DAVILA, A. ... et al, 2003. Measurement of sub-surface delaminations in carbon fibre composites using high-speed phase-shifted speckle interferometry and temporal phase unwrapping. Optics and Lasers in Engineering, 40 (5-6), pp.447-458.
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. Temporalphase 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 subsurface
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
severalphase-shifting algorithms to minimize the influence of the vibration noise caused by the
vacuum pump used to load the specimen is also investigated.