Experimental and Numerical Analysis of Small Caliber Gun Barrels Under Internal Pressure Fatigue Loading

Small caliber gun barrels are subjected to repeatedly applied impulse loads from the ignition and burning of ammunition propellant. The tubes are exposed to tens of thousands of repeated peak pressures applied over very short durations that generate dynamic pressure and thermal stresses. This fundamental fracture mechanics problem of repeated cyclic pressurizations would typically cause cracks to form at the thin layer of the bore surface that would eventually grow deeper with repeated firing leading to abrupt crack growth causing catastrophic failure and potential injury or loss of life to the operator. For small caliber barrel applications, however, design practices dating back nearly 100 years have demonstrated the lack of correlation with fracture mechanics theories.

The research conducted provides a detailed understanding of the design parameters, the operating environment and the material properties that contribute to the reasons why basic fracture mechanic principles have limited application for small caliber gun barrels. Characteristics that influence crack initiation, crack propagation, and overall fatigue life were investigated. The knowledge gained will significantly impact future barrel development efforts related to realizing improvements in accuracy, range, and lethality which involve incorporating significantly increased operating pressures to achieve higher projectile muzzle velocities and energies. The research objective was achieved through material characterization, experimental testing, and numerical modeling of the gun tube environment. With this knowledge, future barrel development efforts can exploit these characteristics in order to achieve improved performance.