AIAA 2002-1372 Shape Memory Composite Development for Use in Gossamer Space Inflatable Structures David P. Cadogan, Stephen E. Scarborough, John K. Lin, George H. Sapna III ILC Dover, Inc. Frederica, DE
43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference & Exhibit AIAA Gossamer Spacecraft Forum April 22-25, 2002 / Denver, CO For permission to copy or republish, contact the copyright owner named on the first page. For AIAA-held copyright, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, VA 20191-4344
2002-1372
SHAPE MEMORY COMPOSITE DEVELOPMENT FOR USE IN GOSSAMER SPACE INFLATABLE STRUCTURES David P. Cadogan*, Stephen E. Scarborough, John K. Lin, George H. Sapna III ILC Dover, Inc. Frederica, DE inflate the structure numerous times on the ground for testing prior to launch, and deployment in space. The materials are initially consolidated at a highly elevated temperature (Ts) to set the material’s geometric shape. This is the shape the structure will naturally return to when heated above its glass transition temperature (Tg) in subsequent heating events. The material is heated above its Tg, but not above its set temperature (Ts), to soften it for packing into small volumes. The packed structure is heated above its Tg prior to deployment in space (or during ground operations), to make it flexible enough to be deployed by inflation. The shape restoration stress Figure 1. ILC Dover SMP Inflatable memory of the composite is a Space Frame 3,4,10 weak function relative to the (Patent Pending) stress realized from 1,2,7 inflation. Stress is required for component deployment, control, and tensioning the wall for optimal shape accuracy. Therefore, the shape memory function is utilized as a microscopic shape restoration feature in most applications. The shape memory function also allows the fabrication of structures that consist of small diameter tubes where it would be inefficient to inflate all elements individually (Figure 1). The individual tubes return to shape by the shape memory of the resin, while an outer polymeric film shell is inflated to deploy the structure.3,4
ABSTRACT Several new shape memory composite materials have been developed that allow the requirements of gossamer space structures (high packing efficiency, low mass, high stiffness, etc.) to be met. A detailed analysis and test program has been conducted on several different materials at the coupon level, as well as at the component level in the form of inflatable deployable columns. Materials have been tested to determine their degradation from folding and packaging, storage life and aging characteristics, vacuum stability, outgassing characteristics, and ability to return to shape when heated after packing. Shape memory composites have also been tested at the sub-component and system level in several applications. Isogrid beam columns have been designed, manufactured, and structurally tested to verify materials performance parameters. The columns were repeatedly packed and deployed to assess the degradation of the materials in actual use and the resultant strength and stiffness loss. Compression, and torsion strength and stiffness were assessed in the test program. INTRODUCTION One of the most important components of the gossamer inflatable structure is the material of which it is composed. A leading candidate among the field of potential materials is shape memory composite material. The shape memory composite consists of a fibrous reinforcement, such as carbon, and a polymeric matrix resin such as polyurethane or epoxy. The matrix resin component provides the shape memory behavior to the composite. The reinforcement can be utilized in several forms such as individual tow elements or fabrics of various weave styles. The fibers are coated with the resin and formed into various structural shapes. Geometric shapes such as monocoque, isogrid, and IsoTruss™ columns can be manufactured from a shape memory composite material.
This paper will examine system requirements for rigidizable materials, performance characteristics of several shape memory materials, and relevant test data. Most of the data presented herein is from an isogrid
Shape memory composite materials utilize a reversible heating process to provide the ability to collapse and re*
[email protected] – Associate Fellow AIAA “Copyright 2002 by ILC Dover, Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.” IsoTruss is a registered Trademark of Brigham Young University and is licensed to ILC Dover for space applications.
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American Institute of Aeronautics and Astronautics
development program under the Inflatable Solar Array Experiment (ISAE-II) program.
bundles (tows) during the packing of a completed structure. When the tows are folded 180o for packing, the fibers on the inside of the bend radius will be in compression, while the fibers towards the outside of the bend will be in tension. To minimize structural damage in a tightly packed structure, the fibers must either be able to move, which is a function of the resin, or they must be able to withstand high strain rates, a function of both the resin and the fiber. IM9 carbon fiber was selected for further study because of its high modulus, high strength, and high strain capability.
MATERIAL REQUIREMENTS ILC generated an in-depth requirement list for the development of potential rigidizable materials. Using these requirements, ILC has developed a battery of tests that are conducted in series. This provides a “gated” approach to the development of advanced materials, one that screens out materials efficiently and reduces development cost. The driving requirements are identified as: Ø Ø Ø Ø Ø
Table 1. Select Carbon Fiber Properties1 Brand & Type
o
Tight Packing Without Damage (180 Folds) Low Outgassing (
