CN104730146A - Ultrasonic array composite imaging method for quantitative evaluation of plate structure cracks - Google Patents

Abstract

The invention relates to an ultrasonic array composite imaging method for the quantitative evaluation of plate structure cracks and belongs to the field of nondestructive detection. By carrying out omnifocal imaging and polarity-coherence imaging on a Lamb wave signal which is received by an ultrasonic transducer array, integrating the omnifocal imaging technology with the polarity-coherence imaging technology to obtain a composite imaging technology, carrying out omnifocal vector imaging on the basis of omnifocal imaging, determining the positions of defects according to the energy intensity of a reflected characteristic signal, and calculating the directions of the defects according to the directions of vectors in a vector graph, the directions of cracks can be identified effectively.

Description

A kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle

Technical field

The present invention relates to a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle, the method relates to the direction identification technology of crack defect, belongs to technical field of nondestructive testing.

Background technology

Plate structure is one of industrial the most frequently used version, is widely used for manufacturing various container, furnace shell, stove plate, bridge.In use, plate structure often requires to bear dynamic loading, impact, vibrations, anti-corrosion etc., easily cracks class defect.As in thermal power plant, nuclear power plant's unit running process; turbine blade is operated in the rugged surroundings such as high temperature, high pressure, high rotating speed or wet-steam region; undergo the acting in conjunction of centrifugal force, steam power, corrosion and vibration and the erosion of wet-steam region high velocity water droplets; add the impact of the factors such as the design, manufacture, installation quality and operating condition, the maintenance craft that are difficult to avoid be not good; blade often there will be crackle; light then cause Turbo-generator Set Vibration, heavy then cause runaway accident.All there is certain directivity for crack defect, the directivity obtaining defect can improve production, the use procedure of plate structure effectively, enhances productivity.

In plate, common defect mainly contains crackle, perforation etc.The domestic main lossless detection method adopted at present has the methods such as ultrasonic, ray, magnetic powder inspection.Supersonic guide-wave technology, as one lossless detection method fast and efficiently, has been widely used in the Nondestructive Evaluation of various engineering structure.The supersonic guide-wave propagated in plate structure is called Lamb wave.When Lamb wave is propagated in plate, sound field is throughout whole wall thickness, and propagation distance is longer and decay is less, and therefore Lamb wave is used widely in the Non-Destructive Testing of solid panel structure as a kind of effective means.

Lamb wave detects according to numbers of transducers, and single transducer can be divided into detect and array detection.When utilizing single transducer (reflective) or dual transducers (transmission-type) to carry out Lamb wave detection to plate structure, the defects detection within the scope of certain single direction can only be realized, single (two) transducer Lamb wave detection sensitivity is lower, poor signal to noise.For overcoming the shortcomings such as single transducer power dissipation, resolution is low, detection signal analysis is difficult, multiple array element can be utilized to form transducer array and to carry out Ultrasonic Detection.

Therefore, this problem utilizes Lamb wave array technique to carry out plate structure Study on nondestructive detection method on a large scale.

Conventional supersonic array imaging technique comprises the methods such as total focus imaging, the imaging of vector total focus, scattering coefficient matrix imaging, the consistent imaging of phase place, the consistent imaging of polarity, complex imaging.Caroline Holmes in 2005 etc. deliver " Post-processing ofthe full matrix ofultrasonic transmit – receivearray datafor non-destructive evaluation " article and propose and summarize supersonic array total focus formation method, and the amplitude information utilizing supersonic array to collect signal carries out defect imaging.Paul D.Wilcox in 2007 etc. deliver " Advanced Reflector Characterization with Ultrasonic Phased Arrays in NDEApplications " article and propose supersonic array vector total focus imaging algorithm, are that imaging basis utilizes excitation to identify with the direction of reflectance signature to defect receiving array element with total focus.Jie Zhang in 2008 etc. deliver " Defect Characterization Using an Ultrasonic Array to Measure the ScatteringCoefficient Matrix " article and propose to utilize the scattering coefficient feature of defect to carry out the direction discernment of defect.Jorge Camacho in 2009 etc. deliver " Phase Coherence Imaging " article and propose the consistent imaging of phase place and the consistent formation method of polarity, the phase information of supersonic array collection signal is utilized to carry out defect imaging, compared to total focus imaging, the defective locations information of phase imaging is more accurate.In 2013 Master's thesis " pulse compression technique and the applied research in forging phased array detects thereof ", total focus imaging and optimization method thereof are studied, realize the detection and localization to defect, and improve the precision of imaging by optimization method.2014 Master's thesis " based on vector total focus supersonic array defect identification method research and application " with total focus algorithm for imaging basis to the identification of defect travel direction.But the supersonic array formation method that above-mentioned article proposes is ultrasonic bulk wave techniques, said method is not extended to supersonic guide-wave technical field, and uses single formation method defect imaging effect to have much room for improvement.

Propose a kind of Lamb wave composite imaging method in 2009 Master's thesis " Lamb wave linear array plate structure complex imaging Study on nondestructive detection method ", utilize logical operation to choose defect imaging result under different amplitude Apodization techniques.Vander T.Prado in 2013 etc. deliver " Lamb mode diversity imaging fornon-destructive testing ofplate-like structures " article and propose a kind of Lamb wave composite imaging method, consistent with polarity for total focus imaging imaging are carried out synthesizing and carry out imaging to defect.(patent No.: the total focus formation method 201110281076) processes time-domain signal data, achieves the location to defect in storage tank bottom plate structure to patent " storage tank bottom plate corrosion detection system and method based on ultrasonic Lamb wave ".Supersonic array technology is extended to supersonic guide-wave field and achieves defect imaging by said method, can realize defect imaging, but can not realize the direction discernment of defect.

The innovative point of this patent is to propose a kind of supersonic array complex imaging algorithm, with complex imaging algorithm for imaging basis, by vector total focus algorithm application to supersonic guide-wave technical field, to the identification of plate structure defect travel direction.This method can improve the signal to noise ratio (S/N ratio) of defect imaging effectively, and the precision effectively improving direction of check measurement can realize the measurement of crack length simultaneously.

Summary of the invention

The object of the invention is to propose a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle.The method is used for the direction discernment to plate structure crack defect, first data acquisition system (DAS) is utilized to obtain complete matrix Lamb wave signal, the signal collected is used to carry out total focus imaging imaging consistent with polarity respectively, again synthesis is carried out to two kinds of imagings and obtain complex imaging result, be that the calculating of vector total focus is carried out on imaging basis with complex imaging, the position of defect is determined the most by force by target defect reflectance signature signal energy, the Local Vector figure of target defect is extracted according to the position of defect, finally utilize the direction of vector in Local Vector figure to determine the direction of target defect.

The data acquisition system (DAS) that the method needs comprises oscillograph, function generator, linear array transducer and test specimen, and wherein, linear array transducer is coupled by couplant with test specimen, as shown in Figure 1.When carrying out test experience, first adjustment function generator produces pumping signal, motivates ultrasonic Lamb waves signal and launches along test specimen, and received the ultrasonic Lamb waves signal reflected by array energy transducer by array energy transducer; The data of being carried out ultrasonic time-domain signal by oscillograph store.

For achieving the above object, the technical solution used in the present invention is a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle, specifically can according to following steps examinations, and method flow as shown in Figure 2.

Step one: test under pick-up unit as shown in Figure 1, wherein, testing array energy transducer centre frequency used is f, the total number of array element is N, and the width of single array element is a, and the centre distance of adjacent two array elements is p, the propagation velocity of wave of ultrasound wave in test specimen is c, then wavelength time-domain signal y is collected by the mode encouraged successively _{(i) j}(t) (i=1,2,3 ..., N, j=1,2,3 ..., N), wherein, subscript (i) represents i-th array element excitation in array energy transducer, and j represents that in array energy transducer, a jth array element receives.

Step 2: set up imaging coordinate system, as shown in Figure 3.Definition represent the vector of initial point to imaging point P. represent the position vector of i-th excitation array element to imaging point P, represent vector component in the direction of the x axis, represent vector component in the z-axis direction, represent vector mould. represent that jth receives the position vector of array element to imaging point P, represent vector component in the direction of the x axis, represent vector component in the z-axis direction, represent vector mould.

Step 3: total focus imaging.Whole array data is calculated acoustic transit time t by encouraging, receiving the distance of array element and imaging point, focuses in each imaging point position, and signal amplitude is superposed.Therefore, the amplitude I of full array at each imaging point is calculated by formula (1) _a.

$I_A=\frac{1}{N^2}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{y}_{\left(i\right)j}(t=\frac{\left|{\stackrel{\→}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\→}{d}}_j\right|}{c})---\left(1\right)$

In formula, c is the propagation velocity of wave of sound wave in test specimen; N is array number;

Step 4: the consistent imaging of polarity.To whole array data y _{(i) j}t () carries out polarity process by formula (2).If t y _{(i) j}t () amplitude is less than zero, then defining polarity is-1, y _{(i) j}t () amplitude is more than or equal to zero, then defining polarity is+1.

$b_{\mathrm{ij}}\left(k\right)=\left\{\begin{array}{c}-1,y_{\mathrm{ij}}\left(t\right)<0\\ +1,y_{\mathrm{ij}}\left(t\right)\&GreaterEqual;0\end{array}\right.---\left(2\right)$

After polarity process, according to encouraging, receiving the distance of array element and imaging point, acoustic transit time t is calculated to whole array data, carries out polarity superposition in each imaging point position by formula (3).

$I_B=1-\sqrt{1-{\left(\frac{1}{N^2}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}\underset{i=j}{\overset{N}{\mathrm{\&Sigma;}}}{b}_{\mathrm{ij}}(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{c})\right)}^2}---\left(3\right)$

Step 5: complex imaging.Consistent with polarity for total focus imaging imaging is synthesized by formula (4).

I _C＝I _A·I _B(4)

Step 6: constructor array.Array element to be add up in the array energy transducer of N multiple continuous print array element as a subarray, corresponding time-domain signal is called subarray data.This array energy transducer is divided into K subarray, containing M array element (M<N) in each subarray, the array element between adjacent two subarrays is spaced apart N1 (N1<N).The sequence number minimum value of array element in full array that then a kth subarray is corresponding is 1+M (k-1), and maximal value is 1+M (k-1)+N1, wherein, k=1,2,3 ..., K.

Step 7: calculate the amplitude vector of each subarray at each imaging point.

According to the ready-portioned subarray of step 6, calculate the amplitude vector of each subarray at each imaging point, can the following steps be divided into:

(1) according to excitation corresponding in each subarray, reception array element, repeat step 2, three, in formula, the minimum value of subscript i, j is 1+M (k-1), and maximal value is 1+M (k-1)+N1, can obtain the amplitude of each subarray at each imaging point place vector wherein, subscript k represents a kth subarray.

(2) according to excitation corresponding to each subarray, receive the position vector of array element to imaging point the unit direction vector of each subarray at each imaging point can be obtained it is the unit direction vector receiving the normal direction formed after i-th array element excitation ultrasound wave incides any imaging point through a jth array element, known according to reflection theorem, the direction of this unit direction vector can be vertical with reflecting surface, calculated by formula (5).

${\stackrel{\&RightArrow;}{s}}_{\left(i\right)j}({\stackrel{\&RightArrow;}{d}}_{\left(i\right)},{\stackrel{\&RightArrow;}{d}}_j)=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|{\stackrel{\&RightArrow;}{d}}_j+\left|{\stackrel{\&RightArrow;}{d}}_j\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}}{\left|\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}|{\stackrel{\&RightArrow;}{d}}_j+|{\stackrel{\&RightArrow;}{d}}_j\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|}---\left(5\right)$

(3) will to obtain in upper two steps with correspondence is multiplied and can obtains the amplitude vector of each subarray at each imaging point place calculated by formula (6).

Step 8: to the amplitude vector of the subarray of K in step 7 synthesize, obtain the synthesis amplitude vector of K subarray at each imaging point calculated by formula (7).

In formula, α gets 1 to just infinite Arbitrary Digit, when α value is larger, and the synthesis amplitude vector of any imaging point direction more close to the direction that imaging point place reflected signal energy is the strongest.

Step 9: amplitude vector will be synthesized carry out unitization, be then multiplied by the I in step 4 _c, the amplitude vector of each imaging point under full array N can be obtained calculated by formula (8).

${\stackrel{\&RightArrow;}{V}}_{\left(i\right)j}=\frac{{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}}{\left|{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}\right|}{I}_C(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{c})---\left(8\right)$

According to above-mentioned calculating, full array is at the amplitude vector of each imaging point size equal in the amplitude of each imaging point with the full array in step 5, and vector direction can be vertical with the reflecting surface at imaging point place.

Step 10: by the amplitude vector of the full array in step 9 at each imaging point carry out imaging display, the global vector image of full array at each imaging point can be obtained.

Step 11: according to the polar plot in step 10, determines the position of target defect, extracts the Local Vector figure of target defect then by the amplitude I in step 5 _ccarry out decibel, find out the maximal value of amplitude in Local Vector figure, solve the imaging region area corresponding to maximal value decline-6dB.Last vertical with target defect according to the direction of vector in Local Vector figure, according to geometric relationship, the direction of target defect calculates by formula (9).

${\mathrm{\&theta;}}_m=\arctan \left(\frac{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{i}\mathrm{dA}}{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{j}\mathrm{dA}}\right)---\left(9\right)$

In formula, with represent the vector of unit length parallel with vertical with array energy transducer, A represents in target defect Local Vector figure, by amplitude I _cthe imaging region area corresponding to maximal value decline-6dB, arctan function is the arctan function in mathematics, θ _mrepresent the angle of vector and z-axis forward, namely equal the angle of defect and x-axis forward.

Compared with existing detection method, the present invention has the following advantages: (1) complex imaging algorithm can improve the signal to noise ratio (S/N ratio) of defect imaging effectively; (2) complex imaging improves the precision that direction of check is measured; (3) crack length can be realized measure.

Accompanying drawing explanation

Fig. 1 is pick-up unit block diagram of the present invention.

Fig. 2 is the process flow diagram of the inventive method.

Fig. 3 is the imaging coordinate system set up in the inventive method embodiment.

Fig. 4 a is plate structure defect complete matrix image.

Fig. 4 b is the consistent imaging original graph of plate structure defect polarity.

Fig. 4 c is plate structure defect compound imaging original graph.

Fig. 4 d is that the imaging of plate structure defect defective locations is amplified.

Fig. 5 is the Local Vector total focus figure of plate structure defect.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.

This example detection instrument is function generator, oscillograph and linear array transducer.The linear array transducer centre frequency f=300kHz used in experiment, the total number N=8 of array element, single array element width a=6mm, the centre distance p=2mm of adjacent two array elements, the propagation velocity of wave c=5300m/s of sound wave in test specimen, then wavelength detected object is aluminium sheet, and length and width are 1000mm, and thickness is 1mm.

The technical solution used in the present invention is a kind of concrete steps of the supersonic array composite imaging method for the quantitative evaluation of plate structure crackle:

Step one: test under pick-up unit as shown in Figure 1, collects time-domain signal y by the mode encouraged successively _{(i) j}(t) (i=1,2,3 ..., 8, j=1,2,3 ..., 8), wherein, subscript (i) represents i-th array element excitation in array energy transducer, and j represents that in array energy transducer, a jth array element receives.

Step 2: set up imaging coordinate system, as shown in Figure 3.To arrange imaging region x direction length be L=1000mm, z direction length is H=500mm, and imaging precision is step=2mm.

Definition imaging region is P (m, n).Wherein, m, n are respectively x, z direction discrete point numbering, m=L/step=1000/2=500, n=H/step=500/2=250, then m=1, and 2,3 ..., 500, n=1,2,3 ..., 250.Work as m, n gets particular value m ₀, n ₀time, P (m ₀, n ₀) represent specific imaging point, wherein m ₀=0.002 × (m ₀-1), n ₀=0.002 × (n ₀-1),

When excitation array element is i, when reception array element is j, for imaging point P (m ₀, n ₀), ${\stackrel{\&RightArrow;}{d}}_j=({\stackrel{\&RightArrow;}{d}}_{\mathrm{jx}},{\stackrel{\&RightArrow;}{d}}_{\mathrm{jz}}),$ can be expressed as:

${\stackrel{\&RightArrow;}{d}}_{\left(i\right)x}=0.002\&times;(m_0-1)-((i-1)-(8-1)/2)\&times;0.002$

${\stackrel{\&RightArrow;}{d}}_{\left(i\right)z}=0.002\&times;(n_0-1)$

${\stackrel{\&RightArrow;}{d}}_{\left(j\right)x}=0.002\&times;(m_0-1)-((j-1)-(8-1)/2)\&times;0.002$

${\stackrel{\&RightArrow;}{d}}_{\left(j\right)z}=0.002\&times;(n_0-1)$

$\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|=\sqrt{{{\stackrel{\&RightArrow;}{d}}_{\left(i\right)x}}^2+{{\stackrel{\&RightArrow;}{d}}_{\left(i\right)z}}^2}$

$\left|{\stackrel{\&RightArrow;}{d}}_j\right|=\sqrt{{{\stackrel{\&RightArrow;}{d}}_{\mathrm{jx}}}^2+{{\stackrel{\&RightArrow;}{d}}_{\mathrm{jz}}}^2}$

Step 3: total focus imaging.Whole array data is calculated acoustic transit time t by encouraging, receiving the distance of array element and imaging point, focuses in each imaging point position, and signal amplitude is superposed.Therefore, the amplitude I of full array at each imaging point is calculated by formula (1) _a.

$I_A=\frac{1}{8^2}\underset{i=1}{\overset{8}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{8}{\mathrm{\&Sigma;}}}{y}_{\left(i\right)j}(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{5300})---\left(1\right)$

Step 4: the consistent imaging of polarity.To whole array data y _{(i) j}t () carries out polarity process by formula (2).If t y _{(i) j}t () amplitude is less than zero, then defining polarity is-1, otherwise then defining polarity is+1.

$b_{\mathrm{ij}}\left(k\right)=\left\{\begin{array}{c}-1,y_{\mathrm{ij}}\left(t\right)<0\\ +1,y_{\mathrm{ij}}\left(t\right)\&GreaterEqual;0\end{array}\right.---\left(2\right)$

After polarity process, according to encouraging, receiving the distance of array element and imaging point, acoustic transit time t is calculated to whole array data, carries out polarity superposition in each imaging point position by formula (3).

$I_B=1-\sqrt{1-{\left(\frac{1}{8^2}\underset{i=1}{\overset{8}{\mathrm{\&Sigma;}}}\underset{i=j}{\overset{8}{\mathrm{\&Sigma;}}}{b}_{\mathrm{ij}}(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{5300})\right)}^2}---\left(3\right)$

Step 5: complex imaging.Synthesize by formula (4).

I _C＝I _A·I _B(4)

Step 6: constructor array.Array element to be add up in the array energy transducer of 8 multiple continuous print array element as a subarray, corresponding time-domain signal is called subarray data.This array energy transducer is divided into 4 subarrays, containing 2 array elements in each subarray, the element number of array between adjacent two subarrays is 1.The sequence number minimum value of array element in full array that then a kth subarray is corresponding is 1+2 (k-1)=2k-1, and maximal value is 1+2 (k-1)+1=2k, wherein, and k=1,2,3,4.

Step 7: calculate the amplitude vector of each subarray at each imaging point.

According to the ready-portioned subarray of step 6, calculate the amplitude vector of each subarray at each imaging point, can the following steps be divided into:

(1) according to excitation corresponding in each subarray, reception array element, repeat step 2, three, in formula, the minimum value of subscript i, j is 1+2 (k-1), and maximal value is 1+2 (k-1)+1, can obtain the amplitude of each subarray at each imaging point place vector wherein, subscript k represents a kth subarray.

(2) according to excitation corresponding to each subarray, receive the position vector of array element to imaging point the unit direction vector of each subarray at each imaging point can be obtained it is the unit direction vector receiving the normal direction formed after i-th array element excitation ultrasound wave incides any imaging point through a jth array element, known according to reflection theorem, the direction of this unit direction vector can be vertical with reflecting surface, calculates by formula (5).

${\stackrel{\&RightArrow;}{s}}_{\left(i\right)j}({\stackrel{\&RightArrow;}{d}}_{\left(i\right)},{\stackrel{\&RightArrow;}{d}}_j)=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|{\stackrel{\&RightArrow;}{d}}_j+\left|{\stackrel{\&RightArrow;}{d}}_j\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}}{\left|\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}|{\stackrel{\&RightArrow;}{d}}_j+|{\stackrel{\&RightArrow;}{d}}_j\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|}---\left(5\right)$

(3) will to obtain in upper two steps with correspondence is multiplied and can obtains the amplitude vector of each subarray at each imaging point place calculate by formula (6).

Step 8: to the amplitude vector of 4 subarrays in step 7 synthesize, get α=8, obtain the synthesis amplitude vector of 4 subarrays at each imaging point calculate by formula (7).

Step 9: amplitude vector will be synthesized carry out unitization, be then multiplied by the I in step 4 _c, obtain the amplitude vector of each imaging point under 8 array elements calculate by formula (8).

${\stackrel{\&RightArrow;}{V}}_{\left(i\right)j}=\frac{{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}}{\left|{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}\right|}{I}_C(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{5300})---\left(8\right)$

According to above-mentioned calculating, 8 array elements are at the amplitude vector of each imaging point size equal in the amplitude of each imaging point with the full array in step 5, and vector direction can be vertical with the reflecting surface at imaging point place.

Step 10: by the amplitude vector of the full array in step 9 at each imaging point carry out imaging display, the global vector image of full array at each imaging point can be obtained.

Step 11: according to the polar plot in step 10, determines the position of target defect, extracts the Local Vector figure of target defect as shown in Figure 5; Then by the amplitude I in step 5 _ccarry out decibel, find out the maximal value of amplitude in Local Vector figure, solve the imaging region area corresponding to maximal value decline-6dB.Last vertical with target defect according to the direction of vector in Local Vector figure, according to geometric relationship, the direction of target defect calculates by formula (9).

${\mathrm{\&theta;}}_m=\arctan \left(\frac{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{i}\mathrm{dA}}{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{j}\mathrm{dA}}\right)---\left(9\right)$

In formula, with represent the vector of unit length parallel with vertical with array energy transducer, A represents in target defect Local Vector figure, by amplitude I _cthe imaging region area corresponding to maximal value decline-6dB, arctan function is the arctan function in mathematics, θ _mrepresent the angle of vector and z-axis forward, namely equal the angle of defect and x-axis forward.

Finally, by Local Vector figure, as shown in figures 4a-4d, can find out, fault location vector magnitude is comparatively obvious, by the form of arrow performance, and other containing defect place due to amplitude very little, can't see arrow, only present the form of round dot, the position of defect can be judged thus; And by calculating the angle θ trying to achieve fault location _m=24.0366 °, namely represent that the angle of defect and x-axis forward is 24.0366 °.

Above-mentioned steps is an exemplary embodiments of the present invention, and enforcement of the present invention is not limited thereto.

Claims (8)

1., for a supersonic array composite imaging method for plate structure crackle quantitative evaluation, it is characterized in that: the method specifically according to following steps examinations,

Step one: test under data acquisition system (DAS), wherein, testing array energy transducer centre frequency used is f, the total number of array element is N, and the width of single array element is a, and the centre distance of adjacent two array elements is p, the propagation velocity of wave of ultrasound wave in test specimen is c, then wavelength time-domain signal y is collected by the mode encouraged successively _{(i) j}(t) (i=1,2,3 ..., N, j=1,2,3 ..., N), wherein, subscript (i) represents i-th array element excitation in array energy transducer, and j represents that in array energy transducer, a jth array element receives;

Step 2: set up imaging coordinate system; Definition represent the vector of initial point to imaging point P; represent the position vector of i-th excitation array element to imaging point P, represent vector component in the direction of the x axis, represent vector component in the z-axis direction, represent vector mould; represent that jth receives the position vector of array element to imaging point P, represent vector component in the direction of the x axis, represent vector component in the z-axis direction, represent vector mould;

Step 3: total focus imaging; Whole array data is calculated acoustic transit time t by encouraging, receiving the distance of array element and imaging point, focuses in each imaging point position, and signal amplitude is superposed; Therefore, the amplitude I of full array at each imaging point is calculated by formula (1) _a;

$I_A=\frac{1}{N^2}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{y}_{\left(i\right)j}(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{c})---\left(1\right)$

In formula, c is the propagation velocity of wave of sound wave in test specimen; N is array number;

Step 4: the consistent imaging of polarity; To whole array data y _{(i) j}t () carries out polarity process by formula (2); If t y _{(i) j}t () amplitude is less than zero, then defining polarity is-1, y _{(i) j}t () amplitude is more than or equal to zero, then defining polarity is+1;

$b_{\mathrm{ij}}\left(k\right)=\left\{\begin{array}{c}-1,y_{\mathrm{ij}}\left(t\right)<0\\ +1,y_{\mathrm{ij}}\left(t\right)\&GreaterEqual;0\end{array}\right.---\left(2\right)$

After polarity process, according to encouraging, receiving the distance of array element and imaging point, acoustic transit time t is calculated to whole array data, carries out polarity superposition in each imaging point position by formula (3);

$I_B=1-\sqrt{1-{\left(\frac{1}{N^2}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}\underset{i=j}{\overset{N}{\mathrm{\&Sigma;}}}{b}_{\mathrm{ij}}(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{c})\right)}^2}---\left(3\right)$

Step 5: complex imaging; Consistent with polarity for total focus imaging imaging is synthesized by formula (4);

I _C＝I _A·I _B(4)

Step 6: constructor array; Array element to be add up in the array energy transducer of N multiple continuous print array element as a subarray, corresponding time-domain signal is called subarray data; This array energy transducer is divided into K subarray, containing M array element (M<N) in each subarray, the array element between adjacent two subarrays is spaced apart N1 (N1<N); The sequence number minimum value of array element in full array that then a kth subarray is corresponding is 1+M (k-1), and maximal value is 1+M (k-1)+N1, wherein, k=1,2,3 ..., K;

Step 7: calculate the amplitude vector of each subarray at each imaging point;

According to the ready-portioned subarray of step 6, calculate the amplitude vector of each subarray at each imaging point, be divided into the following steps:

(1) according to excitation corresponding in each subarray, reception array element, repeat step 2, three, in formula, the minimum value of subscript i, j is 1+M (k-1), and maximal value is 1+M (k-1)+N1, can obtain the amplitude of each subarray at each imaging point place vector wherein, subscript k represents a kth subarray;

(2) according to excitation corresponding to each subarray, receive the position vector of array element to imaging point the unit direction vector of each subarray at each imaging point can be obtained it is the unit direction vector receiving the normal direction formed after i-th array element excitation ultrasound wave incides any imaging point through a jth array element, known according to reflection theorem, the direction of this unit direction vector can be vertical with reflecting surface, calculated by formula (5);

${\stackrel{\&RightArrow;}{s}}_{\left(i\right)j}({\stackrel{\&RightArrow;}{d}}_{\left(i\right)},{\stackrel{\&RightArrow;}{d}}_j)=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|{\stackrel{\&RightArrow;}{d}}_j+\left|{\stackrel{\&RightArrow;}{d}}_j\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}}{\left|\right|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}|{\stackrel{\&RightArrow;}{d}}_j+|{\stackrel{\&RightArrow;}{d}}_j\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|}---\left(5\right)$

(3) will to obtain in upper two steps with correspondence is multiplied and can obtains the amplitude vector of each subarray at each imaging point place calculated by formula (6);

Step 8: to the amplitude vector of the subarray of K in step 7 synthesize, obtain the synthesis amplitude vector of K subarray at each imaging point calculated by formula (7);

In formula, α gets 1 to just infinite Arbitrary Digit, when α value is larger, and the synthesis amplitude vector of any imaging point direction more close to the direction that imaging point place reflected signal energy is the strongest;

Step 9: amplitude vector will be synthesized carry out unitization, be then multiplied by the I in step 4 _c, the amplitude vector of each imaging point under full array N can be obtained calculate by formula (8);

${\stackrel{\&RightArrow;}{V}}_{\left(i\right)j}=\frac{{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}}{\left|{\stackrel{\&RightArrow;}{O}}_{\left(i\right)j}\right|}{I}_C(t=\frac{\left|{\stackrel{\&RightArrow;}{d}}_{\left(i\right)}\right|+\left|{\stackrel{\&RightArrow;}{d}}_j\right|}{c})---\left(8\right)$

According to above-mentioned calculating, full array is at the amplitude vector of each imaging point size equal in the amplitude of each imaging point with the full array in step 5, and vector direction can be vertical with the reflecting surface at imaging point place;

Step 10: by the amplitude vector of the full array in step 9 at each imaging point carry out imaging display, obtain the global vector image of full array at each imaging point;

Step 11: according to the polar plot in step 10, determines the position of target defect, extracts the Local Vector figure of target defect then by the amplitude I in step 5 _ccarry out decibel, find out the maximal value of amplitude in Local Vector figure, solve the imaging region area corresponding to maximal value decline-6dB; Last vertical with target defect according to the direction of vector in Local Vector figure, according to geometric relationship, the direction of target defect calculates by formula (9);

${\mathrm{\&theta;}}_m=\arctan \left(\frac{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{i}\mathrm{dA}}{\underset{A}{\&Integral;}\stackrel{\&RightArrow;}{V}.\hat{j}\mathrm{dA}}\right)---\left(9\right)$

In formula, with represent the vector of unit length parallel with vertical with array energy transducer, A represents in target defect Local Vector figure, by amplitude I _cthe imaging region area corresponding to maximal value decline-6dB, arctan function is the arctan function in mathematics, θ _mrepresent the angle of vector and z-axis forward, namely equal the angle of defect and x-axis forward.

2. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, it is characterized in that: data acquisition system (DAS) comprises oscillograph, function generator, linear array transducer and test specimen, wherein, linear array transducer is coupled by couplant with test specimen; When carrying out test experience, first adjustment function generator produces pumping signal, motivates ultrasonic Lamb waves signal and launches along test specimen, and received the ultrasonic Lamb waves signal reflected by array energy transducer by array energy transducer; The data of being carried out ultrasonic time-domain signal by oscillograph store.

3. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described transducer array is classified as multiple piezoelectric patches.

4. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described transducer Lamb wave signal comprises A0 mode Lamb wave and S0 mode Lamb wave.

5. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described complex imaging algorithm synthesizes total focus algorithm and polarity unification algorism.

6. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described plate structure is aluminium sheet, the steel plate that thickness is less than the homogenous material character of 10mm.

7. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described vector total focus is imaged as the image that direction arrow is formed.

8. a kind of supersonic array composite imaging method for the quantitative evaluation of plate structure crackle according to claim 1, is characterized in that: described defect is crack defect.