Single-axis combined shearography and digital speckle photography instrument forfull surface strain characterization

摘要

Full characterization of the surface strain requires the measurement of sixdisplacement gradient components of the surface strain tensor. The out-of-planedisplacement gradient component may be directly measured using the full-fieldspeckle interferometry technique of shearography, but to fully characterize thesurface strain using shearography, a minimum of three illumination, or viewing,directions are required. The image processing technique of digital specklephotography (DSP) is sensitive to in-plane displacement for normal collinearillumination and viewing, with the displacement gradient components obtained bydifferentiation. A combination of shearography and digital speckle photographyis used to perform full characterization of the surface strain using a singleillumination and viewing direction. The increase in complexity compared with astandard single-channel shearography system lies predominantly in the additionalimage processing requirements. Digital speckle photography image processing isperformed using the optical flow field technique and the advantages of thistechnique compared with correlation are discussed. The design of the instrumentis described and full surface strain measurements made with the system arepresented.