| This thesis presents a study of ductile failure under high strain rate deformation based on the study of interrupted test specimen microstructures using light microscopy and Scanning Electronic Microscopy (SEM). The materials used in this study are tantalum, tantalum-tungsten, Armco iron, and leaded brass which are of different crystal structures, (i.e. BCC and FCC) and purities. The effects of triaxility on damage rates are also studied using different specimen configurations, corresponding to uniaxial, c-notch, and e-notch.; The study has demonstrated that ductile failure is dependent upon the material purity, second phase particle size and distribution, and stress triaxiality level. The high purity metals studied (tantalum and tantalum-tungsten alloy) failed by ductile rupture to form a chisel point. Conversely, with the presence of inclusions or second phase particles, the Armco iron and brass failed by ductile fracture through void nucleation, growth, and coalescence. Under high triaxiality, the tantalum-tungsten alloy displayed cleavage fracture triggered by the presence of small inclusions.; The Gurson damage model is also employed to simulate ductile fracture through void nucleation, growth, and coalescence in the iron and brass samples. These calculations were performed using the explicit finite element code LS-DYNA. A comparison of measured and predicted damage rates reveals a reasonable degree of accuracy using the Gurson model. |
