Electroactive Shape-Memory Actuation And Biomimetic Study Of Polyether-ether-ketone By Additive Manufacturing

In mechanical manufacturing,automatic control and aerospace,the shape change of components relies on actuation.Traditional actuation,which consists of motors and rigid transmission mechanisms,has the limitation of large volume,heavy mass and complex composition,and restricted capabilities to interact with the changing environments.Emerging shape memory materials can effectively sense the surrounding environment and convert stimuli into highly responsive deformation,break through the technological barriers of passive susceptibility to environmental change,and achieve energy saving lightweight design and low-cost autonomous actuation.Therefore,they have been widely used as smart devices in many fileds.Nevertheless,with the innovative exploration of aerospace technology in the moon,Mars and other areas,the shape memory response and actuation under complex working conditions are still facing severe challenges.As a shape memory material with high performance,polyether-ether-ketone(PEEK)can perform tasks in higher temperature and radiation environment.Thus,PEEK has broad application prospects.However,due to their customized and complex structures,as well as multi-dimensional composite characteristics,it has great limitations in the composite molding of PEEK.The rapid development of additive manufacturing technology,which has achieved the highperformance manufacturing of shape memory materials with complex structures,precise dimensions and excellent performance.The shaped polymers can change with time under external stimulation.This 4D printing technology provides an effective means for the high-precision molding of PEEK composite structures.This paper used PEEK as the shape memory actuation material,and used the fusion deposition molding as the additive manufacturing technical means.Firstly,the additive manufacturing of high-performance PEEK had been realized,and the thermodynamic properties and shape memory performance of PEEK were explored.In order to achieve more efficient and convenient shape memory deformation,coextrusion 4D printing of shape memory PEEK with continuous fibers had been developed,and the embedded structures of PEEK with electrothermal fiber was manufactured.On this basis,the controllable shape memory deformation and selfsensing were demonstrated,while the electroactive shape memory actuation characteristics of PEEK structure were explored and the application of smart actuation in engineering field was proposed.Meanwhile,the material components and structures of PEEK were optimized by the bionic design principle to achieve a larger actuation range,that provided an important reference for the lightweight design and energysaving actuators of extensible structure in aerospace field.The main research work is as follows:(1)A high-performance shape-memory PEEK material and functional parts were prepared using fused deposition modeling.The effects of printing conditions on the shape memory properties of PEEK were explored,and it was found that a substrate temperature of 130℃,a nozzle temperature of 370℃,a raster angle of 45°,a layer thickness of 0.25 mm and annealing at 210℃ were the best additive manufacturing conditions for shape memory PEEK.Additionally,it was fonud the shape recovery ratio of PEEK shape memory was higher for structures with fewer edges or larger angles in different structure unit and arrays,revealing the regulation of shape memory performance.The PEEK shape memory functional part was able to grab object weighing 60 times its own weight in high-temperature silicone oil at 130℃.(2)Aiming at the difficulty of providing a high-temperature environment for shape-memory PEEK,co-extrusion printing strategy was used to prepare PEEK embedded with electrothermal fibers,and the slippage phenomena of the fiber were discovered.A theoretical model,based on the principle of fused deposition modeling,and evaluation criteria for co-extrusion printing were established.For different print parameters,with the increase of printing interval and height,the decrease of printing speed and substrate temperature,the better the printing quality.Ultimately,an integrated in situ additive manufacturing technology for PEEK-fiber was developed.The electrothermal fibers with specific distribution path were successfully embedded into the PEEK matrix.The tensile modulus of the PEEK-fiber embedded structure increased by 17.6%,the toughness increased by 78.9%,the tensile strength increased by 24%,and the shear strength increased by 67%.(3)PEEK-fiber embedded structure made by integrated additive manufacturing technology achieved high-efficiency and energy-saving shape memory deformation.The heating rate increased by over 70 times,and the energy consumption reduced by several orders of magnitude.By designing the distribution and electrification mode of the electrothermal fibers,the controllable and programmable multi-shape memory deformation of PEEK were realized.Because of the strain sensitivity of embedded nickel-chromium fibers,the shape memory deformation of PEEK was endowed with the self-sensing characteristics.Furthermore,the designed shape memory PEEK actuation parts could transport 50 times its own weight,and successfully actuate the deployments of dragging sail and catcher within 40 s,indicating its promising applications for deployable structures in the aerospace field.(4)The precise control of electroactive shape memory actuation for PEEK was realized.For different structure parameters of PEEK: As the thickness increased,the actuation range and driving speed first increased and then decreased,and the actuation force increased.With the increased of bending arc length,the actuation range and speed increased,while the fixed force and actuation force decreased.With the increased of the programming angle,the actuation range decreased,and the actuation speed,fixed force and actuation force increased.For different time parameters in shape memory process: Compared with natural cooling,forced air cooling method would increas the actuation range,speed and force of PEEK.The greater the recovery current was,the greater the actuation range and speed,while the actuation force decreased first and then increased.The longer the idling time,the smaller the actuation range,speed and force.(5)Inspired by the multilayer "brick-mortar" structure of high-toughness nacre,the brittle PEEK was composited with the tough shape memory polylactic acid layerby-layer by integrated additive manufacturing technology.A rigid-flexible coupling biomimetic multilayer composite structure was designed and prepared.The tensile modulus of biomimetic PEEK composite structure increased by 16.3%,the tensile fracture energy increased by 21.6%,the toughness increased by 4.6%,the shape memory actuation range increased by 21%,and the actuation speed increased by 30%.Based on the optimized biomimetic PEEK,the actuation range of the developable mechanism was increased by 13%,the actuation time was reduced by 41%,and the extensible surface was increased by 30%.