As well as providing 3D deformation measurements, the arrangement has also been used to determine the object shape by moving one of the illuminating beams. For the shape and deformation measurements, thirteen independent speckle patterns are acquired and processed. Phase maps are produced using a conventional 3-step technique and hence surface contours, displacements and strains can be obtained.
A speckled object-reference beam is used and has the advantage that the measurements are less sensitive to vibration and whole body motion than a smooth reference beam arrangement. A flat surface mounted in proximity to the surface under investigation acts as a reference plane and is used to improve the accuracy of the measurements by validating the phase-stepping steps and verifying geometric and sensitivity parameters.
The technique has been applied to the measurement of a cylinder under internal pressure. The experimental results are compared with conventional point measurements. The optical arrangement and experimental methodology are described. Advantages and limitations of the technique, together with sources of error and measurement uncertainties are discussed.