the phase angle. This paper presents an experimental and a mathematical procedure to separate the nonlinear viscoelastic from the fatigue damage response for asphaltic materials. Stress sweep tests were used to characterize a hot mixture asphalt at nine conditions (three temperatures and three frequencies). Once all strain values were obtained in a stress controlled sweep test, a statistical analysis was used to find the maximum stress that can be applied to the material without invoking the damage response. The results showed that the transition stress value is directly associated with material properties, the stiffness being an important factor in this result. Consequently, stress, temperature and frequency determine together the mechanical response of the material (linear or nonlinear viscoelastic, fatigue damage and/or plastic deformation). Results from this study can be associated with other fatigue damage approaches in order to better select the stress or strain amplitude that should be used in fatigue tests, and to eliminate the amount of energy that is dissipated in the nonlinear viscoelastic region.     

Experimental and theoretical investigation on mechanical behaviors of TB991 weld sealant under cyclic loading

The mechanical behaviors of TB991 weld sealant under cyclic loading conditions were experimentally investigated. The evolution of relaxation stress, cyclic softening, and dissipated energy was evaluated with the effect of strain amplitude and mean strain. The experimental results showed that the stress–strain response curves of the first loading-unloading and cyclic loading-unloading were significantly different. The phenomenon of stress relaxation and cyclic softening occurred under cyclic strain loading conditions. Furthermore, the relaxation stress and dissipated energy decreased rapidly during the initial cyclic loading and then steadily decreased with the increase of cycle number, while the cyclic softening increased rapidly at first and then steadily. Besides, a viscoelastic constitutive model was proposed which can describe the different shapes of stress–strain curve between the initial loading-unloading and the cyclic loading-unloading and also considers the cyclic stress relaxation and cyclic softening of the materials under cyclic loading condition. Comparisons between the numerical results and the experimental data demonstrated that the proposed model can better describe the mechanical behavior of TB991 weld sealant under cyclic loading conditions.     

Evaluation of crack tip stress and strain fields under nonproportional loading in a viscoelastic material

The crack tip strain and stress fields in a viscoelastic material under nonproportional loading conditions are evaluated. In order to evaluate the strain field, the crack tip displacement field is measured by using the digital image correlation (DIC) technique. This displacement field is then approximated by using the theoretically obtained crack tip displacement field in viscoelastic materials. The result shows that the approximation method can smoothly reconstruct the experimentally obtained displacement field. From the approximated displacement field, the crack tip strain field can be precisely obtained by using the differential form of the theoretical displacement. On the other hand, the crack tip stress field is analyzed by using the stress function. This suggests that the strain and stress fields can be independently evaluated. In addition, different time dependencies between stress and strain fields near the crack tip are observed. Based on this experiment, we can discuss the several criteria for the crack propagation directions in viscoelastic materials.     

粘弹性耗能器的性能试验研究

本文根据土木工程的特点和要求,选用三种国产粘弹性材料制作相应的耗能器,分别进行了变频、变温、变应变、常温与低温疲劳及极限变形等大量试验,研究了这些材料的主要性能指标—剪切模量、耗能因子的变化规律,分析了频率、温度、应变和疲劳效应等因素对粘弹性材料性能参数的影响。在此基础上,提出了粘弹性耗能器设计和制作的一些要求以及国产粘弹性材料用于土木结构减振时进一步改性的目标     

计算粘弹结构动力学参数的新模态应变能方法

粘弹结构在噪声与振动控制领域已得到广泛应用,然而准确地计算粘弹结构的动力学参数一直存在困难,模态应变能法及其修正方法常用作近似计算。在分析模态应变能方法和已有修正方法的原理及其相互关系的基础上,提出一种基于损耗因子幅值的新模态应变能方法,用于计算粘弹结构的损耗因子与固有频率。新方法的修正因子随粘弹结构对应模态阶次损耗因子幅值变化。取可等价为粘弹性夹层梁/板的四参数原型系统和新型高阻尼航天载荷隔振器为算例,通过与已有方法的对比分析了新方法的准确性。     

The effects of plastic deformation on stress wave propagation in multi-layer materials

The behavior of a multi-layer material at high strain rate and the effect of plastic deformation on stress wave propagation were investigated by a combination of experimental and numerical techniques. Plastic deformation effects were studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. First, stress wave propagation behavior for the monolithic metals was studied, and then extended to multilayer combinations of these metals with each other and with a ceramic layer. The axial stress distributions were found to be non-uniform in the elastic deformation range of the specimen. The degree of non-uniformity was much more pronounced in the multi-layer samples consisting of different materials. The presence of a ceramic layer increased the magnitudes of stress gradients at the interfaces. It was also found that a major effect of plastic deformation is a tendency to produce a more homogeneous stress distribution within the components. The implications of these observations for practical systems are discussed.