Erosion test facility for small caliber gun barrels

Small caliber gun barrels show multiple failure mechanism in use, like bore expansion, fatigue, wear and specially erosion. Erosion is caused by thermal and mechanical effects when the gun barrel material is exposed to the hot gun propellant gases and the friction between the projectile and barrel by moving through the barrel. Additionally, a chemical reaction between the reaction products of the gun propellant and the gun barrel can take place, which makes the process of erosion to a very complex and hard to modelling process. Consequences of an eroded gun barrel are for example gas slippage, a lower muzzle velocity and an expansion of the hit pattern. Small caliber guns are furthermore often used in continuous firing mode through which the erosion effects are multiplied and the end of life of the gun barrel is reached far earlier. To investigate the erosion mechanisms, an experimental setup was drafted and assembled at Fraunhofer-ICT. In addition to the basic characterization of the gun propellant in a closed vessel, a vented vessel equipped with a pressure sensor was used. Thus, erosion is represented by the weight loss of the nozzle during the combustion of the propellant. Uncoated nozzles exposed to the hot gases show heat affected zone and gas wash erosion. In addition, a test bench was established to investigate erosion in small caliber gun barrels under laboratory conditions, analyzing the barrels with an optical laser-based surface mapping system. The aim of this research is to get a better understanding of the erosion process, to investigate the influence of different gun propellants and to determine factors resulting in higher erosivity. First results are presented in the following using the propellant powder of the ammunition 7.62x51 mm DM111A2.