杆中嵌入薄板的应力波传播行为

采用一维理论分析和二维有限元模拟,研究了杆中嵌入薄板的应力波传播行为.首先根据一维弹性应力波理论,推导了反射波,透射波以及板中应力的表达式.结合算例,分析了薄板厚度对应力波传播的影响,然后采用有限元方法,验证了一维理论分析结果,同时也研究了不同界面处理方式对结果的影响.结果表明板越薄,对应力波传播的影响越小,薄板中应力越能真实地反映杆中的应力状态;在SHPB实验中,嵌入薄片/薄膜传感器测量微弱应力信号是可行的.     

梯形应力脉冲在弹性杆中的传播过程和几何弥散

在应力波传播过程中,几何弥散效应往往难以避免.对应力波在弹性杆中传播的几何弥散效应进行解析分析,对于基础波动问题研究以及材料动态力学行为表征等课题,显得至关重要.本文简单说明了弹性杆中考虑横向惯性修正的一维 Rayleigh-Love应力波理论,概述了其波动控制方程的变分法推导过程;针对 Hopkinson杆实验中常用的梯形应力加载脉冲,建立了相应的偏微分方程初边值问题的求解模型,并运用 Laplace变换方法研究了脉冲在杆中传播的几何弥散现象;根据留数定理进行 Laplace反变换,给出了杆中不同位置和时刻的应力波的级数形式解析解,分析了计算项数对结果收敛性的影响;将解析计算结果与采用三维有限元数值模拟的计算结果进行对比,两者吻合程度良好,从而证明 Rayleigh-Love横向惯性修正理论可以有效地表征典型 Hopkinson杆实验中的几何弥散效应.在此基础上围绕梯形加载脉冲的弥散效应进行参数研究,定量描述了传播距离、泊松比、脉冲斜率等参数的影响.本文给出的 Rayleigh-Love杆在梯形加载条件下的解析解,揭示了几何弥散效应的本质规律,可以用于实际实验的弥散修正过程.      

梯形应力脉冲在弹性杆中的传播过程和几何弥散

在应力波传播过程中,几何弥散效应往往难以避免.对应力波在弹性杆中传播的几何弥散效应进行解析分析,对于基础波动问题研究以及材料动态力学行为表征等课题,显得至关重要.本文简单说明了弹性杆中考虑横向惯性修正的一维Rayleigh-Love应力波理论,概述了其波动控制方程的变分法推导过程;针对Hopkinson杆实验中常用的梯形应力加载脉冲,建立了相应的偏微分方程初边值问题的求解模型,并运用Laplace变换方法研究了脉冲在杆中传播的几何弥散现象;根据留数定理进行Laplace反变换,给出了杆中不同位置和时刻的应力波的级数形式解析解,分析了计算项数对结果收敛性的影响;将解析计算结果与采用三维有限元数值模拟的计算结果进行对比,两者吻合程度良好,从而证明Rayleigh-Love横向惯性修正理论可以有效地表征典型Hopkinson杆实验中的几何弥散效应.在此基础上围绕梯形加载脉冲的弥散效应进行参数研究,定量描述了传播距离、泊松比、脉冲斜率等参数的影响.本文给出的Rayleigh-Love杆在梯形加载条件下的解析解,揭示了几何弥散效应的本质规律,可以用于实际实验的弥散修正过程.     

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。。     

爆炸应力场的动态云纹-光弹分析

作者首次成功地完成了爆炸加载的动态云纹-光弹混合试验,并借助于国产多火花式动态光弹性仪获得了一次爆炸加载下双折射材料中与应力波相应的云纹条纹和光弹条纹。根据云纹-光弹条纹分析了炸药爆炸产生的应力场,获得了应力场各分量随径向距离分布的规律,为定量研究爆炸应力波传播和衰减规律开创了一项新的实验技术,提供了理论分析依据。     

炮孔之间爆炸应变场的光力学分析

本文分别运用动态云纹-光弹性和电阻应变量测方法研究了相邻两炮孔之间爆炸应变场。多火花式高速像机和超动态量测系统被用于动态记录。根据动态云纹-光弹条纹分析了应力波的叠加作用,定量地计算了爆炸应力波叠加作用期间内不同时刻地孔连心线上_x(沿连心线方向)和_r(垂直于连心线方向)的分布以及_x在连心线中垂线上的分布。用应变片记录了爆炸应力波叠加作用时连心线上应变-时间示波器轨迹。测量和计算所得炮孔间应力波叠加和衰减的规律与理论分析和动光弹模拟分析结果一致。     

混凝土SHPB试验数值模拟研究

基于混凝土HJC动态本构模型,分析了该模型方程及参数获得方法,以混凝土材料的基本力学参数确定了HJC模型中各参数值,并运用LS-DYNA软件完成混凝土SHPB试验的三维数值模拟.对比分析数值模拟结果重构所得试样的应力应变曲线与实际试验结果的相似性,研究表明,数值模拟结果可再现试验中混凝土的动态力学行为与破坏特征,而且,数值模拟可很好的反映应力波在波导杆与试件中传播过程,符合一维弹性波理论规律.     

界面对应力波作用的动光弹试验研究

用动光弹法分析研究了在冲击载荷作用下界面上应力波的传播过程,利用应力波理论分析了界面上应力波的作用机理,证实了界面上存在着能量累积和阻滞能量传递的作用,并结合弹性波动理论和应力 光学定律导出了波动方程与条纹级数之间的关系式。     

应变式压杆压力传感器在冲击波载荷测试中的应用

在近区爆炸冲击波载荷测量中,压电式压力传感器因上升时间短且强度高的高频压力脉冲作用而可能产生疲劳和过载失效。本文根据应力波在细长圆柱弹性杆中的传播特性,设计了一种应变式压杆压力传感器,当圆柱杆的一端受到压力波作用时,产生的弹性应力波沿杆轴向传播,通过测量杆的轴向应变可计算出杆中传播的应力波,从而得到作用在杆端的压力波。为了检验压杆压力传感器的性能,采用一个厚壁圆柱形爆炸容器,并将传感器安装在容器壁面不同位置上,测量中心装药产生的爆炸冲击波载荷,经反复试验,结果表明这种传感器性能是稳定可靠的。     

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。     

Effects of initial stress on the reflection and transmission waves at the interface between two piezoelectric half spaces

The effects of initial stress on the reflection and transmission waves at the interface between two piezoelectric half spaces are studied in this paper. First, the secular equations in the traverse isotropic piezoelectric half space are derived from the general dynamic equation with initial stress taken into consideration. Then, the interface conditions that displacement, stress, electric potential, and electric displacement are continuous across interface are required to be satisfied by three sets of coupled waves, namely, quasi-longitudinal wave, quasi-transverse wave and the electric–acoustic wave. The algebraic equations resulting from the interface conditions are solved to obtain the amplitude ratio of various waves and furthermore the energy reflection and transmission coefficients of various waves. The numerical results are shown graphically and the effects of initial stress are discussed.     

Dynamic stress concentration around two interacting coated nanowires with surface/interface effect

In coated nanowires, the surface/interface effects are particularly prominent due to a larger ratio of surface area to volume. In this paper, the effect of surface/interface stress on the macroscopic dynamic stress concentration around two nanowires under anti-plane shear waves is studied. The analytical solutions of displacements around the coated nanowires, in the coating layers, and inside the nanowires are expressed by wave function expansion method. The expanded mode coefficients are determined by satisfying the boundary conditions at the two interfaces around the nanowires. To accomplish the superposition of displacement fields, the addition theorem for cylindrical wave function is employed. Analyses show that the effect of interface properties on the dynamic stress is significantly related to the wave frequency, the material properties of nanowires and coating layers, and the relative position and distance between the two nanowires. If the wires and coating layers are softer, the dynamic stress decreases greatly, and the interface effect on the dynamic stress is also little. The results may be potentially useful for providing information on the mechanical properties and interactions among array of nanowires under different external mechanical stimulus.     

Internal wave computations using the ghost fluid method on unstructured grids

Two‐layer incompressible flows are analysed using the ghost fluid method on unstructured grids. Discontinuities in dynamic pressure along interfaces are captured in one cell without oscillations. Because of data reconstructions based on gradients, the ghost fluid method can be adopted without additional storages for the ghost nodes at the expense of modification in gradient calculations due to the discontinuity. The code is validated through comparisons with experimental and other numerical results. Good agreements are achieved for internal waves generated by a body moving at transcritical speeds including a case where upstream solitary internal waves propagate. The developed code is applied to analyse internal waves generated by a NACA0012 section moving near interfaces. Variations of the lift acting on the body and configurations of the interfaces are compared for various distances between the wing and the interface. The effects of the interface are compared with the effects of a solid wall. Copyright © 2004 John Wiley & Sons, Ltd.     

爆炸波与地下结构物相互作用的动光弹性探讨

本文用动态光弹性探讨了地表爆炸产生的应力波与地下结构物相互作用的机理,根据等差条纹分布分析了P波、S波、von Schmidt波及R波与结构物基础的相互作用过程。研究表明R波是对地下结构物危害最大的波。可以采取防护措施来反射和消耗R波的能量。     

TWO-DIMENSIONAL NUMERICAL ANALYSIS OF STRESS-WAVE-AMPLIFIER

Using dynamic finite element method,the propagation of stress waves in two-dimensional conically shaped stress-wave-amplifiers is analysed.The effects of gometricalfactors,input-pulse shape and pulse rising time on amplifying multiplication and waveshape of transmission waves are discussed.The consistency between numerical results andexperimental results based on Hopkinson bar is satisfactory.The numerical accuracy isinploved comparing with the characteristic method.     

Reflection and transmission of elastic waves at five types of possible interfaces between two dipolar gradient elastic half-spaces

Reflection and transmission of an incident plane wave at five types of possible interfaces between two dipo-lar gradient elastic solids are studied in this paper. First, the explicit expressions of monopolar tractions and dipolar trac-tions are derived from the postulated function of strain energy density. Then, the displacements, the normal derivative of displacements, monopolar tractions, and dipolar tractions are used to create the nontraditional interface conditions. There are five types of possible interfaces based on all possible combinations of the displacements and the normal derivative of displacements. These interfacial conditions with consid-eration of microstructure effects are used to determine the amplitude ratio of the reflection and transmission waves with respect to the incident wave. Further, the energy ratios of the reflection and transmission waves with respect to the incident wave are calculated. Some numerical results of the reflection and transmission coefficients are given in terms of energy flux ratio for five types of possible interfaces. The influences of the five types of possible interfaces on the energy parti-tion between the refection waves and the transmission waves are discussed, and the concept of double channels of energy transfer is first proposed to explain the different influences of five types of interfaces.     

Elastic wave scattering and dynamic stress in composite with fiber

IntroductionTheproblemofscatteringofelasticwavesinsolidstructureshasnotonlytheoreticalsignificancebutalsowideoutlookinengineering .Thisproblemhasabsorbedmanypeople’sattentionsinmanyfieldssuchasaeronautics,compositemechanics,civilengineeringandearthquakeengineering[1～ 3 ] .Thepropagatingvelocityanddirectionofelasticwaveareinvariableasitpropagatesinaninfiniteuniformmedium .Butscatteringofelasticwavescanoccurifthereexistsincontinuitysuchasinclusion ,crackandcavityinelasticmedium .Fiber_reinfor…     

Reflection and transmission of elastic waves at an interface with consideration of couple stress and thermal wave effects

The reflection and transmission of the thermo-elastic coupled waves at an interface of two different couple stress elastic solids are studied in this paper. Based on the Green-Lindsay theory, the governing equations and the constitutive equations are derived. Different from the classic elastic solid, the interface conditions include the surface couple, the rotation angle, the heat flux and the temperature change. The interface conditions are used to obtain the linear algebraic equations set from which the amplitude ratios of reflection and transmission waves to the incident wave can be determined. Then, the normal energy flux conservation is used to validate the numerical results. At last, the influences of two characteristic relaxation times and the five kinds of thermally and micromechanically interface conditions are discussed based on the numerical results. It is found that the thermal wave effects affect only the longitudinal wave while the couple stress effects affect only the transverse waves. The thermo-elastic coupling makes the longitudinal wave and the thermal wave not only dispersive but also attenuated.     

Dynamic effective property of fibrous piezoelectric composites with spring- or membrane-type imperfect interfaces

The present paper studies the dynamic effective property of piezoelectric composites embedded with cylindrical piezoelectric fibers under anti-plane harmonic electro-elastic waves. By using the dynamic generalized self-consistent method (DGSM) of electro-elastic coupling wave, the problem of randomly distributed cylindrical fibers in a piezoelectric medium can be analyzed in terms of a representative volume element with a coated fiber embedded in an equivalent effective medium. The interfaces between the fibers and the matrix are assumed to be imperfect which are here modeled as spring- or membrane-type interfaces. Through wave function expansion method and an iterative method, the effective piezoelectrically stiffened shear modulus and the effective wave number are obtained. Examples are conducted to verify the present solutions and to illustrate the dependence of the effective piezoelectrically stiffened shear modulus on the wave number (frequency) as well as the interface properties. The special size effect related to interfacial imperfection is also discussed.