【作者】 刘旭；

【导师】 卢荣胜；

【作者基本信息】 合肥工业大学 ， 仪器科学与技术， 2021， 博士

【摘要】 随着精密制造业的不断发展,器件结构设计趋向微型化,需要测试材料微小尺寸力学性能参数,为相关器件设计和性能评价提供合理的依据。现代光测力学技术作为实验力学的重要分支,因其具有非接触、全场测量、灵敏度高、无损等优点而广泛应用于力学性能测试领域。其中,三维显微图像相关力学性能测试技术更可对毫微米级试样进行力学性能测试。然而,三维显微图像相关力学性能测试技术在应用过程中也面临着一些问题和挑战。本文针对其中的几个关键问题进行深入研究,主要工作成果如下:(1)针对工程应用中材料毫微米级力学性能测试问题,研究一种基于体视显微镜成像的三维显微图像相关(DIC)力学性能测试技术,采用三维显微图像相关技术测量试样直接拉伸过程中的变形量,进而反演毫微米级尺寸试样的材料力学性能参数。(2)针对体视显微镜成像系统因景深小、光路较复杂、畸变大且分散等因素而难以精确标定的问题,本文提出了一种基于非共面特征点加权径向约束的标定方法,提高了成像模型参数的标定精度。该方法给予特征点不同的权重值,基于物点与像点的径向约束关系建立加权目标函数,经过迭代计算获取成像模型参数的最优解,标定结果的重投影误差小于0.2pixel。利用特征点的重投影误差构建显微成像系统的畸变偏差曲面,替代传统的非线性畸变模型。(3)本文通过模拟散斑图案的刚体平移、旋转、均匀和非均匀变形数值实验,分析了不同阶次形函数图像相关方法对计算精度的影响。根据试样单轴双向拉伸过程中局部变形大的特点,采用组合形函数近似子区域变形的图像相关方法计算全场变形量,有效避免单一形函数表征子区域变形产生的局部欠匹配或过匹配现象。在极线约束的基础上,利用视差曲面确定待测点的预估匹配点,可以进一步缩小匹配点的搜索范围。针对对应点匹配中存在的误匹配点,采用环形闭合检验的方法剔除粗大误差数据。(4)针对微小尺寸试样的夹持、微位移加载问题,本文设计了一种基于蜗轮蜗杆反向滚珠丝杆传动的微拉伸机,蜗轮蜗杆多级减速机构提供了极大的减速比,使得微拉伸机的稳定拉伸速度达到0.07μm/s,可以获取试验中试样整个拉伸过程,便于图像相关方法计算试样的全场变形和应变。反向滚珠丝杆的传动方式可以实现试样真正的原位拉伸,有效避免试样一端固定另一端拉伸时出现根部断裂的现象。(5)利用QT平台编写了三维显微图像相关力学测试系统的软件界面,实现图像和数据的采集、微拉伸机控制、系统标定、显微图像相关计算、三维坐标计算和显示以及反演材料弹性模量、泊松比等力学性能参数等功能,使用状态迁徙图保证拉伸试验过程的安全性,使用多线程技术实现图像相关匹配计算,可以有效减少计算时间。最后,利用所搭建系统测试标准钢球直径、标准台阶高度以及纯铜试样拉伸变形的全场应变、弹性模量和泊松比等参数,并与商业软件DANTEC Q400的测量结果作对比,验证了测试系统能够满足材料毫微米级试样力学性能的测试需求。更多还原

【Abstract】 With the continuous development of material technology and precision manufacturing industry,the structure of various devices tends to be miniaturized and the mechanical properties of materials of devices directly determine the reliability of structural design.It is of great significance to measure the mechanical properties of materials in millimeter and micrometer.Traditional testing methods are usually contact methods which are restricted by factors such as contact interference,small measurement range,single measurement point,low testing efficiency and cannot meet the full-field requirements of millimeter and micrometer specimen.As an important branch of experimental mechanics,testing technology of modern optical mechanical property is widely used in the field of mechanical property measurement due to its advantages of non-contact,full field measurement,high sensitivity and non-destructive.Among them,the three-dimensional(3D)microscopic digital image correlation(DIC)mechanical properties testing technology has the advantages of high resolution,low test environment requirements,and full-field measurement.It can perform non-contact high-precision fullfield measurement of mechanical parameters of materials in millimeter and micrometer.However,there are some problems and challenges in the application of three-dimensional microscopic image related mechanical property testing technology.In this thesis,several key issues are studied in depth and the main achievements are as follows:(1)Aiming at the problem of millimeter and micrometer level mechanical properties testing of materials in engineering applications,a three-dimensional microscopic image correlation(DIC)testing technology based on stereo light microscope is studied.The three-dimensional microscopic digital image correlation technology is used to measure the deformation of the specimen during the direct stretching.Furthermore,we can invert the material mechanical properties of millimeter and micrometer scale specimen.(2)The 3D microscopic imaging system based on SLM has the characteristics of small depth of field,complex optical path,large distortion and dispersion and it is difficult for traditional calibration methods to accurately obtain imaging model parameters.This thesis proposes a method based on non-coplanar feature points and the weighted radial constraint calibration method improves the calibration accuracy of the imaging model parameters.In this method,different weight values were given to the feature points and the weighted objective function was established by using the radial constraint relationship between the object point and the phase point.)The optimal solution of imaging model parameters is obtained by iterative computation and the reprojection error of the calibration result is less than 0.2pixel.The reprojection error of the characteristic points is used to construct the distortion deviation surface of the microscopic imaging system in the u and v directions of distortion and deviation surface to replace the traditional nonlinear distortion model.Finally,the validity of the proposed calibration method is verified by the shape and displacement experiments.(3)This thesis analyzes the influence of DIC method with different order shape functions on the calculation accuracy through numerical experiments of rigid body translation,rotation,uniform and non-uniform deformation that simulate the speckle pattern.According to the characteristics of large local deformation in the process of uniaxial biaxial stretching of the specimen,the DIC method of combining shape function to approximate the deformation of the sub-region is used to calculate the full-field deformation,which effectively avoids the phenomenon of local under-matching or overmatching caused by the deformation of a single shape function representing the sub-region.Matching phenomenon.On the basis of limit constraints,using the parallax surface to determine the estimated matching points of the points to be calculated can reduce the search range of matching points.(4)Aiming at the problem of clamping and micro-displacement loading of small-scale specimens,a micro-stretching machine based on worm and worm reverse ball screw transmission power is designed.The worm gear multi-stage reduction mechanism provides a great reduction ratio,which makes the s Tab stretching speed of the microstretching machine reach 0.07 μm/s.The entire stretching process of the specimen in the test can be obtained and it is convenient to calculate the full-field deformation and strain of the specimen by DIC method.The transmission mode of the reverse ball screw can implement the true in-situ stretching of the specimen and it can effectively avoid the phenomenon of root fracture when one end of the specimen is fixed and the other end is stretched.Aiming at the mismatched points in the matching of corresponding points,a loop closure test method is used to eliminate gross error data(5)The software interface of DIC of testing system based on 3D microscopic images was written by QT platform.Through this interface,functions such as image and data acquisition,stretching machine control,system calibration,microscopic image correlation calculation,three-dimensional coordinate calculation and display,and inversion of material elastic modulus,Poisson’s ratio and other mechanical properties parameters can be implemented.The built system is used to test the standard steel ball diameter,standard step height and in-situ tensile test of pure copper specimen.These data are compared with the measurement results of the commercial software DANTEC Q400 and the results of the experiments also verified that the test system can meet the test requirements of the mechanical properties of millimeter and micrometer scale specimen of materials.更多还原