Research On Temperature Resistance Effect Of Carbon Nanofibers Modified Carbon Fiber Composites

With the increasing amounts of large-scale structural engineering,the damage and destruction of components and structures have been attracted.Structural health monitoring has gradually developed into a hot-spot in the research field of engineering structures.With the support of the National Natural Science Foundation of China “ the self-sensing characteristics and application of prestressed concrete structures based on carbon fiber materials(51478209)”,the essay mainly studied the effect of different resistance test methods on the resistance test of CNFs(Carbon Nano Fibers,CNFs)modified CFRP(Carbon fiber reinforced polymer,CFRP)sensing elements and the influence of the amount of carbon nanofibers on the temperature resistance effect of the carbon fiber composite sensor element.Finally,the CFRP sensor element modified by CNFs was embedded in the concrete member in order to verify its applicability under construction conditions.The main contents are as follows:1.Carrying out a comparative test of the resistance test of the four-electrode method and the two-electrode method.CFRP sensing elements with different dosages of CNFs(0 wt%,0.5 wt%,1.0 wt%,and 1.5 wt%)were fabricated.The influence of different resistance test methods on the test results was analyzed.Inputting a constant current of 1mA to 6mA to the sensing element,testing the element voltage through different resistance test methods,comparing and analyzing the voltage-current relationship.Conclusions are as follow,The resistance test result of the two-electrode method is larger than that of the four-electrode method.The four-electrode method eliminates the effect of contact resistance,and the test result is closer to the actual resistance of the sensing element.Because the contact resistance is non-ohmic.The two-electrode method includes a contact resistance voltage-current curve that is non-ohmic,The voltage-current curve of the four-electrode method is ohmic.2.Designing and manufacturing CFRP sensing elements with four different dosages of CNFs(0 wt%,0.5 wt%,1.0 wt% and 1.5 wt%).A temperature rise test(-20?~70?)and a repeated cycle temperature loading test were carried out on the sensor element respectively to study the temperature resistance change law of the CFRP sensor element modified with different dosages of CNFs,and a better CNFs dosage was obtained.And the mechanism of resistance change law is discussed in preliminary.Conclusions are as follow,In the first heating-up test,the sensing elements showed PTC effect,and the linear relationship was good.When the proportion of CNFs is 0.5 wt%,it is closer to the percolation threshold of the material,and the optimal proportion is near the percolation threshold.In the repeated temperature loading test,There is a “hysteresis loop” in the volume resistivity temperature curve as a whole.As the number of temperature cycles increases,the “hysteresis loop” becomes smaller,heater and cooler.The curves tend to coincide,and the repeatability of the sensing element becomes better.3.The CNFs modified CFRP sensor element was embedded in the reinforced concrete member to monitor the temperature and change of concrete in the construction stage in real time.Comparing it with the hydration heat curve of mass concrete to explore the applicability of the CNFs modified CFRP sensor element in the hydration heat monitoring of mass concrete structure.Conclusions are as follow,The change trend of resistance of CNFs modified CFRP sensor element is similar to the heat release curve of hydration heat of mass concrete,which proves it feasible for CNFs modified CFRP to be used for hydration heat monitoring of mass concrete structure under actual working conditions.