Measurement of three-dimensional surface shape and deformations using phase stepping speckle interferometry
A complete system for the measurement of 3D shape and deformation of curved surface under 3D loading has been developed based on a digital speckle pattern interferometer and the phase shifting technique. A system incorporating an optical arrangement of four beams and a personal computer- based image processor has been devised and built. When the four beams are appropriately arranged, six sensitivity vectors are provided, of which three are independent. Measurements along these three independent vectors are jointly utilized to solve for the 3D displacement components. During the calculation of the displacements, the surface shape coordinates are required, which in our case are provided by a shape measuring procedure. This procedure is implemented by traversing one of two selected beams in the optical setup. A four-step phase retrieving algorithm is employed to automatically perform the data reduction. To this end, 16 speckle patterns are first acquired and then analyzed to obtain the surface height distribution and the 3D displacements and their derivatives. Measurement results for a closed cylindrical specimen under internal pressure are presented.