Ballistic impact response of high strength aluminium alloy 2014-T652 subjected to rigid and deformable projectiles

Experimental and numerical studies were conducted to determine the impact response of 15 mm thick AA2014-T652 forged plates in the velocity region from 800 m/s to 1300 m/s. Spherical projectiles (10 mm diameter) of hardened steel and soft iron were launched from propellant gun of 30 mm bore diameter and their impact and residual velocities were measured by capturing the impact phenomena with a high speed camera. Residual velocities of projectiles were in good agreement with Recht-Ipson analytical model, when kinetic energy of the fragments ejected from the target was accounted for in the energy balance. Failure in target plates occurred due to a combination of failure mechanisms such as hydrodynamic flow, spalling, ductile hole growth and scabbing. A comprehensive material characterization program was executed to study the plastic flow and failure of the material. Tensile tests were carried out on target and projectile materials at different stress triaxialities, strain rates and temperatures. The experimental data of stress-strain curves were used to calibrate the material parameters of Johnson-Cook constitutive model, which relates the flow stress of the material to effective plastic strain, strain rate and temperature. Fracture strain values were used to calibrate the material parameters of Johnson-Cook failure model, which relates the fracture strain of a material to stress triaxiality, strain rate and temperature. Finite element analyses of all the impact experiments were carried out using a two dimensional axisymmetric model. Numerical results overestimated the ballistic limit velocities as the quasi-brittle fracture of target could not be captured using Johnson-Cook failure model. Limitations of Johnson-Cook failure model were analyzed and numerical simulations were repeated using hydrostatic tensile stress failure model. A non-linear equation of state was also introduced in the model for more accurate calculations of hydrostatic stress. These modifications resulted in an excellent correlation between experimental and numerical results.