Effect of Filament Color and Fused Deposition Modeling/Fused Filament Fabrication Process on the Development of Bistability in Switchable Bistable Squares

Abstract

Switchable multistable structures (SMS) are additively manufactured metamaterials. SMS are printed in polylactic acid, a shape memory polymer, and pre-strain is stored in bilayers during fused deposition modeling 3D printing process that encode different stable states can be activated above the glass transition temperature (Tg). Eight filament colors were used to 3D print sample squares. A hot water bath was used to determine sample bistability or monostability. Differential scanning calorimetry determined the Tg and melting temperature, (Tm). Thermogravimetric analysis was used to investigate colored filament thermal stability. The viscoelasticity of colored filament was investigated with melt rheology and the crystallinity of the printed samples was studied with X-ray diffraction. Filament color was an indicator of bistability and colors with lower Tm values tended to be bistable. Polyethylene terephthalate glycol SMS exhibited the shape memory effect but did not show bistability with the given print parameters. Bistability is achieved when the difference between the pre-strain of the bilayers is less than the energy needed to snap the sample to a given state. The relationship between monostability, self-snapping back to a favored state, and bistability is explained by a series of mathematical equations. Future work includes printing pre-strain relationship and the molecular level impact.