Biomimetic Design And 3D Printing Of Composite By Coupling Heterogeneous Materials And Microstructures

Comparing to the traditional artificial materials,the components of biomaterials could be simplified as two heterogeneous materials with stiff and soft properties.Therefore,biological tissues enjoy the superior mechanical properties and self-adaptive ability just by the exquisite microstructural design and the optimized coupling method.Take plant tissues as example,by coupling stiff cellulose and soft lignin-hemicellulose matrix with special microstructure(porous structure,helical structure and asymmetric fiber structure),they combine light,tough and strong stability or other mechanical properties(wood cell),but also to drive the material by the environmental humidity changes to induce the reverse deformation(Pelargonium seed).This kind of heterogeneous material and microstructure coupling method not only exists in the micro-nano scale,but also in the millimeter scale(trunk ring)and the joint interface between different organs(adductor muscle-shell interface).Although these characteristics belong to different organisms,but the core mechanisms behind their are interlinked.The purpose and significance of this study lies in that: the microstructure of the typical biomaterials are extracted,and the corresponding biomimetic structure models are established by appropriate amplification and simplification.Furthermore,a series of biomimetic design methods for improving the mechanical properties and passive actuation ability of the composites were established by coupling the rigid and soft heterogeneous materials with the micro-structure design units.Specific research content can be summarized as the following:1.Aiming at the problem of insufficient fracture toughness of traditional porous structure,we imitated the annual ring to change the cellular material into a composite made from two heterogeneous materials with stiff and soft property.Under the same geometrical configuration,the fracture toughness of the radial direction and axial direction in improved cellular composite increased by 107.6 and 143% separately.Besides,the constitutive relationship between the modulus ratio of two substances and the fracture mode of the whole composite had been revealed,making the design of the porous material more flexible.2.In order to increase the compressive mechanical properties of traditional fiber reinforced composites,the new composite was created through integrating the stiff continuous fiber with helical configuration to the soft matrix.Test results showed that,the mechanical properties of the biomimetic composite can be adjusted by changing the fiber angle of the helical structure while keeping other structural parameters unchanged.Then,a double-layer helical structure is designed to program the composites,which effectively improves their stability and compressive properties.3.In order to introduce the intelligent passive actuation function to the biomimetic composites,the three-dimensional structure of Pelargonium seeds were obtained by micro-CT,then the corresponding biomimetic structure model and composite mechanical model were extracted.Furthermore,the finite element method was used to analyze the coiling deformation mechanism of the awn: stiff cellulose fibers with special tilted helix structures could direct the shrinkage forces resulted from the matrix,so as to generate torsional and bending movement simultaneously.Therefore,the inner layer cell could generate an anti-clockwise coiling deformation macroscopically.This principle provides a theoretical basis for the design of new passive actuation composites.4.A new biomimetic 4D printing technology was developed by combining general multi-materials 3D printing and the infusion molding process.Furthermore,three kinds of intelligent materials with passive actuation function were prepared based on the microstructure of Pelargonium seed.Compared with the existing bionic 4D printing material,it can achieve more complex non-uniform bending,twisting and spiral deformation,and has better mechanical properties.5.In order to solve the problem of stress concentration in the connection part of two heterogeneous materials,the structure of the adductor muscle-shell interface in scallop is imitated,and the heterogeneous material connection structure with regular arrangement of reinforcement fibers is fabricated by multi-material 3D printing technique.The experimental results show that the stress concentration can be effectively alleviated and the connection strength of the interface can be improved by reasonably optimizing the distribution density of the reinforcing fibers.From the above,based on the study of the composite structure of soft wood from the mesoscopic to microscopic,the helical deformation mechanism of the Pelargonium seed and the microstructure of the adductor muscle-shell interface in Patinopecten yessoensis,design and 3D printing of a series of biomimetic structures with the rigid and soft heterogeneous materials as raw materials.The research results have potential application value in high-tech composite materials,micro-actuators and the technique on joining of dissimilar advanced materials.