Damage leading to ductile fracture under high Strain-Rate conditions

Quantitative metallographic studies of damage evolution leading to ductile fracture under high strain-rate loading conditions are presented. A model material is considered, namely, leaded brass, which contains a dispersed globular lead phase that acts as void nucleation sites. Interrupted tensile split Hopkinson bar tests have been performed to capture the evolution of porosity and void aspect ratio with deformation at strain rates up to 3000 s-1. Both uniaxial and notched specimen geometries were considered to allow the effects of remote stress triaxiality to be investigated. Plate impact testing has also been performed to investigate the evolution of damage under the intense tensile triaxiality and extremely high rates of deformation (105 s-1) occurring within a spall layer. Quantitative metallographic measurements of damage within deformed specimens are used to assess predictions from a Gurson-based constitutive model implemented within an explicit dynamic finite element code. A stress-controlled void nucleation treatment is shown to capture the effect of triaxiality on damage initiation for the range of experiments considered.