Carbon Nanowire Sensing Properties And Applications Based On Three-dimensional Braided Composites

Three-dimensional multi-directional braided composites are widely used in modern automobile manufacturing,aerospace and other fields because they have many advantages such as high strength,high modulus,low density,impact resistance,fatigue resistance and structural design.However,during the weaving and use of the three-dimensional braided composites,the interior of the material may cause various types of defects or damages such as fracture,crack or fiber deboning which may cause serious accidents,such as significant economic losses,environmental pollution,and even cause casualties.Therefore,the development of intelligent composite materials and structural health monitoring of composite materials is particularly important.The core for sensing and monitoring is the sensor,the research on weaving process and sensing characteristics based on three-dimensional braided composite sensor is of great significance.Because of the advantage of small volume,light quality,strong electrical conductivity,high thermal stability and liable to construct sensor network,carbon nanoyarn sensor provides a new way for intelligent material and structural health monitoring.Based on carbon nanoyarn sensors of three-dimensional braided composites,the paper focus on the strain sensing property of carbon nanoyarns,the optimal configuration of sensors and the sensing properties of carbon nanoyarn sensor embedded in three-dimensional braided composites and its application in structural health monitoring.This paper firstly introduces the importance of the sensor technique and structure health monitoring of composite materials,elaborates the current research on the carbon nanoyarn strain sensor based on piezoresistive effect in the structural health monitoring of composite material at home and abroad,explores the way to prepare carbon nanoyarns in addition to its influence to the mechanical property and electrical property and the selection of carbon nanoyarns.The paper systematically studies the sensing property of carbon nanoyarns,analyzes the relationship between its mechanical property(stress and strain)and electric property(resistance and strain sensitivity coefficient).The result shows a better linear relationship between the variational rate of resistance and strain,making it very suitable for monitoring of composite material whose destruction limit is much smaller than its strain(mean damage strain of carbon nanoyarns:10.0%,minimum value:2.5%).When carbon nanoyarns are used as piezoresistive strain sensors,strain can be sensed based on the variational rate of resistance.Besides,carbon nanoyarns display the strain sensitivity coefficient between 1.27 and 2.15 with the mean value being approximately 1.90.equivalent to the value obtained from conventional strain monitoring.These make it a perfect option for composite structural health monitoring sensors.Secondly,the paper introduces the weaving technology and curing molding process of carbon nanoyarns embedded in three-dimensional braided composites.the three--dimension five-direction four-step approach is employed to embed carbon nanoyarns in three-dimensional braided composites and prepare trial pieces.Afterwards,the paper studied the optimal configuration of the carbon nanoyarn sensors in structural health monitoring system,proposing the maximum sensor optimal configuration discipline based on the maximal stress signal detection rate.and realizes the optimizing configuration of sensor based on genetic algorithm.On the basis of the research mentioned above,we established carbon nanoyarn strain sensing experiment system based on the three-dimensional braided composites,studied monotonic stretching and cyclic loading stretching strain sensing character of carbon nanoyarn sensor based on the three-dimensional braided composites.The experimental results show that the embedment of carbon nanoyarns will not affect or degrade the mechanical performance of three-dimensional braided composites,at different incremental cyclic loading and unloading stages,the variation rate of resistance of carbon nanoyarn sensors and the material strain exhibit a good linear correlation when the test pieces are under monotonic tensile and cyclic loading/unloading tensile forces,progressive damage analysis(PDA),and the correlation of resistance to strain(CRS)can be used to describe the strain sensor equation,and analyze the quantitative relationship in damage detection when carbon nanoyarns are used as sensors embedded in three-dimensional braided composites,the residual resistance of carbon nanoyarn sensors is caused by damage or accumulated damage of test pieces,which can be used to detect failures of the structure itself or overload damage caused during service.All of the researches provide experimental reference for the appliance of carbon nanoyarn sensors based on three-dimensional braided composites structure health monitoring.