Title: A Non-Contact Technique for Vibration Measurement of Automotive Structures
text: The automotive and aerospace industries are increasingly using the light-weight material to improve the vehicle performance. However, using light-weight material can increase the airborne and structure-borne noise. A special attention needs to be paid in designing the structures and measuring their dynamics. Conventionally, the structure is excited using an impulse hammer or a mechanical shaker and the response is measured using uniaxial or multi-axial accelerometers to obtain the dynamics of the structure. However, using contact-based transducers can mass load the structure and provide data at a few discrete points. Hence, obtaining the true dynamics of the structure conventionally can be challenging. In the past few years, stereo-photogrammetry and three-dimensional digital image correlation have received special attention in collecting operating data for structural analysis. These non-contact optical techniques provide a wealth of distributed data over the entire structure. However, the stereo camera system is limited by its field of view of the cameras and can only measure the response on the parts of the structure that cameras have the line of sight. Therefore, a single pair of Digital Image Correlation (DIC) cameras may not be able to provide deformation data for the entire structure. In current work, a multi-view 3D DIC approach is used to predict the vibrational characteristics of a full vehicle. A pair of DIC cameras is roved over the entire vehicle to capture the deformation data of each field of view. The measured data includes the geometry and displacement data which is mapped into the global coordinate system using 3D transformation matrices. The obtained data in the time domain for each field of view is transformed to the frequency domain using the Fast Fourier Transformation (FFT) to extract the operational deflection shapes and resonant frequencies for each field of view. The obtained deflection shapes are scaled and stitched in the frequency domain to extract the operating deflection shapes of full vehicle.