Experimental evidence and numerical simulation of size effects on the ductile fracture of metallic materials

The results of experimental tests investigating the size effects on single-edge-notched metallic specimens loaded in three-point bending are presented. Five different specimen scales were tested, with dimensions varying within the range 1:16. The samples were subjected to a fatigue pre-cracking to pro- duce a sharp crack stemming from the notch root and, then, a quasi-static loading process was carried out up to the complete failure, in order to capture also the post-peak response. Notable size effects on the overall behaviour were obtained, with a variation of the fail- ure mode from plastic collapse to ductile fracture and brittle failure by increasing the specimen size. An inter- pretation of the obtained size effects on ductile fracture is proposed based on numerical simulations carried out with a finite-element model that combines the cohesive method and the J 2 plasticity to take into account all the possible mechanisms for energy dissipation. The best- fitting of the experimental results is obtained by scaling the mechanical properties with the specimen size, thus proving the need of considering size-dependent con- stitutive laws to correctly predict the ductile fracture.