Fatigue crack propagation can significantly reduce component lifespan and potentially lead to failure. The objective is to establish an equivalence relationship between variable and constant loading, thus avoiding complex cycle-by-cycle calculations, in order to determine, by means of finite element modelling, the residual stress field σr formed in front of the crack tip under an equivalent loading scheme and to compare it with that produced by real variable-amplitude loading. The analysis is conducted within a two-parameter fatigue model in which crack propagation is governed by both the maximum total stress intensity factor Kmax _ tot and the stress intensity factor range ∆Ktot. Initially, the interaction effects of the plastic zone are neglected. The Willenborg model is then used to determine the equivalent stress that ensures a comparable crack growth rate.