Fatigue Insensitivity of Nanoscale Freestanding Aluminum Films

We demonstrate a microelectromechanical-system-based setup for fatigue studies on 200-nm-thick freestanding aluminum specimens in situ inside the transmission electron microscope. The specimens did not show any sign of fatigue damage even at 1.2 ×10⁶ cycles under nominal stresses about 80% of the static ultimate strength. We show direct evidence to propose that the conventional theory of fatigue crack nucleation through slip bands does not work for nanoscale freestanding thin films, which gives rise to the anomalous fatigue insensitivity.