HYBRID STRUCTURES FOR IMPROVED DAMAGE TOLERANCE OF UBITIZED STRUCTURES

ABSTRACT: Recent developments of advanced hybrid metallic structural concepts have been promising for enhancing durability and damage tolerance (D & DT) of unitized aircraft structures. The Alpha STAR team, comprised of Alcoa, Northrop Grumman (NGC), and Southwest Research Institute, proposes to demonstrate and verify/validate the application of advanced hybrid materials in a realistic large scale military aircraft structure. The proposed effort consists of: (1) design of low cost fiber metal laminates for insertion in lower wing panel of NGC"s conceptual military transport plane; (2) layout, sizing, robust design, manufacture, and test of structural component. The test plan includes static testing to design limit loads, fatigue testing in presence of discrete source damage, and residual strength after fatigue. This effort will apply multi-scale, multi-site virtual simulation progressive failure analysis and metallic/composite material characterization tool, developed and building block validated in Phase I effort. Phase II will utilize the developed analytical tool to achieve robust design considering uncertainties in geometrical, material and fabrication processes. We will verify D & DT performance, weight, and life cycle cost benefits obtained from hybrid materials compared to those of a baseline. We will apply our expertise in hybrid material and aircraft design, advanced virtual simulation, and testing to meet program objectives. BENEFIT: Based on work done in Phase I, the Alpha STAR team (Alcoa, Northrop Grumman Corporation NGC, South west Research Institute SwRI) analytically demonstrated enhanced damage tolerance capability for unitized aircraft structures. A 20% reduction in weight and 20% reduction in life cycle cost (20/20) coupled with improved performance are anticipated from the use of Fiber Metal Laminates (FML). Improved damage tolerance under fatigue loading is obtained with these advanced materials as compared to conventional all metallic construction. NGC, as a premier developer, fabricator and integrator of manned and unmanned aircraft expressed great interest in exploring use of these advanced materials in conceptual military transport aircraft. As demonstrated in Phase I, this work will also lead to expanded use of software simulation-based tools for assessing structures made from advanced material concepts with minimum testing support. The availability of well-established, well verified tools will aid in the certification by analysis of components from advanced materials. This will reduce testing by at least 30% as compared to current standards and will open the way to use these advanced materials to their maximum potential.