NASA’s Langley Research Center has developed a novel design for a lightweight energy absorbing (EA) composite subfloor structure. The technology’s primary application is to increase occupant survivability in the event of an aircraft crash. Current airframe subfloors unpredictably buckle, splay, and collapse under crash loads. This technology exploits the inherent stability associated with a conusoidal geometry and material combination of carbon and aramid fibers to allow the structure to bend and fold in a controlled manner at a particular load level.
The technology’s conusoidal geometry is based on right-side-up and up-side-down half cones placed in an alternating and repeating pattern. This geometry combines a simple cone design with a sinusoidal beam geometry to create a structure that utilizes the advantages of both designs. The first major advantage of the conusoidal design is it provides crush trigger mechanisms due to dissimilar conical radii dimensions on the crash front. This is consistent with many EA designs that contain trigger mechanisms to limit the peak crush load and achieve acceptable crush initiation behavior. Second, because the conical walls are formed at an inward angle relative to the geometric centerline of each cone, the crushing is self-stabilizing. Finally, the dissimilar radii create an inherent forward-leaning angle (see the figure), which offers advantages when examining loading conditions with a multi-axial component of loading.
Many potential materials and layup combinations were candidates for the fabrication of the conusoidal EA. Specific interest was given to both the conventional and hybrid families of woven fabrics. Hybrid material systems consisting of carbon and aramid fibers were considered for use since they would potentially contain desirable characteristics for energy-absorbing performance. These material systems would offer both stiffness characteristics from the carbon fibers and deformation/ ductility characteristics from the aramid fibers.
Langley Research Center’s technology is simple to manufacture, and is more lightweight than metallic airframe alternatives. It has better lateral loading effects compared to traditional metallic structures that are less stable and can buckle or break. The EA composite subfloor structure will be tested under full-scale helicopter conditions, providing additional comparison data. Potential applications include aircraft, rotorcraft, spacecraft re-entry vehicles, automobiles, and packaging containers.