For High Energy Dynamic Impact (HEDI) events, testing to evaluate the structural response of primary aircraft structure for design and certification is both expensive and time consuming. This paper discusses current work seeking to assess, develop, and validate appropriate analytical models that accurately predict physical response, damage, and failure modes for large scale composite structures in HEDI events. Four state-of-the-art Progressive Damage Analysis (PDA) methods were employed for this phased project: LS-DYNA MAT162, LS-DYNA MAT261, Smoothed Particle Galerkin (SPG), and EMU Peridynamics. Multiple material systems were considered, namely T700/5208 textile-infusion triaxial braid, T800/AMD-825 textile-infusion triaxial braid, IM7/8552 uni-directional tape, and SPG 196-PW/8552 plain-weave fabric. Extensive ballistic impact testing was performed to support this activity and measured results were compared to predictive models for assessment using panel delamination, panel displacement, force at the load cells, and threshold velocity as measures. Ultimately, the work under this activity provided significant progress in advancing the state-of-the-art in the use of PDA for HEDI events. Each material model had favorable performance comparing to test in some parameters and needed improvement in others. With the lessons learned from this activity, significant progress was made in the ability to predict panel behavior for a more general case beyond the flat panel in a ballistic impact event. Subsequent Phase II of the NASA ACC HEDI effort will continue to build on the coupon testing, flat panel ballistic impact testing, and analysis performed to-date with application of the PDA methods for intended material selections to test articles with greater complexity of configuration, curvature, and scale. It is not the intention of this paper to present a full set of data, but rather to give an overview of the NASA HEDI effort and show a small representative subset of the test and analysis results.
Corrosion affects the maintenance of metal aircraft. Because the onset of corrosion is unpredictable, sensing corrosion is a challenge and scheduled inspections are mandated by corrosion prevention and control programs. Visual inspection is the most common method of corrosion detection. Visual inspections of aircraft structures that are difficult to access are costly and invasive. Beyond visual inspection, several non-destructive corrosion detection methods exist, such as ultrasonic scanners and pulsed eddy current systems. The functionality of these systems, however, does not minimize the invasiveness of inspections. Access to the structure under inspection is required to use these systems or to perform visual inspections. This paper describes a self-powered, wireless corrosion detection system which could enable modification of existing inspection schemes in difficult-to-access areas where corrosion is expected to develop, for example, on structure beneath an aircraft galley or lavatory. The system consists of an energy harvester, an energy storage and conditioning circuit, a corrosion sensing element, and a wireless transceiver network. Advances in energy harvesting and low-power wireless transceivers have enabled the design. The system allows users to download corrosion data from a sensor through a wireless connection, without the need for costly structural disassembly. Because the device is self-powered and wireless, it operates indefinitely without battery replacement, and does not require power or data wiring from the aircraft.
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