Simulation Analysis And Design Of Small Hollow Blade Eddy Current Thickness Sensor

Error in the procedure of engine blade production and various structure will directly affect the structural strength and fatigue properties of th e blade, makes the overall property of the engine debilitate, shorten it’s service life. To make sure that the engine is security, it’s required that the normal direction thickness error of the outer surface to the inner surface of the hollow blade must be in the permitted range, to ensure the intensity index and structure parameters of the hollow blade. For now, the small hollow blade thickness measurement range of new aircraft engine is 0.1 mm to 3 mm, and the measurement uncertainty must be no more than 0.05 mm. This topic chooses a kind of NDT test, namely eddy current testing, and designs a kind of precision small hollow blade eddy current thickness sensor, which can satisfy the measurement requirements in the accuracy, stability and measuring range. Firstly, this paper recommend the fundamental theory of eddy current thickness as well as the basic theory of electromagnetic field, beginning with the basic theory of electromagnetic field, applying impedance analysis method, sums up the relationship between intensity of eddy current and detection distance(thickness measurement) as well as the excitation frequency, and that eddy current sensor is affected by the temperature, and the radial and longitudinal distribution of eddy current. Then using finite element software ANSYS simulate the electromagnetic field of eddy current thickness, establish the axisymmetric model in two-dimensional, considering the surrounding air, applying the far field units, which can draw the conclusions as follows: The change of measuring small hollow blade thickness can makes the change of imaginary part of measurement coil impedance obvious, which provide the basis for the signal extraction; The greater the text frequency is, the more obvious skin effect of eddy current on the metal base, and the increase of the frequency makes the coil impedance’s imaginary part increased, but the real part is almost the same, so for different detection range, different excitation frequency must be selected; The radius of the eddy current ring on the basal is roughly the same as the average radius of coil. The difference basal material makes the magnetic field’s spread distinct, through comparing the four kinds of basal material, the basal material of copper causes that the coil impedance’s imaginary part change range is the most minimal, and the effect of silicon steel is best, and the change of impedance’s imaginary part is the biggest, which can have an effect on a better sensitivity and stability. Through finite element simulation can only qualitative analysis the influence of various parameters, and it can’t get accurate numerical, so finally, the optimal level of each parameter and the best combination are obtained by orthogonal text. After the actual measurement verification, the eddy current thickness sensor is successfully developed which can both meet the measuring accuracy and measuring range.