基于分子发光原理的光弹性涂层测量方法

在简单介绍分子荧光产生过程的基础上,系统介绍了新的光弹性涂层方法------发光光弹性涂层法的基本原理、涂层结构、系统组成及实验方法.由于新方法采用了气雾剂技术, 并通过在光弹性涂层中添加荧光染料,使新方法与传统的光弹性涂层方法相比, 具有如下优点: (1)更简单、快捷,特别是对于有复杂几何形状的构件; (2)只会引起较小的基底加强效应;(3)能提供更高的空间分辨率; (4)省去了条纹计数和位相去包裹的过程,简化了后续的数据处理过程; (5)发光涂层的发射光是漫射光,使得对曲面进行测量时有较高的相对强度.最后指出了新方法今后的研究方向及其在诸如产品设计流程中与有限元分析相结合等方面的广阔应用前景.      

发光光弹性涂层荧光信号强度的影响因素

为提高发光光弹性涂层方法中涂层的荧光信号强度,以液态E-44型环氧树脂为光弹性材料、罗丹明B为荧光染料,制作了新、旧两种不同结构的发光光弹性涂层.通过对新、旧两种结构发光光弹性涂层受465nm光波激发时荧光发射光谱的比较,说明新的发光光弹性涂层结构比原有发光光弹性涂层在提高测量信号强度方面的优势,测量结果还表明:发光光弹性涂层测量信号的强度提高还与合理选择涂层中荧光染料浓度、荧光信号发射波长有直接关系.     

复合材料光弹性分析的近似方法

本文提出了一种用于光弹性复合材料的简化应变——光学定律。按照这一简化定律。模型材料的主应变差和主应变方向只要利用光弹性实验测出的等差线与等倾线即可求得。些是一种正交异性光弹性分析的近似方法,这一方法所得结果与实验数据比较,最大误差在10％左右。由于采用简化应变——光学定律使得正交异性光弹性分析工作大为简便,因此它是一种适合于工程应用的近似方法。     

数字光弹性法综述

将光弹性法与计算机图像处理技术相结合 ,来自动采集光弹性数据和分析应力的方法 ,称为数字光弹性法 ,与传统光弹性法相比 ,它可以进一步提高实验速度和精度。本文详细讨论了以下两个方面 :一是光弹性条纹的细化和倍增处理技术 ;二是自动确定光弹性参数的技术 ,包括相移法、傅立叶变换法、逐步载荷法、广谱分析法和RGB光弹性法等。通过对近二十年来国内外在这些方面的研究、应用和进展作了综述 ,认为采用白光的彩色域相移技术计算光弹性等倾角 ,结合采用白光源或三色光源的相移法来确定光弹性等色线级数 ,有望成为解决静态二维和三维冻结模型薄切片应力分析的最佳方法 ;另外 ,设计一种能实时和同步采集多幅条纹图的实验装置 ,通过相移法来自动获取动态光弹性数据 ,是数字动态光弹性法很有前景的发展方向     

全息光弹性夹片法解三维接触问题

本文应用反射式同轴全息干涉法与光弹性夹片技术结合,为测定三维模型内部应力的完全实验解提供了一种新方法。该方法能方便地获得单独的等和线干涉条纹图,光路简单且灵敏度高。文中给出了半无限体受集中力作用的实验解与理论解的结果比较,两者能很好地吻合。最后还给出了接触问题的应用实例,所得结果的静力校核误差小于5%。     

一种求解平面接触应力问题的光弹性—数值组合方法

本文提出一种求解平面接触应力最大值的光弹性—数值计算组合方法,仅从光弹性等差线上采集实验数据,然后用牛顿—拉斐逊技术与最小二乘法相结合计算出结果。文中推导了控制方程,阐述了方法,研究了实验数据取值区域、取值个数以及接触长度测试误差等因素的影响。用两类平面接触问题作为应用实例,结果符合工程要求的精度。     

复合材料光弹性分析的工程方法

本文在推导均衡光弹性复合材料应力(应变)—光定律的基础上,导出了均衡光弹性复合材料的近似应变—光定律。然后加以推广,提出适用于一般光弹性复合材料的近似应变—光定律.精度分析及实验验证表明:作为工程计算,在采用本文推荐的参数时,光弹性复合材料可视作各向同性材料进行光弹性分析。     

分离主应力的一种新方法—综合法

提出了从光弹性数据中分离主应力的一种新方法——综合法。该法简单实用,容易掌握,有足够的精度,不需单独测定材料条纹值,简化了实验步骤。     

一种动光弹模型材料的制作方法及其应用

基于#618环氧树脂、甲基六氢苯酐、促进剂DMP-30、环氧树脂消泡剂四种原料,提出制作光弹性模型的新配方和新方法,并利用单轴压缩实验、电测法和动态光弹法分别测定了制作的光弹模型的动态力学参数。新方法工艺简单,制作周期短,对人体无害。制作的光弹模型初始应力小,表面光洁,质地均匀,透光性好,光学灵敏度高,具有良好的机械加工和切削性能。通过三点弯曲梁冲击实验,得到了清晰的光弹等差条纹图像,验证了该配方和方法制作的模型可以应用于动态光弹性实验。     

光弹性—数字散斑相关混合法在光弹条纹主应力分解中的应用

光弹性法是研究结构内部应力分布问题的一个有效方法.光弹性实验中,通常可以方便地得到等色线条纹图.确定了等色线条纹级数以后,为获得平面模型中任意点的应力完全解,需要借助其它方法给出一个补充方程.本文将光弹性法与数字散斑相关法相结合,提出一种用于光弹性法分离主应力的新方法:光弹性-数字散斑相关混合法.在理论研究的基础上,设计了光弹性-数字散斑相关混合法实验系统,并通过相应的三点弯曲实验对该方法和实验系统的有效性做出分析和论证.该研究为光弹全场应力分解以及动态光弹性-数字散斑相关混合法提供了理论和实验基础.     

Strain Separation on a Nonplanar Object Using a Luminescent Photoelastic Coating

This paper presents the theoretical modeling and corresponding experimental results of the oblique incidence response of a luminescent photoelastic coating (LPC) applied to a cylinder under load. LPC is a measurement technique to acquire full-field maximum shear strain and its principal strain direction. The technique uses an absorption dye and a luminescent dye within a photoelastic coating, and the coating is applied on the surface of the specimen using conventional aerosol techniques. On 3D objects, the response of the emission field is dependent on the excitation orientation due to the surface inclination of the structural component and the out-of-plane strain component within the coating. Full-field strain separated results have been previously demonstrated on a 2D specimen. The extension of the strain separation technique to a 3D specimen—a cylinder in bending—is the focus of this investigation. Two different responses were obtained from normal and oblique excitation. As a result, the principal strain was separated over ±56° of circumference of the cylinder with RMS error relative to the theoretical result of 87 μɛ for maximum principal strain and 78 μɛ for minimum.     

Characterization of a new luminescent photoelastic coating

The luminescent photoelastic coating (LPC) technique measures the full-field shear strain and its principal direction on the surface of complex three-dimensional components. The measured optical strain response is also dependent on the coating thickness. Achieving uniform coating thickness is difficult, and thus requires thickness correction for accurate quantitative strain measurements. The original formulations of LPC employed a dual-layer coating containing luminescent dyes to transmit both strain and thickness information. This paper will document (theory and experiment) a new strategy: a single-layer coating that incorporates both a luminescent dye and an absorption dye. Dependent on the concentration of the absorption and luminescent dyes, the solution is sprayed onto the object of interest to a minimum threshold thickness that corresponds to a predefined penetration depth. Advantages of the single-layer coating are the elimination of thickness dependency, the elimination of compliance and adhesion issues between multiple layers, simpler data acquisition and post-processing methods, and easier and faster coating preparation and application.     

Luminescent photoelastic coatings

In this paper we describe a new technique to measure the surface strain field on complex three-dimensional structural components under static load. It is cost-efficient to implement and suitable to be integrated in the product design cycle in conjunction with finite element analysis tools. The technique employs novel luminescent photoelastic coatings and digital imaging to map the in-plane strain field. The coatings consist of a binder, generally polymeric in nature, and luminescent dyes that are applied to the surface of a test part using conventional aerosol techniques. When excited with circular polarized ultraviolet or blue illumination, the corresponding emission intensity from the coating is measured via a digital camera. The relative change in emission magnitude and phase as measured after passing through an analyzing polarizer is related to the in-plane shear strain and its corresponding principal direction. Several basic test results are presented and discussed, showing quantitative, repeatable, and high spatial resolution measurements.     

Effects of the thickness of birefringent coatings

It is known that birefringent coatings are a powerful experimental technique for the determination of surface strains of metals or other opaque bodies. In this paper the complete state of strain in such a coating is determined for an arbitrary one-dimensional variation of the displacement at the metal surface. It is shown that strain gradients or curvature of the surface have a pronounced effect on the observed birefringence, and must be taken into consideration. This can be done by means of two correction factors derived in the paper which take into account the elastic properties of the coating and its thickness. An experimental procedure is outlined for determining an unknown distribution of strain at the metal surface on the basis of the observed photoelastic pattern.     

Full-field strain measurement using a luminescent coating

In this paper we describe an optical-based technique, called strain sensitive skin (S³), for measuring in-plane strain data on structural members under static load. The technique employs a coating consisting of a luminescent dye and polymer binder that is applied to the surface of a test part via conventional aerosol techniques. Proper illumination stimulates the dye, which in turn emits higher wavelength luminescence. The excitation and emission intensities have different wavelengths; therefore, enabling optical filtering to separate the two signals. The optical strain response is intensity based. A network of randomized microcracks within the binder scatters the waveguided luminescence from the excited dye molecules. The amount of scattered luminescence is related to the changes in the microcrack openings and orientations via mechanical strain. Various calibration tests show the optical strain response to be proportional to the sum of in-plane principal strains. With this new experimental testing tool, full-field high-resolution strain measurements can be acquired. The optical strain response of this new sensor is minimally dependent on viewing and lighting directions, rendering the technique viable to imaging and determining strain fields for three-dimensional complex geometries.     

Coupled Strain and Fresnel Response of Photoelastic Coatings at Oblique Incidence

This paper presents a theoretical model and corresponding experimental results of the oblique-incidence response of a luminescent photoelastic coating (LPC). LPCs use a luminescent dye that both partially preserves the stress-modified polarization state and provides high emission signal strength at oblique surface orientations. These characteristics enable the technique to acquire full-field strain separated measurements and principal strain directions, potentially on complex three-dimensional geometries, without the use of supplemental experimental or analytical techniques. Results of a single-layer LPC on a disk in diametral compression are presented to assess a theoretical model and evaluate the measurement sensitivity.

Photoelastic coatings

While photoelastic-model analysis is an effective method to measure stresses, its practical use is limited to solving problems under well-defined loading conditions which can be successfully applied on a simulated basis to the model. Further, model analysis does not take into account such conditions as hidden material defects, assembly stresses, residual stresses, inelastic behavior, and other parameters that are contributing factors to the structural integrity of a part or structure. On the other hand, with photoelastic coatings, the stress analysis is conducted on real parts operating under actual service conditions. The coating reveals the true surface strains occurring on a part, since most, if not all, of the contributing stress conditions mentioned above can be taken into account during testing. Photoelastic coatings are easy to apply and, with proper test planning, are very economical to use. Since a visible picture of the stress field is provided over the entire area coated, intelligent application of the technique can save many hours of testing time and provide quick solutions to design or service-failure problems.     

Full-field isopachic generation in photoelastic coatings

A method has been developed for the generation of isopachic fringes in photoelastic coatings. This method requires that the front (outer) surface of the coating be deposited with a thin metallic film to increase the front-surface reflellctivity. The light which penetrotes the photoelastic coating reflects from the rear surface, emerges from the front surface and then combines with the frontsurface reflection to yield a system of “carrier” fringes. When the model is loaded, the carrier-fringer system is modulated by the principal-strain sums and the principalstrain differences. Superposition of the modulate carrierfringer system with the original one (by double exposure or by superposition) yields isopachic and isochromatic fringes. The isochromatics can be suppressed by proper selection of the photoelastic material to yield only isopachics for the unambiguous determination of principal-strain sums over the full field.