Mechanical Properties Of Staggered Overlay Bio-inspired Nacre-like Materials Based On Graphene Oxide-CNTs

With the development of the times and the advancement of science and technology,lightweight materials play an important role in energy conservation,emission reduction and reduce operating costs,and become a hot topic in many advanced fields such as aerospace,military and transportation.Recently,researchers have constructed some lightweight materials that have high strength and toughness by imitating their internal microstructure from natural materials like horseshoe,mantis shrimp,bird skulls,etc.For example,the shell nacre is a lightweight material with excellent tensile strength and fracture toughness.It is just composed of the hard phase(e.g.mineral aragonite,95 vol%)and a small amount of softer phase(e.g.biopolymers,5 vol%)with a "brick-mortar" laminated structure,and researchers are inspired to prepare high performance composites by mimicking this structure.This “brick-mortar” staggered laminated bioinspired nacre-like composites have light weight and excellent mechanical properties due to its special internal microstructure.It provides a material reference for the development of many high-tech fields,and also shows possibilities for innovation in more scientific fields.The inspiration for this work comes from the layered aragonite microplatelets/chitin-nanofibers-protein structure of natural nacre.Graphene oxide prepared by modified Hummers methods(GO)and adjusting the distance between the graphene sheets of oxide layer by the evaporation self-assembly method to obtain the bio-inspired nacre-like composites with different microstructures.The obtained specimens were taken tensile test to study the damage stress histogram,stress-strain curve graph and toughness graph under the external loading.The fracture surface was characterized by scanning electron microscope(SEM).Finally,using the finite element simulation software ABAQUS to simulate the behavior of material under the external loading.A simplified nacre structure model was obtained based on the "tension-shear chain theory",and to observe the stress distribution inside the material and the stress concentration near the defect.Through the research,it is found that the optimized microstructure can improve the distribution of normal stress and shear stress inside the material,and the reasonable optimization of the microstructure inside the material can effectively improve its overall macroscopic mechanical properties.For composite materials,the interface bonding often has an important impact on the overall mechanical properties.Therefore,based on the preliminary work,this paper designs three kinds of carbon nanotubes(CNTs)materials in the original material system,and obtains three heterostructures with different GO-CNTs composite degree.According to the experimental data and analysis,it is found that the content of CNTs have some impact on the mechanical properties of the material.Under the same content,the higher the degree of combination is,the more obvious the synergistic effects on the mechanical properties,and the better the mechanical properties of the material.After the microstructure optimization and interface enhancement of composites,the synergistic effect of heterogeneous structure has a significant effect on the overall mechanical properties of bio-inspired nacre-like structures.Inspired by this,this paper adopts large and small GO film layers as the hard phase,and optimizes the internal structure of the hard phase by adjusting the scale of the hard phase layer,so that it can be respectively compounded with CNTs to form a new heterogeneous structure.Through experiments and analysis,it is found that due to the scale effect and the special microstructure arrangement inside,large GO sheets play a leading role.Therefore,the heterogeneous structure composed of CNTs and large GO sheets inside the composite material can improve the stress transfer efficiency inside the material more effectively,thus improving its overall mechanical properties.In summary,the different kind of bio-inspired nacre-like interlaced laminated structure composites was prepared by experiments.The specimens were taken some testing and the results of finite element simulation were used to analyze the reasons for the excellent mechanical properties.The stress transfer mechanism and toughening mechanism of nacre structure were studied.These results have reference significance for the design of structural composites,and provide available theoretical guidance and methods for the microstructure optimization design and interface design of high-performance biomimetic materials.