Sensor synchronized DIC: A robust approach to linear and nonlinear modal analysis using low frame rate cameras

Abstract

Digital image correlation (DIC) is a non-contacting, optical method for measuring full-field displacements. Recently, there has been interest in DIC as a tool for experimental modal analysis. Currently DIC necessitates the use of high-speed cameras that satisfy the bandwidth requirements for the system under investigation. High-speed cameras, however, tend to be expensive, bulky, and low-resolution, thus limiting their application. In contrast, low-speed cameras tend to be cheaper, smaller, and higher-resolution. In this work an alternative approach that utilizes low-speed cameras is developed. The approach functions by synchronizing image capture against a high bandwidth reference sensor. This enables images to be precisely captured at prescribed moments in a waveform. A basic algorithm is developed for the synchronization, including an uncertainty analysis to estimate phase errors arising from the approach. The method is then demonstrated by using low-speed cameras to estimate the full-field amplitude response of a thin, cantilevered plate. This is achieved by alternating image capture between extremums during a swept-sine test. The excitation level is then increased to elicit a highly nonlinear response from the plate. Measurements are repeated to demonstrate that the approach works even when the system exhibits large harmonic distortions.