Fatigue evolution during the flaw initiation phase and under high cycle fatigue conditions is described at the level of the representative volume element by the probability that this element fails in a given period of time under given stimulus. This probability is calculated as a function of the accumulated inelastic work density. For the calculation of small amounts of inelastic work in the quasi-elastic domain of materials, a microplasticity model is developed using the hypothesis of strain energy density equivalence and a statistical distribution of work concentration within the RVE. The model is successfully fitted to experimental data. (C) 2015 Elsevier Ltd. All rights reserved.