Smartphone-Based Digital Image Correlation for Vibrating Structures

Digital Image Correlation (DIC) is a promising non-contact method for measuring the full-field dynamics of vibrating struc-tures. This method needs one or two cameras to measure 2D or 3D dynamics. The frames of the recorded videos are then post-processed to correlate the structure points at different times and obtain displacement information. A plethora of cameras is available - in terms of frame rate, resolution, versatility, and overall quality - the choice of which depends on the specific application and spending constraints. The idea behind this work is to evaluate the feasibility of making DIC-ready videos using cameras built into a device that is part of everyday life: the smartphone. The proposed approach is an easy-to-handle procedure, suitable for teaching purposes or an early qualitative investigation. This paper discusses a simple experiment students or be-ginners can perform on simple vibrating structures. First, a simple 2D dynamics was investigated. The vibration of a clamped beam with moving constraints was recorded with a single smartphone. The beam had an L-type cross section to emphasize in-plane motion. The frames were post-processed with open-source DIC software and the first modal shape was extracted. The goal of this assignment was to introduce students to the basics of DIC. Second, the 3D dynamics of a beam was studied with a single smartphone. The image of the beam was reflected by two mirrors and the reflected images were recorded by a single smartphone. A tool was developed to split the recorded frame into two independent images. The images were post processed to obtain the full 3D dynamics of the beam. Third, the 3D dynamics of a beam was studied with two smartphones.