Stress Wave Characteristics and Damage Analysis of the Helicopter Tail Drive Shaft with the High-Speed Projectile Impact

The tail drive shaft is easily hit by the ground antiaircraft machine gun in low-altitude helicopter combat, resulting in projectile penetration damage and directly jeopardizing the helicopter’s safety during flight. The projectile penetration damage will cause elastic–plastic deformation and failure damage to the tail drive shaft, and excite high-frequency stress waves suitable for projectile impact monitoring. To examine the effects of different impact parameters on the stress wave characteristics and damage from the tail drive shaft during projectile impact, the LS-DYNA is used to establish a dynamic model of projectile impact on the tail drive shaft. The passive monitoring experiment of projectile impact on the tail drive shaft is carried out based on the PZT piezoelectric sensor. It is concluded that both methods can obtain reliable stress wave signals and damage conditions through the comparison of experimental and simulation results. Then, the wavelet transform and short-time Fourier transform three-dimensional time–frequency are used to select the best frequency band for extracting the stress wave eigenvalues, along with the statistics and analysis of the stress wave characteristic values and damage degree under different impact parameters. The results show that the impact stress waveforms and high-frequency components are significantly different with the change in projectile impact parameters. There are significant differences among different impact parameters on the first trough amplitude, the two peak time intervals, the kurtosis factor, and the bullet hole damage generation laws. The functional relationship between the projectile impact parameters and the characteristic parameters of the stress wave, as well as the damage degree, are established. The research conclusion can provide theoretical reference and data support for projectile impact monitoring and damage assessment of the helicopter tail drive shaft.