Investigation On Mechanical And Self-healing Properties Of Different Composite Structures Of "G-CNT" Synergistic Enhance TPU Composites

Thermoplastic polymers are widely used in automotive,medical equipment,electronic equipment,engineering and civil applications due to it possess excellent properties high strength,high wear resistance,high elasticity,high toughness,and impact resistance.However,due to the low mechanical strength of conventional thermoplastic polymers and the fact that they are susceptible to micro-cracking on the inside or surfaces of materials due to external loads or impact loads,their lifespan and safety of the conventional thermoplastic polymer are reduced.Thus limiting their applications in some important projects and cutting-edge fields.In order to further broaden the field of application of thermoplastic polymers,it is important to explore a thermoplastic polymer composite that not only has excellent mechanical properties,but also has self-healing properties to promote its further development and application.In this paper,thermoplastic polyurethane(TPU)was selected as matrix material,acidified graphene and carbon nanotubes were used as reinforcing phase.The "G-CNT" hybrid structure reinforced TPU composites with three different compounding degrees were prepared by classical solution blending method.The composite material not only has excellent mechanical properties,but also can achieve micro-damage self-repairing function under microwave induction.Through mechanical properties testing,SEM technology,shear lag theory,finite element numerical simulation and other methods to study the mechanical properties and microwave-induced self-healing performance of TPU composite materials.The main research content is as follows:(1)In the study of mechanical properties of TPU composites.Firstly,TPU composites with graphene and carbon nanotubes mass ratio of 3:1 and a total nano filler content of 1.5% were prepared using different experimental schemes.Through the study of its mechanical properties,it is found that the three-dimensional structure was formed by graphene and carbon nanotubes can effectively improve the dispersion of the reinforced phase in the matrix and improve the interface binding and load transfer between the matrix and the reinforced phase.Thereby improving the macroscopical mechanical properties of the TPU material.And the higher the degree of compounding,the more significant the improvement effect.When TPU composites was prepared by the pre-compounded method,the "G-CNT" had the highest degree of compounding,and it had the best mechanical performance enhancement effect(61.95 MPa)for TPU composites,which was 37.65% higher than that of pure TPU,which was 27.1% higher than G/TPU.Subsequently,based on Cox’s shear lag theory,a mesoscopic mechanical model of TPU composites with four different "G-CNT" compounding degrees was established,combined with the micro-morphology of composite powders and tensile fracture surface of specimens.The mechanical enhancement mechanisms of the synergistically reinforced TPU composites with different "G-CNT" composite structures were comprehensively analyzed.The results show that the three-dimensional structure formed by the graphene sheet and CNT not only increases the contact area between the reinforcing phase(graphene,CNT)and the TPU matrix,but also increases the roughness between the graphene and the TPU matrix.As a result,the crack propagation path is increased,and it has a positive promotion effect in improving the stress transfer efficiency between the base body and the tensile strength of the material.Finally,using the ABAQUS numerical simulation software,the RVE model of four kinds of TPU composites was established.The simulation results show that graphene is the site that mainly bears the external load.With the increase of the number of CNTs,the tensile stress on the graphene gradually decreases,the shear stress gradually increases,and the external load is shared by the graphene and the carbon nanotubes.This will further increase the stress transfer efficiency between the reinforcement phase and the matrix and the macro-mechanical properties of the material.(2)In the research of damage healing mechanism of composite materials.Firstly,microwaves healing the TPU composites of four prefabricated damaged cracks of G/TPU,G/TPU+CNT/TPU,G-CNT/TPU,and G+CNT/TPU were performed.Self-healing effect of TPU material was examined by SEM technique and tensile test.The experimental results show that the four kinds of TPU composite materials can achieve crack self-healing under microwave induction.When the amount of CNTs loaded on the graphene sheets is moderate,the heterogeneous interface structure composed of them uniformly disperses in the matrix,which improves the coupling with the microwaves.Thereby promoting the self-healing efficiency of cracks.In this process,the healing efficiency of the G-CNT/TPU composite material is as high as 138%.Secondly,the influence of the heterogeneous interface of G-CNT on the electromagnetic field distribution is studied by finite element numerical simulation.The results show that the heterogeneous interface composed of G-CNT can absorb more electromagnetic energy and provide sufficient energy for cracking of the composite material,thereby improving the self-healing efficiency of the system.