Introduction

1. Theoretical research on eddy current testing

• Theoretical research includes detection probability research, detection system reliability design research and skin effect research.
• In recent years, the skin effect of eddy current detection has been systematically and in-depth studied, including the detection of skin effect by flat coil of metal sheet, the detection of skin effect by inner coil of metal pipe, the detection of skin effect by outer coil of metal bar, and the detection of skin effect by metal bar with limited thickness. Eddy current detection of skin effect of flat plate, eddy current detection of skin effect of composite metal plate, eddy current detection of skin effect of multilayer metal plate, eddy current detection of skin effect of anisotropic material, detection of skin effect of pulsed eddy current, The effect of skin depth. The eddy current diffusion-cancellation theory and the eddy current reflection theory are proposed to reveal the skin effect mechanism of eddy current detection. The concept of equivalent skin depth is proposed to measure the actual eddy current decay speed.

2. Research on numerical analysis methods

• Taking electromagnetic nondestructive testing as the application background, the element-free Galerkin (EFG) method and finite element analysis method are studied.
• The EFG method was applied to the electromagnetic field calculation earlier, and the EFG method to solve the problems of steady magnetic field, eddy current field and microwave scattering was studied. The microwave scattering problem is solved by combining the EFG method with the ideal matching layer technology, and the microwave detection of concrete reinforced structures is simulated.
• Research on the finite element method based on double scalar bits. The double-scalar potential method is improved to solve the steady-state magnetic field problem with anisotropic ferromagnetic materials with multiple curved shapes.
• In recent years, the main research is on the finite element simulation method of eddy current testing. A region decomposition method for low-frequency electromagnetic field analysis is proposed to solve the simulation problem of magnetic core coil scanning eddy current detection. It has the characteristics of simple mesh division and high calculation efficiency. Based on the area decomposition method, the simulation of magnetic core coil scanning pulse eddy current testing, carbon fiber reinforced resin matrix composite (CFRP) layup deformation eddy current testing simulation, and CFRP panel-aluminum honeycomb core sandwich structure eddy current testing simulation are realized. A mixed representation domain decomposition finite element method is proposed, which further improves the computational efficiency of eddy current testing simulation.

3. Research on detection technology

• Carry out eddy current testing research on CFRP life cycle. On the basis of finite element analysis, the distribution law of eddy currents in the layer and in the thickness direction in unidirectional CFRP and multidirectional CFRP was investigated, and its mechanism was revealed. Utilizing the structural characteristics and electrical anisotropy of CFRP, the far-field eddy current method is used to detect fiber fracture defects according to the slow decay of eddy current along the fiber direction, and the orthogonal rectangular coil is used to detect prepreg and CFRP according to the characteristic that eddy current mainly flows along the fiber direction Fiber bend defects and reconstruct fiber distribution. To solve the problem that the traditional eddy current testing method cannot detect area-shaped defects parallel to the detection surface, a vertical eddy current method is proposed to detect CFRP delamination defects.
• Carry out eddy current testing research on CFRP panel-aluminum honeycomb core sandwich structure to detect core fracture, node detachment, node compression, core wrinkle and impact damage.
• On the basis of the skin effect research results of eddy current testing, the research on thickness measurement of single-layer metal plate, the measurement of cladding thickness of composite metal plate, and the measurement of air-gap thickness of double-layer metal plate are carried out. The relationship between the coil voltage and the thickness of the single-layer plate, the coil voltage and the thickness of the cladding layer of the composite plate, and the coil voltage and the thickness of the air gap of the double-layer plate are proved, the mechanism is revealed, and the high-precision thickness measurement based on the eddy current method is realized.
• Research on eddy current testing of aluminum alloy residual stress. The eddy current response plane is constructed to describe the relationship between the eddy current response and the stress state, and a fast inversion method is proposed to realize the eddy current detection of the residual stress state of the aluminum alloy, and obtain the magnitude and direction of the principal stress at the same time.
• He has carried out other electromagnetic non-destructive testing research, such as magneto-optical imaging detection finite element analysis and system parameter optimization, pulsed eddy current detection signal feature selection and defect characterization, metal additive manufacturing eddy current testing, and rail crack quantitative eddy current testing, etc.