Structural Response of Flat Panels to Hydraulic Ram Pressure Loading

Abstract : Aircraft structural surfaces often serve as the walls of integral fuel cells. Projectiles penetrating the fuel generate intense pressure waves capable of producing catastrophic failure of the cell walls. This phenomenon, termed hydraulic ram, can lead to structural kill of the aircraft. Massive fuel loss, resulting from fuel cell failure, can also lead to aircraft kill by on- board fires or by fuel starvation. Drag forces acting to decelerate the projectile are the source of pressure waves that propagate into the fuel. A prominent characteristic of the fluid flow is a cavity that extends from the projectile back to the impact point.The theory for hydraulic ram effects in fuel tanks impacted by high-speed projectiles is extended. Experiments were performed with a simple, instrumented water tank and the test results compared with theoretical predictions. The comparison was good for hydraulic ram pressure in the water tank and for strain in the water tank walls. Predictions of catastrophic failure in the aluminum wall panels were in agreement with observations. The extended theory allows calculation for multiple impacts of projectiles that are supersonic with respect to the fluid. Energy-absorbing foam and air gaps at the fluid/structure interface are now included in the theory. Effects of dynamic cavitation at the fluid/structure interface on pressure loading are accounted for. (aw)