CN104749253A - Ultrasonic back scattering imaging method and device for inner defects of cylindrical workpiece - Google Patents

Abstract

The invention discloses an ultrasonic back scattering imaging method and an ultrasonic back scattering imaging device for inner defects of a cylindrical workpiece. An ultrasonic energy converter is arranged towards the middle axis vertical to the cylindrical workpiece; a coupling agent is filled between the ultrasonic energy converter and the cylindrical workpiece; the ultrasonic energy converter can rotate along the middle axis and emits an incidence signal after rotating for an angle; the incidence signal is subjected to pulse echoes and then is received to obtain a defect back scattering signal; after the ultrasonic energy converter rotates for one circle, each signal is subjected to Fourier transform and is simulated through a sound field numerical value simulation method; the amplitude of the defect back scattering signal is compensated and then is put into a corresponding frequency domain space; then a Gridding meshing method is used for carrying out interpolation processing, and a rapid Fourier transform method is used for obtaining a defect image; and a series of defect images are overlapped to obtain three-dimensional image information. The ultrasonic back scattering imaging method has relatively detection cost, is simple to operate and can easily realize automation, and can be widely applied to automatic and quantitative detection of the cylindrical workpiece and materials.

Description

Defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method and device in a kind of cylindrical workpiece

Technical field

The present invention relates to a kind of defect inspection method of workpiece, especially relate to defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method and device in a kind of cylindrical workpiece.

Background technology

The cylindrical workpiece such as axle class, bar have a wide range of applications in national economy and national defense construction association area.In the manufacture process and follow-up use procedure of workpiece, all likely produce defect at inside workpiece, if defect can not be detected timely, immeasurable consequence will be caused safely to the people's lives and property.Although Dynamic Non-Destruction Measurement huge number, but because the reliability of ultrasonic non-destructive inspection techniques is constantly improved, in addition it has the advantage that additive method is difficult to match in excellence or beauty in security, applicability and characteristic parameter are rich etc., this technology has become field of non destructive testing and has been most widely used and one of the method containing great potential, and becomes the focus of correlative study.

At present, industrial Ultrasonic NDT also rests on mostly to understand in workpiece whether defectiveness, or only roughly judges the size of defect and the level of position by rule of thumb.People have higher requirement to Ultrasonic NDT in recent years, not only to know presence or absence and the position thereof of defect, also wish the size, shape, direction, position etc. of knowing defect, so just likely determine the harmfulness size of defect and the serviceable bife of defect place workpiece.Image has abundant quantity of information, imaging is a kind of desirable technological means realizing defect quantitative, but traditional ultrasonic imaging technique (as ultrasonic B, C scanning imaging technology) is based on ray theory, have ignored ultrasonic transducer send the diffraction effect of sound field, therefore imaging effect is unsatisfactory.

Although phased-array technique can control acoustic beam to a certain extent effectively, imaging effect is improved, but according to domestic and international pertinent literature, still certain difference is there is between its imaging results and actual defects shape, meanwhile, ultrasonic phased array technology makes it need very high testing cost due to the complicacy of manufacturing process and detection system, limits its popularization in industrial nondestructive testing field.

Summary of the invention

For the deficiency that conventional ultrasound imaging technique exists, the present invention proposes defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method and device in a kind of cylindrical workpiece.The objective fact of a large amount of useful information is comprised in the scattered signal produced after interacting according to ultrasound wave and defect, based on wave theory, the scattering phenomenon produced after utilizing detection sound field and defect to interact, set up the mathematical model between defect geometry quantity of information and backscatter signal, obtain the distributed image of defect in cylindrical workpiece on this basis, good defect imaging effect can be obtained under lower testing cost, realize the quantification Non-Destructive Testing of defect in cylindrical workpiece.

The technical solution used in the present invention is:

One, defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece:

1) ultrasonic transducer is vertically placed in the axis of cylindrical workpiece, between ultrasonic transducer and cylindrical workpiece, be filled with couplant, make ultrasonic signal effectively to import in workpiece;

2) by ultrasonic transducer around cylindrical workpiece axis at uniform intervals angle circumferentially rotate, incoming signal is launched to cylindrical workpiece after often turning over interval angles, impinge perpendicularly on cylindrical workpiece inside to be received by ultrasonic transducer after pulse echo, obtain defect backscatter signal;

3) after ultrasonic transducer rotates one week around the axis of cylindrical workpiece, the defect backscatter signal collected under each angle is carried out Fourier transform respectively, by Sound Field Numerical Simulation method, the sound-filed simulation in cylindrical workpiece is emulated, compensate according to the amplitude of simulation result to defect backscatter signal;

4) polar angle that the defect backscatter signal after compensation rotates around cylindrical workpiece axis according to ultrasonic transducer is placed into corresponding domain space, recycling Gridding gridding method carries out interpolation processing, the defect backscatter signal frequency domain data of non-uniform Distribution under cartesian coordinate system is converted to and is uniformly distributed, finally utilize Fast Fourier Transform (FFT) method to obtain defect imaging.

Described step 3) in carry out emulation to the sound-filed simulation in cylindrical workpiece be specifically utilize Sound Field Numerical Simulation method (as multivariate Gaussian acoustic beam method of superposition, angular spectrum method, finite element method or rayleigh integral method etc.) to calculate to detect the distribution of sound field in cylindrical workpiece adopt following formula to compensate to the amplitude of defect backscatter signal according to AULD reciprocal theory, obtain revised defect backscatter signal amplitude:

Wherein, revised ultrasonic longitudinal wave scattering amplitude under representing i-th incident direction, for probe is relative to the position vector of coordinate origin, k _lrepresent the compressional wave wave number in workpiece, i represents the ordinal number of incident direction, represent the unit vector of i-th incident direction, a represents ultrasound wave incoming signal amplitude, λ, μ is respectively first, second Lame's constant of workpiece material, Δ λ, Δ μ represent that the first Lame's constant of workpiece material and defect body material is poor and the second Lame's constant is poor respectively for the form factor of the frequency domain form for describing defect shape fundamental function, ρ represents workpiece material density, and Δ ρ represents the density difference of workpiece and defect body material, and ω represents incident wave frequency.

Described step 3) in Gridding gridding method comprise: divided by polar coordinates the defect backscatter signal frequency domain data spatial division planted to be equally spaced rectilinear grid unit, the algebraic sum of all defect backscatter signal frequency domain data in single grid cell is this grid cell assignment, by non-uniform Distribution defect backward scattering data S (k under Cartesian coordinates _x, k _y) convert equally distributed data to

$\hat{S}(k_x,k_y)=\left\{\right[S(k_x,k_y)\·W(k_x,k_y)]*C(k_x,k_y)\}\·R(k_x,k_y)$

In formula, W (k _x, k _y) represent Sampling density compensation function, C (k _x, k _y) represent convolution function, R (k _x, k _y) be the sampling function under Cartesian coordinates; k _xand k _yrepresent the horizontal ordinate of data and the coordinate position of ordinate in frequency domain respectively;

Revised defect backscatter signal amplitude acquires the shape information of defect by the inverse Fourier transform of following formula;

$S(k_x,k_y)=S(\hat{r},k_L)=\frac{{i4A}_i(\hat{r},k_L)}{a(\stackrel{\→}{r},\mathrm{\ω})k_L^{2}F(\mathrm{\ρ},\mathrm{\λ},\mathrm{\μ})}$

Wherein, F (ρ, λ, μ)=(Δ ρ/ρ)-(Δ λ+2 Δ μ)/(λ+2 μ), ρ represents workpiece material density, and Δ ρ represents the density difference of workpiece and defect body material, it is revised ultrasonic longitudinal wave scattering amplitude under i-th incident direction.

Described step 4) in Fast Fourier Transform (FFT) method specifically adopt following formulae discovery:

$\mathrm{\γ}(x,y)={(-2\mathrm{\π})}^{-2}{\∫}_{-\∞}^{\∞}{\∫}_{-\∞}^{\∞}\hat{S}(k_x,k_y)\exp \left[i(k_{x}x+k_{y}y)\right]{\mathrm{dk}}_x{\mathrm{dk}}_y$

Wherein, γ (x, y) is the fundamental function for describing defect shape.

Described couplant adopts water or oil.

Described Sound Field Numerical Simulation method adopts multivariate Gaussian acoustic beam method of superposition.

Described step 4) after further the axis direction of described ultrasonic transducer along cylindrical workpiece is moved, for each xsect of cylindrical workpiece repeat above-mentioned steps 2 ~ 4) imaging process, obtain the defect image of each xsect, the defect image of each xsect is carried out superpose the three-dimensional image information obtaining defect in cylindrical workpiece.

Two, defect MEASUREMENT OF ULTRASONIC BACKSCATTERING imaging device in a kind of cylindrical workpiece:

Comprise ultrasonic transducer, rotating mechanism, stepper motor, controllor for step-by-step motor, reflectoscope, data collecting card; The side of cylindrical workpiece placed by ultrasonic transducer, and vertically in cylindrical workpiece axis, couplant is filled with between ultrasonic transducer and cylindrical workpiece, ultrasonic transducer is connection traversing mechanism and reflectoscope respectively, rotating mechanism connects stepper motor, controllor for step-by-step motor connects stepper motor and controls, and defectoscope connection data capture card, controllor for step-by-step motor, reflectoscope and data collecting card are all connected to industrial computer.

Described rotating mechanism comprises small synchronous pulley, large synchronous pulley, elevating lever, main shaft, rotating disk and elevating lever, stepper motor is fixedly mounted in frame by electric machine support, motor shaft and the small synchronous pulley of stepper motor are connected, and drive large synchronous pulley to rotate by Timing Belt, large synchronous pulley is fixed on main shaft, main shaft and rotating disk are by screw rigid attachment, and rotating disk side is provided with elevating lever, is fixed on elevating lever by ultrasonic transducer.

The beneficial effect that the present invention has is:

Instant invention overcomes the deficiency of conventional ultrasound image checking, take full advantage of the scattered signal produced after effect between sound field and defect, set up the relation between defect geometry information and defect backscatter signal, for the design feature of cylindrical workpiece, can realize defect imaging by little several backscatter signals, and structure of the detecting device is simple, testing cost is lower, simple to operate, easily be automated.

The present invention can play larger effect in the robotization of the cylindrical workpiece or material with widespread use occasion and huge market potential, quantification in detecting.

Accompanying drawing explanation

Fig. 1 is detection system schematic diagram of the present invention.

Fig. 2 is the acoustic scattering principle schematic of defect in cylindrical workpiece.

Fig. 3 is the implementing procedure figure of the inventive method.

Fig. 4 is structure of the detecting device figure of the present invention.

Fig. 5 is the imaging results before the correction of oval defect backscatter signal.

Fig. 6 is the revised imaging results of oval defect backscatter signal.

In figure: 1, ultrasonic transducer, 2, cylindrical workpiece, 3, defect, 4, couplant, 5, organic glass cylinder, 6, screw, 7, main shaft, 8, large synchronous pulley, 9, Timing Belt, 10, small synchronous pulley, 11, stepper motor, 12, electric machine support, 13, rotating disk, 14, elevating lever.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described.

As shown in Figure 1, defect MEASUREMENT OF ULTRASONIC BACKSCATTERING imaging device of the present invention, comprises ultrasonic transducer 1, rotating mechanism, stepper motor, controllor for step-by-step motor, defectoscope, data collecting card; The side of cylindrical workpiece placed by ultrasonic transducer, and vertically in cylindrical workpiece 2 axis, couplant 3 is filled with between ultrasonic transducer and cylindrical workpiece, ultrasonic transducer is connection traversing mechanism and defectoscope respectively, rotating mechanism connects stepper motor, controllor for step-by-step motor connects stepper motor and controls, and defectoscope connection data capture card, controllor for step-by-step motor, defectoscope and data collecting card are all connected to industrial computer.

Ultrasonic transducer can adopt centre frequency to be the immersion type plane ultrasonic transducer of 2.5MHz, controllor for step-by-step motor is utilized to control stepper motor, after stepper motor receives signal, rotating mechanism will be driven to turn over the angle of specifying, this makes it possible to make the transducer be fixed on rotating mechanism carry out rotation to workpiece detect, and utilize high-speed data acquisition card the backscatter signal received to be carried out A/D conversion and uploads to industrial computer carrying out subsequent treatment.

In Fig. 1, ultrasonic transducer is fixed on rotating mechanism, and make the central axis of ultrasonic transducer in cylindrical workpiece axis, guarantee that supersonic beam impinges perpendicularly on inside workpiece, utilize pulse echo detection mode, flaw echoes receive by same transducer, and utilize high-speed data acquisition card the backscatter signal received is carried out A/D conversion and uploads to industrial computer.

As shown in Figure 2, the principle of defect MEASUREMENT OF ULTRASONIC BACKSCATTERING of the present invention imaging is as follows:

In Fig. 2, in isotropic medium D, the density, the elastic constant that there is a defect R, medium D are respectively ρ, C _jklm, λ, μ represent first, second Lame's constant of medium, and the density of defect body, elastic constant and two Lame's constant are then expressed as ρ '=ρ+Δ ρ, C' _jklm=C _jklm+ Δ C _jklm, λ '=λ+Δ λ, μ '=μ+Δ μ, wherein Δ ρ, Δ C _jklm, Δ λ, Δ μ all represent that the material constant of medium and defect body is poor.The shape of defect body R can pass through fundamental function represent, when discrete point in defect is relative to the position vector of coordinate origin time in defect value is 1, otherwise value is zero:

Plane wave incidence is on defect body R, and defect and ultrasound wave interaction can cause scattering, scattering acoustic field with incident sound field together constitute total sound field u of i-th incident direction _i:

Wherein, ω represents incident wave frequency.

According to dynamic elasticity, can by scattering acoustic field be expressed as integrated form,

Have employed the tensor subscript representation of standard in formula, if the subscript in expression formula repeats, represent and need traversal summation, if there is comma in subscript, then need to ask partial derivative to variable.Variable u in formula represents total sound field, g _ijwhat represent is Green function, and for two-dimensional case, Green function can be expressed as

In formula, represent Hankel function, k _tand k _lrepresent the wave number of shear wave and compressional wave respectively, δ _ijrepresent Kronecker symbol, Green function done far-field approximation and substitute into above formula, the far field expression formula of defect scattering sound field can be obtained:

$\begin{array}{c}{u}_i^{\mathrm{sc}}={\hat{r}}_i{\hat{r}}_j{f}_j\left(k_L\right)\left[\exp \left(i(k_{L}r-\mathrm{\π}/4)\right)\right]{\left(\frac{2}{{\mathrm{\πk}}_{L}r}\right)}^{1/2}+({\mathrm{\δ}}_{\mathrm{ij}}-{\hat{r}}_i{\hat{r}}_j)f_j\left(k_T\right)\left[\exp \left(i(k_{T}r-\mathrm{\π}/4)\right)\right]{\left(\frac{2}{{\mathrm{\πk}}_{T}r}\right)}^{1/2}\\ =A_i(\hat{r},\mathrm{\ω})\left[\exp \left(i(k_{L}r-\mathrm{\π}/4)\right)\right]{\left(\frac{2}{{\mathrm{\πk}}_{L}r}\right)}^{1/2}+B_i(\hat{r},\mathrm{\ω})\left[\exp \left(i(k_{T}r-\mathrm{\π}/4)\right)\right]{\left(\frac{2}{{\mathrm{\πk}}_{T}r}\right)}^{1/2}\end{array}---\left(5\right)$

In formula, represent the unit vector along i direction and j direction respectively, with represent compressional wave scattering amplitude and shear wave scattering amplitude respectively.Of the present inventionly all carry out based on ultrasonic pulse-echo detection mode, what transmit and receive is all compressional wave signal, therefore discusses mainly for compressional wave scattered signal.

The expression formula of compressional wave scattering amplitude is

According to Born approximation theory, total sound field u of the jth incident direction in above integral equation _jbe can be similar to use incident sound field substitute, therefore formula (6) can be reduced to

Wherein for form factor, its representation feature function in the Fourier transform form of wavenumber domain, the backscatter signal frequency amplitude therefore when all incident directions and all frequencies is known, just can obtain shape factor S (k _x, k _y), to S (k _x, k _y) Fourier transform of inverting can obtain fundamental function γ (x, y),

$\begin{array}{c}\mathrm{\γ}(x,y)={\left(2\mathrm{\π}\right)}^{-2}{\∫}_{-\∞}^{\∞}{\∫}_{-\∞}^{\∞}S(k_x,k_y)\exp \left[i(k_{x}x+k_{y}y)\right]{\mathrm{dk}}_x{\mathrm{dk}}_y\\ ={\left(2\mathrm{\π}\right)}^{-2}{\∫}_{-\∞}^{\∞}{\∫}_{-\∞}^{\∞}4A(k_x,k_y)/\left({\mathrm{ak}}_L^{2}F(\mathrm{\ρ},\mathrm{\λ},\mathrm{\μ})\right)\exp \left[i(k_{x}x+k_{y}y)\right]{\mathrm{dk}}_x{\mathrm{dk}}_y\\ ={\mathrm{\π}}^{-2}{\∫}_{-\∞}^{\∞}{\∫}_{-\∞}^{\∞}A(k_x,k_y)/\left({\mathrm{ak}}_L^{2}F(\mathrm{\ρ},\mathrm{\λ},\mathrm{\μ})\right)\exp \left[i(k_{x}x+k_{y}y)\right]{\mathrm{dk}}_x{\mathrm{dk}}_y\end{array}---\left(8\right)$

Wherein, S (k _x, k _y) represent the distribution of backscatter signal frequency amplitude in Cartesian coordinates of all incident directions and all frequencies.

F(ρ,λ,μ)＝(δρ/ρ)-(δλ+2δμ)/(λ+2μ) (9)

More than deriving is carry out in the hypothesis that incident wave is plane compressional wave, and because the aperture of transducer is limited, the sound field therefore given off spreads because diffraction effect can produce acoustic beam.In the case, if when the relative position of transducer and defect changes, then the incident wave amplitude inciding blemish surface also can produce corresponding change.For eccentric defect, when sound wave incident direction changes, also can there is corresponding change in the incident wave intensity inciding blemish surface, thus make scatter echo that same defect obtains in different incident direction not in same yardstick, makes defect shape there is comparatively big error;

Therefore need in different incidence angles situation, the sound-filed simulation of blemish surface calculates, utilize result of calculation by the normalization of incident wave amplitude, thus realize the correction of scattering acoustic field amplitude, utilize the mode of Sound Field Numerical Simulation to calculate and detect the distribution of sound field in cylindrical workpiece according to AULD reciprocal theory, revised defect backscatter signal amplitude can be obtained

Namely obtain the shape information of defect by inverse Fourier transform according to revised backward scattering amplitude;

$S(\hat{r},k_L)=\frac{{i4A}_i(\hat{r},k_L)}{a(\stackrel{\→}{r},\mathrm{\ω})k_L^{2}F(\mathrm{\ρ},\mathrm{\λ},\mathrm{\μ})}---\left(11\right)$

Consider data S (k _x, k _y) under Cartesian coordinates distribution be uneven, two-dimensional fast fourier transform directly can not be utilized to carry out computing according to formula (8), the problem that counting yield is lower can be produced, therefore by Gridding GRIDDING WITH WEIGHTED AVERAGE, the data space planted is divided by polar coordinates to be divided into equally spaced rectilinear grid, be grid cell assignment according to the algebraic sum of the data dropped in unit, can by the data S (k of non-uniform Distribution under Cartesian coordinates _x, k _y) convert equally distributed data to

$\hat{S}(k_x,k_y)=\left\{\right[S(k_x,k_y)\·W(k_x,k_y)]*C(k_x,k_y)\}\·R(k_x,k_y)---\left(12\right)$

In formula, W (k _x, k _y) represent Sampling density compensation function, C (k _x, k _y) represent convolution function, R (k _x, k _y) be the sampling function under Cartesian coordinates, backward scattering data both can utilize fast Fourier algorithm to obtain defect image efficiently after Gridding gridding process:

$\mathrm{\γ}(x,y)={(-2\mathrm{\π})}^{-2}{\∫}_{-\∞}^{\∞}{\∫}_{-\∞}^{\∞}\hat{S}(k_x,k_y)\exp \left[i(k_{x}x+k_{y}y)\right]{\mathrm{dk}}_x{\mathrm{dk}}_y---\left(13\right)$

Wherein, γ (x, y) for horizontal ordinate in defect image be x, ordinate is the pixel value of the pixel of y, represents defect image with the set γ (x, y) of all pixels.

Embodiments of the invention are as follows:

The water logging planar transducer that the mechanical rotating mechanism that the Applications of Ultrasonic Testing system that the present embodiment adopts manufactures primarily of an autonomous Design, reflectoscope, data collecting card (sample frequency 100MHz) and centre frequency are 2.5MHz is formed.

Concrete structure as shown in Figure 4, machinery mechanism of walking around is driven by stepper motor 11, stepper motor 11 is fixed by electric machine support 12, motor shaft and the small synchronous pulley 10 of stepper motor 11 are connected, and driving large synchronous pulley 8 to rotate by Timing Belt 9, large synchronous pulley 8 is fixed on main shaft 7, and main shaft 7 and rotating disk 13 are by screw 6 rigid attachment, rotating disk 13 is furnished with elevating lever 14, ultrasonic transducer 1 is fixed on elevating lever 14; The cylindrical workpiece 2 with defect 3 is placed in organic glass cylinder 5, and be filled with couplant 4 in organic glass cylinder 5, ultrasonic transducer 1 is installed for cylindrical workpiece 2; After stepper motor receives signal, rotating mechanism will be driven to turn over the angle of specifying, this makes it possible to make the ultrasonic transducer 1 pair of workpiece be fixed on rotating mechanism carry out rotation and detect.

1) ultrasonic transducer 1 is vertically placed in the axis of cylindrical workpiece 2, between ultrasonic transducer 1 and cylindrical workpiece 2, be filled with couplant 4, make ultrasonic signal effectively to import in workpiece;

2) by ultrasonic transducer 1 around cylindrical workpiece axis at uniform intervals angle circumferentially rotate, incoming signal is launched to cylindrical workpiece after often turning over interval angles, impinge perpendicularly on cylindrical workpiece inside to be received by ultrasonic transducer after pulse echo, obtain defect backscatter signal;

3) after ultrasonic transducer rotates one week around the axis of cylindrical workpiece, the defect backscatter signal collected under each angle is carried out Fourier transform respectively, by Sound Field Numerical Simulation method, the sound-filed simulation in cylindrical workpiece is emulated, compensate according to the amplitude of simulation result to defect backscatter signal;

4) polar angle that the defect backscatter signal after compensation rotates around cylindrical workpiece axis according to ultrasonic transducer is placed into corresponding domain space, recycling Gridding gridding method carries out interpolation processing, the defect backscatter signal frequency domain data of non-uniform Distribution under Cartesian coordinates is converted to and is uniformly distributed, finally utilize Fast Fourier Transform (FFT) method to obtain defect imaging.By Gridding gridding method interpolation processing, the present invention can adopt Fast Fourier Transform (FFT) to realize defect imaging thus, greatly improves the counting yield of defect imaging.

Finally the axis direction of ultrasonic transducer along cylindrical workpiece is moved, for each xsect of cylindrical workpiece repeat above-mentioned steps 2 ~ 4) imaging process, obtain the defect image of each xsect, the defect image of each xsect is carried out superpose the three-dimensional image information obtaining defect in cylindrical workpiece.

Thus, instant invention overcomes the deficiency of conventional ultrasound image checking, the scattered signal produced after taking full advantage of between sound field and defect effect, can the defect that cylindrical workpiece inside is in non-central location be detected.

The defects detection of the cylindrical workpiece xsect described by the above process, only transducer need be moved along axis of workpiece, repeat above-mentioned imaging process again, a series of defect cross sectional image can be obtained, numerous xsect imaging results is carried out superpose the three-dimensional image information that can obtain defect in workpiece.

Cylindrical work diameter used by the present embodiment is 80mm, high 100mm, depart from workpiece centre 10mm place and have a minor axis 6mm, the ellipse hole of major axis 10mm, adopt water as couplant in test, therefore, in testing process, transducer and test specimen all can be placed on one and be of a size of in the organic glass water tank of 500mm × 500mm × 200mm.In order to can cavitation damage that is virtually reality like reality, the two ends adhesive waterproof tape of defective hole seals.

Ultrasonic transducer is fixed on rotating mechanism, utilize pulse echo detection mode, flaw echoes receive by same transducer, obtain defect backscatter signal to rebuild for defect, if backward scattering amplitude unmodified is directly used in imaging, as shown in Figure 5, backward scattering amplitude is after revising, and imaging results as shown in Figure 6 for its imaging results.

In order to can more objectively evaluate defect reconstruction quality, introduce shape error function SE (γ herein ^o, γ ^r):

$\mathrm{SE}({\mathrm{\γ}}^O,{\mathrm{\γ}}^R)=\underset{x=0}{\overset{M-1}{\mathrm{\Σ}}}\underset{y=0}{\overset{N-1}{\mathrm{\Σ}}}|{\mathrm{\γ}}^O(x,y)-{\mathrm{\γ}}^R(x,y)|/[\underset{x=0}{\overset{M-1}{\mathrm{\Σ}}}\underset{y=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{\γ}}^O(x,y)+\underset{x=0}{\overset{M-1}{\mathrm{\Σ}}}\underset{y=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{\γ}}^R(x,y)]---\left(14\right)$

Wherein, M, N are respectively longitudinal columns and horizontal line number, γ ^oand γ ^rrespective representation theory reconstructed results and actual reconstruction result, γ ^o(x, y) and γ ^r(x, y) is corresponding pixel value.Shape error function is utilized to evaluate with revised defect reconstructed results before backward scattering amplitude correction respectively, shape error before correction is 10.93%, revise rear 4.99%, result shows that the reconstructed results error obtained after amplitude correction is significantly less than without revising the result obtained.

As can be seen here, instant invention overcomes the deficiency of conventional ultrasound image checking, take full advantage of the scattered signal produced after effect between sound field and defect, defect imaging is realized by little backscatter signal, and structure of the detecting device is simple, and testing cost is lower, simple to operate, easily be automated, there is significantly outstanding technique effect.

Above-mentioned embodiment is used for explaining and the present invention is described, instead of limits the invention, and in the protection domain of spirit of the present invention and claim, any amendment make the present invention and change, all fall into protection scope of the present invention.

Claims (9)

1. a defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in cylindrical workpiece, is characterized in that:

1) ultrasonic transducer is vertically placed in the axis of cylindrical workpiece, between ultrasonic transducer and cylindrical workpiece, be filled with couplant, make ultrasonic signal effectively to import in workpiece;

2) by ultrasonic transducer around cylindrical workpiece axis at uniform intervals angle circumferentially rotate, incoming signal is launched to cylindrical workpiece after often turning over interval angles, impinge perpendicularly on cylindrical workpiece inside to be received by ultrasonic transducer after pulse echo, obtain defect backscatter signal;

3) after ultrasonic transducer rotates one week around the axis of cylindrical workpiece, the defect backscatter signal collected under each angle is carried out Fourier transform respectively, by Sound Field Numerical Simulation method, the sound-filed simulation in cylindrical workpiece is emulated, compensate according to the amplitude of simulation result to defect backscatter signal;

4) polar angle that the defect backscatter signal after compensation rotates around cylindrical workpiece axis according to ultrasonic transducer is placed into corresponding domain space, recycling Gridding gridding method carries out interpolation processing, the defect backscatter signal frequency domain data of non-uniform Distribution under cartesian coordinate system is converted to and is uniformly distributed, finally utilize Fast Fourier Transform (FFT) method to obtain defect imaging.

2. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, is characterized in that: described step 3) in carry out emulation to the sound-filed simulation in cylindrical workpiece be specifically utilize Sound Field Numerical Simulation method (as multivariate Gaussian acoustic beam method of superposition, angular spectrum method, finite element method or rayleigh integral method etc.) to calculate to detect the distribution of sound field in cylindrical workpiece adopt following formula to compensate to the amplitude of defect backscatter signal according to AULD reciprocal theory, obtain revised defect backscatter signal amplitude:

Wherein, revised ultrasonic longitudinal wave scattering amplitude under representing i-th incident direction, for probe is relative to the position vector of coordinate origin, k _lrepresent the compressional wave wave number in workpiece, i represents the ordinal number of incident direction, represent the unit vector of i-th incident direction, a represents ultrasound wave incoming signal amplitude, λ, μ is respectively first, second Lame's constant of workpiece material, Δ λ, Δ μ represent that the first Lame's constant of workpiece material and defect body material is poor and the second Lame's constant is poor respectively for the form factor of the frequency domain form for describing defect shape fundamental function, ρ represents workpiece material density, and Δ ρ represents the density difference of workpiece and defect body material, and ω represents incident wave frequency.

3. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, it is characterized in that: described step 3) in Gridding gridding method comprise: divided by polar coordinates the defect backscatter signal frequency domain data spatial division planted to be equally spaced rectilinear grid unit, the algebraic sum of all defect backscatter signal frequency domain data in single grid cell is this grid cell assignment, by non-uniform Distribution defect backward scattering data S (k under Cartesian coordinates _x, k _y) convert equally distributed data to

$\hat{S}(k_x,k_y)=\left\{\right[S(k_x,k_y)\·W(k_x,k_y)]*C(k_x,k_y)\}\·R(k_x,k_y)$

In formula, W (k _x, k _y) represent Sampling density compensation function, C (k _x, k _y) represent convolution function, R (k _x, k _y) be the sampling function under Cartesian coordinates; k _xand k _yrepresent the horizontal ordinate of data and the coordinate position of ordinate in frequency domain respectively;

Revised defect backscatter signal amplitude acquires the shape information of defect by the inverse Fourier transform of following formula;

$S(k_x,k_y)=S(\hat{r},k_L)=\frac{{i4A}_i(\hat{r},k_L)}{a(\stackrel{\→}{r},\mathrm{\ω})k_L^{2}F(\mathrm{\ρ},\mathrm{\λ},\mathrm{\μ})}$

Wherein, F (ρ, λ, μ)=(Δ ρ/ρ)-(Δ λ+2 Δ μ)/(λ+2 μ), ρ represents workpiece material density, and Δ ρ represents the density difference of workpiece and defect body material, be _irevised ultrasonic longitudinal wave scattering amplitude under individual incident direction.

4. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, is characterized in that: described step 4) in Fast Fourier Transform (FFT) method specifically adopt following formulae discovery:

Wherein, γ (x, y) is the fundamental function for describing defect shape.

5. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, is characterized in that: described couplant adopts water or oil.

6. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, is characterized in that: described Sound Field Numerical Simulation method adopts multivariate Gaussian acoustic beam method of superposition.

7. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING formation method in a kind of cylindrical workpiece according to claim 1, it is characterized in that: described step 4) after further the axis direction of described ultrasonic transducer along cylindrical workpiece is moved, for each xsect of cylindrical workpiece repeat above-mentioned steps 2 ~ 4) imaging process, obtain the defect image of each xsect, the defect image of each xsect is carried out superpose the three-dimensional image information obtaining defect in cylindrical workpiece.

8. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING imaging device in a kind of cylindrical workpiece according to claim 1, is characterized in that: comprise ultrasonic transducer (1), rotating mechanism, stepper motor (11), controllor for step-by-step motor, reflectoscope, data collecting card; The side of cylindrical workpiece placed by ultrasonic transducer (1), and vertically in cylindrical workpiece (2) axis, couplant (3) is filled with between ultrasonic transducer (1) and cylindrical workpiece (2), ultrasonic transducer (1) is connection traversing mechanism and reflectoscope respectively, rotating mechanism connects stepper motor (11), controllor for step-by-step motor connects stepper motor (11) and controls, defectoscope connection data capture card, controllor for step-by-step motor, reflectoscope and data collecting card are all connected to industrial computer.

9. defect MEASUREMENT OF ULTRASONIC BACKSCATTERING imaging device in a kind of cylindrical workpiece according to claim 8, it is characterized in that: described rotating mechanism comprises small synchronous pulley (10), large synchronous pulley (8), elevating lever (14), main shaft (7), rotating disk (13) and elevating lever (14), stepper motor (11) is fixedly mounted in frame by electric machine support (12), motor shaft and the small synchronous pulley (10) of stepper motor (11) are connected, and drive large synchronous pulley (8) to rotate by Timing Belt (9), large synchronous pulley (8) is fixed on main shaft (7), main shaft (7) and rotating disk (13) are by screw (6) rigid attachment, rotating disk (13) side is provided with elevating lever (14), ultrasonic transducer (1) is fixed on elevating lever (14).