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 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 armours, intelligent medical devices, and other various morphing structures.
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.
The incorporation of conductive fillers into the polymer matrix allows for a faster response time than that of typical SMPs due to a combined response from both Joule heating and dielectric loss. 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 is 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.
1 Electric field activated shape memory behaviour of LaRC VSPc. (a) permanent shape, (b) programmed temporary shape, and (c) recovered permanent shape (inset: infrared images).
2 The LaRC VSPc shows hard and glassy behaviour at room temperature or under NO electric field; however, when the electric field or direct heat is applied, the LaRC VSPc shows soft and elastic behaviour.