| CPC G01N 21/8806 (2013.01) [G01N 21/1702 (2013.01); G01N 2021/1706 (2013.01); G01N 2201/104 (2013.01)] | 4 Claims |
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1. A subsurface defect detecting method for cylindrical components, the subsurface defect detecting method for the cylindrical components is applied to a subsurface defect detecting device for the cylindrical components, wherein, the subsurface defect detecting device for the cylindrical components comprising an electric rotating platform, a three-jaw chuck, a first linear supporting base, and a second linear supporting base;
wherein the three-jaw chuck being mounted on the electric rotating platform, and the three-jaw chuck is configured to fix a workpiece to be detected; and
the first linear supporting base and the second linear supporting base being arranged close to the electric rotating platform, and the first linear supporting base and the second linear supporting base are in contact with each other and are perpendicular to each other; and
a first electric telescopic rod being installed on a slider of the first linear supporting base, and a second electric telescopic rod being fixed at an upper end of the first electric telescopic rod; and the second electric telescopic rod is perpendicular to the first linear supporting base and parallel to the second linear supporting base; and
a pulse laser focusing probe being fixed at a movable end of the second electric telescopic rod; and
a rotating base being mounted on a slider of the second linear supporting base, and a third electric telescopic rod is rotatably mounted on the rotating base; and
a fourth electric telescopic rod being fixed at an upper end of the third electric telescopic rod, and a continuous laser focusing probe being fixed at a movable end of the fourth electric telescopic rod; and
the electric rotating platform, the first linear supporting base, the second linear supporting base, the first electric telescopic rod, the second electric telescopic rod, the third electric telescopic rod, and the fourth electric telescopic rod being communicated with a personal computer (PC) terminal; and
the PC terminal being communicated with a control terminal of the pulse laser and an output terminal of a dual-wave mixing interferometer; and
the pulse laser is connected to the pulse laser focusing probe to emit pulse laser, and the dual-wave mixing interferometer is connected to the continuous laser focusing probe to convert laser ultrasonic signals received by the continuous laser focusing probe into electrical signals and transmit them to the PC terminal;
wherein, the subsurface defect detecting method for the cylindrical components comprising:
S1, installing the workpiece to be detected, and establishing a plane rectangular coordinate system (x-y) with an intersection of the first linear supporting base and the second linear supporting base as a coordinate origin, and the first linear supporting base is located on the y-axis, and the second linear supporting base is located on the x-axis; and setting coordinates of the first electric telescopic rod in the x-y plane rectangular coordinate system to (0, y), and setting coordinates of the third electric telescopic rod in the x-y plane rectangular coordinate system to (x, 0), and setting coordinates of the workpiece to be detected in the x-y plane rectangular coordinate system to (x0, y0); and
S2, adjusting a position of the pulse laser focusing probe, and adjusting a position and an angle of the continuous laser focusing probe to ensure that the laser ultrasonic signal received by the continuous laser focusing probe is optimal; and
S3, performing a layer-by-layer scanning of the workpiece to be detected through a cooperation of the electric rotating platform, the first electric telescopic rod, and the third electric telescopic rod, while synchronously recording rotational angles and measurement heights of the workpiece to be detected and corresponding laser ultrasonic signals; and
S4, analyzing collected laser ultrasonic signals by the PC terminal; and determining whether the workpiece to be detected has the subsurface defect by observing variations in positive peak values of the Rayleigh wave in the collected laser ultrasonic signals; and calibrating a location of the subsurface defect based on the workpiece rotation angles and the measurement heights; and
calibrating a subsurface defect depth d by calculating a depth feature value pr of the Rayleigh wave in the laser ultrasonic signals; and extracting positive peak value Rpos and negative peak value Rneg of the Rayleigh wave in the laser ultrasonic signals, and calculating a subsurface defect width w;
wherein, S4 comprises the following steps:
S4.1, calibrating a time-domain and a frequency-domain of the laser ultrasonic signals for the workpiece to be detected in a defect-free state;
S4.2, comparing the peak values of the laser ultrasonic signals collected in S3 with the calibrated laser ultrasonic signals from S41; and marking the rotational angles α1, α2, α3 and α4, where α1 represents a rotational angle at which the subsurface defect starts to enter the detection area, α2 represents a rotational angle at which the subsurface defect completely enters the detection area, α3 represents a rotational angle at which the subsurface defect begins to shift out the detection area, and α4 represents a rotational angle at which the subsurface defect completely shifts out the detection area; and α1 corresponds to a maximum positive peak value of the Rayleigh wave peak curve, α2 and α3 correspond to two negative peak values in a Rayleigh wave peak curve, and α4 corresponds to the Rayleigh wave positive peak value which increases from a minimum value to a positive value of the Rayleigh wave positive value of the defect-free state calibrated in S41; and the detection area is a sector-shaped region between the pulse laser focusing probe and the continuous laser focusing probe; and a circumferential position of the subsurface defect is calibrated based on the rotational angles and the measurement heights of the workpiece to be detected; and
S4.3, if it is determined by comparing the peak values of S41 that the subsurface defect is present at the corresponding position of the laser ultrasonic signal, the subsurface defect depth d is calibrated by calculating the depth feature value pr of the Rayleigh wave in the laser ultrasonic signal through the PC terminal;
wherein, S4.3 comprises the following steps:
S4.3.1, performing a wavelet packet decomposition to the laser ultrasonic signal, and the laser ultrasonic signal φ(t) is expressed as:
Ci,kj=∫φ(t)·Wi,k(t)dt;
Wi,k(t)=2−i/2W(2−it−k);
where, t is a time series, i is a frequency band order, j is a wavelet decomposition level, k is a wavelet packet decomposition parameter, and C is a wavelet packet function, and Wi,k(t) is a wavelet packet decomposition coefficient;
S4.3.2, constructing a time-frequency matrix A of the laser ultrasonic signal that contains information about subsurface defect through the wavelet packet decomposition, and the time-frequency matrix A is expressed as follow:
 where, a=N/2j, b=2j, N is a number of sampling points of the laser ultrasonic signal φ(t);
S4.3.3, A=UΣVT;
where, T is a matrix transpose operator, U is a orthogonal matrix of a×a, and V is a orthogonal matrix of b×b, and Σ is the diagonal matrix of a×b;
where,
 where, λ is eigenvalues of a rank of the time-frequency matrix A, and the rank of the time-frequency matrix A is denoted as r=rank(A);
calculating the depth feature value pr of the Rayleigh wave in the laser ultrasonic signal;
where,
 computing the subsurface defect depth d, where d=A1·pr, and A1 is a correction factor;
S4.4, averaging the laser ultrasonic signals within the angular range from α2 to α3 through the PC terminal, and extracting positive peak value Rpos and negative peak value Rneg of the Rayleigh wave in the laser ultrasonic signals, and calculating a subsurface defect width w using a width feature value |Rneg/Rpos| and the subsurface defect width w is calculated according to the following formula:
 S5, outputting subsurface defect information of the workpiece to be detected, and the subsurface defect information comprises whether the subsurface defect is present, the location of the subsurface defect on the workpiece to be detected, the subsurface defect depth, and the subsurface defect width.
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