6. A Multi-view DIC Approach to Extract Operating Mode Shapes of Structures

Accelerometers have been conventionally used to measure the response of structures for modal analysis. These pointwise sensors only provide information at a few discrete locations being measured. Additionally, the use of accelerometers to capture the response at discrete locations can mass-load the structure. Thus, the obtained results may not predict the true dynamics of the structure. Stereo-photogrammetry and Three-Dimensional Digital Image Correlation (3D DIC) have recently been adopted to collect operating data for vibration analysis. These non-contact optical techniques provide a wealth of distributed data over the entire structure. One of the limitations of a stereo-camera system is its line of sight, which limits the field of view; a single pair of DIC cameras may not be able to provide deformation data for the entire structure. Several pairs of cameras may be coupled simultaneously to perform DIC measurement on large complex structures. However, the use of multiple cameras involves huge costs and may not be a viable choice. In this paper, a multi-view 3D DIC approach is used to predict the dynamic characteristics of a cantilever beam as a sample structure. A pair of DIC cameras is roved over the entire structure to capture the deformation data of each field of view. Each measured data includes the geometry and displacement data which is later mapped into a universal coordinate system. The measured data is stitched in the frequency domain to extract the operating shapes of the entire structure.