Damage Precursor Indicator for Aluminum 7075-T6 Based on Nonlinear Dynamics

In this work, a damage precursor indicator for aluminum 7075-T6 is proposed based on the nonlinear dynamics of a cantilevered beam system. A shouldered beam specimen is used to move the region of highest stress away from the clamped end. The beam is subject to harmonic base excitation in a uniaxial shaker. Fatigue damage accumulates in the beam with damage forming most quickly in the region of highest stress. By monitoring the tip deflection, changes in the natural frequency and response to a given excitation are correlated to fatigue life. Despite the absence of large-scale cracks, detectable changes in the nonlinear dynamics are discovered. The nonlinear dynamic parameters are estimated capturing the change in the forward and backward nonlinear sine sweeps. These changes could lend themselves to being a trackable damage precursor. The presence of microstructural precursors are confirmed using nanoindentation.