NASA’s Langley Research Center has developed a novel shape memory polymer (SMP) made from composite materials for use in morphing structures. In response to an external stimulus such as a temperature change or an electric field, the thermosetting material changes shape, but then returns to its original form once conditions return to normal. Through a precise combination of monomers, conductive fillers, and elastic layers, the NASA polymer matrix can be triggered by two effects — Joule heating and dielectric loss — to increase the response. The new material remedies the limitations of other SMPs currently on the market; namely, the slow stimulant response times, the strength inconsistencies, and the use of toxic epoxies that may complicate manufacturing. NASA has developed prototypes and now seeks a partner to license the technology for commercial applications.
Joule heating is achieved by the application of a low-level current that is diffused uniformly across the polymer when an electric field is applied. The addition of an alternating field shortens the thermal response time due to dielectric loss. Voltage application is determined by the specific material dimensions. For a benchtop-scale device, about 10-40V was required for activation of the material.
Furthermore, the technology’s variable stiffness polymer composite (VSPc) is laminated with highly elastic layers to provide additional stored elastic energy, resulting in a higher recovery force than that of similar materials currently on the market.
The technology is being used in a laboratory setting at NASA, and prototypes have been built, with durability and fatigue testing underway.
The NASA Langley SMP was originally designed for smart active structures in morphing spacecraft and airfoils to provide noise reduction and increased stability. The technology may also have applications in self-deployable structures, smart armors, intelligent medical devices, and other various morphing structures.