ANALISI ELASTOPLASTICA DI PROVE DI FATICA AD ELEVATO RAPPORTO DI CARICO SU ACCIAIO BONIFICATO E PALLINATO, COMBINANDO IL MODELLO DI CHABOCHE E LA TEORIA DELLA DISTANZA CRITICA

This study investigated the fatigue strength of plain and notched specimens of a shot peened quenched and tempered steel. The cyclic-plastic behaviour of the material was modelled by the Chaboche kinematic hardening rule with four backstress components. The parameters of the hardening model were obtained by the global properties extracted from the stabilized cycles of strain-controlled tests and from a stress-controlled test. The residual stresses were measured by the XRD technique immediately after the shot peening process and for a run-out specimen, and both were represented by FEM. The former were reproduced with the eigenstrain technique while the latter were reproduced assuming a hardening of the material in the shot peened zone. Finally, the line method and the multiaxial fatigue criterion of Smith Watson and Topper were combined for fatigue strength predictions, resulting in a good level of accuracy.