Hydrodynamic Ram Analysis of Bonded Composite Fuel Tanks

Abstract

Military aircraft are tested against a variety of ballistics threats as part of their design to assess their vulnerability. One aspect of this approach/requirement is Hydrodynamic Ram testing which accounts for projectile impact into fuel tanks. Hydrodynamic Ram (HRAM), which occurs due to overpressure created in an enclosed fluid as a result of the transfer of energy and momentum from a penetrating projectile, can be quite destructive to the enclosing structure, which makes testing expensive. Therefore the need arises for numerical methods to supplement the testing and provide more test data than can be obtained directly from the article test. This research uses the building block approach to extrapolate failure from a single joint coupon level testing to a fuel tank using a progressive damage failure model. Independent joint testing by way of a Ram Simulator or RamGun, which is a device capable of creating HRAM order pressure, enables evaluation of T-joints to assess HRAM resistance. The ALE fluid-structure interaction technique is used in concert with Cohesive Zone Modeling via the commercial explicit finite element software LS-DYNA to predict damage in a fuel tank. Previously-used numerical techniques have minimum requirements that demand a fine mesh size to ensure accurate results. That approach is impractical for analyzing dynamic behavior in large articles like fuel tanks. Therefore a coarse mesh approach is devolved to satisfy the requirement for both CZM and ALE FSI techniques to ensure accurate damage prediction results. The developed model is used to study the effect of velocity and projectile location on tank damage as well as HRAM damage mitigation techniques.