Bistable Actuators Based on Shape Memory Alloy/ Polymer Composites

Abstract

The thermal induced martensitic phase transition in TiNiHf was exploited for bi-directional actuation with TiNiHf/SiO2/Si composites. When compared to free-standing films of similar thickness, films on a substrate exhibit a reduced fatigue effect upon thermal cycling and a smaller hysteresis width. Differential scanning calorimetry (DSC) and cantilever deflection measurements (CDM) results showed that the transition temperatures of fabricated TiNiHf films and TiNiHf/SiO2/Si bimorph composites decrease with thermal cycling. The change in transition temperatures after 40 thermal cycles is significantly reduced for TiNiHf films bound to a SiO2/Si substrate compared to the functional fatigue DSC results reported for freestanding films. The thermal hysteresis width is also reduced for TiNiHf films constrained by SiO2/Si and Si substrates compared to freestanding films of similar thicknesses. With proper composition selection and microstructural control, TiNiHf films can be promising SMA films for bistable actuators with PMMA/TiNiHf/Si composites.

Shape Memory Alloy Thin Film Auxetic Structures

“…They have been investigated as relatively large‐format auxetic TiNi antennas [ 15 ] 4D printed ballistic panels with TiNi, [ 16 ] 4D printed Fe‐Mn‐Si based SMAs, [ 17 ] and auxetic unit cells made of superelastic TiNiCuCo thin‐films for stretchable electronics. [ 18 ]…”

“…They have been investigated as relatively large-format auxetic TiNi antennas [15] 4D printed ballistic panels with TiNi, [16] 4D printed Fe-Mn-Si based SMAs, [17] and auxetic unit cells made of superelastic TiNi-CuCo thin-films for stretchable electronics. [18] SMAs are generally used in two ways: either by employing the shape memory effect or leveraging superelastic behavior provided by the thermally or stress-induced martensitic phase transformations. In TiNi-based SMA, reversible intrinsic strains up to 8% [19] can be achieved, while using the shape memory effect heating to the high-temperature phase austenite is required to recover the deformation reversibly.…”