An energy density zone model for fatigue life prediction accounting for non-equilibrium and non-homogeneity effects

• Five scaling functions depict non-equilibrium and non-homogeneity effects in fatigue.
• Scatter of fatigue test data can be reflected by the proposed EDZ model.
• Microscopic effects can be taken into account.

An energy density zone (EDZ) model for the description of fatigue crack growth from micro-scale to macro-scale is developed. Five parameters in the model are scale functions that depend on the fatigue crack size or time. Therefore, the non-equilibrium and non-homogeneity (NENH) effects in a fatigue failure process can be reflected. 40CrNi2Si2MoVA steel material is a low alloy and super-high strength steel material. The trans-scale fatigue behaviors are investigated. Five scale functions in the EDZ model are determined from the S–N test data for the smooth specimens with the stress concentration factor Kt = 1. When the microscopic effects are taken into account, the scattered fatigue test data are precisely re-produced by the proposed model. Then, the fatigue lives for the notched specimens with different values of Kt (i.e., Kt = 2, 3) are predicted. In addition, the influences of microscopic effects on the fatigue behaviors are discussed. The results show that the initial micro-defects and the evolution of material micro-structures have a large influence on the material fatigue life. This is the main reason of the scatter of fatigue test data. Otherwise, the NENH effects in a fatigue failure process can be indeed reflected by the EDZ model.