?The Applicability of the Manson-Coffin Law and Miner's Law to Extremely Low Cycle Fatigue

Attention has been focussed on the characteristics of the fatigue life of annealed low carbon steel in the extremely low cycle fatigue regime. In this regime, a transition of the fracture mode occurs from the surface to internal cracking with an increase in the plastic strain range. Results show that in this regime the final fracture occurs at a strain cycle count less than that expected from the Manson-Coffin law for an ordinary low cycle fatigue regime in which the development of small surface cracks leads to the fracture of the specimen. Such a reduction in fatigue life is caused by the cracking of pearlite inside the material at a high plastic strain range. The applicability of Miner's law to the prediction of the fatigue life under a variable plastic strain amplitude in the extremely low cycle fatigue regime has also been discussed.