| In recent years,3D printing of shape memory polymers has triggered a wide range of research upsurge in the academia and engineering areas,especially for the cases of customized shape memory polymers and their structures by electrical stimulation,which shows great application prospects in aerospace(such as self-deployable mechanism),biomedical(such as drug release,personalized correction)and textile industry.3D printing electro-stimulated shape memory polymer breaks through the limitation of traditional material design and preparation technology,and can construct more complex 3D structure,and obtain high intelligence structural composite materials.If continuous fiber is introduced into the printing process,light and high strength structural composite materials can be prepared.The integrated design and preparation process can not only reduce the production cost,but also simplify the production process,which has a higher industrialization prospect.However,the research shows that the current printing process is not perfect,the prepared composite materials often have defects,in addition to the shape memory substrate research is not systematic,the printing technology of continuous fiber reinforced memory materials is not mature.Therefore,how to design and develop shape memory polymer substrate with excellent performance,how to design and prepare continuous fiber reinforced shape memory composite material and optimize the path of 3D printing,so as to construct composite material with excellent mechanical and shape memory performance and explore its application in specific fields,are the key scientific issues in this thesis.It is of great significance to guide and develop 3D printing intelligent structure and lightweight,high-strength composite materials.Based on 3D printing technology and shape memory mechanism,the raw materials like polylactic acid(PLA),thermoplastic polyurethane(TPU)and multiwalled carbon nanotubes(MWCNTs)were used as matrix to prepare PLA/TPU/CNTs composite wire for 3D printing with different filling ratios by single screw extrusion mechanism.Continuous carbon fiber tow was introduced into PLA/TPU matrix by continuous fiber based FDM 3D printing technology,in which carbon fibers are connected to conductive particles of CNTs to form a continuous integrated conductive network.At the same time,the printing path and extrusion amount are optimized,and the printing process of continuous fiber reinforced polyline structure is optimized.Based on the curved support structure of orthopedic insole,a fast electro-responsive shape memory polyline compression support structure composite with good mechanical properties was prepared,and the properties of the composite were explored.Finally,the electro-thermal dual shape memory drive of the carbon fiber reinforced polyline structure composite was realized,and the shape memory and compressive properties of the composite structure were explored,as well as the practical application potential of the composite as shape memory reinforced composite.The main research contents and conclusions of this topic are as follows:(1)Shape memory composites with different proportions of fillers were prepared.PLA/TPU/CNTs wires were fabricated by melting and extrusion by mixing PLA,TPU nanoparticles and multi-walled carbon nanotubes in different proportions,and polyline structures of different sizes were designed.The mechanical and shape memory properties of the lightweight polyline structure composite material were studied by using the extruded amount.The preparation scheme of 3D printed PLA/TPU/CNTs wire with uniform dispersion and optimal performance was proved by experiments that the optimal ratio was PLA:TPU=70:30,and 6wt% CNTs was added.(2)The polyline structure was designed as the internal compressive support structure,and lightweight corrected surface insole was prepared(front,middle and back were selected,among which the middle and back were curved structures).The compressive-resistant performance and shape memory performance of the composite materials with support structure at different positions were studied.After CNTs nanoparticles were added,the shape memory recovery time of PLA/TPU/CNTs samples could be reduced by up to 58%,and the middle sample printed by PLA/TPU/CNTs showed the best shape memory performance: high shape fixity(an increase of 2.8%)and shape recovery ratios(an increase of 6.1%)as well as low shape recovery time(shortened by 46.7%),but the compressive strength and modulus of materials were significantly reduced in all samples after the addition of CNTs,which had a negative impact on the mechanical properties.(3)Based on FDM continuous fiber 3D printing technology,the carbon fiber filament was introduced into the printed structure on the basis of the printed polyline structure..The trapezoidal printing path was used to optimize the printing path and reconfigure the extrusion amount.The continuous conductive network was constructed inside the composite material by carbon fiber and multi-walled carbon nanotubes.The electro-thermal response shape memory composite material with excellent compressive resistance was prepared,and the thermal activation and electrical activation shape memory performance of the polyline structure was realized.Carbon fiber significantly improved the compressive strength and modulus of the material.In the front three structures,the compressive strength was 13.4 times,7.63 times and 6.97 times of the sample without carbon fiber,and the compression modulus was 22.6 times,13.1 times and 16.5 times of the sample without carbon fiber,respectively.In terms of heat-induced shape memory performance,the shape memory recovery time of the samples increased after the addition of carbon fiber,but it still showed good shape memory fixation rate and shape memory recovery rate.However,the carbon fiber would misposition in the matrix after being subjected to external forces during the shape fixation process,which would have a negative impact on its shape memory performance.In terms of electro-induced shape memory performance,the 3D-printed strip samples of PLA/TPU/CNTs enhanced by carbon fiber could complete the shape memory recovery process within 19 s under the condition of loading 10 V,and the shape recovery ratio was about 93%.The other front,middle and back samples can trigger the electro-induced response of the composite within 2 s under the condition of 10 V voltage at both ends.It shows good potential of electroresponsive shape memory performance.The shape memory performance of the insole support structure can intelligently adjust the habit of plantar force and change the poor gait,which lays a theoretical basis and data support for the design and development of new plantar correction devices.(4)The 3D printed polyline structural support composite material simulated the fit of human foot,studied its compressive performance and the feasibility of application of this kind of structural support material in the field of orthopedic insole.It is found that its good compressive performance can show excellent supporting effect on the plantar of human body,especially the support material after the introduction of carbon fiber shows excellent compressive-resistant performance.It can provide the corresponding needs of foot correction for people of different ages.The use of this support material to prepare orthopedic insole can reduce the accumulation of fatigue caused by poor gait,and contribute to the future development of customized orthopedic insole materials to meet the needs of children growing up or sports injury prevention and other groups.In this thesis,3D printing technology was used to construct the shape memory structure composite material reinforced by continuous carbon fiber filament.By optimizing the composition ratio of shape memory substrate and printing path of continuous fiber,the compression support material of 3D printing electrothermal response shape memory PLA/TPU/CNTs composite polyline structure was studied.Combined with the actual demand,the potential of its application is explored,which is of great value for the development of customized intelligent structure and lightweight,high-strength materials,and provides guidance for the future design of flexible structure and excellent performance of fiber reinforced structural materials,and lays a good foundation for future applications in medical and health fields. |
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