Crack propagation mapping at component-level fatigue testing by means of natural frequency tracking control

Advancements seeking structural components' strength and weight reduction necessarily pass through fatigue testing. Understanding failure phenomena and crack evolution is a way of methodologically achieving such a goal. An own-designed resonant fatigue test rig was used to study the behavior of three distinctly manufactured crankshaft batches. A control system and a resonant frequency estimator were developed to follow the overall stiffness reduction with crack advancement. The control algorithm followed the frequency decay to compensate for the input load. The control strategies were validated by finding the system's natural frequency at the beginning of the test and maintaining a constant nominal load. Fractographies made with failed and non-failed specimens revealed the connection between the expected physical results and the natural frequency shift evolution. The implemented logic enables crack advancement tracking and failure determination. The developments here can be overflown to different resonance fatigue systems to characterize their endurance performance.