| 4D printing refers to 3D printed objects that can produce predetermined changes in shape,performance,or function under specific excitation conditions.This 4D change is carried out in a pre-designed way and is programmed through the design of material structure,process parameters and excitation conditions.4D printing embeds the factors that control changes into smart materials with excitation-response characteristics through 3D printing.Under the stimulation of specific factors(temperature,humidity,light,electricity,magnetism,and vibration,etc.),it can spontaneously change it over time Physical properties,functions and shapes to achieve specific functions.The difficulty and core that 4D printing needs to break through at present is to create programmable changes and "print" them in parts,that is,to "bury" preset instructions in materials through programming of materials and structures,so that the materials produce predetermined response behaviors.In order to adapt to survival,some biological materials have evolved characteristics that change according to the environment,which provides ideas for 4D printing design.Such as pine cones and pods can deform according to changes in humidity to discharge seeds.Some plant organs,such as pine cones,pods,etc.,achieve a controlled shape change through tissue microstructure.In addition to plants,some animals,such as octopuses and chameleons,can achieve controlled color changes by changing the structure and arrangement of pigment cells in their skin.Inspired by the relationship between biological deformation and discoloration characteristics and material structure,a bionic design method for 4D printing can be established.Despite a lot of research in recent years,4D printing is still limited to changes in geometric features such as shape and structure,and its potential has not been fully recognized,tapped,and utilized.Therefore,studying bionic 4D printing with dual changes in shape and color can expand the connotation of 4D printing,help deepen the understanding of 4D printing,and inspire people to explore and tap the inherent potential of 4D printing and develop applications in multiple fields.Inspired by the deformation and discoloration functions of cephalopods,this paper studies a 4D printing method that realizes dual changes in shape and color,and defines it as a bionic dual response 4D printing.First,a 3D printing complete hardware system capable of realizing bionic dual-response 4D printing was created,thereby realizing the key technology of controlling printing parameters to program anamorphic 4D printing.Polymer printing materials were then developed that can produce both color and shape changes when temperature changes.By designing and printing 4D samples with different process parameters,the applicability and programmability of the bionic design,dual response 4D printing process,and self-made composite printing materials were verified.Finally,through the concept of bionic design and 4D printing technology,research on deformed and discolored 4D printing was carried out.The effects of process parameters on the recovery rate,recovery speed,and force of shape memory polymers were studied,and the principle of 4D deformation control of process parameters was explored.The influence of process parameters on color change was studied,and the influence of printing parameters on the speed and degree of color change was revealed.Finally,two response changes were controlled simultaneously through the process parameters,and the speed matching of the two 4D changes was studied and verified.Multi-stage deformation function,multi-stage discoloration function,and dual response 4D change function of deformation and discoloration were realized.The specific research results of this article are as follows:1)Developed 3D printing systems and dual-response smart materials required for dual-response 4D printing.The printing system is designed based on the fused deposition process.It integrates the necessary functions required for dual-response 4D printing such as process parameter modeling,data conversion,environmental temperature control system,and multi-material fused deposition printing,and establishes a full-process 3D printing software and hardware.surroundings.The 4D printing material is a shape-memory polymer polylactic acid as a matrix,which is prepared into a composite smart material that is deformed and discolored by a composite thermochromic material.2)The effects of printing process parameters(printing temperature,printing height,filling angle,filling rate,geometric thickness,etc.)on the shape changes of 4D printed samples were studied.First,a method for measuring the recovery rate and recovery time of shape memory polymers was established,and a test system for shape memory resilience was developed.Then,the shape memory recovery rate,recovery speed and recovery force of 4D samples with different parameters were quantitatively analyzed,and the influence of process parameters on the shape change of 4D printed shape memory polymers was analyzed.Finally,according to the law of change,a variety of actuators with multi-stage 4D deformation were designed and printed,and the feasibility of 4D printing deformation control using process parameters was verified.3)Combining 3D printing and materials with temperature-sensitive color-changing functions,a 4D color-changing printing strategy is proposed,that is,the color can be changed spontaneously over time(fourth dimension)under external stimulus conditions.By adjusting the type of thermochromic material added to the polylactic acid,a variety of different reversible color changes can be achieved.In addition,a strategy for controlling the speed of color change using process parameters of 4D printing is also proposed.Through the test and analysis of the color changing speed of samples with different printing processes,a quantitative relationship between the process parameters and the color changing speed is established,and the effect mechanism is analyzed using the heat transfer principle.Finally,based on the color changing behavior of some animals and plants,4D printed bionic flowers and bionic octopus actuators with multiple color changes and different color changing speeds.4)Based on the influence of printing parameters on deformation and discoloration performance,the matching characteristics of deformation and discoloration response behavior under thermal excitation were studied.The research results show that by changing the process parameters,not only the sequence of the two changes in shape and color can be controlled,but also two types of response changes can occur at the same time.Finally,a bionic octopus actuator with coordinated deformation and discoloration characteristics is designed and printed.Double-response 4D printing with octopus deformation and discoloration camouflage function. |
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