Investigations into slope and curvature fringe formation using digital speckle shear interferometry

Abstract

Shearography is an interferometric technique that enables real-time, non-contact and fullfield

measurement of surface displacement derivatives to overcome the limitations of

holographic interferometry techniques. This technique is highly efficient for nondestructive

testing (NOT) of many industrial materials such as composites to disclose the

defects in an object by identifying defect-induced deformation anomalies which are

pertinent to structural weakness. In this project, shearography based NOT studies were

conducted with the designed circular diaphragm samples under defect and defect free

conditions using the developed shearography system. Defect-induced changes of the

fringe patterns in honeycomb panels with and without defect under thermally loaded

conditions were also studied. The first derivative of the displacement gradient known as

shear fringes were digitally processed by computer integrated software to extract curvature

fringes by adopting Fast Fourier Transformation (FFT) method. Different image

processing based contrast enhancement schemes were applied on the acquired shear fringes

prior to compute second order derivative (curvature fringes). The effect of shearing and

the defect detection capability of shearography system have also been investigated.