A combined optical technique for 360-degree measurement of 3D shape and deformation field of discontinuous surface

Many applications in industry require non-contact, fast and accurate measurement of both surface profile and deformation field for manufacturing quality control and structural testing purposes. The fringe projection technique has been widely used due to its high accuracy and spatial resolution in measuring shape and out-of-plane displacement fields, but it cannot identify in-plane displacements reliably for surfaces without macroscopic 3D texture. The 3D digital image correlation (DIC) is on the other hand a proven technique for accurately measuring 3D displacement fields, whilst its performance in shape measurement is inferior to that of the fringe projection technique primarily due to its lower spatial resolution. This paper therefore presents a novel technique that combines the strengths of the two well-recognised techniques on one measurement system. A one-camera one-projector system based on fringe projection is used to measure shape and 3D displacement field of surface with complex discontinuities. In order to achieve this, the conventional image correlation technique is modified to cope with discontinuities. The method is then extended to a multi-camera multiprojector system so that complete 360-degree surface profile and 3-D displacement field can be obtained within a unified global coordinate system. The accuracy of the current system has been validated with a plate bending experiment in comparisons with a standard 3D DIC technique and a finite element model.