Kinetic-energy-absorbing shrouds have been proposed to protect nearby persons and equipment against high-speed debris ejected by disintegrating machines. Examples of machines that could eject high-speed debris include turbines and gyroscopes. The shrouds would be laminated composites of several materials that would be designed to transform the kinetic energy of impinging debris into controlled, progressive breakage of the materials, so that the debris would become trapped harmlessly within the shrouds.
Each shroud (see figure) would contain two layers of overlapping longitudinal metal strips surrounded by circular straps made of a strong webbing material (e.g., made from aromatic polyamide fibers). Before wrapping around the cylinder defined by the metal strips, each strap would have a circumference greater than that of the cylinder. Each strap would be sized to fit snugly on the cylinder in the following way: At numerous equidistant points around the circumference, the strap would be doubled to form loops that would be sewn together with a stitch that would rip apart by an applied load slightly below the breaking strength of the webbing itself. Thus, the straps would be capable of absorbing energy in a controlled manner by progressive ripping of the stitches.
All the looped straps thus fabricated would be assembled side by side over the cylinder of metal strips. The sewn loops would be folded to lie circumferentially against the outer surface. Depending on the specific design, another subassembly comprising another two layers of metal strips and another layer of straps with sewn loops could be formed around the previous one. The entire assembly would then be encapsulated in a rigid, low-strength foam, thereby forming a unitary energy-absorbing cylinder that would be mounted around the rotating component that posed a disintegration hazard.
Upon disintegration of the rotating component, fragments of the component would first impinge on the metal strips, forcing them into the energy-absorbing straps. The force in each affected strap would increase until it reached the ripping load, at which point the stitches in the loops would begin to come apart. During this process, the foam would break, allowing the straps to react to the force. The total energy absorbed in this way would be approximately equal to the product of the ripping force and the displacement of each strap. If the shroud were to contain multiple layers (in contradistinction to a single layer) of energy-absorbing straps, the overall radial displacement could be limited to a smaller value because each layer of straps would absorb a fraction of the total energy.
This work was done by William C. Schneider of Johnson Space Center.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Johnson Space Center
Refer to MSC-22823