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. 2015 Sep 8:5:13616.
doi: 10.1038/srep13616.

Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

Yiqi Mao  1 , Kai Yu  1 , Michael S Isakov  1 , Jiangtao Wu  1 , Martin L Dunn  2 , H Jerry Qi  1
Affiliations

Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

Yiqi Mao et al. Sci Rep. .

Abstract

Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.

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Figures

Figure 1
Figure 1
(a) Glass transition temperatures of the seven digital SMPs used for hinge materials; the inset shows a schematic view of the folding of an SMP hinge; (b) folding time of hinges to obtain 98% recovery ratio at various recovery temperatures.
Figure 2
Figure 2
(a) The schematic graph of the helical SMP component. Series of photographs showing the shape recovery process of the helical SMP component (a) with uniform hinge sections, and (c) with graded hinge sections.
Figure 3
Figure 3
(a) The Finite element simulation of shape memory recovery activated sequential self-folding after the strip is firstly programmed at high temperature. (b) The simulations of folding angles of three representative hinges by ROM and compared with those by FEA and experiments. Solid-line only: FEA; round dot: ROM; square: experiments. Red color: H-1; magenta color: H-4; Blue color: H-7. Comparison between ROM simulations and experiments for (c) Sample 1 and (d) Sample 2, where red lines indicate the simulation results.
Figure 4
Figure 4. The self sequential self-folding (a) without collisions; (b) with collisions.
When there is no collision, all collision indices are out of span (0, 1) (shown in (a)), and when there is a collision, the index falls in span (0, 1) (as shown in (b), two points (a red and a blue point) are in span (0, 1)). The red dot between (0, 1) corresponds to first collision; the blue dot corresponds to the second collision.
Figure 5
Figure 5
(a) The schematic graph of the interlocking SMP component. (b) The ROM simulation of the sequential folding resulting in interlocking, and (c) the collision indices of the chosen design. (d) The comparison of experiments (plan and side views) and the ROM simulations (red lines).
Figure 6
Figure 6. 3D folding structures mimicking the USPS mailbox.
(a) A USPS mailbox is folded into a box by following a sequence of folding. (b) A programmed 3D printed sheet with different materials assigned at different hinges. (c–f) The design of the folding box with some details at the hinges. (g–j) Upon heating, the sheet folds into a box with self-locking mechanism.
Figure 7
Figure 7. Schematic of two arbitrary strips having a factitious intersection point.
See this image and copyright information in PMC

References

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