Shape Memory Behaviors Of 4D Printed Angle-ply Laminated And Rectangular Braided Preforms And Their Composites

Multi-directional textile structures,such as triaxial woven fabric,angle-ply laminates,three-dimensional(3D)angle-interlock woven fabric,3D orthogonal woven fabric and 3D braids,are often used for the preparation of lightweight high-strength composites.These multi-directional textile structural composites have good structural integrity,excellent mechanical property,good damage tolerance,etc.But the traditional textile forming processes for fabricating multi-directional preforms are complex,timeconsuming and laborious,and it is necessary to explore new methods to prepare preforms.Additive manufacturing,also known as 3D printing,features on rapid and precise fabrication,providing a new approach for the processing of multi-directional textile preforms.Furthermore,the convergence of 3D printing and stimulus-responsive materials(e.g.,shape memory polymer,SMP)has led to a new research branch,named as four dimensional(4D)printing,which can rapidly fabricate smart composites.However,there are lack of basic understanding on preparation,structural optimization and shape recovery performance of 4D printed textile structural preforms and their composites,which is of great significance for developing new textile functional composites.In this work,4D printing Miura-origami,angle-ply laminated and rectangular braided preforms were fabricated using shape memory polylactic acid(PLA).The effects of recovery temperature and structural parameter on shape recovery behaviors and recovery force of 4D printed preforms were studied.Aiming to improve the shape recovery performance of thermoplastic SMP,three compositing approaches were proposed,namely,filling PLA with carbon nanotube(CNT),infusing preforms with silicone elastomer,and stacking SMP preforms with spring steel strip(SSS).Also,the angle-ply laminated preforms were printed using CNT/PLA filament to fabricate electro-activated actuator.The relations of the printing parameters,electrical property,Joule-heating induced temperature variation,and electro-activated shape recovery behavior were systematically investigated.We found that:(1)The 4D printed Miura-origami specimens had a good deformation recoverability,and their shape recovery processes were accompanied with obvious volume changes.The specimens had shorter recovery time and larger final recovery ratio as recovery temperature was increased.The recovery time and recovery force of 4D printed angleply laminated preforms were increased in order of 90°,±45°,and 90°/0°.Besides,the 4D printed laminated preforms with larger infill percentage had longer recovery time and larger recovery force.Based on above results,a sequential "unlock" process was demonstrated.The recovery time and recovery force of 4D printed rectangular braided preforms were increased as increasing braiding angle,which resulted from the increase in yarn volume fraction.(2)The 3D reconstruction model based on the ?-CT images showed that the 4D printed angle-ply laminated and rectangular braided preforms had good model-to-part fidelity.Compared to pure PLA preforms,4D printed CNT/PLA preforms had an earlier recovery start and smaller final recovery ratio,which could be attributed to the slippage of CNT in matrix.The infusion of silicone elastomer resin in the preforms could improve the final recovery ratios due to the release of the elastic strain energy.The additions of CNT and silicone elastomer resin gave rise to a significant increase in recovery force of 4D printed preforms,and the CNT/PLA laminated preform/silicone composite had the highest recovery force.The PLA laminated preform showed good bending toughness while the PLA braided preform had good damage tolerance.The additions of CNT and silicone could also enhance the bending property of 4D printed preforms.(3)Compared to the pure SMP specimen,the stacked composite specimen of spring steel strip(SSS)and 4D printed SMP laminated preform had a 39% decrease in recovery time and a 198-times increase in recovery force.During shape memory cycle of the SSS/SMP composite specimen,SMP helped SSS to store its elastic strain energy and the release of SSS elastic strain energy facilitated the shape recovery and improved the recovery force of SMP.Structure parameters,such as the stacking configuration of SSS and SMP,SMP infill percentage and SSS thickness,have a significant influence on recovery behavior and recovery force.The composite specimen with smaller SMP infill percentage and larger SSS thickness had shorter recovery time.Also,the composite specimen with SSS stacked on the SMP and larger SSS thickness had larger recovery force.(4)It was also found that the volume resistivity of the 4D printed CNT/PLA laminated specimens were increased in the order of 0°,45°,and 90°.When the temperature was increased from 25 °C to 90 °C,the volume resistivity first increased and then decreased.The printing structure parameters had an obvious effect on the Joule-heating temperature variation and electro-activated shape recovery behavior.The results showed that the specimens with smaller printing speed,larger layer thickness and smaller printing angle had smaller resistance and faster temperature increase,resulting in the shorter electro-activated recovery time.The 0°/90° specimen had shorter recovery time than that of the 0° specimen.It could be attributed to the fact that the homogenization degree of surface temperature distribution of the 0° specimen was less than that of the 0°/90° specimen.The remotely and sequentially electro-activated shape recovery behavior of a three-pronged device was also demonstrated.In this dissertation,the shape recovery behaviors of 4D printed Miura-origami,angleply laminated and rectangular braided preforms and their composites were systematically studied.The effects of recovery temperature,structural parameters and material compositing on the heat-activated shape memory performance were revealed.The systematical study on the relations of printing parameters,electrical property,Joule-heating temperature increase and electro-activated shape recovery behavior were also given.These fundamental understandings benefit for future developing textile functional composites with multi-stimuli activation and good recovery performance.