Measuring Shape and Surface Strain of Curved Objects Using Digital Speckle Photography and Gap Effect

Abstract: We explore the validity of moiré gap equation in terms of the digital speckle photography technique and show that the equation can be adapted to measure the shape or surface strain of curved objects. Examples of the utility of this approach are demonstrated using a spherical rubber ball.     

Characterisation of Thermal Expansion Coefficient of Anisotropic Materials by Electronic Speckle Pattern Interferometry

Abstract:  Carbon fibre composites find wide applications in aerospace, sporting goods industry and biomedicine. Mechanical and thermal properties of such materials are highly anisotropic; therefore, adequate experimental measuring methods are requested to determine them. This paper describes the application of electronic speckle pattern interferometry to full-field, real-time characterisation of the coefficient of thermal expansion (CTE) of anisotropic materials. The topics such as correlation fringes tilt and influence of small rigid body rotation were theoretically described and experimentally verified. A series of measurements was carried out to determine the CTE tensor for unidirectional and bi-directional carbon fibre laminates and to prove the feasibility of the method. The measuring set-up developed includes a temperature control unit for cooling and heating and a one-dimensional in-plane speckle interferometer.     

不确定度的评定在热膨胀特征参数检测中的应用

讨论了测量不确定度的来源和在热膨胀特征参数检测中不确定度的影响因素，介绍了热膨胀测量不确定度评定的实例。     

Recording of In-plane Surface Displacement by Double-exposure Speckle Photography

Local displacements in the plane of an object surface illuminated by coherent light may be measured by recording double-exposure photographs of it. When the surface is illuminated symmetrically by two oblique beams, ‘speckle correlation fringes’ appear in the doubly exposed negative, due to the non-linear nature of the photographic recording. Factors affecting the visibility of these fringes and the range of displacement which can be measured are discussed. The fringe visibility falls to zero for displacements larger than a speckle width, but measurements can then be performed upon the optical transform of the negative image. With uni-directional object illumination, the in-plane displacement can be measured on a point-by-point basis in magnitude and in direction from Young's fringes observed. With two symmetrical oblique illuminating beams the effect of a small surface strain is displayed, even if large lateral displacement has occurred, by using spatial filtering when viewing the photographic image.     

利用数字散斑照相术测量面内位移

采用数字图像处理技术直接对双曝光散斑图进行全场分析,获取了杨氏条纹图．通过对条纹图的滤波增强、二值化、细化等操作,提取了条纹周期,实现了物体面内微小位移的测量．实验结果表明,该方法可获得高对比度的散斑干涉条纹,经过数字图像处理,条纹细化无断点和毛刺,有利于条纹判读,提高测量精度,其微位移测量误差小于4％．由于散斑图及条纹图像均是在计算机内存储、处理,实现了散斑照相术的数字化,具有一定的应用价值．     

Speckle Photography Applied to the Measurement of in-plane Rotation

Speckle photography provides a simple, non-contact method of measuring in-plane displacements. By using the technique to measure the displacement at two points on an object which is being rotated about an axis parallel to the line of sight, the amount of rotation can be calculated without the need to identify the actual axis of rotation.     

Pulsed TV Holography Combined with Digital Speckle Photography Restores Lost Interference Phase

The measuring of situations with optical measuring methods is difficult when a deformation field must be determined while it is superposed to comparatively large rotating or translating object motion. Interferometric methods such as pulsed TV holography might be suitable to measure the small transient deformation, but the often-large bulk motion makes the phase information disappear. However, by a combination of digital speckle photography (DSP) (also called digital image correlation) with pulsed TV holography, such measuring problems can be mastered. A method to calculate the bulk in-plane motion by DSP from the usual pulsed TV holography recordings and then to use this information to restore the interference phase is proposed. This technique may be attractive in the study of transient vibrations overlaid on rotating or translating motions.     

The Extension of the Electronic Speckle Photography to the Measurement of In-Plane Displacement

In this paper, a modified speckle photography technique is demonstrated for the measurement of a variable range of the in-plane displacement. The modification focuses on coupling the diode pump solid state laser DPSS with the conventional speckle photography technique. The DPSS laser emerges different wavelengths to provide speckle patterns of suitable size to measure the desired range of the in-plane displacement. The second harmonic generation in a nonlinear crystal of wavelength 532 nm and the principle diode laser wavelength 808 nm are employed in identifying the object positions within a lateral displacement made by a standard linear stage in the range from few microns up to 1.2 mm. The sensitivity and the correlation of the speckles formed by both wavelengths suit both small and large movements. A continues measurement by the modified technique can be achieved by identifying a scale factor in the uniform area in which both wavelengths are effective, and high correlation between the results obtained by 532 and 808 nm is maintained. The uncertainty in measuring 1.2 mm lateral movement by the modified speckle photography is found to be 26.8 μm.     

氟硅酸盐微晶玻璃的热膨胀性能研究

氟硅酸盐微晶玻璃的热膨胀性能主要取决于微晶玻璃的晶相组成及其相对含量．透辉石结晶相的含量增加使微晶玻璃的热膨胀系数降低,与此相反碱镁闪石结晶相的含量增加却使微晶玻璃的膨胀系数增加．K2O－MgO－SiO2－CaF2系统氟硅酸盐微晶玻璃的最小热膨胀系数为：78．4×10－7（20～300℃）;最大热膨胀系数为：85．6×107（20～300℃）．     

新型"负热膨胀"氧化物材料

综述了近年来新发现的新型负热膨胀氧化物材料AM2O8,AM2O7,A2（MO4）及其负热膨胀机理,并对其潜在的应用作了简单论述。     

Origami Metamaterials for Tunable Thermal Expansion

Materials with engineered thermal expansion, capable of achieving targeted area/volume changes in response to variations in temperature, are important for a number of aerospace, optical, energy, and microelectronic applications. While most of the proposed structures with engineered coefficient of thermal expansion consist of bi‐material 2D or 3D lattices, here it is shown that origami metamaterials also provide a platform for the design of systems with a wide range of thermal expansion coefficients. Experiments and simulations are combined to demonstrate that by tuning the geometrical parameters of the origami structure and the arrangement of plates and creases, an extremely broad range of thermal expansion coefficients can be obtained. Differently from all previously reported systems, the proposed structure is tunable in situ and nonporous.     

High-Resolution Thermal Expansion of MgB2

The thermal expansion of polycrystalline MgB₂ from 5–300 K is studied using high-resolution capacitance dilatometry. The thermal expansivity exhibits a small jump of –5.8×10^–8 K^–1 at T _c (in accord with expectations from the Ehrenfest relationship and published specific heat and pressure data) and a negative peak-like feature close to 5 K. No indications of any structural instabilities are observed.     

Measuring the Heavens: Charles S. Peirce and Astronomical Photography

Taking its point of departure from the current digitisation of the Harvard Astronomical Plate Collection, this article follows the plates back to the time when the status of photography as a research tool for astronomers was still to be established. It focuses on Charles S. Peirce, who, while employed by the US Coast Survey, made astronomical observations and contributed to the deliberation over visual and photographic methods. Particular attention is paid to Peirce’s involvement in early explorations of photography’s potential as a measurement tool. The guiding assumption is that approaching photography as a tool, rather than as a sign or representation, offers new inroads into the old problem of photography’s revealing powers and its capacity to serve as a means of discovery in science. Drawing on Peirce’s scientific practice as an alternative resource for theory construction, this article contributes to the ongoing efforts to conceptualise the productive or generative dimension of photographic methods. It concludes by pointing to the diagrammatic notion of evidence developed late in Peirce’s philosophical career, proposing that photography be reconceived as a diagrammatic tool.     

X射线照相法测量超细金属丝直径

本文基于X射线照相技术与数字图像处理方法,实现了对超细金属丝直径的测量。与扫描电镜测量结果对比分析表明,该方法对超细金属丝直径的测量具有较高的置信度,测量不确定度分析表明,其合成测量不确定度在0.27μm左右。     

数字散斑相关技术在微结构平面运动测试中的应用

微结构是微器件或微系统的基本组成部分,对其运动特性的测试有助于对器件或系统的性能和稳定性进行评价．为此,针对频闪成像技术获得的微结构运动图像序列,对数字散斑相关技术应用于微结构平面运动特性测试的实现方法进行了探讨,采用梯度法实现全局刚性位移的精确测量,并作为牛顿迭代法的初值进行区域变形量的提取。具有较高的计算效率SiCRF微谐振器平面运动特性测试实验表明,微结构平面刚性位移测量的分辨率和偏差分别能够达到1／100像素和1／20像素,区域变形信息提取的有效性也得到了初步验证．     

交变温场对高温腐蚀的影响

金属在受高低温交变影响时，由热膨胀系数的差异在金属内部引起了晶格畸变，并产生了微上的空间——高温空洞。在热胀冷缩的不断的作用下，高温空洞连成一片，穿透金属基体表面，构成高温隧洞。高温隧洞的不断堆积就形成不可逆转的疏松，导致耐温金属抗高温摩擦性能的降低，最终造成构件失效。本文主要讨论以Ｆｅ、Ｃｒ、Ｃ为主要成份的合金     

先进近零膨胀陶瓷研究进展

陶瓷材料易受外界温度剧变的影响,在材料中产生热引力,导致陶瓷材料失效.因此近零膨胀陶瓷在耐热冲击性能上具有显著优势,应用十分广泛,一直是材料学界研究的热点.介绍了磷酸盐、钛酸铝、微晶玻璃、钨酸锆几类典型的耐热冲击陶瓷材料,重点介绍了其热膨胀性能、现阶段的应用情况和国内外的发展状况.并提出了研究中存在的问题及其今后的发展方向.