Dynamic Multiaxial Tests for Ductile Fracture Characterisation of 17‐4PH and Ti6Al4V at High Strain Rates

The assessment of ductile damage at high strain rates poses challenges both at an experimental and numerical modelling levels. Indeed, testing requires special facilities, such as the split-Hopkinson bar (SHB), through which it is not trivial to reproduce the multiaxial stress states that are mandatory for a robust material characterisation and tuning of numerical damage models. The paper proposes the use of a minimal but effective set of cylindrical, notched and shear-tension specimens which can be tested using a conventional SHB only to investigate material strains to fracture at different (low) triaxialities and Lode angles. The materials investigated are a 17-4PH steel and a Ti6Al4V titanium alloy. Experimental ultimate fracture strains corresponding to the different stress states are shown, along with the results of damage model calibration. It is proved that the approach can lead to an accurate dynamic characterisation, and that two widely used damage models can provide effective predictions even when high strain rates are involved. Finally, a comparison between dynamic and quasi-static ductile fracture behaviour for the two materials is presented and discussed.