A TV Holo-Shearography System For Nde
Basanta Bhaduri, N. Krishna Mohan and M.P. Kothiyal
TV holo-shearography is a powerful non contact optical measurement technique for non destructive evaluation (NDE). The technique combines both TV holography and TV shearography into one unit to detect defects in structures by correlating the anomalies of out-of-plane deformation and its derivatives in lateral direction (slope), respectively. We present here such a system which detects the anomalies in honeycomb structures. ALabVIEW based software has been developed to control the precision movement of the piezoelectric transducer unit for phase shifting, storing, and for real-time visualization of deviations of the correlation speckle and speckle shear patterns near the defect area. A (5,1) phase shifting algorithm is used for quantitative analysis. Such an algorithm is suitable for NDE of structures under quasi-dynamic loads. An advanced filtering technique has been incorporated to reduce the speckle noise and improve the wrapped or modulo-2&Mac185; phase map obtained from the phase shifted speckle and speckle shear fringe patterns. Phase unwrapping software has been developed using a discrete cosine transform (DCT) to generate the 3-D profiles.