How deep does it go? — the physics behind the concrete-penetration tool
Play the two-zone penetration model, then read where every symbol and constant comes from. The on-ramp to the A4 tool.
Impact Engineering
Concrete Penetration Depth — Analytical Pipeline (Li & Chen 2003)
From projectile geometry and impact velocity to penetration depth — dimensionless formulation, regime selection (shallow/deep), and numerical verification against 82 test points.