Optimized design for projectile impact survivability of a carbon fiber composite drive shaft

Helicopter power transmission systems consist of aluminum drive shafts which are connected together with flexible couplers to accommodate misalignment and hanger bearings to secure each drive shaft to the airframe. The development of carbon fiber composites have resulted in designs which reduce the weight of the system as well as eliminate parts which can be integrated into the composite material itself. The reduction in weight and parts provide transmissions which are more maintenance cost conscious as downtime related to manual part inspection for defects and damage is reduced. One barrier to fielding composite systems is impact qualification to ensure passing of survival standards. Some certainty that a design will not increase the vulnerability of a vehicle must exist and this paper provides an impact study for flexible composite drive shafts and performs a design analysis on tradeoffs between weight, and residual strength. 16 drive shafts with two different thicknesses and the optimized lamination [±456/±402] were manufactured and impacted with either 7.62 or 12.7 mm projectiles while under 252 N-m of torque.