金属板中Lamb波波速与应力关系的实验研究

本文给出了金属板中Lamb波波速对同向应力变化率测量的装置,探讨分析了测量原理及误差,并对Lamb波的波速与应力关系进行了实验研究。结果表明Lamb波的波速对应力有较好的线性关系,Lamb波相速度对应力的变化率的实验值与理论值符合很好。     

金属薄板缺陷的超声多途Lamb波检测

金属薄板在动车等现代化设计中应用广泛,其是否存在缺陷等检测具有很重要的意义。为此,利用超声多途提供的额外数据来检测金属薄板的缺陷,提出相应的算法,多途路径在直接反射的路径上是可以预测和识别的,直接反射路径是相对比较容易识别的。同时利用ANSYS有限元建模不同的薄板缺陷模型,在不同的传感器位置、缺陷位置、缺陷大小情况下分别进行仿真。通过ANSYS仿真和实验检测都得出了良好的结果,误差在可控制范围之内,证明了超声多途应用与金属薄板Lamb波检测的是可行的;仿真和实验表明超声多途通过实际和多途虚拟扩展的传感器数据的分析证明了超声多途能够对薄板缺陷进行定位并检测其大小。提出的超声多途检测方法,通过单次测量即可检测出薄板缺陷的位置和大小,具有良好的检测性能。     

浅水波波速公式的推导

在不同的介质中,波速的不同导致波的传播方向发生偏折.新教材中重新引入了波的折射的相关内容,并通过调整水的深浅来观察波的折射现象.因而就有必要建立波速v和水深h之间的关系,许多教师对如何推导二者之间的关系不甚了解,本文试图解决这一困惑.     

激光衍射法测量表面张力和毛细波波速与温度的关系

利用激光衍射对液体表面张力和毛细波波速与温度的关系进行了研究.当激光斜入射到毛细波上,观察到稳定的、清晰的衍射图样,运用光栅衍射理论对该实验现象进行了分析,测量了不同温度下蒸馏水的表面张力和毛细波波速,用最小二乘法对实验数据进行拟合,给出了表面张力和毛细波波速与温度的解析关系,发现表面张力和毛细波波速随着温度的增加而减小,并和温度呈近似线性关系.根据其机理,建立了激光衍射法实时的和非接触的测量不同温度下液体表面张力和毛细波波速的方法.     

石墨烯力常数和弹性波波速随温度变化规律研究

在哈里森键联轨道法框架下,考虑到原子的短程相互作用和原子的非简谐振动,建立石墨烯弹性模型并求出原子振动的简谐系数和非简谐系数.在此基础上,确定了石墨烯的力常数随温度和形变势参量的变化关系式,以及弹性波波速随温度和形变势参量的变化关系式,并探讨了原子非简谐振动对它们的影响.结果表明:(1)石墨烯的力常数和弹性波波速均随温度升高而非线性减小,但有不同的变化特征:在C_(11)、C_(12)、C_(44)这三个力常数中,以C_(12)随温度的变化最大,以C_(44)的变化最小;纵波波速随温度的变化要大于横波;(2)石墨烯的三个力常数随形变势参量的变化有不同的特征:C_(11)随η和γ的增大而增大、而C_(12)则随η的增大而减小,随γ的增大而增大;C_(44)随η的增大而增大,而几乎不随γ而变;(3)若不考虑原子振动的非简谐项,则石墨烯的力常数和弹性波波速均为常数.考虑到非简谐项后,不仅它们均随温度的升高而减小,而且,非简谐情况的力常数C_(ij)和弹性波波速v_i与简谐近似的值C_(ij)~0、v_i~0的差|C_(ij)-C_(ij)~0|、|v_i-v_i~0|均随温度的升高而增大,即温度愈高,非简谐效应愈显著.     

石墨烯力常数和弹性波波速随温度变化规律研究

在哈里森键联轨道法框架下,考虑到原子的短程相互作用和原子的非简谐振动,建立石墨烯弹性模型并求出原子振动的简谐系数和非简谐系数。在此基础上,确定了石墨烯的力常数和弹性波波速随温度和形变势参量的变化关系式,探讨了原子非简谐振动对它们的影响。结果表明：（1）石墨烯的力常数和弹性波波速均随温度升高而非线性减小,但有不同的变化特征：在C11、C12、C44这三个力常数中,以C12随温度的变化最大,以C44的变化最小;纵波波速随温度的变化要大于横波;（2）石墨烯的三个力常数随形变势参量的变化有不同的特征：C11随η和γ的增大而增大、而C12则随η的增大而减小,随γ的增大而增大;C44随η的增大而增大,而几乎不随γ而变;（3）若不考虑原子振动的非简谐项,则石墨烯的力常数和弹性波波速均为常数。考虑到非简谐项后,不仅它们均随温度的升高而减小,而且,非简谐情况的力常数Cij和弹性波波速vi与简谐近似的值Cij0、vi0的差|Cij－Cij0|、|vi－vi0|均随温度的升高而增大,即温度愈高,非简谐效应愈显著。     

石墨烯力常数和弹性波波速随温度变化规律研究

在哈里森键联轨道法框架下,考虑到原子的短程相互作用和原子的非简谐振动,建立石墨烯弹性模型并求出原子振动的简谐系数和非简谐系数。在此基础上,确定了石墨烯的力常数和弹性波波速随温度和形变势参量的变化关系式,探讨了原子非简谐振动对它们的影响。结果表明：（1）石墨烯的力常数和弹性波波速均随温度升高而非线性减小,但有不同的变化特征：在C11、C12、C44这三个力常数中,以C12随温度的变化最大,以C44的变化最小;纵波波速随温度的变化要大于横波;（2）石墨烯的三个力常数随形变势参量的变化有不同的特征：C11随η和γ的增大而增大、而C12则随η的增大而减小,随γ的增大而增大;C44随η的增大而增大,而几乎不随γ而变;（3）若不考虑原子振动的非简谐项,则石墨烯的力常数和弹性波波速均为常数。考虑到非简谐项后,不仅它们均随温度的升高而减小,而且,非简谐情况的力常数Cij和弹性波波速vi与简谐近似的值Cij0、vi0的差|Cij－Cij0|、|vi－vi0|均随温度的升高而增大,即温度愈高,非简谐效应愈显著。     

铝板中Lamb波检测的实验研究

Lamb波在传播过程中具有频散及多模态特性,若相关参数选择不当,会导致在实际应用中信号相互叠加而无法识别。本文基于Lamb波的频散曲线是其频散方程实数解分布的特点,采用二分法绘制了铝板中Lamb波的频散曲线、波结构曲线和入射角曲线。根据曲线选择S0模态的Lamb波对1mm厚铝板中不同类型的缺陷进行检测。实验结果表明,S0模态的Lamb波对裂纹型缺陷和贯穿型缺陷十分敏感,但对于裂纹型缺陷,其幅值变化并不与缺陷大小成线性关系,并且S0模态Lamb波的声场指向性十分集中,在偏离声束轴线时无法检测到缺陷。     

基于Lamb理论的激光陀螺光强调谐线型研究

He-Ne气体环形激光器是激光陀螺的核心器件。为了避免环形激光器内部与转动方向同、反向的运转模对产生模竞争效应,单纵模工作激光陀螺需要调整增益介质内Ne同位素构成,采取双同位素增益介质。为此,采用Lamb理论和等离子体色散函数,研究增益介质Ne同位素频率分裂、同位素配比、充气压力等因素对环形激光器光强调谐曲线线型的影响。实验上搭建了激光陀螺光强调谐曲线检测实验平台,在Ne²⁰和Ne²²充气比例分别为1:1和7:3,充气压力为400 Pa的条件下,检测环形激光器的光强调谐曲线,验证了理论分析的正确性,该研究为激光陀螺在双纵模频率非对称位置处实现稳频奠定了基础。     

基于迟滞应力应变关系的非线性声学检测理论与方法研究

本文将传统PM(Preisach-Mayergoyz)模型由一维介质拓展到二维介质,引入迟滞细观弹性单元概念,得到迟滞变化的应力应变关系.并采用一阶有限差分方程进行了声场计算和分析,发现空间声场中含有明显的高阶奇次谐波成分.对接收到的全波信号进行滤波、放大、时间反转后加载到接收换能器对应阵元上再进行发射,观察到高次谐波在微损伤区域实现聚焦.这为利用非线性高次谐波检测微损伤提供了可能的途径,也为疲劳损伤等缺陷的早期检测提供了理论和方法依据.     

Research on relationships between Lamb wave velocity and static stress in metal plate

On the fact that an isotropic metal solid produces anisotropic property in the state of static stress, based on the theory of the nonlinear acoustoelasticity, the equivalent second order elastic constants are calculated for metal plate with static stress. For the case of thin metal plate with stress, the two kinds of dispersion equation for Lamb waves propagating parallel and vertical to the direction of static stress are derived. Using the equations, the relationships between Lamb wave velocity and static stress in a metal plate are discussed.     

兰姆波各模式声速与板材疲劳关系研究

为了研究由于材料疲劳造成的材料弹性系数变化对兰姆波各模式相速度的影响,对兰姆波传播特性进行了理论计算与实验测量。研究表明高阶模式兰姆波相速度对于弹性系数的变化要比零阶模式敏感。对于LY-12-CZ合金铝板,A₃模式由于材料疲劳产生的相速度相对变化量要比A₀模式约高4倍。因此采用高阶模式兰姆波进行无损检测,其灵敏度要远优于当前常用的零阶模式。     

The group velocity variation of Lamb wave in fiber reinforced composite plate

Experimentally measured Lamb wave group velocities in composite materials with anisotropic characteristics are not the same as the theoretical group velocities which is calculated with the Lamb wave dispersion equation. This discrepancy arises from the fact that the angle between the group velocity direction and the phase velocity direction in anisotropic materials exists. Wave propagation in a composite material with anisotropic characteristics should be considered with respect to magnitude correction in addition to direction correction. In this study, S0 mode phase velocity dispersion curves are depicted with the variation of degree with respect to the fiber direction using a Lamb wave dispersion relation in the unidirectional, bidirectional, and quasi-isotropic composite plates. Slowness surface is sketched by the reciprocal value of the phase velocity curves. The magnitude and direction of the group velocity could be calculated from the slowness surface. The recalculated group velocities with consideration of the magnitude and direction from the slowness surface are compared with experimentally measured group velocities. The proposed method shows good agreements with theoretical and experimental results.     

金属板疲劳损伤非线性兰姆波混频检测

针对金属板结构安全运行需要,开展了金属板结构疲劳损伤非线性兰姆波混频检测方法研究。通过数值仿真,研究了两列A₀兰姆波与材料损伤间的非线性相互作用。结果表明,两列共线A₀兰姆波在结构材料损伤处产生单向传播的和频S₀波,且和频波幅值随传播距离具有积累增长效应。对不同疲劳程度金属板试件进行了共线混频兰姆波检测实验,结果表明,和频波幅值随试件疲劳周数的增加呈单调递增趋势,提出的兰姆波混频技术可用于金属板结构疲劳程度的表征。研究工作为金属板结构疲劳损伤检测提供了可行的技术方案。     

Lamb wave dispersion in a PZT/metal/PZT sandwich plate with imperfect interface

Abstract

The Lamb wave dispersion in a PZT/Metal/PZT sandwich plate is investigated by employing the exact linear equations of electro-elastic waves in piezoelectric materials within the scope of the plane-strain state. It is assumed that at the interfaces between the piezoelectric face layers and metal core layer, shear-spring and normal-spring type imperfect conditions are satisfied. The degree of this imperfectness is estimated through the corresponding shear-spring and normal-spring type parameters which appear in the contact condition characterizing the transverse and normal displacements’ discontinuity. The corresponding dispersion equation is derived, and as a result of the numerical solution to this equation, the dispersion curves are constructed for the first and second lowest modes in the cases where the material of the face layers is PZT and the material of the middle layer is Steel (St). Consequently, for the PZT/St/PZT sandwich plate, the study of the influence of the problem parameters such as the piezoelectric and dielectric constants, layer thickness ratios, non-dimensional shear-spring, and normal-spring type parameters, is carried out. In particular, it is established that the imperfectness of the contact between the layers of the plate causes a decrease in the values of the wave propagation velocity.     

Local vibration of an elastic plate and zero-group velocity Lamb modes

Elastic plates or cylinders can support guided modes with zero group velocity (ZGV) at a nonzero value of the wave number. Using laser-based ultrasonic techniques, we experimentally investigate some fascinating properties of these ZGV modes: resonance and ringing effects, backward wave propagation, interference between backward and forward modes. Then, the conditions required for the existence of ZGV Lamb modes in isotropic plates are discussed. It is shown that these modes appear in a range of Poisson's ratio about the value for which the cutoff frequency curves of modes belonging to the same family intercept, i.e., for a bulk wave velocity ratio equal to a rational number. An interpretation of this phenomenon in terms of a strong repulsion between a pair of modes having a different parity in the vicinity of the cutoff frequencies is given. Experiments performed with materials of various Poisson's ratio demonstrate that the resonance spectrum of an unloaded elastic plate, locally excited by a laser pulse, is dominated by the ZGV Lamb modes.     

兰姆波在自由端面上的反射

对于板材的内部缺陷,常用兰姆波作超声无损检测。兰姆波在板材自由端面上的反射呈现复杂现象,即使在纯模入射条件下,通常也要产生无数个其它模式的反射兰姆渡。由于兰姆波本征模式正交关系同时涉及位移和应力,使其反射问题的分析较复杂,我们采用了一种新方法,应用最小二乘原理,将兰姆波本征模式作为试验函数,实现了一种较简单的分析方法。在一般情形下,利用8位微处理机就可取得满意的结果。应用该方法,给出了兰姆波在自由端面上反射时各模式的反射系数,阐明了纯模反射条件,并发现了关于模式转换的一些有趣的新现象。     

Lamb wave radiation from plate termination in a liquid

The liquid wedge method is used to excite leaky Lamb waves on an aluminium plate while the plate is immersed in water. The excitation occurs near the end of the plate so that sonic energy of the excited mode radiates into the liquid. A Schlieren method is used to observe the radiation pattern and a correlation is made between the radiation lobe structure and the symmetric or antisymmetric nature of the excited mode. Theoretical calculations of the transfer of energy from the plate to the liquid are made and agreement between theory and experiment is obtained.