共查询到20条相似文献,搜索用时 31 毫秒
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High-speed photographic systems are necessary for recording and visualization of dynamic events in stress analysis, fluid mechanics, etc. Current imaging systems are fairly expensive and generally not simple to use. Furthermore, most are based on photographic film recording systems requiring time consuming and tedious wet processing of the films. Recently, there is lot of interest in developing and modifying CCD architectures and recording arrangements for dynamic scene analysis. Herein we report the use of a CCD camera operating in the time delay and integration mode for digitally recording dynamic photoelastic stress patterns. Applications in strobe and streak photoelastic pattern recording and system limitations will be explained in the paper. In addition, a scheme for dynamic phase shifting using is also explained. 相似文献
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基于斯托克斯参量的光弹性应力分布及成像方法研究 总被引:4,自引:0,他引:4
提出了一种基于斯托克斯参量测量的实时光弹性应力测量及其成像的新方法,对该方法的原理及参量测量方法进行了深入研究。根据分振幅斯托克斯参量测量原理设计一个实验系统,利用Equator-Poles(E-P)法定标系统,采用4个性能一致的光电探测器实现光束斯托克斯参量的快速实时测量。用实验系统测量单色平面偏振光通过光弹性样品后的斯托克斯参量,求得出射与入射偏振光的相位延迟量,再求得样品的应力值。运用该方法对有应力分布的平板玻璃和轴向受压有机玻璃进行测量并扫描成像,得到它们的应力分布图像。结果表明,该方法能够准确、快速和无损地测量光弹性样品任意位置的应力,实现对应力的实时测量。 相似文献
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Use of phase shifting has revolutionized the acquisition of photoelastic data. Even since its introduction, various researchers have improved the methodology. In phase shifting the problem of ambiguity exists in the sign of fractional retardation in some zones of the model. This has been overcome with the development of load stepping. However, the conventional approach to data processing in load stepping introduces several noise points in the phase map. In this paper a new methodology for data reduction in load stepping, which removes the noise points in the domain is presented. Results from four- and six-step algorithms are analyzed. A normalization scheme to improve the results has been proposed. A comparative study has also been carried out on the evaluation of phase map by phase shifting, load stepping and the new methodology. 相似文献
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Quarter wave plates are optical elements commonly used in photoelasticity to obtain circularly polarized light. They divide the incident light field into two linearly polarized orthogonal components with a phase difference of a quarter of the light wavelength. Due to the tolerance in manufacturing, however, the actual phase shifting produced by the plates is affected by an error, which noticeably influences the photoelastic measurements performed by means of various automated methods. This paper presents a technique, based on the phase stepping method, for the full field automatic evaluation of the quarter wave plate error. 相似文献
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Photoelastic stress analysis is a full-field optical technique for experimental stress analysis whose automation has received considerable research attention over the last 15 years. The latest developments have been made possible largely due to the availability of powerful calculators with large memory capacity and colour, high resolution, cameras. A further stimulus is provided by the photoelastic resins now used for rapid prototyping. However, one critical aspect which still deserves attention is phase unwrapping. The algorithms most commonly used for this purpose have been developed in other scientific areas (classical interferometry, profilometry, moiré, etc.) for solving different problems. In this article a new algorithm is proposed for temporal phase unwrapping, which offers several advantages over those used today. 相似文献
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Photoelasticity is a whole field experimental technique to obtain stress fields in both 2-D and 3-D elasticity problems. The accuracy of parameter evaluation by digital photoelastic techniques depends on the choice of the optical arrangements for parameter estimation, the inherent error in optical elements and any misalignments introduced during experimentation. A generic approach to simulation of error in digital photoelasticity by Jones calculus is presented in this paper. Of late it has been shown that the quarter-wave plate mismatch error is varying and is not a constant value. The present simulation accounts for inherent variable error in quarter-wave plates and also accommodates the error arising due to the optical misalignment of the various optical elements. The applicability of the new methodology is shown for different phase shifting techniques. A comparative study among various techniques is done regarding sensitivity to general error sources and it is found that the ten-step method is the least sensitive among them all. Therefore usage of the ten-step method is thus recommended while using manual polariscope for digital photoelastic applications. 相似文献
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The effect of photoelastic relaxation is investigated using triglycine sulfate ferroelectric crystals as an example. The optical and deformation contributions to the photoelastic relaxation are described, and their percentage in the combined effect is determined. Consideration is given to the temperature dependences of the relaxation amplitudes of the path difference and birefringence, which are induced by mechanical stress. 相似文献
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Automatic methods of photoelasticity have had a significant progress with the development of automatic acquisition and image processing methods. This article concerns RGB photoelasticity, which allows the determination of the photoelastic retardation using, usually, a single acquisition of the isochromatic fringes in white light by a colour camera. In particular, the article presents an overview of the main characteristics of RGB photoelasticity that is influence of the quarter-wave plate error, number of acquisitions, type of light source, determination of low and high fringe orders, methods for searching the retardation, scanning procedures, calibration on a material different from that under test, combined use of the RGB and phase shifting methods. A short section on the applications of RGB photoelasticity completes the article. 相似文献
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Among data acquisition techniques in digital photoelasticity, the integrated phase shifting technique (IPST) can real-time analyze the photoelastic parameters at a video rate of the high speed CCD camera. In this paper, fourteen algorithms are described by different configurations of the rotating an analyzer at a constant rate and an output quarter-wave plate at another constant rate. The theoretical comparisons of the algorithms are given by the simulated phase distributions of the isochromatic and isoclinic parameters of the disk under two cases that the load keeps unchangeable or linearly increasing in exposure time of the camera. Then a guideline is given to alleviate the influence of the load changing with time on the IPST. 相似文献
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Among data acquisition techniques in digital photoelasticity, the integrated phase shifting technique (IPST) can real-time analyze the photoelastic parameters at a video rate of the high speed CCD camera. In this paper, fourteen algorithms are described by different configurations of the rotating an analyzer at a constant rate and an output quarter-wave plate at another constant rate. The theoretical comparisons of the algorithms are given by the simulated phase distributions of the isochromatic and isoclinic parameters of the disk under two cases that the load keeps unchangeable or linear increasing in exposure time of the camera. Then a guideline is given to alleviate the influence of the load changing with time on the IPST. 相似文献
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In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference is one of the widely used techniques for stress separation in photoelasticity and one needs the value of fringe order and the isoclinic angle free of noise at every pixel over the domain. For accurate parameter determination, a ten-step phase shifting approach which uses a plane polariscope for isoclinic determination and a circular polariscope for isochromatic determination is proposed. A new quality guided approach for isoclinic unwrapping is developed. Isochromatic phasemap free of ambiguous zones is obtained by a new methodology and is unwrapped by a quality-guided approach. Whole field evaluation of stress components and its representation is then presented. The models used in this study are intentionally subjected to moderate loads showing a high level of isochromatic–isoclinic interaction. In view of this, the isoclinic data has several kinks which is found to cause streak formation in the whole field representation of separated stress components. An outlier smoothing algorithm is proposed for getting a smooth variation of the digital photoelastic parameters over the domain. Use of such smoothed data for stress separation has removed the streaks and has also greatly improved the accuracy of the separated stress components. 相似文献
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对于三维光弹模型,次主应力及其方向沿入射光连续变化,根据光学等效的原理,可以将三维光弹模型等效为一个包含线性相位延迟器和旋光器的光学模型。在集成光弹法中,对于每一个测量点,研究者必需通过实验获取三个特征参数。提出了一种用于确定集成光弹中全场特征相位差的五步相移法,给出了偏振光场中元器件的设置方法,并运用Jones算子推导出相移法得出的光强公式。最后使用斜射法对径向受压圆盘进行实验,验证了方法的有效性。 相似文献
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In this work, digital photoelasticity technique is used to estimate the crack tip fracture parameters for different crack configurations. Conventionally, only isochromatic data surrounding the crack tip is used for SIF estimation, but with the advent of digital photoelasticity, pixel-wise availability of both isoclinic and isochromatic data could be exploited for SIF estimation in a novel way. A linear least square approach is proposed to estimate the mixed-mode crack tip fracture parameters by solving the multi-parameter stress field equation. The stress intensity factor (SIF) is extracted from those estimated fracture parameters. The isochromatic and isoclinic data around the crack tip is estimated using the ten‐step phase shifting technique. To get the unwrapped data, the adaptive quality guided phase unwrapping algorithm (AQGPU) has been used. The mixed mode fracture parameters, especially SIF are estimated for specimen configurations like single edge notch (SEN), center crack and straight crack ahead of inclusion using the proposed algorithm. The experimental SIF values estimated using the proposed method are compared with analytical/finite element analysis (FEA) results, and are found to be in good agreement. 相似文献
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A digital speckle pattern interferometry and hole drilling combined system is developed to determine the magnitude of the residual stress in a aluminum thin plate subjected to an uniform uniaxial tensile load. Performing automated fringe analysis, the optical data contained in the speckle interferograms are quickly converted into values of residual stress. The evaluation is carried out through the measurement of the in-plane displacement field generated by the introduction of the small hole. The displacement field is determined from the calculation of the optical phase distribution by means of a phase shifting method. The magnitude of the residual stress is finally evaluated through a least-squares calculation and compared with the stress value applied to the specimen. 相似文献