Research
Scott’s research interests are in the areas of smart materials including shape memory alloys and cellular composites including active cellular materials. Active Cellular Materials (ACMs) represent a new class of materials that join the defining characteristics of two existing material types: cellular solids and active, or "smart" materials. ACMs have a relative density (ratio of solid to overall volume) comparable to other cellular solids, on the order of 30% or less, and incorporate one or more smart materials or actuators into their cellular structure.
Potential applications for ACMs include shape-morphing wings for aircraft, tunable rotors for helicopters and turbine generators, space deployable structures, seismic dampeners for civil structures, expeditionary air fields, deployable protective armor or “cushions”, etc. All these applications require shape-morphing, energy absorbing, self-healing, and/or on-demand (deployable) functionality.
The photograph above is of an ACM having a 2-D (lamellar) cellular structure. The structure comprises an assemblage of cells, each cell constructed of four rigid strut members (referred to as “links”) joined by pivot pins at their ends and configured into a diamond shape. The pivot pins extend to engage adjoining cells that repeat in the horizontal and vertical direction to form the scissor structure. The cellular layers may then be stacked in the depth direction to create a lamellar structure.
The SMA member extending diagonally across the unit cell serves as the deformation and actuation mechanism of the scissor structure. As a compressive force is applied to the structure, the horizontally opposed pins are forced apart, thereby sacrificially deforming the SMA element in tension. The scissor structure is then in its compressed configuration. The links do not plastically deform but remain elastic and rotate on the pivot pins. On heating the SMA to its austenite start temperature (A s), a martensite-to-austenite phase transformation begins that partially recovers the undeformed configuration of the SMA. The horizontally opposed pins are drawn together by the SMA, which is trained to contract on heating, and the vertically opposing pins are forced apart, returning the scissor structure to its recovered (or deployed) configuration. Heating the SMA to the austenite finish temperature (A f) brings the phase transformation to completion. As the SMA cools below the martensite start temperature (M s), an austenite-to-martensite phase transformation occurs with no shape change, so that the scissor structure remains in the deployed configuration. Cooling below the martensite finish temperature (M f) completes the phase transformation. This cycle of compression, heating and recovery (deployment) is repeatable. Heating of the SMA may be achieved by means of a heated/cooled fluid, direct resistance (Joule heating), or by other means.
Click here for a link to a video showing recovery of the ACM from a compressed configuration.