Numerical investigation of kinetic-energy reduction and tip equivalent (von Mises) stress of an RPG surrogate inside a 3D-printed UAS fuselage under high-speed impact

Abstract

Additive manufacturing offers a practical approach for producing low-cost UAS structures; however, the impact response of additively manufactured fuselage sections carrying internal payloads remains insufficiently established. This study numerically investigates the high-speed impact response of a 3D-printed UAS forward fuselage carrying an inert RPG surrogate. An explicit-dynamics model was developed in ANSYS Explicit Dynamics and evaluated against published battery-to-plate impact data. Additional numerical verification included a PLA failure-strain sensitivity study and local surrogate-tip mesh refinement, while a 3.0 m drop-test simulation provided an approximately 400 MPa mechanical reference stress. Nine UAS impact cases were then simulated using velocities of 15, 20, and 25 m/s and approach angles of 0°, 22.5°, and 45°. Impact severity was characterized using the kinetic-energy reduction of the surrogate assembly, deltaKE=KE(t₀)-KE(t), and equivalent (von Mises) stress at the surrogate tip. Increasing impact velocity generally increased the maximum observed kinetic-energy reduction, while greater impact obliquity reduced its magnitude and delayed its development. The highest observed deltaKE was 804.74 J at 25 m/s and 0°, while the lowest was 104.83 J at 15 m/s and 45°. Tip stress behavior exhibited a less uniform trend, with five of the nine cases reaching or exceeding the 400 MPa reference and the highest value, 564 MPa, occurring at 25 m/s and 45°. In eight cases, the maximum tip stress occurred before the maximum observed kinetic-energy reduction. Results indicate that although the global kinetic-energy reduction of the RPG surrogate assembly and the maximum local tip stress are influenced differently by impact velocity, approach angle, and fuselage-collapse behavior, they still provide complementary measures of impact severity.