层状柱壳磁电复合材料的非线性磁电效应研究

本文基于超磁致伸缩材料非线性本构,从基本的控制方程出发,对层状柱壳磁电复合材料的非线性磁电响应进行理论研究,讨论了不同边界下磁场频率以及压电材料厚度比对磁电系数的影响,并得到了不同预压力下磁场大小对于磁电系数的影响。数值计算结果显示,对于Tefernol-D/PZT-5层状磁电复合材料,随着预压力值增大,磁电系数最大值减小,取得最大值时对应的磁场值逐渐增大;不同边界条件、磁场频率和磁场大小下,材料厚度比对磁电系数的也有着不同的影响。特别地当外加磁场频率较大时,相应于压电层厚度比,磁电系数呈现多极值现象。     

短纤维复合材料的压缩强度

细观力学理论得到的复合材料内应力是均值应力,在进行破坏和强度预报前,必须转化到真实值.对于短纤维复合材料,除了轴向压缩真实应力外,基体其它方向真实应力计算已得到解决,等于其均值应力乘以基体应力集中系数.论文基于弹性力学方法得到了短纤维复合材料轴向压缩下基体的应力场,并据此定义基体的轴向压缩应力集中系数.与基体其它方向应...     

超声表面波检测金属材料表面应力的实验研究

本文应用声弹性理论研究了表面波在金属材料表面的传播速度和表面应力之间的关系,优化了表面波声弹性公式,建立了应力和表面波相对传播时间差的关系。通过构造实用的微型表面波探头,采用数字相关法计算了不同应力下的表面被传播时间差,确定了A3钢的表面波传播时间差与应力的关系式。同时分析了试件表面粗糙度和平整度对表面波速度变化的影响,最后给出了金属材料在不同表面条件下的实验分析结果。     

复杂板壳结构声振耦合特性的理论与实验研究

0引言 在国家民用工业及国防工业减振降噪重大应用需求的牵引下,本文通过理论建模、实验验证和数值计算研究了汽车、高速列车、舰艇/潜艇及航空航天飞行器中常用典型复杂板壳结构的声振耦合特性[1-13],建立了相对完善可靠的结构声振耦合特性理论表征体系,分析了关键结构参数对结构声振耦合特性的影响,揭示了弯曲波在结构中的传播规律及结构的声辐射/传声特性,提山了轻质、高强度、声辐射小及隔声性能优良的复杂板壳结构的创新优化设计概念,初步建立了综合结构质量、力学刚度和声振耦合特性的优化设计理论和判据,为典型板壳/板腔结构在民用工业及国防工业中的应用奠定了理论基础、实验依据并提供了技术支撑.     

一个新的声应力系数及其确定

为建立声焦散线与平面应力条件下裂尖应力强度因子的关系,定义了一个新的声应力系数——声程差随应力线性变化的比例系数,该系数的大小既取决于材料常数又取决于耦合介质及声束的传播历程.借助6061-T6铝、EPTI钢两种材料的实验结果,说明了确定新的声应力系数的方法与步骤.所得结论是:只要确定了平面应力条件下超声纵波速度相对变化与主应力和之比,便可确定新的声应力系数.     

层状地基参数的频域识别

在分析水平层状地基运动特征的基础上, 通过研究地层系统的特征值和特征向量与地层参数之间的关系, 修正测量得到的数据与理论计算结果之间的偏差, 建立了层状地基参数的频域识别方法。并利用大型振动台上的地基模型试验数据, 实施了层状地基的参数识别过程。结果表明, 该方法产生良好的地基参数估计。     

瞬态波在层合板中传播的粘弹比拟法

本文发展了粘弹比拟理论,并将之用于求解半无限空间三层复合材料在垂直层合方向传播的瞬态波问题。对于层合板中应力波的传播问题,寻找到了一等效粘弹体,并用一种较好的Laplace变换的数值反演法求得了等效松弛函数和其它一些必要的辅助函数。用特征线法求得了等效粘弹体的应力和速度,进而得到了三层复合材料中心的应力、速度,进一步就得到了层中任意点的应力和速度。对于一个可由精确理论(射线理论)给出计算结果的问题,将粘弹比拟理论的结果和射线理论的结果进行了比较,结果表明,粘弹比拟理论对三层复合材料的瞬态波传播问题是相当成功的。     

不同参数波浪型辐板列车车轮的振动声辐射特性研究

为了分析不同参数对波浪型辐板车轮声辐射特性的影响,根据列车波浪型辐板的建模方法,建立了不同波浪个数、不同波浪幅度的波浪型辐板车轮。首先,利用分块Lanzos法计算出不同波浪个数、不同波浪幅度的波浪型辐板车轮的固有模态;然后运用模态叠加法计算出简谐力作用下车轮的动态响应,并进行了对比分析;最后利用有限元-边界元方法,将车轮外表面的位移响应处理成声学边界元输入,得到不同波浪个数、不同波浪幅度车轮的声辐射功率大小。计算结果表明:波浪型辐板车轮在2波浪和6波浪时具有较低的声辐射功率;6波浪辐板车轮在波浪幅度约为30mm时,具有较低的声辐射功率。此结果为国内波浪型辐板车轮的研究提供了一定的参考。     

一个新的声应力系数及其确定

 为建立声焦散线与平面应力条件下裂尖应力强度因子的关系，定义了一个新的声应力系 数------声程差随应力线性变化的比例系数, 该系数的大小既取决于材料常数又取决于 耦合介质及声束的传播历程. 借助6061-T6铝、EPTI钢两种材料的实验结果，说明了确 定新的声应力系数的方法与步骤. 所得结论是：只要确定了平面应力条件下超声纵波 速度相对变化与主应力和之比，便可确定新的声应力系数.     

三相多重铁性复合材料的有效磁电弹性模量预测

采用平均场Mori-Tanaka模型,计算了三相复合材料的有效磁电弹性模量,研究了复合材料磁电系数与微观结构之间关系;结果表明掺杂相的体积分数与颗粒形状系数对复合材料的有效磁电系数有很大的影响,这些结果可为复合材料的实验设计提供理论参考和指导.     

Ultrasonic waves in layered anisotropic media: characterization of multidirectional composites

An efficient and stable recursive compliance/stiffness matrix algorithm is presented to model wave propagation in multidirectional composites. The models are applied to clarify angle beam transmission through a multidirectional composite and to process ultrasonic data for determination of the elastic properties of a composite lamina (single ply) from measurements on a multidirectional composite. Ultrasonic characterization of composites using double-through-transmission and time-resolved line focus acoustic microscopy has been addressed. The double-through-transmission measurements and simulations show that the transmission amplitude is highly dependent on ply orientation and angle of incidence. The transmission amplitude decreases rapidly with incident angle deviation from the normal; however, a transmission window is found in the incident angle range 45–60° at frequencies below 2.25 MHz. The time-delay measurements by the double-through-transmission technique have been used to reconstruct lamina properties using the Floquet wave concept. A unidirectional lamina elastic properties measurement using line focus acoustic microscopy of a multidirectional composite sample is also briefly discussed. The effective elastic properties for the composites are determined from the lamina properties by a Floquet wave dynamic homogenization method.     

Ultrasonic waves in layered anisotropic media: characterization of multidirectional composites

An efficient and stable recursive compliance/stiffness matrix algorithm is presented to model wave propagation in multidirectional composites. The models are applied to clarify angle beam transmission through a multidirectional composite and to process ultrasonic data for determination of the elastic properties of a composite lamina (single ply) from measurements on a multidirectional composite. Ultrasonic characterization of composites using double-through-transmission and time-resolved line focus acoustic microscopy has been addressed. The double-through-transmission measurements and simulations show that the transmission amplitude is highly dependent on ply orientation and angle of incidence. The transmission amplitude decreases rapidly with incident angle deviation from the normal; however, a transmission window is found in the incident angle range 45–60° at frequencies below 2.25 MHz. The time-delay measurements by the double-through-transmission technique have been used to reconstruct lamina properties using the Floquet wave concept. A unidirectional lamina elastic properties measurement using line focus acoustic microscopy of a multidirectional composite sample is also briefly discussed. The effective elastic properties for the composites are determined from the lamina properties by a Floquet wave dynamic homogenization method.     

SH0导波在粘接结构中传播时的相位变化1）

对粘接结构进行超声导波无损检测与评估是一个有挑战性的前沿性课题.针对此问题,研究了SH₀导波在界面为理想连接的三层板状粘接结构中传播时的相位变化情况.首先基于波传播的控制方程,建立了粘接结构中反射和透射SH₀导波相对于入射SH₀导波的相位差解析模型.然后利用数值模拟计算了铝/环氧树脂/铝粘接结构中反射和透射SH₀导波的相位差曲线.最后分析了入射角度和频厚积的变化对反射和透射SH₀导波相位差的影响.结果表明,对于具体的粘接结构,反射和透射SH₀导波在其中传播时的相位差变化主要依赖于入射角度、频率等参数.在特定的频厚积下,当声波水平入射时,反射和入射SH₀导波同相位.无论入射角度为多大,随着频厚积的增大,反射SH₀导波的相位差曲线均会产生周期性谐振.对于透射SH₀导波,当声波垂直入射时,其相位差曲线的改变无规律可循;但是随着入射角度逐渐增大,透射SH₀导波的相位差曲线逐渐变规则.所得结果可为实验时研究板状粘接结构中SH₀导波的传播特性以及提取SH₀导波回波中的有用信息和定位提供一定的理论指导.     

非线性变形节理中纵波传播特性的理论研究

基于波前动量守恒理论和位移不连续方法所提出的时域分析新方法,引入岩石非线性法向本构关系,对弹性纵波在岩石非线性节理中的传播特性进行了理论分析。采用节理变形的双曲线模型(BB模型),获得纵波P波斜入射非线性节理的传播波动方程,并通过参数研究分析了在岩石节理中节理非线性系数、节理初始刚度、应力波入射角和入射波幅值等因素对纵波传播规律的影响。结果表明:所推导的应力波传播方程在考虑多种非线性问题时,通过迭代计算即可方便求出透射波和反射波的数值解,避免了复杂的数学运算;当波斜入射节理面时,产生了波型转换,节理变形的非线性对透射波和反射波有较大影响,透射系数和反射系数并非随着非线性参数的变化而单调变化。时域内所推导的波传播方程更有益于波斜入射时非线性参数的广泛研究,为开展该方面的理论研究工作提供了借鉴。     

In-plane wave motion and resonance phenomena in periodically layered composites with a crack

This paper investigates the transmission and propagation of two-dimensional (2D) time-harmonic plane waves in periodically multilayered elastic composites with a strip-like crack. The total wave field in the composite structure is represented as a sum of the incident wave field determined by the transfer matrix method and the scattered wave field described by integral representations in terms of the Green’s matrices and the crack-opening-displacements. A numerical scheme is developed to compute the wave propagation characteristics and the crack-characterizing quantities. The effects of the crack location and size as well as the angle of wave incidence are investigated using the averaged crack-opening-displacements and the stress intensity factors. Special attention of the paper is devoted to resonance wave motion and wave localization phenomena in a stack of periodical elastic layers weakened by a single strip-like crack. Numerical results are presented and discussed to reveal the usual and the resonant wave transmission by using the power-density vector and the energy streamlines in the vicinity of the crack. Wave localization due to interior and interface cracks is analyzed by considering the energy captured by a crack, and resonance induced crack growth is also discussed.     

Experimental and numerical investigation on the damping effect of net cages in waves

A series of laboratory experiments were conducted to investigate the damping effect of net cages in waves. The wave transmission coefficient of the net cage was investigated with different wave periods, wave heights, numbers of net cages, net solidities, measurement positions, geometrical shapes of the net cage and Reynolds numbers. The experimental results show that the net cage has noticeable influence on wave propagation and the damping effect of net cages has a close relationship with many parameters. For multiple net cages, the transmission coefficient tends to increase as the wave period increases. The transmission coefficient of net cages decreases with increasing wave height. As the number of net cages increases, the wave transmission coefficient will decrease gradually. The damping effect of net cages on wave propagation tends to increase with increasing net solidity. The measurement position has an effect on the value of wave transmission coefficient. For net cages with different geometrical shapes, the circular net cage has more noticeable damping effect than the square net cage. A numerical model is introduced to simulate the interaction between waves and net cages with the fishing net treated as the porous media fluid model. The wave transmission coefficient downstream from net cages shows good agreement between experimental and numerical results. The study will contribute to understanding of the damping effect of a large fish farm on wave propagation.     

PVDF应力测试技术及其在多孔材料爆炸冲击实验中的应用

通过精确测量Hopkinson杆子弹速度,实现了对PVDF压力传感器的动态标定,测试数据线性度良好,误差不超过1.9%,得到动态灵敏度系数K=32.83 pC/N,采用500 g TNT对“钢板-泡沫铝-钢板”复合结构进行爆炸冲击加载,测量结构间应力波的传播情况。研究结果表明:电压测试信号可以较为准确地反映弹性波与塑性波的加载时间和传播速度,PVDF对弹性应力波段高频信号的动态响应灵敏准确,与理论数据的相对误差为3.5%。测得泡沫铝材料中塑性波的传播速度为590 m/s,A₁-B₁界面塑性波透射系数达到了0.53,远高于弹性波透射系数。从机理上对应力时程曲线中出现的特殊现象进行了阐述,为相关爆炸测试提供参考。     

Shear horizontal wave in multilayered piezoelectric structures: Effect of frequency,incidence angle and constructive parameters

In this paper, the global matrix method is applied to find the behavior of transmission coefficients for shear horizontal (SH) wave propagation with oblique incidence in piezocomposite layered systems. The elemental periodic cells of these piezocomposites are formed by two types of components: a piezoelectric PZT material and an Araldite polymer. The behavior of the transmission coefficient with respect to the frequency, incidence angle and piezoelectric volume fraction is studied. Some numerical calculations for different configurations of the composite are shown. The influence of the bonding films made of polymeric material is also studied. These results could be used to versatile transducers design.     

竖直平面激波与水平热层作用后流场的理论计算方法研究

围绕竖直平面激波与固壁附近水平热层作用问题,提出了流动进入准自相似阶段后固壁附近流场参量的理论计算方法。与已有的Mirels方法相比,本文的方法在下列三个方面进行了改进:（1）舍弃“热层内激波速度与入射激波速度相等”的假定,分析了热层内激波的传播过程,并基于几何激波动力学理论计算热层内激波强度;（2）假定在与入射激波后流体而非入射激波阵面固连的坐标系中,波后流体在定常等熵波作用下,形成沿固壁运动的“活塞”,驱动其前方的热层气体运动;（3）“活塞”内流体与其毗邻的热层气体满足压力和速度连续,不再引入速度比例系数。利用改进后的方法,对于马赫数为2.00的竖直平面激波,在不同热层密度条件下进行计算。本文方法得到的热层内激波强度以及物质界面处的压力、速度和密度等参量,与数值模拟结果偏差均小于10%,优于Shreffler和Mirels计算方法。对于马赫数为1.36的竖直平面激波,当其传播速度小于热层内气体声速时,Shreffler和Mirels计算方法不再适用,而本文中提出的方法得到的计算结果与数值模拟结果和已有实验数据基本吻合,最大偏差约20%。上述结果表明,本文中提出的理论计算方法提高了现有方法的合理性,扩大了适用范围。     

梯度密度黏弹性材料的波传播研究

梯度密度黏弹性材料中波的传播比较复杂。为了研究其在冲击载荷作用下黏弹性响应特征,基于控制方程的Euler形式,利用Laplace变换,得到了这种材料中的波传播规律的一个理论公式;并据此分析了双层周期性黏弹性介质中的应力情况。选择具有梯度密度特性的钛-硼化钛（Ti-TiB₂）材料和碳纤维树脂材料,采用不同的叠合方向和方式,利用分离式霍普金森压杆（split Hopkinson pressure bar,SHPB）加载装置进行了动态冲击实验,并用三波法对得到的实验结果进行处理。同时,采用数值Laplace逆变换方法,结合SHPB测得的入射波与透射波数据,使用推导的理论公式计算出理论解,并与实验结果进行了比较。结果表明:（1）梯度钛-硼化钛材料由于内界面和叠层界面的存在,表现出一定的黏性特性;单层Ti-TiB₂材料的计算结果和三波法分析得到的结果基本一致,双层Ti-TiB₂材料叠合后的计算结果与三波法分析结果存在一定的差异。（2）双层碳纤维树脂材料表现出较强的黏弹性特征,应力波的衰减幅度较大,三波法分析结果与该材料的冲击性能有较大的差异。由此可知,无论是细微观结构特征产生的黏性,还是材料本身的黏性,对材料动力学行为的影响都不可忽略。。