Multi-material inspection system and velocity measurement method of critically refracted longitudinal wave based on single-angle wedges

A multi-material sound velocity measurement method of critically refracted longitudinal wave based on single-angle wedges, wherein a phased array ultrasonic law is calculated and optimized, the arrival time of a received signal is read and interpolation is performed, and a critically refracted longitudinal wave velocity of a material is calculated, the method including the steps of:

• (1) preliminarily calculating a phased array ultrasonic delay law
• preliminarily selecting a number of array elements in an aperture n according to the ultrasonic attenuation coefficient of the wedges, giving a longitudinal wave velocity vm value, calculating a corresponding first critical angle α1 by formula (1), and calculating a phased array ultrasonic incident deflection angle θ by formula (2) according to the angle of the wedges:
• θ′=α1−θw (2)
• then, calculating a delay law of the phased array ultrasonic transmitting probe by formula (3):
• {
• t
• i
• =
• (
• i
• -
• I
• )
• ×
• P
• ×
• sin
• ⁢
• θ
• V
• w
• θ
• >
• 0
• t
• i
• =
• (
• J
• -
• i
• )
• ×
• P
• ×
• sin
• ⁢
• (
• -
• θ
• )
• V
• w
• θ
• <
• 0
• (
• 3
• )
• where i is a serial number of any aperture array element, I is a serial number of an initial aperture array element, J is a serial number of a final aperture array element, I≤i≤J≤n (i, I, J, and n are all positive integers), ti is a delay time of the i-th array element, and P is a spacing between array elements;
• (2) optimizing the calculated delay law
• selecting a certain value from 5% to 10% in a longitudinal wave velocity range of the to-be-measured material as a step, setting the longitudinal wave velocity vm of the to-be-measured material in sequence from low to high in the phased array ultrasonic inspection system, and exciting and receiving a critically refracted longitudinal wave according to the calculated delay law of the transmitting probe when the receiving probe is not delayed;
• adjusting a gain of instruments and fixing the gain to a certain value to ensure that a maximum amplitude in the received signals is not less than 80% of a full screen and does not exceed the full screen;
• building a relation curve between longitudinal wave velocities vm of the material and amplitudes A of critically refracted longitudinal waves, fitting and determining a vm corresponding to the maximum A;
• setting different numbers of array elements in an aperture n, obtaining a relation curve between the numbers of array elements in an aperture n of the transmitting probe and the amplitudes A of the critically refracted longitudinal waves by exciting and receiving a critically refracted longitudinal wave according to the calculated delay law of the transmitting probe when the receiving probe is not delayed;
• selecting a number of array elements in an aperture n according to quality of the received signals, adjusting the gain of instruments, and determining an optimized delay law to ensure that the amplitude of the received signals is not less than 50% of the full screen, and a signal-to-noise ratio is not less than 12 dB;
• (3) reading and interpolating the arrival time of a received signal
• exciting and receiving a critically refracted longitudinal wave on the basis of the optimized calculated delay law, and recording A scan and B scan signals in the computer at a sampling frequency of not less than 50 MHz;
• performing linear interpolation on the A scan signal corresponding to each array element, to ensure that a sampling frequency is not less than 500 MHz;
• (4) calculating the longitudinal wave velocity of the material to be tested
• calculating a delay time tij between two array elements in the aperture used by the receiving probe by reading and interpolating the arrival time of a received signal, and calculating an angle Δθ between the critically refracted longitudinal wave and a plane of phased array ultrasonic array elements in the B scan in step (5) by formula (4):
• Δ
• ⁢
• θ
• =
• sin
• -
• 1
• (
• t
• t
• ⁢
• j
• ×
• v
• w
• (
• j
• -
• i
• )
• ×
• P
• )
• (
• 4
• )
• calculating the longitudinal wave velocity vm of the material to be tested according to the solved Δθ by formula (5):
• v
• m
• =
• v
• w
• sin
• ⁡
• (
• θ
• w
• -
• Δ
• ⁢
• θ
• )
• (
• 5
• )
• (5) calculating an optimal delay law
• further repeating the preliminary calculation of the phased array ultrasonic delay law on the basis of the calculated longitudinal wave velocity vm of the to-be-measured material, and calculating to obtain the optimal delay law so that high-quality excitation and reception of critically refracted longitudinal wave based on single-angle wedges on the to-be-measured material is enabled to inspect defects and evaluate damages.