DIC vibration measurement through smartphone devices

Abstract

Digital Image Correlation (DIC) stands as a promising non-contact method for assessing the complete dynamics of vibrating structures. Utilizing one or two cameras, DIC can capture either 2D or 3D dynamics. Through subsequent post-processing of images, structural points are correlated across different time frames to derive displacement information. Given the abundance of camera options available, spanning frame rate, resolution, versatility, and quality, the selection process is dictated by specific application needs and financial considerations. This study seeks to explore the feasibility of utilizing the cameras integrated into a ubiquitous device of everyday life: the smartphone. The proposed approaches offer straightforward procedures suitable for educational purposes or early investigation of structure dynamics. The paper presents case studies and discusses simple experiments that students or DIC beginners can conduct on simple vibrating structures. Initially, a simple 2D dynamics was investigated by recording the vibration of a clamped beam with moving constraints using just a single smartphone. The L-type cross section of the beam emphasizes its in-plane motion. The frames were post-processed with open-source software and the deformed shapes were extracted. This assignment serves as an introductory exercise in DIC fundamentals. Subsequently, the focus shifts to investigating the 3D dynamics of the beam. Given the challenges associated with synchronizing multiple smartphone video acquisitions, the image of the beam was instead reflected by two mirrors, and these reflected images were recorded by a single smartphone. Then, the recorded images were split and processed to obtain the full-field 3D dynamics of the beam.