| On the basis of the detailed introduce of single-probe eddy current testing basic principles and the basic theories about electromagnetic field, this thesis took finite element analysis (FEA) software ANSYS as basic analysis tool and took the infinite slab as the research object, the thesis analyzed low-frequency harmonic electromagnetic field around the sensor in reflex eddy current testing and simulated the distribution of electromagnetic field around tested object. The effects of the tested material parameters, testing distance, crack sizes, frequency and coil shape on the properties of eddy current sensor (ECS) are addressed in detail and respectively in the thesis. The characters and rules of the distribution of electromagnetic field and coil impedance of tested object are studied under every factor. The thesis laid a good foundation for the design and application of reflective eddy current sensor (single-probe) for crack detection.Using the impedance analysis method, simplifying the model, the thesis established a two-dimensional finite element model with axial symmetry seems stable exchange electromagnetic field. Based on this, the thesis has done a lot of simulations and has attained the main conclusions as follows:(1) Measured in different materials, the distribution of magnetic force lines and coil impedance of probe are also different.(2) Changed Lift-off distance of coil has a great impact on amplitude of the impedance while the impedance phase almost prevents from the effect.(3) The smaller distance between the probe and tested object, the higher intensity of electromagnetic induction, the greater eddy current strength of tested object.(4) When cracks was within the tested object, the amplitude of the impedance has no big change, but the phase of the impedance changes significantly. It turn to a negative angle from a positive angle that without cracks.(5) With the same width increasing the depth of the crack will increase the amplitude of the impedance while the phase angle become smaller in absolute terms; and when the depth of the crack is greater than the depth of impenetrating. The amplitude of the impedance is no longer increasing(6) The incentive frequency of the coil has no big effect on the distribution of the electromagnetic force line, but it has effect on the magnetic induction intensity of electromagnetic field. The higher the frequency, the lower the intensity of magnetic induction; in addition, with the increasing of the incentive frequency, the quality factor of the eddy current sensor will increase, that is, the less eddy current strength.(7) The changes of the inside diameter of the coil has no big effect on the distribution of magnetic force line around the sensor. But the changes of the outside diameter will affect a lot on the eddy current within the tested object. The location of the maximum eddy current density value is more or less the same with the outside diameter of the coil.(8) With the same density of the coil turns, the smaller inside diameter the larger outside diameter and the thicker axial thickness of the coil, the higher sensitivity of the sensor the smaller linear range; the greater density of the coil turns, the higher sensitivity of the sensor the larger linear range.Unfortunately, the thesis didn't discuss the edge effects in eddy current testing.
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