Computer-aided speckle interferometry: Part II--an alternative approach using spectral amplitude and phase information

摘要

Abstract: An alternate approach of fully-automatic speckleinterferometry is developed. Two speckle patterns of aspecimen, one before and one after deformation, areregistered by a video camera. These digital specklepatterns are segmented into many very small subimages.Analysis of corresponding subimage pairs is performedpointwise at various locations from both specklepatterns. Basic data process involves two-step fastFourier transform (FFT). Local displacement vector isrevealed by detecting a signal hill in the secondaryspectral domain. Accurate characterization ofdisplacement components is achieved by a biparabolicfitting and maximum-searching near the signal hill.Whole field displacement distribution is deduced byanalysis of all subimage pairs. An artificial rigidshift between the two speckle patterns is introduced incase of very large displacement. The range ofmeasurable displacement is unlimited as long as the twospeckle patterns remain correlated. Incrementaldeformations in a dynamic loading process can bemeasured by registering more speckle patterns atconsecutive deformation stages and analyzing each pairof successive speckle patterns. The technique has beenapplied to the study of crack tip deformationfields.!26