| Carbon fiber reinforced polymer(CFRP)is a new structural material which appeared in the middle 1960s.Compared with traditional metal materials,it has higher specific stiffness,specific strength,temperature resistance,corrosion resistance and other excellent performance.Therefore,it is widely used in aerospace and other industries.But in the process of manufacture and use of CFRP,it can appear various types of damages,such as delamination,fiber breakage,fiber bending,crack,etc.,because of faulty production processes and external impacts.Among them,the delamination is the main damage.Once a large area of delamination occurs in the CFRP,it will affect the mechanical properties of CFRP components seriously.Therefore,the research on nondestructive testing of delamination in CFRP has very important significance.Eddy current testing is a kind of nondestructive testing technology which is based on the principle of electromagnetic induction.It is applicable to all conductive materials.Compared with the ultrasonic testing,X-ray testing,infrared testing,microwave testing,it has many advantages,such as being safe,easy operation and amenability to automation,etc.The delamination of CFRP means that the degumming appears in the laminated plate and the gap is formed eventually.The eddy current induced by pancake coil is parallel to the surface of sample.Thin delamination has small influence on the eddy current,which is not conducive to test delamination by using the pancake coil.Based on the actual problem,the paper adopts the vertical eddy current method to test delamination.The rectangular coil is used to test the delamination.The rectangular coil will induce the vertical eddy current inside CFRP.The vertical eddy current will be disturbed by the delamination.It will affect the detection signal.According to the method,two new probes are designed,namely thebridge type probe and the plane receive type probe.The corresponding experiment system is built.The paper adopts the method of numerical simulation and experiment to research on eddy current testing of delamination in CFRP.The results validate the feasibility of the vertical eddy current method. |
