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An externally deployable honeycomb structure is investigated with respect to crash energy management for light aircraft. The new concept utilizes an expandable honeycomb-like structure to absorb impact energy by crushing. Distinguished by flexible hinges between cell wall junctions that enable effortless deployment, the new energy absorber offers most of the desirable features of an external airbag system without the limitations of poor shear stability, system complexity, and timing sensitivity. Like conventional honeycomb, once expanded, the energy absorber is transformed into a crush efficient and stable cellular structure. Other advantages, afforded by the flexible hinge feature, include a variety of deployment options such as linear, radial, and/or hybrid deployment methods. Radial deployment is utilized when omnidirectional cushioning is required. Linear deployment offers better efficiency, which is preferred when the impact orientation is known in advance. Several energy absorbers utilizing different deployment modes could also be combined to optimize overall performance and/or improve system reliability as outlined in the paper. Results from a series of component and full scale demonstration tests are presented as well as typical deployment techniques and mechanisms. LS-DYNA analytical simulations of selected tests are also presented.

The feasibility of using scale model testing for predicting the full-scale behavior of flat composite coupons loaded in tension and beam-columns loaded in flexure is examined. Classical laws of similitude are applied to fabricate and test replica model specimens to identify scaling effects in the load response, strength, and mode of failure. Experiments were performed on graphite-epoxy composite specimens having different laminate stacking sequences and a range of scaled sizes. From the experiments it was deduced that the elastic response of scaled composite specimens was independent of size. However, a significant scale effect in strength was observed. In addition, a transition in failure mode was observed among scaled specimens of certain laminate stacking se quences. A Weibull statistical model and a fracture mechanics based model were applied to predict the strength scale effect since standard failure criteria cannot account for the in fluence of absolute specimen size on strength.

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The effect of specimen size upon the response and strength of ± 45° angle-ply laminates has been investigated for two graphite fiber-reinforced plastic systems and several stacking sequences. The first material system was an epoxy-based system, AS4 fibers in 3502 epoxy, and the second was a thermoplastic-based system, AS4 fibers in PEEK matrix. For the epoxy-based system, two generic ±45° layups were studied; ( + 45°n/-45°n)2s (blocked plies), and ( + 45°/-45°)2nS (distributed plies), where n = 1, 2, 3, and 4. In the case of the thermoplastic system, only the layup with distributed plies was investigated, ( + 45°/-45°)2nS, for n = 1 and 2. The in-plane dimensions of the specimens were varied such that the width/length relationship was 12.7 × n/127 × n mm, for n = 1, 2, 3, or 4. It is shown that the stress/strain response and the ultimate strength of these angle-ply laminates depends on the laminate thickness and the type of generic layup used. The ultimate strength of the epoxy matrix material was found to be much more sensitive to specimen size when compared to the thermoplastic matrix system. Scaling effects defined with respect to the first ply failure, strain at ultimate failure, and ultimate strength are isolated and discussed. Furthermore, it is shown that first ply failure occurs in the surface plies as a result of normal rather than shear stresses. The implications of the experimental findings upon the validity of the ±45° tension test, which is used to determine the in-plane shear response of unidirectional composites, are discussed.