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 produce 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 failure mode from plastic collapse to ductile fracture and brittle failure by increasing the specimen size. An interpretation 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 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 constitutive laws to correctly predict the ductile fracture. Finally, scale-invariant cohesive properties are derived on the base of the fractal approach to the size effect.