Detection of fatigue damage before crack initiation

© Photo Fraunhofer IWM

With a micro resonance fatigue set-up, we are capable of detecting early-stage fatigue damage in samples with thicknesses of approximately 200 µm. This is accomplished by tracking changes in the sample’s eigenfrequency. Through SEM analysis of fatigued nickel samples, it was possible to correlate measured eigenfrequency changes with the following fatigue stages: extrusion development, crack initiation in single grains, and micro-crack growth. The bending and torsion fatigue set-up consists of two piezoactuators and a laser system used for the measurement of sample displacement and the control of the oscillation amplitude.