7075 Aluminum Alloy And Ti-1300 Titanium Adiabatic Shear Damage And Fracture Mechanisms

The effects of pre-notches with different radii of curvature on the self-organization of multiple adiabatic shear bands (ASBs) in the 7075 aluminum alloy were investigated by means of the thick-walled cylinder (TWC) technique and finite element method (FEM) for the first time. Most of the shear bands nucleate at the notch tips, and distribute in the clockwise (or anticlockwise) direction. The number of shear bands initiated in the notched specimen is much less than that in the un-notched specimen. The simulation results are in good agreement with the experimental results. The stress concentration is noticeable at the notch tip. Shear bands nucleate firstly at the notch tips under perturbation in the strain/stress fields, which produce a greater shielding effect on the large area in the vicinity of the notch. Sharper notches experience higher levels of local effective strains, whose values are about one order of magnitude higher than the global effective strains. The sharper the notches, the stronger the shielding effect in the self-organization of multiple shear bands.The fracture behaviors of the 7075 aluminum alloy under two different dynamic loading conditions are investigated by means of a light gas gun. The fracture surfaces obtained in the spall test are compared to the fracture surfaces obtained with a blunt projectile struck to the aluminum alloy plate. Optical and scanning electron microscopes are used in the investigation. For the plate impact test, spall in the target was attributed to intergranular fracture caused by the tensile stress. The fracture behavior during projectile penetration is complex and consists of several fracture modes in addition to that the fracture is also of dynamic character. The penetration process of aluminum alloy target included: plugging stage, the microcracks nucleation stage and the final tensile fracture stage. Mixed intergranular brittle/ductile fracture was observed, and brittle fracture played a dominate role.The effects of microstructure on the adiabatic shearing behaviors in the Ti-1300 alloy were investigated by means of the split Hopkinson pressure bar (SHPB) with hat-shaped specimens. Shear bands were developed in both Ti-1300 alloys withβphase andα+βlamellar microstructures during a forced dynamic shear deformation. The microstructures have a significant influence on the adiabatic shearing behaviors of Ti-1300 alloy. The critical strain for the initiation of shear bands in a+P lamellar microstructure is less than that inβphase microstructure. Theα+βlamellar microstructure experiences more extensive microscopic damage thanβphase microstructure. Therefore, theα+βlamellar microstructure is more susceptive to adiabatic shear localization deformation than P phase microstructure at the same strain rate.