Shape and displacement measurement of discontinuous surfaces by combining fringe projection and digital image correlation

Abstract

We describe how a shape-measurement system (SMS) based on fringe projection can be combined with a two-dimensional digital image correlation (DIC) technique to accurately measure both surface profile and displacement fields at the same time. Whereas the measurement of all three displacement components by traditional DIC requires the use of at least two cameras, the approach presented here provides the full three-dimensional (3-D) displacement field from a single-camera, single-projector SMS with no additional hardware requirements. Furthermore, the single-pixel spatial resolution of the fringe projection technique can be exploited to prevent the correlation peak-splitting phenomenon that occurs when a DIC subimage straddles a global geometrical discontinuity. Thus, unlike traditional 3-D DIC techniques, the proposed method can measure displacement fields on discontinuous surfaces as easily as on smooth ones. Details of the algorithm are given together with experimental results of a rigid-body translation test. Measurements made during a routine fatigue test on a part of a wing panel are also presented.