Effect of irradiation damage and indenter radius on pop-in and indentation stress-strain relations: Crystal plasticity finite element simulation

•A strain-gradient crystal plasticity theory involving the pop-in mechanism is proposed for ion-irradiated materials.•Effect of indenter radii and irradiation defects on pop-in is analyzed by crystal plasticity finite element simulation.•Numerical results can match well with corresponding experimental data under spherical nano-indentation. [Display omitted] In this work, a crystal plasticity finite element model is developed to simulate the spherical nano-indentation of ion-irradiated metallic materials. Two critical features are addressed by the proposed theoretical framework, which include the pop-in event observed in the loading force-indentation depth (P−h) relations and irradiation hardening characterized by the transformed indentation stress-strain (ISS) curves. For the former, the pop-in event is dominated by the dislocation nucleation mechanisms, which are affected by both the density of irradiation-induced dislocation nucleation sites and indenter radii. For the latter, irradiation hardening is closely related to the heterogeneously distributed irradiation-induced defects within the irradiated layer with a limited depth. By applying the developed model to the spherical nano-indentation of helium-irradiated single crystal tungsten, it is informed that the simulated results can match well with corresponding experimental data, which include the unirradiated and irradiated P−h and ISS relations at different indenter radii. Moreover, the evolution of different hardening mechanisms during the indentation process is systematically analyzed, which can help comprehend the fundamental deformation mechanisms of ion-irradiated materials under spherical nano-indentation.