三维电子散斑干涉全场高精度应变同步测试系统研制

Digital image correlation method (DICM) is one of main techniques for three-dimensional deformation measurement. However, its precision is limited by speckles' quality of the testing object, and its sensitivity is no more than 100 micro-strain for strain analysis. The proposed project will develop a new device for simultaneously measuring three-dimensional deformation of a deformed object in electric speckle pattern interferometry (ESPI). In the proposed method, lasers of three wavelengths are used to simultaneously illuminate the object along various directions so that a unique wavelength is used for a given direction, and three PZT drivers are used for generating 4-step phase-shifting. The speckle patterns with phase-shifting formed by multiple reference-object beam pairs of different wavelengths are recorded by a 3-color CCD camera with red, green and blue channels. Each channel stores the speckle patterns related to the corresponding wavelength and hence for the specific direction. The phase of interference fringes is obtained for each wavelength by digital processing of the recorded speckle patterns before and after deformation. Time sequence phase method and multiple-thread image processing technique will be used for demodulating fringes' phase and calculating strain. The strain sensitivity of the measurement system in developing is no less than 5 micro-strain, and the measuring range of strain is from 20 to 2000 micro-strain. The measurement system in developing can simultaneously obtain the results of displacement and strain without using shear components. The system in developing can be used in testing mechanical properties of materials, components and structures. It will also provide a good testing platform for characterization of dielectric elastomers deformation responding to electric or magnetic loading.

目前数字图像相关方法是测量三维全场应变的主要手段之一，但其应变测试精度受试件表面散斑质量优劣的影响较大,且灵敏度一般在100微应变左右。本项目拟采用独立多波长激光散斑干涉方法、同步相移控制、三色CCD相机采集及数字图像处理技术，发展新的能够直接测量材料或结构三维应变的系统。本课题通过不同颜色激光散斑干涉同时调制不同方向的变形，由彩色相机获取同步相移散斑干涉图像，应用时间序列图像并结合多线程后台图像快速处理技术实现灵敏度不低于5微应变、20-2000微应变量级的静态三维全场应变测量,该测量系统无需光学剪切硬件实现材料或结构的静态变形与应变信息的同步检测；同时，拟研制的测试装置除了用于常规固体材料外，还适合于凝胶等软性材料的变形测量，这将为研究凝胶类材料在电场、磁场等载荷作用下的力学性能研究提供可靠与精确的测试平台。

当前三维全场应变的非接触测量方法主要基于双目视觉的双相机数字图像相关方法，其三维应变测量时除需在试件表面制作散斑的同时，还需进行复杂的标定。由于该方法通过对变形前后的图像进行相关计算获取应变，其测量结果一般不能实时显现且精度易受试件表面散斑质量优劣的影响。本项目的目标就是利用单一3CCD彩色相机，无需标定和散斑制作进行三维变形同步、可视化实时测量。. 本项目完成的主要研究内容包括：(1) 三维测量光路集成系统设计及机械调节系统；(2) 多光路同步相移触控系统；(3) 研究自适应相位散斑图滤波算法解决不同倍率成像时散斑大小变化对测量精度的影响，保证全场测试数据处理的精度与速度；(4)适合于不同维数变形测量的自动、手动控制图像采集软件模块。. 通过本课题的研究，实现了采用独立的多波长激光散斑干涉方法、改进了初始方案中三维相移控制设计，仅用单一相移控制完成对三色光路的同步相移、具备三色CCD相机三色同步采集及三色通道可独立调控的采集系统，研制了能够直接测量材料或结构三维变形、应变的光学测量系统样机。. 在散斑条纹处理方面提出了基于径向基函数的高精度变形测量方法，将径向基插值方法应用与电子散斑干涉条纹图、相位图的处理；并将径向基函数与数字图像相关方法相结合，提出了偏导径向基方法以及径向基函数与局部最小二乘相结合的的应变计算。在散斑相位条纹的去噪方面提出了窗口形状和大小可变的自适应滤波技术，确保变形及应变的精确测量。在研制三维变形系统的过程中，利用激光散斑干涉测量技术首次在不使用传统的拉伸、压缩加载方式测量了泡沫铝的名义弹性模量，阻尼比，以及泡沫铝的非线性振动特性；同时采用本方法首次测得昆虫羽翼的振动模态。. 本项目研制的测试装置除了用于常规块状固体材料外，还适合于软性材料的变形测量，同时也能为土壤、沙粒等颗粒物质的力学性能研究提供可靠与精确的测试平台。