Study On Sensory Properties Of Carbon Nanotube-modified Underwater Cured Epoxy Resin

After a long period of service,the hydraulic structures are in urgent need of effective structural reinforcement and long-term health monitoring.Self-sensing polymer composites(SSPC)are mainly made of underwater curing epoxy resin(UWEP)and carbon nanotubes(CNTs),which not only have good bonding properties,durability and underwater curing properties,but also have self-sensing characteristics.Adding conductive fillers into epoxy resin has become an effective method to prepare self-sensing materials.But the researches on underwater cured epoxy resin modified by carbon nanotubes are rare,there is a certain gap from the actual application.Therefore,the research on sensing properties of CNTs/UWEP is necessary,the main research contents are as follows:Resin components,underwater curing agent and CNTs with better properties are used to prepare test specimens.The preparation process is optimized by high speed shear and magnetic stirring to improve the dispersion effect of fillers.The embedded copper mesh electrode forms a good contact with the material matrix.In terms of electrode setting,it is confirmed that the four-probe method is the better electrode setting form,the resistance of the test specimens are lower and more stable.Through the comparison of the preparation process,it is found that the melt-mixing is more suitable for preparing CNTs/UWEP than the solution blending.Through testing the mechanical properties of CNTs/UWEP composites with different CNT concentrations,it is found that the tensile strength of the composites increases with the increase of CNT concentration,while the fracture elongation,Young's modulus and compression strength increase firstly and then decrease.By changing the concentration of CNT,the percolation threshold of the material is obtained as the concentration of CNT reached around2wt%,and its good volt-ampere characteristics is verified.Based on the variation law of strain,stress and resistance rate of the material under uniaxial tensile and compression loading,it is concluded that the composite material exhibits relatively good force-sensitive properties when the concentration of CNT reaches or exceeds the percolation threshold.By changing the temperature,diving time,loading rate and other conditions,it is concluded that the influence of the temperature to the force sensitive properties is significant,but the interference of diving time is less obvious.But with the increase of displacement load rate,the resistance change rate of the test specimen increases faster,the perceptual characteristics are significantly affected by the load rate.Through the analysis and numerical simulation of the conductive network model of CNTs/UWEP composites,it is concluded that the conductivity of CNT network increases greatly when the concentration of CNT in the composites reaches the percolation threshold.The simulation results are close to the experimental results,and the material has reliable conductive characteristics.