Enhanced multimaterial 4D printing with active hinges

Abstract

Despite great progress in four-dimensional (4D) printing, i.e. three-dimensional (3D) printing of active (stimuli-responsive) materials, the relatively low actuation force of the 4D printed structures often impedes their engineering applications. In this study, we use multimaterial inkjet 3D printing technology to fabricate shape memory structures, including a morphing wing flap and a deployable structure, which consist of active and flexible hinges joining rigid (non-active) parts. The active hinges, printed from a shape memory polymer (SMP), lock the structure into a second temporary shape during a thermomechanical programming process, while the flexible hinges, printed from an elastomer, effectively increase the actuation force and the load-bearing capacity of the printed structure as reflected in the recovery ratio. A broad range of mechanical properties such as modulus and failure strain can be achieved for both active and flexible hinges by varying the composition of the two base materials, i.e. the SMP and the elastomer, to accommodate large deformation induced during programming step, and enhance the recovery in the actuating step. To find the important design parameters, including local deformation, shape fixity and recovery ratio, we conduct high fidelity finite element simulations, which are able to accurately predict the nonlinear deformation of the printed structures. In addition, a coupled thermal-electrical finite element analysis was performed to model the heat transfer within the active hinges during the localized Joule heating process. The model predictions showed good agreement with the measured temperature data and were used to find the major parameters affecting temperature distribution including the applied voltage and the convection rate.

PolyJet-Printed Bellows Actuators: Design, Structural Optimization, and Experimental Investigation

“…Thereby, time dependent mechanical behavior is typical for elastomeric structures (Saccomandi and Ogden, 2004;Bergström, 2015) and originates mainly from the rearrangement of the molecular chains (entropic elasticity) induced by deformation. Several publications confirm our qualitative experiences concerning the time dependency of PolyJet materials in general (Blanco et al, 2014;Zhang and Albert, 2016) and-most importantthe PolyJet elastomers TangoBlack TM (a predecessor of TB+) (Kundera and Bochnia, 2014), and A30 (Akbari et al, 2018). However, to our knowledge no closer investigations on the time dependent behavior of A30 bellows structures were published yet.…”

4D printed tunable mechanical metamaterials with shape memory operations

“…Another great potential of this unit is to serve as an active part of a thermo-mechanical valve to close or open a closure. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 22 If the horizontal constrains of the mechanical metamaterial unit as shown in Fig. 5a are removed, it can be used to design self-deployable bio-medical stents.…”

Developments in 4D-printing: a review on current smart materials, technologies, and applications

“…4D-printers are essentially a specialized subset of 3D-printers. Currently, the applicable 4Dprinting methods include direct inkjet cure [32,[46][47][48][49], fused deposition modeling [37,50,51], stereolithography [52], laser-assisted bioprinting [53] and selective laser melting [54]. The choice of the printer should be carefully made based on different types of smart materials which will be introduced further in the next section.…”

“…The choice of the printer should be carefully made based on different types of smart materials which will be introduced further in the next section. Research on deformation mechanisms focuses on the understanding of sequential folding [38,41], hinge design [32,49,55], geometry design [37,56], and pattern design [48,52]. Understanding these mechanisms is critical for 4D-printing functional structures.…”