High strain rate compression and tension response of high hard tool steel

Abstract
The cores of armor piercing (APM2) bullets are generally made of high hard (Rc ≈ 60-62) 1070 steel. Tool steel of type AISI O1 is very similar in composition to 1070 steel and can be heat-treated to Rc 60-61. We are conducting a study to generate material model data to numerically simulate the penetration of .30 and .50 caliber M2AP bullets into a variety of ceramic/aluminum/steel ballistic targets. Compression and tension properties of heat treated tool steel are to be presented. The compressive and tensile behavior of AISI O1 tool steel is studied through quasi-static tests, Hopkinson bar experiments and Taylor impact tests. Compressive strength of the heat-treated tool steel increases by a factor of 3 compared to untreated tool steel. Furthermore, experimental data suggest that hard tool steel is strain rate insensitive in tension as well as in compression. However, measured compressive strength (3.5 GPa) and tensile strength (2.5 GPa) at high strain rates (10³/s) are different, suggesting that the material behaves almost like a ceramic. A constitutive model for the material is developed based on the experimental data and is used to simulate ballistic penetration into 6061-T6 aluminum and alumina ceramic/aluminum targets.