Abstract
Four-dimensional (4D) printing is an emerging technology by adding the dimension of time-dependent reconfiguration into 3D printing. It enables the 3D printed structure to change the shape, property, or functionality under external stimuli such as temperature, magnetic field, and light, etc. Among the existing 4D printed structures, thermal responsive structures are widely used for their easy operation. However, the slow actuation of the thermal responsive structures impedes the applications like soft robotics. In the current work, a pre-strained strategy is proposed to accelerate the actuation of thermal responsive structures. A 4D printing platform that can apply strain during the printing process is constructed to fabricate the pre-strained structures under the aid of in-situ tensile of the printing base. A bilayer structure with one pre-strained layer and the other non-pre-strained layer is integrally printed. Through experiments and the finite element analysis, it is demonstrated that the aspect ratio has little effect on the deformation of the bilayer structure, whereas the pre-strain plays a key role in the deformation and also greatly accelerates the actuation of the bilayer structure. Based on the 4D printed pre-strained bilayer structure, an energy-free gripper is fabricated and a fully soft crawler is printed to achieve a high running speed.
Highlights
In consideration of the simplicity of operation and the applicability, the thermal responsive structure is one of the most widely used 4D printed structures
Ze et al (2020) report a novel magnetic shape memory polymer composite (M-SMP) that is softened by heating and actuated by a magnetic field
Through experiments and finite element analysis (FEA), it is demonstrated that the aspect ratio has little effect on the deformation of the bilayer structure, whereas the pre-strain greatly affects the deformation and greatly increase the actuation speed of the thermal responsive structure
Summary
In consideration of the simplicity of operation and the applicability, the thermal responsive structure is one of the most widely used 4D printed structures. Through experiments and finite element analysis (FEA), it is demonstrated that the aspect ratio has little effect on the deformation of the bilayer structure, whereas the pre-strain greatly affects the deformation and greatly increase the actuation speed of the thermal responsive structure. Based on this simple and effective strategy, we have designed a soft energy-free gripper with high responsive capacity and a soft crawler with a larger locomotion step and high speed. The current work provides a new solution based on pre-strain to increase the thermal actuation speed of 4D printed structures, which has a wide range of applications such as soft robotics with high locomotion speed, grippers with high responsive capacity and so on
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