Hydraulic Testing of Ordnance Components

Bai

et al. 2023

Fatigue is one of the failure modes in gun barrel. It is still an important problem to understand crack propagation behavior due to fatigue loading of firing cycles. This paper presents a hydraulic fatigue test method to simulate crack propagation in a tube containing a pre-machined defect on its inner surface. A close inherent relation is found between crack propagating rate and hoop strain on the outside surface of the tube, which provides a feasible approach for investigation of fatigue behavior in gun barrel under actual firing condition.

Section: Introductionmentioning

confidence: 99%

Fatigue crack propagation in thick-walled pressure vessels under hydraulic testing condition

Bai

et al. 2023

Damage and fracture of gun barrel under wear-fatigue interaction

Luo

et al. 2020

Gun, projectile and propellant are three fundamental components of a launching system. Generally, a barrel has to be condemned after a number of rounds have been fired. During the total useful life of gun barrel, it bears severe damage induced from erosion by high pressure and high temperature propellant combustion gas, and wear due to high speed friction between projectile and gun bore. Meanwhile, the gun barrel undergoes a dynamic loading of gas pressure, mechanical stress and thermal stress when firing a round. Thousands of firing cycles lead to gun barrel fatigue. Interaction of wear, including erosion, and fatigue damages the gun barrel and eventually the gun will become inaccurate because of wearing away gun bore materials. However, a gun barrel will fracture in a sudden manner because of fatigue. It is found that microcracks form on the bore surface after only a few rounds have been fired, which lays the foundation for growth and propagation of cracks under fatigue loading. In this paper, laboratory hydraulic fatigue tests were carried out on a tube with pre-machined crack on its inner surface by using an MTS 809. Strain gauges were adhered to the outer surface of the tube to monitor strain during testing process. The hydraulic oil pressure was measured by a pressure sensor. The experimental results show that there are three stages of outer surface strain variation, namely stable increase, fast increase and abrupt increase, which corresponds to the history of crack evolution. Crack grew stably in the initial stage under cycle of loading and a major crack is gradually formed. When the major crack size reaches a certain value, the propagation velocity of crack is accelerated fast and the critical size is reached in a short time. Eventually the tube fractured suddenly. The experimental findings will help us to gain new insight into the physical mechanism of fatigue and fracture of gun barrel and provide a possible method to evaluate health of gun barrel in service.

Fatigue failure and launch safety assessment of gun barrel

2021

Hundreds or thousands of projectiles have been fired through a gun barrel. Catastrophic fatigue failure of gun barrel due to cyclic loadings by the stresses induced by the combination of high pressure and temperature combustion gas, and projectile with the rotating band interaction with the bore surface, has not yet been understood. In this paper, laboratory hydraulic fatigue tests on simulated gun barrel were performed on MTS Land. The experimental results show that there is an inherent relation between crack propagation in thick-walled tube and the external surface hoop and axial strains. This fact suggests that fatigue failure of gun barrel should be likely prevented by monitoring the external surface strains of the gun barrel and stopping continued firing before a major crack growing up to the critical size.