Search

Abstract Multifunctional composites have been continuously developed for a myriad of applications with remarkable adaptability to external stimuli and dynamic responsiveness. This study introduces a 4D printing method for liquid crystal elastomer (LCE) composites with continuous fibers and unveils their multifunctional actuation and exciting mechanical responses. During the printing process, the relative motion between the continuous fiber and LCE resin generates shear force to align mesogens and enable the monodomain state of the matrix materials. The printed composite lamina exhibits reversible folding deformations that are programmable by controlling printing parameters. With the incorporation of fiber reinforcement, the LCE composites not only demonstrate high actuation forces but also improved energy absorption and protection capabilities. Diverse shape-changing configurations of 4D composite structures can be achieved by tuning the printing pathway. Moreover, the incorporation of conductive fibers into the LCE matrix enables electrically induced shape morphing in the printed composites. Overall, this cost-effective 4D printing method is poised to serve as an accessible and influential approach when designing diverse applications of LCE composites, particularly in the realms of soft robotics, wearable electronics, artificial muscles, and beyond.

The combination of scientific advances in additive manufacturing (AM) and smart materials (SMs) has enabled the development of a new interdisciplinary research area: 4D printing. This technology offers – via stimuli-responsive materials – promising transformation capabilities to objects whether at the functional, shape, or property levels. By considering such capabilities, researchers from multiple disciplines have investigated a large spectrum of stimuli-SMs associations with proofs-of-concept built from either commercial or custom 3D printers. Despite the abundant initiatives, 4D printing requires additional developments to meet robust system applications for the industry. The paper aims to highlight the status, inherent barriers, and challenges of 4D printing to be addressed from a product-systems design perspective. It firstly reminds the fundamentals of SMs, processes, stimulus, and AM to which a synthesis of significant research works related to 4D printing highlighting the current status as well as scientific, technical, and organizational limitations is provided. Beyond this comprehensive study, the paper emphasizes opportunities and challenges from multiple perspectives and draws a research roadmap for engineering design and cross-disciplinary design. The outcome of the work tends to structure research efforts for the next decade towards the development of smart products that meet use for humans and the industry.

Thermosetting polymers are widely used in 3D printing owing to their superior mechanical stability, but once they are printed, the highly crosslinked polmyers cannot be reprocessed or repaired. Here the authors demonstrate a two-step polymerization strategy toward 3D printing of reprocessable thermosets.

Slender 1D structures are ubiquitous in nature and engineering and serve as building blocks for 3D structures at scales ranging from molecular to architectural. 3D printing enables fabrication of such structures with geometrical complexity that cannot be produced easily by traditional manufacturing methods, but comes with a cost of long building time and need for supporting structures during printing. Some of these limitations are overcome here through an approach that prints 1D rods with composite cross-sections, programmed to deform into a prescribed 3D shape simply upon heating. The straight or curved composite rods consist of a glassy polymer and an elastomer that are bonded to each other as a result of the manufacturing process; the latter is programmed with a compressive stress during the printing process. When heated, the stiff glassy polymer softens, resulting in release of the stress in the elastomer, and causes the 1D structure to deform into a new permanent 3D configuration. The cross-section of the composite rods can be designed to enable deformation modes of bending and twisting, a combination of which can guide the 1D rod into almost any 3D shape. With the use of a nonlinear thermomechanical computational model, several 3D rod structures are designed and demonstrated, highlighting the potential for increased functionality with material and time savings. Keywords: 3D printing, 4D printing, Rod structures, Self-assembly, Active composite