电子错位散斑干涉系统中错位量的研究

电子错位散斑检测系统中,错位量对测量精度、灵敏度以及条纹对比度有很大影响。本文介绍了电子错位散斑干涉原理,研究了错位量与测量精度、灵敏度和条纹对比度之间的对应关系,并利用MATLAB模拟出不同错位量下干涉条纹图,将错位散斑模拟条纹图与理论分析有效结合,总结出选取错位量的方法,并将其应用于轮胎变形检测实验,取得了良好的实验效果。本文研究工作对无损检测中错位量定量选取具有实际指导意义。     

散斑干涉条纹图的总变分去噪方法

去除散斑条纹图中的噪声是电子散斑干涉测量技术的关键问题.提出将总变分图像去噪方法应用于电子散斑干涉条纹图滤波过程中,并对保真系数进行了改进.用总变分模型定义图像的能量函数,利用变分法求得满足能量函数的最优解,将图像去噪过程转化为求解偏微分方程的过程.分别对计算机模拟的条纹图和实验获得的条纹图进行了测试,定性和定量分析的结果表明该技术能够在显著滤波的同时保持条纹的对比度.     

Determination of Residual Stresses by Thermal Relaxation and Speckle Correlation Interferometry

ABSTRACT:  A new technique for the measurement of residual stresses is presented. The technique is based on strain measurements following thermal stress relaxation. The heat input is supplied by a low power infrared laser and the strain is measured with speckle pattern correlation interferometry. This paper presents a comprehensive overview of the technique and an example of how it has been applied in a practical situation.     

Electronic Speckle‐Pattern Interferometry Measurements of Structural Ratcheting Strain

Abstract: Several tensile specimens with a central hole were subjected to a cyclic loading for which the Von Mises stress was beyond the initial yield stress in the vicinity of the hole. The tensile machine was fixed together with a phase‐shifting electronic speckle‐pattern interferometry measurement bench that makes it possible to perform strain measurement along the tensile axis. The plastic strain map corresponding to the 30th cycle was obtained. For the considered measurement field, the resolution of the strain measurement is close to 10^?5. By varying the loading, it was possible to detect and observe the deformation corresponding to an early stage of the ratcheting phenomenon. The non‐ratcheting cyclic plasticity behaviour was not observed during the 30th cycle. In the Discussion section, the experimental results were interpreted using Melans’s theorem, which allowed us to determine an upper bound for the yield stress. Eventually, it is shown that the procedure followed in this work could be a way to obtain some interesting data related to the material behaviour laws.     

Displacement Measurement Through Digital Image Correlation and Digital Speckle Pattern Interferometry Techniques in Cold‐Expanded Holes

Abstract: In this paper, the displacement field induced by the split‐sleeve cold expansion of holes was measured using both digital image correlation (DIC) and digital speckle pattern interferometry (DSPI) techniques. Thus, the experimental results, which were evaluated on the inlet surface of a 6082‐T6 aluminium plate, were compared with those from theoretical prediction. DIC provided accurate measurements up to the elastic–plastic boundary, whereas the DSPI technique highlighted the changes of displacement in the elastic domain. Prediction of the displacement based on the existing analytical model agreed with the experimental results achieved with both techniques. Possible explanations for the differences are discussed.     

用散斑干涉光谱分布检测瞬态温度

为了提高对瞬态温度检测的灵敏度,提出了基于散斑干涉条纹光谱分析的瞬态温度反演算法.系统利用散斑干涉形成干涉条纹,由于瞬态温度的变化会使材料应变,从而使散斑干涉条纹改变.被测表面形变前后获得的干涉条纹由面阵 CCD 采集,其对应的光谱密度分布函数也会发生相应的改变,即由散斑干涉条纹反演得到的中心波长振幅发生改变.通过对两次中心波长幅值的比值的检测和计算,即可获得被测的瞬态温度.在分析计算了瞬态温度变化与材料应变、材料应变与干涉条纹变化的函数关系的基础上,推导了瞬态温度变化与干涉条纹振幅及相位函数关系.实验采用660 nm 半导体激光器,SI6600型面阵 CCD 探测器,从获得的光谱分布函数中提取中心波长处幅值比值,通过计算和标定,最终温度检测精度可达到±2℃.相比传统的直接检测干涉条纹的变化量,由被测面形变量推导温度的方法精度提高了近一个数量级,其精度更高、检测均匀性更好、稳定性更好.     

Advanced Image-Processing Techniques for Automatic Nondestructive Evaluation of Adhesively-Bonded Structures Using Speckle Interferometry

In conventional optical nondestructive evaluation (NDE) of structures using shearography or electronic speckle pattern interferometry (ESPI), results are typically provided in the form of fringe patterns or deformation contour plots. However, in order to fully automate the process of defect detection, it is desirable to obtain simpler results which are easier to interpret. We present here one such optical system based on additive–subtractive shearography/ESPI. This system processes additive–subtractive fringe patterns and provides the sizes and locations of defects such as disbonds in adhesively-bonded composite structures. This is achieved by exciting the structure under inspection using an acoustic stressing mechanism which sweeps a range of vibration frequencies of the structure. Since the defective areas of the structure have different mechanical properties from their neighboring regions, varying and complex fringe patterns are obtained at different stressing frequencies. We propose an algorithm which enables the automatic identification and selection of relevant additive–subtractive fringe patterns that pertain only to localized deformations associated with defects, and which excludes images that pertain to any overall modes of the entire structure. The algorithm also includes a pixel-by-pixel adjustable thresholding scheme which compensates for intensity variations due to nonuniform reflectivity from unpainted and dirty test objects. Morphological processing is then performed to extract the shapes of the defect from the processed fringe clusters. Various structures, from simple aluminum specimens with simulated defects to a complex honeycomb-based aviation repair patch specimen, have been successfully evaluated using this system.     

Thermal expansion characteristics of cast Cu based metal matrix composites

Like any other metal/alloy, copper and its alloys also soften at elevated temperatures. Reinforcing with ceramic or carbon fibres is one of the suggested solutions to overcome this. Very limited literature is available on Cu based metal matrix composites (MMCs); none of these pertain to liquid phase fabrication. Hence, a systematic investigation was carried out on MMCs based on copper, with alumino-silicate fibres and carbon fibres as reinforcements. The MMCs thus produced exhibit a uniform distribution of reinforcement in the matrix. Coefficient of thermal expansion (CTE) values are lower than that of pure copper.     

低膨胀系数材料二铝酸钙的合成及其显微结构研究

采用轻质CaCO3(或纯铝酸钙水泥)和α-氧化铝为原料合成了二铝酸钙(CA2)材料,研究了反应原料、热处理温度和成型压力对CA2烧结性能和显微结构的影响,检测CA2的热膨胀系数,并借助XRD、TG-DSC和SEM等测试手段分析和观察了材料的合成过程及显微结构.结果表明:采用轻质CaCO3(或纯铝酸钙水泥)和活性氧化铝为原料可以合成低膨胀系数CA2材料;坯体成型压力对试样烧结性能没有显著影响;反应原料和热处理温度不同导致CA2材料的烧结性能和显微结构有较大的差异.     

预报复合材料热膨胀系数的细观力学模型

建立了一国观力学模型用于预报复合材料的有效热膨胀第数。利用这一模型计算热膨胀系数无需对复合材料进行热应力分析，仅需知道在某一相关外力场作用下，其组分的内部的平均应力场问题即可解决。     

ZrW2O8可控热膨胀系数复合材料的研究进展

综述了ZrWzO8在金属基、氧化物陶瓷基、水泥基和聚合物基复合材料中的应用情况。重点介绍了Cu-ZrW2O8、Al-ZrW2O8、ZrO2-ZrW2O8、Cement-ZrW2O8、Polyimide-ZrW2O8等复合材料的研究成果和存在的问题；提出了ZrW2O8可控热膨胀系数的复合材料未来研究方向。     

吸湿对印制电路板层压板热膨胀系数的影响

水分对印制电路板的可靠性有重要影响.电路板中的水分子可以改变电路基板的热性能及热力学性能,从而影响电路板及元器件的正常功能.研究了吸湿对两种无卤PCB及两种含卤PCB层压板热膨胀系数的影响,评价了IPC-TM-650 2.4.24测试方法中预处理方法对吸湿样品的适用性.结果表明,PCB层压板中的水分对PCB层压板的热膨胀曲线有明显影响,但传统的热膨胀系数计算方法并不能显示这种影响,对此作了详细分析并提出了改进建议.同时,IPC测试方法中的预处理可以降低湿度对样品热膨胀曲线的影响,但不能完全消除.     

Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料的热膨胀特性

Ca1-xBaxZr4(PO4)6(0≤X≤1.0)属于NZP族磷酸盐陶瓷材料,它是新的一类低热膨胀陶瓷材料。研究发现CaZr(PO4)6(X=0)及BaZr4(PO4)6(X＝1)时的轴膨胀特性正好相反,因此当X为某一值时热膨胀系数将为零。本研究采用共沉淀法合成了Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,当X＝0时,热膨胀系数为－0．86×10-61／℃;当X＝0．25时热膨胀系数为2．7×10-61／℃;当X＝0．75时其热膨胀异向性最小。为了得到热膨胀异向性和热膨胀系数均小的Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,X应在0．6至0．9之间,并通过控制烧结条件抑制晶粒的生长。     

Cf/Mg复合材料的热膨胀系数及其理论计算

采用负压浸渗-液固挤压法制备了定向短切碳纤维（aligned Csf）及穿刺-2D碳纤维织物（2.5DCf）增强镁合金复合材料,观察了两种复合材料的微观组织结构,测定了其在30～350℃范围的热膨胀系数（α）,并在Schapery模型的基础上提出了计算定向Csf/Mg复合材料及2.5DCf/Mg复合材料α值的修正模型。结果表明,在30～200℃范围内,两种Cf/Mg复合材料的α值均表现出随温度的升高而升高的趋势,但在超过250℃以后,α值出现降低或稳定的现象,其原因为随着温度的升高,铝元素固溶度的增大、基体发生部分塑性变形等因素导致的;提出的修正模型理论计算值与其相应的实验测试α值之间的误差均在5%之内,表明该修正模型能够有效预测实验中的α值。     

KxSr(1-x)/2Zr2(PO4)3陶瓷的热膨胀异向性研究

应用湿化学法和低分子有机溶剂分散合成了复合磷酸锆锶钾KxSr(1-x)/2Zr2(PO4)3(x=0,0.25,0.5,0.75,1.0)(简写 KSZP)陶瓷粉体,制备了相应的陶瓷.研究了组成、添加剂种类、烧结条件对热膨胀异向性及热膨胀系数的影响,实现了用两种组成的互溶来消除热膨胀的异向性.当x=0.5时,热膨胀异向性最小且热膨胀系数α接近于零即获得了零膨胀的材料性能.     

Measurement of Thermal Expansion at High Temperature by a Transient Interferometric Technique

A transient interferometric technique to measure the thermal expansion of pure metals and alloys during rapid heating is presented. The metallic specimen is resistively heated from room temperature to a high temperature close to melting within approximately 500 ms by the passage of a high electrical current pulse. The temperature of the specimen is measured and time resolved by a fast pyrometer; the thermal expansion is obtained by a high-speed laser-interferometer. The device used is a modified polarized-beam Michelson-type interferometer with a phase-quadrature detector that distinguishes between expansion and contraction. Details of its principle, the construction, adjustment, and operation are described. In addition, thermal expansion measurements performed on molybdenum and tungsten standard reference materials (SRMs) are presented and compared with results obtained by other researchers.     

滑石粉粒径对PVC/滑石粉复合材料力学性能和热膨胀系数的影响

使用钛酸酯偶联剂对不同粒径的滑石粉改性,并通过熔融共混方法制备了PVC/滑石粉复合材料。通过力学性能测试、线性膨胀测试等方法研究了滑石粉粒径对复合物的形态结构、力学性能和线性膨胀系数的影响。实验结果表明,在实验范围内随着滑石粉含量的增加,400 mesh滑石粉会使复合体系拉伸强度降低较多,冲击强度基本不变;800 mesh及1250 mesh滑石粉则使复合体系拉伸强度降低明显减少,同时增加体系的冲击强度,1250 mesh滑石粉体系冲击强度在滑石粉含量为20份时有极大值。线性膨胀系数结果显示,滑石粉的引入能明显降低PVC体系的线性膨胀系数,滑石粉粒径尺寸为800 mesh和1250 mesh时降低幅度比400 mesh时明显。     

低膨胀聚酰亚胺复合薄膜的制备及应用研究进展

聚酰亚胺（PI）作为一种高性能的功能材料已被广泛应用，但其高的热膨胀系数限制了它在高温和精密状态下的使用，通过添加陶瓷等无机材料制成复合薄膜可有效降低其热膨胀系数。介绍了国内外低膨胀聚酰亚胺复合薄膜的制备和应用研究的最新进展，指出了低膨胀PI合成、改性及应用研究的总趋势。     

Development of a Model for Predicting the Transverse Coefficients of Thermal Expansion of Unidirectional Carbon Fibre Reinforced Composites

A model for predicting the transverse coefficients of thermal expansion (CTE) for carbon fibre composites is presented in this paper. The transverse CTE were calculated by finite element analysis using a representative unit cell. The analytical micromechanical models from literature were reviewed by comparing with the FEA data. It shows that overall Hashin model provides the best accuracy. However, the calculating process of Hashin model is very complicated and inconvenient for practical applications. By using FEA, Design of Experiments (DOE), and Response Surface Method (RSM), the transverse CTE of unidirectional carbon fibre composites were studied and a regression-based model was developed. The model was validated against the FEA and experimental data. It shows that the developed model offers excellent accuracy while reduces complicated computation process. The advantage of this model is that it provides a simple and accurate method for predicting the transverse CTE of composites, which helps effective and efficient design of composite structures.     

粉末冶金法制备SiC_p/Al_2W_3O_(12)/Al复合材料及其热膨胀性能

通过添加适量的Al_2W_3O_(12)负热膨胀粉体来优化碳化硅颗粒增强铝基(SiC_p/Al)复合材料的热膨胀系数。实验采用固相法制备负热膨胀性能的Al_2W_3O_(12)粉体,并按10%,20%,30%的体积比添加至SiC_p/Al复合粉体中,利用粉末冶金工艺制备SiC_p/Al_2W_3O_(12)/Al复合材料。实验结果表明:制备的复合材料组织分布均匀,致密度良好。室温到200℃内,在Al基体质量分数不变的前提下,Al_2W_3O_(12)的加入有效降低了复合材料的热膨胀系数。