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.