Research On The Eddy Current Testing Of Fiber Breakage And Fiber Bending In Unidirectional Carbon Fiber Reinforced Polymer

Carbon fiber is a new type of chemical material which is both tensile and soft to be processed,and it is a kind of reinforced fiber.Carbon fiber reinforced polymer(CFRP)is compounded from the carbon fiber and other matrix material,and it has good specific strength,specific stiffness,fatigue resistance,corrosion resistance and shock absorption.With its excellent performance,unidirectional CFRP is used in the manufacture of wind power blades,building reinforcement materials and oil field drilling rods.However,there are fiber breakage and fiber bending when CFRP are in the use or manufacture.For example,it will cause fiber breakage when the surface of CFRP is impacted or scratched by sharp objects.The residual stress caused by rapid curing will cause the fiber bending.Fiber breakage will greatly reduce the tensile strength of CFRP,and fiber bending will lead to a significant reduction in compressive strength of CFRP.It will threaten the structure safety seriously,so the nondestructive testing of CFRP structure is significant.Eddy current testing(ECT)as one of the five conventional nondestructive testing methods,has its unique advantages.Therefore,it is necessary to detect the fiber breakage and fiber bending through ECT.CFRP is conductive,and defects can be detected through ECT theoretically.However,because of the poor conductivity and the anisotropy,it is very difficult to apply ECT to CFRP.At present,there are few researches on the ECT of fiber breakage and fiber bending in CFRP.In this paper,two ECT methods are proposed to detect the fiber breakage and fiber bending defects in unidirectional CFRP respectively.In this paper,we use the remote field eddy current(RFEC)probe to detect the fiber breakage defect in unidirectional CFRP.Firstly we introduce the construction of RFEC testing system,including the design of the probe,the choice of working frequency and related instruments.Then,we scan the unidirectional CFRP with fiber breakage by the RFEC probe through simulation.It is found that the RFEC probe can detect the fiber breakage defect.After that,a unidirectional CFRP with fiber breakage is tested by the RFEC testing system,and the results show that the fiber breakage can be detected.The simulation results are verified with the experimental results.This paper also proposes the use of directional probe to detect fiber bending defect in unidirectional CFRP.Firstly,the construction of the testing system is introduced.Then,we scan the unidirectional CFRP with fiber bending by the directional probe through simulation.It is found that the directional probe can detect the fiber bending defect.After that,we test the directional probe,and the results show that it is sensitive to the fiber orientation.A unidirectional CFRP with fiber bending is scanned with the directional probe,and the results show that the bending fiber can be detected.