Computer-aided speckle interferometry: Part II--an alternative approachusing spectral amplitude and phase information,

摘要

Abstract: An alternate approach of fully-automatic speckle interferometry is developed. Two speckle patterns of a specimen, one before and one after deformation, are registered by a video camera. These digital speckle patterns are segmented into many very small subimages. Analysis of corresponding subimage pairs is performed pointwise at various locations from both speckle patterns. Basic data process involves two-step fast Fourier transform (FFT). Local displacement vector is revealed by detecting a signal hill in the secondary spectral domain. Accurate characterization of displacement components is achieved by a biparabolic fitting and maximum-searching near the signal hill. Whole field displacement distribution is deduced by analysis of all subimage pairs. An artificial rigid shift between the two speckle patterns is introduced in case of very large displacement. The range of measurable displacement is unlimited as long as the two speckle patterns remain correlated. Incremental deformations in a dynamic loading process can be measured by registering more speckle patterns at consecutive deformation stages and analyzing each pair of successive speckle patterns. The technique has been applied to the study of crack tip deformation fields.!26