Abstract
Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers – digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications.
Highlights
To generate a large shape change under an external stimuli us, such as temperature[19,20,21], light[22], electric[23,24] and magnetic fields[25,26]
We demonstrated the design of components using digital shape memory polymer (SMP) that exploit the spatial variation of dynamic mechanical properties to produce shapes in a precisely controlled temporal shape changing sequence when activated by a uniform thermal stimulus[30,31]
After being programmed into a temporary shape by a simple thermal-mechanical training program, the printed composite is able to change into multiple shapes and recover the flat permanent shape when stimulated by temperature
Summary
To generate a large shape change under an external stimuli us, such as temperature[19,20,21], light[22], electric[23,24] and magnetic fields[25,26]. In order to achieve shape memory effects (SMEs), the polymer should have one transition point, such as glass transition temperature, crystal-melt transition, etc. It is desirable to develop polymers or composites that can predictably change among multiple different shapes. Xie et al reported that they can create triple-shape memory structures by fabricating the composites materials which have well-separated glass transitions points[27]. A new class of composite materials that are created by 3D printing multiple polymers with different properties in precise geometric configurations that are mixed and cured at different ratios, offer an easy and simple way to fabricate materials with desirable properties by design. To understand the shape memory behavior of these composites with multiple active fiber families, we develop a new theoretical model to describe the evolution of curvature during the shape recovery process. Using the theoretical predictions as a guide, we design and manufacture several self-folding and opening structures that demonstrate the performance afforded by the tremendous design freedom
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