Experiments have confirmed the feasibility of a new class of lightweight, reliable, simple, and low-cost expandable structures. The concept called "cold hibernated elastic memory" (CHEM) utilizes the shape memory polymers (SMPs) in open cellular structures. Basically, these structures are SMP foams that are under development by Jet Propulsion Laboratory (JPL) and Mitsubishi Heavy Industry (MHI).
In CHEM concept, the structures of any shape, such as rods, tubes, wheels, boards, chassis, packages, tanks, and the like, are fabricated from larger SMP foam blocks. Subsequently, they are compacted to very small volumes in rubbery (flexible) state above the glass-transition temperature (Tg) and later cooled below Tg to glassy state. When the stowed structure is frozen, the external compacting forces are removed and the part can be stowed in cold hibernated state for unlimited time below Tg. A compacted part can be heated above Tg to rubbery state and the original shape will be precisely restored by simultaneous elastic recovery of the foam and its shape-memory polymer effect. A fully deployed structure can be rigidized by cooling below Tg to glassy state. Once deployed and rigidized, a part could be heated and recompacted. In principle, there should be no limit on achievable number of compaction/deployment/rigidization cycles.
The main advantages of the CHEM structures over conventional polymer foams are as follows:
- Both, elastic and plastic compressive strains are precisely recovered;
- High full/stowed volume ratios are achieved;
- High ratios of elastic modulus (E) below Tg to E above Tg allow to keep original shape in stowed, hibernated condition, without external compacting forces;
- Small temperature range for full transformation from rigid to rubbery state reduces the heat consumption during deployment (shape restoration);
- Wide range of Tg from -70 to +100 °C results in many applications.
Advantages over other expandable/deployable structures are as follows:
- high reliability,
- low cost,
- no deployment/inflation systems,
- clean deployment and rigidization,
- none or very little long-term stowage effects, and
- inexpensive technology development.
The disadvantage of CHEM structure is that heat energy is needed for deployment. However, natural heat sources are considered to be utilized and studies/proof-of-concept are planned to be conducted.
A wide range of Tg from -70 to +100°C results in a myriad possible space and terrestrial commercial applications. The CHEM concept could be applied to shelters, hangars, camping tents or outdoor furniture, to mention just a few. Such articles could be made of an SMP foam with a Tg slightly above the highest outdoor summer temperature. The CHEM parts can be transported and stored in small packages, then expanded by heating at the outdoor site. After expansion, the CHEM parts will be allowed to cool to ambient temperature below their Tg and rigidize.
This work was done by Witold Sokolowski and Artur Chmielewski of Caltech for NASA's Jet Propulsion Laboratory.