Very-High-Cycle Fatigue (VHCF) is the phenomenon of fatigue damage and failure of
metallic materials or structures subjected to 108 cycles of fatigue loading and beyond. This paper
attempts to investigate the VHCF behavior and mechanism of a high strength low alloy steel (main
composition: C-1% and Cr-1.5%; quenched at 1108K and tempered at 453K). The fractography of
fatigue failure was observed by optical microscopy and scanning electron microscopy. The
observations reveal that, for the number of cycles to fatigue failure between 106 and 4×108 cycles,
fatigue cracks almost initiated in the interior of specimen and originated at non-metallic inclusions.
An “optical dark area” (ODA) around initiation site is observed when fatigue initiation from
interior. ODA size increases with the decrease of fatigue stress, and becomes more roundness.
Fracture mechanics analysis gives the stress intensity factor of ODA, which is nearly equivalent to
the corresponding fatigue threshold of the test material. The results indicate that the fatigue life of
specimens with crack origin at the interior of specimen is longer than that with crack origin at
specimen surface. The experimental results and the fatigue mechanism were further analyzed in
terms of fracture mechanics and fracture physics, suggesting that the primary propagation of fatigue
crack within the fish-eye local region is the main characteristics of VHCF.
Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness
