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首页> 外文期刊>Optics and Lasers in Engineering >Effect of surface normal variability on local surface strain measurements in StereoDIC
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Effect of surface normal variability on local surface strain measurements in StereoDIC

机译：表面正常变异性对立体码局部表面应变测量的影响

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摘要

Surface shape and surface displacement measurements for non-planar specimens are obtainable using a stereo vision system with digital image correlation (StereoDIC). The surface measurements can be employed with appropriate local surface fitting methods to extract full-field estimates for surface strains on the specimen surface. Since StereoDIC provides a dense set of 3D surface position measurements, Xi, for the entire field of view in the stereo vision system, it has been shown that these measurements will have inherent variability. This variability will propagate into any optimally defined local surface representation, including the surface's local unit vectors, such as the surface normal, n; a surface tangent, t, and the cross product, b = n x t. Once the unit vectors are estimated at surface position, Y, the surface representation at this point can be used with the orthogonal unit vectors n, b and t to obtain a set of local surface strains at Y, with variability in the initial surface shape measurements propagating into variations in the strain estimates.In the enclosed work, the authors develop a set of equations for local strain variability due to inaccuracies in the local unit vectors n, b, and t. Results are reported for the case where the unit vectors are obtained assuming a local planar fit to an N x N set of measurements Xi, and strains are determined along the two estimated in-plane directions b and t. Simulations show that the resulting strains have variability that is a strong function of the estimated normal, n. Specifically, simulations show that the estimated local strains have errors that are a strong function of both the direction of n and variability in the estimated normal, n, relative to the stereo system bisector, even if the surface strains in the original directions are exact. Experimental studies for cylindrical specimens are shown to be in agreement with the trends predicted by the simulations, demonstrating the potential importance of surface normal estimation in experimental studies.
机译：使用具有数字图像相关性的立体视觉系统（立体码），可以获得非平面样本的表面形状和表面位移测量。表面测量可以采用适当的局部表面配合方法，以提取样品表面上表面菌株的全场估计。由于立体码提供了一组密集的3D表面位置测量，因此在立体声视觉系统中为整个视野提供了XI，因此已经表明这些测量将具有固有的可变性。这种可变性将传播到任何最佳地定义的局部表面表示，包括表面的本地单元向量，例如表面正常，n;表面切线，T和横向产品，B = N x T.一旦在表面位置估计了单位向量，则此时的表面表示可以与正交单元向量N，B和T一起使用，以在Y处获得一组局部表面菌株，在初始表面形状测量中具有可变性在封闭的工作中传播到应变估计的变化中，作者在局部单元向量N，B和T中的不准确性产生了一组用于局部应变变异的方程。报告了在假设局部平面拟合到N×N测量Xi的局部平面件的情况下获得单元向量的情况，并且沿着两个估计的面内方向B和T确定菌株。仿真表明，所得菌株具有可变性，即估计正常的强功能。具体地，仿真表明，即使原始方向上的表面菌株精确，估计的局部株的估计局部应具有误差是估计正常，N的估计正常的方向和估计正常的变化的误差。圆柱形样品的实验研究显示与模拟预测的趋势一致，证明了实验研究中表面正常估计的潜在重要性。

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