Electronic speckle metrology.
详细信息
- 作者：Schwab ; Wilhelm Kurt.
- 学历：Doctor
- 年：1992
- 导师：Taylor,Charles E.,eadvisor
- 毕业院校：University of Florida
- CBH：9331216
- Country：USA
- 语种：English
- FileSize：3985204
- Pages：138
文摘
Researchers at the University of South Carolina have developed Digital Correlation as a technique for the measurement of both two-dimensional and three-dimensional rigid and deformable body motion. Errors in displacement gradients as computed directly by Digital Correlation are generally on the order of 1000 micro strain. Penalty Method Finite Element smoothing has been used to generate displacement surfaces which may be analytically differentiated to compute displacement gradients more accurately. The primary disadvantage of the Digital Correlation method is that it is computationally intensive. Bruck developed a Newton-Raphson based iterative algorithm for computation of displacements and displacement gradients with fewer calculations than are required by the traditional coarse-fine search. The Newton-Raphson method still requires Finite Element smoothing to produce displacement gradients that are useable when actual displacement gradient component magnitudes are smaller than one percent. The primary goal of the current study is to develop an iterative technique for the determination of in-plane displacements and strains with reduced computation. The Perturbation/Least-Squares PLS) and Perturbation/Correlation PC) algorithms are developed to allow the iterative computation of displacement components. Published and analytic models of the correlation process,developed in the current study,indicate that displacement gradients should generally not be computed by direct correlation. The program SPECKLE,developed by the author for the current study,computes strains from center-point displacements in regions sufficiently far apart that the strains can be computed accurately. Average normal strains are computed in three nonparallel directions and then transformed into normal strains and a shear strain using strain-transformation equations. The resulting technique avoids much of the computational overhead of Digital Correlation and does not require Finite Element smoothing. The program SPECKLE is a Microsoft Windows program that runs on personal computers based on the Intel 80386 or higher processor. SPECKLE implements the PLS and PC methods of displacement computation,and normal and shear strain calculation based on strain transformation equations. Experiments performed in the current study indicate that SPECKLE may be used with an 8-bit frame grabber to measure normal and shear strains with maximum errors on the order of 100 micro strain.