Investigations into slope and curvature fringe formation using digital speckle shear interferometry
Sembhu Sundarnath Amarlal
Date of Issue2014
School of Mechanical and Aerospace Engineering
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.