Study of projectile impact damage to the helicopter tail drive shaft and its effect on crack propagation life

The helicopter tail drive shaft is vulnerable to penetration damage from ground anti-aircraft fire in low-altitude combat. The crack around the bullet hole will be propagated under torsional fatigue loading, which can result in shaft fracture and significantly jeopardize flight safety. Considering the effect of the projectile incidence angles and radial offsets on its damage morphology, finite element analysis and two-stage light gas gun experiment are performed to investigate the detailed damage characteristics, and the effects of two typical impact parameters on the crack propagation life of the tail drive shaft have been further analyzed. A simplified bullet hole morphology is established based on geometric similarity. The crack propagation life of the damaged tail drive shaft is investigated through a combined approach of finite element analysis and fracture mechanics theory. The results show that an increase in the incidence angle and radial offset causes the axial and radial damage dimensions of the bullet hole to gradually expand, and the degree of damage of the tail drive shaft gradually increases. The crack propagation life of the damaged tail drive shaft shows a declining trend, and radial offset impacts have a greater effect on crack propagation life than incidence angle impacts.