Dynamic Response of Additively Manufactured Martensitic Steel to Shock, Spall, and Pressure-Shear Loading

The application of additive manufacturing (AM) to create geometrically intricate components for the tailorable mechanical response of systems has been an area of intense research for more than a decade now, and continues to recieve interest from both the industrial and military communities. However, a comprehensive understanding of the mechanical behavior - particularly in extreme environments - of AM materials remains incomplete and so too does our ability for predictive analysis and design. In the following study, multiple AM variants of the relatively low cost, high strength martensitic steel AF9628 was subjected to a variety of dynamic impact conditions in a effort to observe and understand the resulting mechanical response. Shock, spall, and pressure-shear loading conditions were applied, whereafter Photon Doppler velocimetry and post mortem material analysis was used to quanitfy the thermomechanical behavior in-situ and determine the material Hugoniot, elastic limit, dynamic spall behavior, and high strain rate shear behavior. SEM microscopy was then use to examine microstructural factors during deformation based off of samples specimens soft recovered from experiment. Results serve as a basis for discussion regarding the implication of AM build parameters on munitions relevant material characteristics - like compression strength v. fracture resistance. Complimentary simulations were conducted using the CTH hydrocode in an effort to examine how significant a role characteristics such as porosity play in the thermodynamic response as well as in constitutive behavior.