# High strain composite structure

High Strain Composite Structures (HSC Structures) are a class of composite material structures designed to perform in a high deformation setting. High strain composite structures transition from one shape to another upon the application of external forces. A single HSC Structure component is designed to transition between at least two, but often more, dramatically different shapes. At least one of the shapes is designed to function as a structure which can support external loads.
High strain composite structures usually consist of fiber-reinforced polymers (FRP), which are designed to undergo relatively high material strain levels under the course of normal operating conditions in comparison to most FRP structural applications. FRP materials are anisotropic and highly tailor-able which allows for unique effects upon deformation. As a result, many HSC Structures are configured to possess one or more stable states (shapes at which the structure will remain without external constraints) which are tuned for a particular application. HSC Structures with multiple stable states can also be classified as bi-stable structures.
HSC Structures are most often used in applications where low weight structures are desired that can also be stowed in a small volume. Flexible composite structures are used within the aerospace industry for deployable mechanisms such antennas or solar arrays on spacecraft. Other applications focus on materials or structures in which multiple stable configurations are required.

## History

Metals commonly used in springs (e.g. high strength steel, aluminum and beryllium copper alloys) have been utilized in deformable aerospace structures for several decades with considerable success. They continue to be used in the majority of high strain deployable structure applications and excel where the greatest compaction ratios and electrical conductivity are required. But metals suffer from having high densities, high coefficients of thermal expansion, and lower strain capacities when compared to composite materials. In recent decades, the increasing need for high performance deployable structures, coupled with the emergence of a robust composite materials industry, has increased the demand and utility for High Strain Composites Structures. Today HSCs are used in a variety of niche aerospace applications, mostly in areas where extreme precision and low mass are required.
In early 2014 the American Institute of Aeronautics and Astronautics Spacecraft Structures Technical Committee recognized that the level of active research and development in High Strain Composites warranted an independent focus group to distinguish high strain composites as a technical area with uniquely identifiable challenges, technologies, mechanics, test methods, and applications. The High Strains Composite Technical Subcommittee was formed to provide a forum and framework to support HSC technical challenges and successes, and will promote continued advances in the field.

## Space-Flight Heritage

The use of high strain deployable structures dates back to the pioneering days of space exploration and has played a crucial role in enabling a robust spacefaring industry.
Milestones in Space-Based Deformable Structures
| Structure Common Name | Material | Development History | Flight History |
| Tape-Spring Hinge | Spring steel sheet | | |
| Storable Tubular Extendible Mast (STEM) | Metal sheet | Developed by de Havilland Canada and Spar Aerospace Ltd. | 1961-AH2 Transit Research and Attitude Control (TRAAC), launched 1961. Alouette 1, launched in 1962 |
| Wrap Rib Antenna, C-Shaped Ribs | Aluminum sheet | Developed by Lockheed Missiles & Space Company starting in 1962 | ATS-6, launched in 1974. |
| Lenticular Tube | Stainless steel sheet | Developed by NASA Lewis Research Center in 1965 | |
| Continuous Longeron Mast | S2 fiberglass rods | Developed by Astro Aerospace. | USAF S-3 Magnetometer Boom launched in 1974. |
| Lattice Lenticular Tube | Steel music wire | Developed by Astro Research Corporation in 1969. | |
| Wrap Rib Antenna, Lenticular Ribs | Glass fiber reinforced polymer laminate (Fiberite HMS/33) | Developed by Lockheed Missiles & Space Company in the 1970s; ground demonstration 1982. | |
| Spring Back Antenna Parabolic Reflector | Glass fiber reinforced polymer laminate | | Mobile Sat-1, launched in 1996 |
| Foldable Flattenable Tubes | fiberglass and Kevlar laminate | Developed by TRW Astro Aerospace for MARSIS antennas, launched 2003 | Mars Express MARSIS antennas, launched in 2003 |

## Material Classification

Rigid Polymer
Rigidizable Polymer
Elastomeric Polymer

## Technical Challenges

Creep
Thin Shell Buckling
Simulation Methods