Ceramic Fiber Structures for Cryogenic Load-Bearing Applications
- Monday, 27 July 2009
Woven or braided fibers resist embrittlement under cryogenic conditions, enabling ultralow-temperature applications.
This invention is intended for use as a load-bearing device under cryogenic temperatures and/or abrasive conditions (i.e., during missions to the Moon). The innovation consists of small-diameter, ceramic fibers that are woven or braided into devices like ropes, belts, tracks, or cables. The fibers can be formed from a variety of ceramic materials like silicon carbide, carbon, aluminosilicate, or aluminum oxide. The fiber architecture of the weave or braid is determined by both the fiber properties and the mechanical requirements of the application. A variety of weave or braid architectures is possible for this application. Thickness of load-bearing devices can be achieved by using either a 3D woven structure, or a layered, 2D structure. For the prototype device, a belt approximately 0.10 in. (0.25 cm) thick, and 3.0 in. (7.6 cm) wide was formed by layering and stitching a 2D aluminosilicate fiber weave. The circumferential length of the 2D, layered belt was approximately 36 in. (91 cm).
To demonstrate the resistance to abrasion while under load, the ceramic fiber belt was installed on two aluminum spools that were mounted in an Instron load frame. Both spools were completely enclosed in a Lexan box within the load frame. Bearings were used at each end of the spool shafts to allow the spools to spin freely while a load was applied. The lower spool, which was secured to the stationary head of the load frame, was also attached to a small motor to drive the rollers. The upper spool was attached to the movable crosshead of the Instron frame to apply a load to the belt while it was rolling. JSC1a, a highly abrasive lunar regolith simulant, was added to the Lexan box. Enough JSC1a was placed in the bottom of the box to allow the belt to contact and pick up the dust as it traveled around the lower spool. The track was exposed to the dust while rolling under load for several hours to simulate relevant rover mission duration. After 12.5 hours of exposure to the lunar simulant, under loads varying between 50 and 100 N, no elongation or mechanical creep of the belt was measured. Under these loads, which were estimated to be comparable to those required for tracks on the lunar rover, there was no deformation or loss of load carrying ability.
To demonstrate flexibility under cryogenic conditions, individual fibers and fiber tows were exposed to cryogenic temperatures by being submerged in liquid nitrogen for 4 minutes, and then were flexure tested. Immediately upon removal from the liquid nitrogen, the fibers and tows were wrapped around mandrels of progressively smaller diameters. Both the fibers and the tows were successfully wrapped around wire mandrels with a diameter of approximately 0.02 in. (0.5 mm) without any breakage. The continuous ceramic belt that is envisioned for the lunar rover would be a closed-edge, multilayer weave with through thickness holes woven in place. The holes in the weave would engage the sprockets on the drive mechanism of the track device.
This work was done by Martha H. Jaskowiak and Andrew J. Eckel of Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18364-1.
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