Visualizing nonlinearity and non-repeatability in bolted joints through digital image correlation

The dynamics of bolted joints are known to be highly complex in terms of nonlinearity and non-repeatability. This has been established primarily through traditional experimental modal analysis techniques that measure the system response using accelerometers or laser doppler vibrometers. These single-point system identification techniques are powerful tools for detecting nonlinear behavior and non-repeatability but they do not interrogate the underlying physical processes that cause this behavior. High-speed 3D Digital Image Correlation (DIC) is applied to a corner-bolted square plate system under dynamic load to identify the specific region of the frictional interface responsible for nonlinear behavior. Non-repeatability is similarly investigated using DIC by comparing non-repeatability in measured displacement fields to non-repeatability in dynamic response. Multiple plate thicknesses are tested to determine the applicability of the results to generalized systems and whether the mechanical properties of the bolts dominate the repeatability behavior of the joint. DIC and modal testing results are compared to a finite element model to evaluate the performance of current predictive modeling techniques. [Work supported by the Office of Naval Research under Grant No. N00174-22-1-0015.]