The Application Of Field Assisted Quantum Tunneling Enabled Composites To Structural Health Monitoring

Structural health monitoring(SHM)provides a significant approach,for civil and fundamental structures,to obtain the damage information,evaluate the structural integrity,reduce the maintenance expense,as well as to predict the service lifespan.Field assisted quantum tunneling enabled silicon rubber-based composite possesses the unique merits including superior sensitivity,easy preparation,high application adaptability,and high electrical resistivity when not deformed,all together making it possible to be developed into a new kind of SHM sensors.Therefore,this paper will be focused on the three application scenarios of SHM including the monitoring of ship-bridge collision,the monitoring the bridge bearings and traffic detection,so as to determine the material selecting principles,sensing mechanism,sensor design method and working principles of the composite.The main research content and conclusions are as follows:(1)Ship-bridge collision monitoring.Field assisted quantum tunneling enabled silicon rubber-based composite with different thickness and different types of silicone rubber were fabricated and integrated into sensors.A steel ball free-drop model test was designed to simulate the ship-bridge collision,and collision sensing properties of sensors were tested.A method was proposed to collect the collision parameters by measuring the voltage signal across the sensors.The collision positioning was achieved by mounting sensors in different regions of the monitoring area and paralleling the sensors in one circuit.A damage judging flow was proposed along with the classification and method of warning release.Meanwhile,the cushioning effect of composite on the collision was also studied.The results show the fabricated sensors have fast response to the collision,and the measuring range fits for the collision monitoring.It is also proved that it is approachable,by analyzing voltage signals of sensors,to get information such as collision force,collision time,collision position and collision area.(2)Bridge bearing monitoring.Different forms of sensors were designed and verified by numerical modeling in ABAQUS.Under uniaxial compression,factors including content of nickel powder,composite thickness,loading rate were studied about how they affect the sensitivity of rubber bearing sensors.The creep and the electrical resistance relaxation of the composite were under constant load.The results show the stress condition of the bearing would be more precisely measured by totally replacing the mid layer rubber with the composite.It is also found that there exists the hoop effect for the composite in bearings,and the sensing properties of sensors strongly relies on the sensor's dimensions and lateral constrains.The change of lading rate will result in the shift of sensing interval,while the interval length basically remains unchanged.Moreover,the designed smart rubber bearing can be applied to the monitoring of bearing serviceability and bridge safety condition,as well as the detection of traffic condition on bridge.(3)Traffic detection.Composites with different thickness and width were prepared,and the traffic parameter detection performance of the sensors was studied in a rutting simulation test.Stress condition of sensors at work was studied.The origin of voltage signal distortion when tiling on the road surface was discussed.Decay mechanisms of pressure sensitivity under repeated rolling was also investigated.Besides,the Burger equation was used to describe the electrical resistance relaxation of sensors under constant loading.The results show that the electrical deterioration stems from the damage of conduction network and microstructure in the composites caused by the work done by tire movement,and the dimensions of sensor remarkably influence the amount and the exerting time of the work.It is also observed the electrical resistance relaxation can be restored to a large extent after unloading.The designed traffic detection sensor can be used to detect a variety of vehicle parameters and traffic violations.