| With wide application of carbon fiber-reinforced plastic(CFRP)in various engineering field,it plays a very important role in ensuring the safety in production and life and promoting the development of CFRP to use nondestructive testing(NDT)technology to discover the multifarious defects that are produced in the process of manufacturing and use in advance.Currently,there are mainly six kinds of NDT methods for CFRP.However,due to the differences in the detection mode and effective detection content,each method has its own relative merits and application fields.Among them,eddy current testing(ECT)method is gradually becoming a hotspot in the research of NDT technology for CFRP thanks to its advantages of relatively technical maturity,non-contact detection,no auxiliary media,easy automation,low cost,etc.Aiming at the shortcomings that all frequently-used tubular ECT coils require custom processing,cost high and vary widely in coil parameters,a new ECT method for CFRP based on the planar rectangular spiral coil made of printed circuit board(PCB)technology is investigated in this dissertation.The research mainly includes four aspects:In the first aspect,a new method for coil impedance calculation,named vertex description method,is proposed to solve the complex and time-consuming problems of the existing methods based on the previous studies.With this method,the impedance model of any complex-shaped planar orthogonal coil(including planar rectangular spiral coil)can be established fast.In the second aspect,the ECT characteristics of planar rectangular coils are studied on the basis of vertex description method.Accordingly,an ECT probe based on single planar rectangular coil manufactured with PCB is designed and made.And focused on this probe,a specific CFRP ECT platform is constructed and employed to detect a variety of CFRP laminates.The results show that this ECT probe has good detection ability for the two defects of cutting mark and impact on the CFRP.In the third aspect,on the basis of the impedance model of the planar rectangular spiral coil,the mutual inductance model between two planar rectangular spiral coils at any position in space is deduced.In the fourth aspect,with the support of the proposed mutual inductance model,a new T-R probe composed of two PCB-based planar rectangular coils is designed and used to detect various types of defects on multiple CFRP laminates.The results show that the T-R probe not only has good detection ability for the defects such as cutting mark,fiber waviness,fiber loss and abnormal distribution but also has good detection ability of fiber directions. |
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