Presently, metallic aircraft structures extensively use either an isogrid or conventional, rib stiffened, monocoque construction. However, in an attempt to reduce weight an increasing use has been made of adhesively bonded or brazed metallic structures, the most notable example being the internal honeycomb sandwich composite. Unfortunately, honeycomb laminates have in the past been plagued by serious problems associated with ensuring bond integrity, maintainability, accommodating mechanical fasteners, susceptibility to corrosion, and lastly from poor repairability. Attempts to substitute fibrously reinforced composites are met with only limited success, partially due to difficulties associated with poor repairability, high cost, and poorly understood material behavior. Recently, however, a new method has been developed to construct relatively lightweight yet highly reliable and extremely robust bonded or brazed metallic structures. This new construction method referred to as "Grid-Lock", represents an extension to the familiar isogrid construction that is in common usage. Unlike an isogrid which relies primarily on a single rib stiffened skin, "Grid-Lock" achieves superior strength and stiffness by the addition of a second skin. To ensure that there is excellent load transfer, recesses are machined into the surface of the attached skin in order to engage the internal ribribetiffeners. This provides an additional mechanical interlocking effect which substantially reinforces all bond or braze joints. The intent of this proposed study will be to assess the suitability as well as the full potential of the "Grid-Lock" construction method for the production of lightweight yet highly reliable metallic based aircraft structures. This will be accomplished throught analytical studies aimed at identifying the optimum design configuration for various part geometries and applied load states. A limited mechanical test effort will be conducted to corroborate analytical predictions. At the conclusion of the effort, an assessment will be made as to the feasibility of applying "Grid-Lock" to the construction of lightweight aircraft structures as well as the other benefits conferred by this technology.
Keywords: Modified Isogrid Lightweight Robust Sandwich Structures
