A comment on “Predicting metallic armor performance when impacted by fragment-simulating projectiles–model review and assessment”, by W. Schonberg and S. Ryan, Int. J. Impact Eng. (2021)

In a recent article Schonberg and Ryan (2021) reviewed nine analytical models from various sources, and examined their ability to predict the experimental ballistic limit velocities (V_bl) of various metallic plates impacted by fragment simulating projectiles (FSP). These models analyzed the complex FSP/plate interaction, through simplified force equilibrium or energy conservation considerations. Schonberg and Ryan (2021) found that these models can predict the ballistic limit velocities to within ± 50% for more than 50% of the data base entries. On the other hand, they point out that "these models do not include the ductility and toughness properties of the materials involved", referring to the oversimplifications made in these models. The predicted V₅₀ values were given in these models in terms of the plate's properties (strength, density and thickness), as well as the density and dimensions of the projectile. In particular, these models result in monotonic expressions between the predicted V_nl values and the corresponding strengths of the plates. The purpose of our comment is to demonstrate that, in fact, the test data in many cases do not follow this prediction.