Surface Strain Measurement for Non-Intrusive Internal Pressure Evaluation of a Cannon

The U.S. Army has recently developed cutting edge designs for gun barrels, projectiles, and propellants that require testing. This includes measuring the internal pressure during fire. There are concerns with the current method of drilling to mount pressure transducers near the breech and chamber of the gun barrel where pressure is highest. An alternative, non-intrusive strain measurement method is introduced and discussed in the present work. This focuses on determining the feasibility and accuracy of relating tangential strain along the sidewall of a gun barrel to the drastic internal pressure rise created during combustion. A transient structural, numerical modal was created using ANSYS of a 155 mm gun barrel. The pressure gradient was derived using a method outline in IBHVG2 (Interior Ballistics of High Velocity Guns, version 2), and the model was validated using published experimental tangential strain testing data from a gun of the same caliber. The model was used to demonstrate the ideal location for strain measurement along the sidewall of the chamber. Furthermore, three different pressure ranges were simulated in the model. The behavior of the tangential strain in each case indicates a similar trend to the internal pressure rise and has oscillation due to a dominant frequency of the barrel. A method to predict internal pressure from external tangential strain was developed. The internal pressure predicted is within 4% of the pressure applied in the model. A sensitivity study was performed to determine the primary factors affecting tangential strain. The study specifically looked at material properties and geometry of the gun barrel. The thickness and elastic modulus of the gun barrel were determined the most relevant. Overall, the present work helps to understand tangential strain behavior on the sidewall of a large caliber gun barrel and provides preliminary work to establish an accurate prediction of internal pressure from external tangential strain.