Measurement of sub-surface delaminations in carbon fibre composites using high-speed phase-shifted speckle interferometry and temporal phase unwrapping

• Published in: Optics and lasers in engineering Vol. 40; no. 5; pp. 447 - 458
• Main Authors: Davila, A, Ruiz, P.D, Kaufmann, G.H, Huntley, J.M
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2003; Elsevier
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); Imaging and optical processing; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interferometers; Optical instruments, equipment and techniques; Optical metrology; Optics; Phase measurement; Phase shifting; Phase shifting interferometry; Phase unwrapping; Physics; Speckle and moire patterns; Speckle interferometry; Phase shifting; Phase measurement; Phase unwrapping; Speckle interferometry; Optical metrology; Phase shifting interferometry; Fiber reinforced material; Experimental device; Experimental study; Carbon fibers; CCD camera; Composite materials; Matrix fiber interface; Optical method; Delamination; Defect detection
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/S0143-8166(02)00082-9

A high-speed phase-shifted speckle interferometer has been developed recently for studying dynamic events. Speckle interferograms are continuously recorded by a CCD camera operating at 1 kHz with temporal phase shifting carried out by a Pockels cell running at the same frequency. Temporal phase unwrapping through sequences of more than 1000 frames allows the determination of time-varying absolute displacement maps. This paper presents the application of this speckle interferometry system to the detection and measurement of sub-surface delamination defects in carbon fibre specimens. The influence of re-referencing the temporal phase unwrapping algorithm after different time intervals is analysed to reduce the random phase errors produced by speckle decorrelation and vibration. The performance of several phase-shifting algorithms to minimize the influence of the vibration noise caused by the vacuum pump used to load the specimen is also investigated.