CN104090033A - Method for establishing FDTD (Finite Difference Time Domain) ultrasonic detection simulation model of coarse crystal material based on EBSD (Electron Back-Scattered Diffraction) spectrum - Google Patents

Abstract

The invention discloses a method for establishing an FDTD (Finite Difference Time Domain) ultrasonic detection simulation model of a coarse crystal material based on an EBSD (Electron Back-Scattered Diffraction) spectrum and belongs to the technical field of ultrasonic nondestructive detection. The method comprises the following steps: obtaining a crystal orientation spectrum of the coarse crystal material by directly using the EBSD technology, selecting a threshold value for defining crystal grains in the spectrum according to an actual crystal grain structure in a macroscopic metallograph, packing the crystal grains with color corresponding to a principal orientation, and carrying out grey processing to obtain an image consisting of square pixel points, wherein the orientations of the crystal grains are represented by eulerian angles phi1, phi and phi2 corresponding to gray values and can be used for quantitatively calculating elastic anisotropic stiffness matrixes of the crystal grains. Compared with a previous model, the model has the advantages of being capable of accurately describing the structures and the orientations of the crystal grains, realizing high operation efficiency and the like; a model basis is provided for realizing purposes of defect quantification and location and quality determination in ultrasonic detection of the coarse crystal material. The method also can be used for establishing the ultrasonic simulation models of other elastic anisotropic polycrystalline materials such as austenitic welding lines and two-phase titanium alloys; the method has bright popularization and application prospects.

Description

Coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates

Technical field

The present invention relates to a kind of coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates, relate in particular to ultrasonic non-destructive inspection techniques field.

Background technology

The coarse grain materials such as austenitic stainless steel are widely used in the field such as nuclear power and chemical industry, and its security receives much concern.Due to complicated coarse-grain structure and grain orientation, this type of material has very strong elastic anisotropy, cause occurring in Ultrasonic NDT process the phenomenons such as serious acoustic beam deflection, construct noise, signal distortion, be difficult to accurately to defect position, quantitative and qualitative.

For addressing the above problem, researcher in this field attempts to set up corresponding Ultrasonic Detection realistic model, describes the reciprocation between ultrasound wave and elastic anisotropy structure by simulation means.Early stage model is to grow up from the basis of weld seam realistic model, and modeling approach is mainly the macroscopical metallograph with reference to material, is multiple anisotropy unit by model partition.Meanwhile, according to column crystal grain growth feature, bond material is gained knowledge, the crystal orientation of artificial setting unit.Due to this semiempirical method not the orientation to crystal grain and distribution carry out Measurement accuracy, cause the ultrasonic calculating of model and experimental result to have very big-difference.Although the later stage has been introduced XRD (X-Ray Diffraction, X-ray diffraction) crystal orientation of material part is measured, revise to a certain extent the orientation setting of model, but still cannot accurately record grain-oriented distribution characteristics, make the development of model be subject to restriction.

Within 2009, French atomic energy committee member has developed a kind of realistic model based on Thiessen polygon graphic-arts technique in CIVA business software.This model utilizes convex surface closed region that Thiessen polygon surrounds as simulation crystal grain, and supposes that crystal grain is elastically isotropic medium.Although this model can be described crystalline granular texture comparatively exactly, but, the velocity of sound that elastically isotropic intergranule is set by the random function anisotropic method of Equivalent Elasticity that fluctuates, do not consider the variation characteristic of the velocity of sound with ultrasonic propagation direction, cause having greater difference between the result of calculation of model and experimental result.

In recent years, Electron Back-Scattered Diffraction EBSD is accepted by increasing investigation of materials scholar both at home and abroad.This technology can exosyndrome material grain morphology again can quantitative description material grain orientation, be considered to the combination of SEM and XRD.2009, the researchist of University of Birmingham has utilized EBSD technology to analyze austenitic weld seam cross section, obtained crystal orientation collection of illustrative plates.With reference to figure spectrum signature, the model being formed by 157 elastic anisotropy unit that utilized CAD draw in CIVA software.Finally, according to the crystal orientation of unit, it is composed with corresponding stiffness matrix, complete the foundation of model.Than model in the past, the model of this data acquisition by experiment can be described crystalline granular texture and grain orientation more exactly.

But, because elastic anisotropy element number affects the operation efficiency of this model, in order to shorten operation time, have to adopt the mode simplified model that reduces element number, nonetheless,, for the model of 157 unit, operation once still needs nearly 100 hours.In addition,, for having thick ordered orientation column crystal, this simplification is less on the impact of result of calculation.Different from weld seam, coarse grain material not only contains the column crystal of ordered orientation, also contain the equiax crystal that is orientated stochastic distribution, and crystallite dimension is relatively little.If adopt above-mentioned short-cut method, can cause crystalline granular texture and orientation distortion serious, affect the computational accuracy of model.Therefore, the elastic anisotropy dividing elements of coarse grain material is crossed range request and is reduced as much as possible crystalline granular texture, to ensure computational accuracy.Meanwhile, also need to take corresponding method to improve the counting yield of this high precision model.

Summary of the invention

The object of the present invention is to provide a kind of coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates.Than model in the past, this model should have crystalline granular texture and grain orientation is described accurately, more advantages of higher of model calculation efficiency.Can also simulate the construct noise in coarse grain material Ultrasonic Detection, contribute to the deep reciprocation of understanding between ultrasound wave and anisotropic grain, for solving defect quantitative, location, qualitative question in the coarse grain material basis that supplies a model.The present invention simultaneously can also expand to the foundation of the ultrasonic realistic model of other elastic anisotropy polycrystalline materials such as austenitic weld seam, biphase titanium alloy, has good prospect for promotion and application.

The technical solution used in the present invention is: a kind of coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates, comprises the steps:

(1) according to " GB/T19501-2004 Electron Back-Scattered Diffraction analytical approach general rule " national standard, to sample cut, the pre-service such as polishing, mechanical buffing, destressing electropolishing.Select 40 μ m scanning steps to carry out EBSD analysis to sample to be tested;

(2) utilize EBSD device to scan the whole cross section of sample, each about 6mm ², then in order the zonule collection of illustrative plates obtaining is spliced to the final perfect crystal orientation collection of illustrative plates being spliced by multiple collection of illustrative plates that obtains;

(3) according to the crystalline granular texture of real material, utilize channel5 analysis software to adjust the threshold angle in crystal orientation collection of illustrative plates, determine the grain contours of model, set it as the elastic anisotropy unit of model;

(4) utilize channel5 analysis software to count the color range value that in each unit, pixel quantity is maximum, be then this color range value by the color unification of all pixels in crystal grain, and write down Eulerian angle corresponding to this color range value;

(5) EBSD collection of illustrative plates is exported as to the picture of JPG form, then in Photoshop software, open, be converted into gray level image, the color range value of crystal grain is arranged to corresponding gray-scale value, derive and preserve gray-scale map with PCX picture format;

(6) utilize the Eulerian angle that crystal grain is corresponding Φ, try to achieve the direction cosine matrix R that represents crystal orientation,

By 9 array element R in R ₁₁to R ₃₃derive rotation matrix R _d,

$R_D=\left(\begin{array}{cccccc}{R}_{11}^2& R_{12}^2& R_{13}^2& 2R_{11}{R}_{12}& 2R_{11}{R}_{13}& 2R_{12}{R}_{13}\\ R_{21}^2& R_{22}^2& R_{32}^2& 2R_{21}{R}_{22}& 2R_{21}{R}_{23}& 2R_{22}{R}_{23}\\ R_{31}^2& R_{32}^2& R_{33}^2& 2R_{31}{R}_{32}& 2R_{31}{R}_{33}& 2R_{32}{R}_{33}\\ R_{11}{R}_{21}& R_{12}{R}_{22}& R_{13}{R}_{23}& R_{11}{R}_{22}+R_{12}{R}_{21}& R_{11}{R}_{23}+R_{13}{R}_{21}& R_{12}{R}_{23}+R_{13}{R}_{21}\\ R_{11}{R}_{31}& R_{12}{R}_{32}& R_{13}{R}_{33}& R_{11}{R}_{32}+R_{11}{R}_{31}& R_{11}{R}_{33}+R_{13}{R}_{31}& R_{11}{R}_{33}+R_{13}{R}_{31}\\ R_{21}{R}_{31}& R_{22}{R}_{32}& R_{23}{R}_{33}& R_{21}{R}_{32}+R_{22}{R}_{31}& R_{21}{R}_{33}+R_{23}{R}_{31}& R_{22}{R}_{23}+R_{23}{R}_{31}\end{array}\right)---\left(2\right)$

Utilize R _dto this structure stiffness matrix, C is rotated, obtain elastic stiffness Matrix C under this grain orientation ',

$C^{\′}=R_{D}C{R}_D^{-1}---\left(3\right)$

Wherein, C is 6 × 6 matrixes, by 3 independently elastic constant form,

$C=\left(\begin{array}{cccccc}{C}_{11}& C_{12}& C_{12}& 0& 0& 0\\ C_{12}& C_{11}& C_{12}& 0& 0& 0\\ C_{12}& C_{12}& C_{11}& 0& 0& 0\\ 0& 0& 0& C_{44}& 0& 0\\ 0& 0& 0& 0& C_{44}& 0\\ 0& 0& 0& 0& 0& C_{44}\end{array}\right)---\left(4\right)$

(7) mode input is arrived to the ultrasonic numerical simulation program of FDTD, the lower boundary of model is set to solid-vacuum interface, its excess-three border is set to infinite boundary, select Gauss pulse matching waveform as sound source, be placed on the diverse location of model, carry out numerical evaluation, finally analog result and experimental result are contrasted.

Effect of the present invention and benefit are: the FDTD Ultrasonic Detection realistic model that utilizes EBSD experimental data to build, solve the problem that model is in the past difficult to accurate description crystalline granular texture and elastic anisotropy, also improved counting yield problem, and can calculate to reality and detect similar ultrasonic time domain waveform, contribute to the deep propagation characteristic of ultrasound wave in coarse grain material of understanding, for defect quantitatively, location, qualitative analysis provide reliable model basis.

Brief description of the drawings

Fig. 1 is the EBSD crystal orientation collection of illustrative plates of Z3CN20-09M axle-radial section.

Fig. 2 is that different threshold angle are on grain contours impact (a) 0 degree, (b) 5 degree, (c) 10 degree, (d) 15 degree, (e) 20 degree, (f) 30 degree.

Fig. 3 is macroscopical metallograph of Z3CN20-09M.

Fig. 4 is the definite grain contours of 20 degree threshold angle.

Fig. 5 is gray scale gray-scale map after treatment.

Fig. 6 is the position of Analogue probe.

Fig. 7 is ultrasonic time domain waveform and the FFT spectrum curve of Analogue probe.

Fig. 8 is simulation and the experimental result contrast of ultrasonic time-domain signal.

Embodiment

Coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates, the pressurized-water reactor nuclear power plant Z3CN20-09M main pipeline material taking thickness as 96mm is example, comprises that step is as follows:

(1) using the Z3CN20-09M of 96mm thickness as research object, along pipe axis-radially cut 96mm × 12mm × 2mm sample, then sample is cut into 4 24mm × 12mm × 2mm, carry out EBSD analysis, remainder is as ultrasonic tesint time domain waveform.According to " GB/T19501-2004 Electron Back-Scattered Diffraction analytical approach general rule " national standard, to sample polish, the pre-service such as mechanical buffing, destressing electropolishing.Select 40 μ m scanning steps to carry out EBSD analysis to sample to be tested;

(2), as a kind of microscopic measurement instrument, EBSD can only scan 6mm at every turn ²region, needs to scan successively in order.4 specimen surfaces amount to the EBSD collection of illustrative plates that obtains 271 zonules, utilize channel5 analysis software to splice it, the final EBSD orientation collection of illustrative plates being spliced into by 271 pictures that obtains, as shown in Figure 1.

(3) utilize channel5 analysis software to determine the grain contours in original orientation collection of illustrative plates, and then the crystal grain that obtains realistic model is as elastic anisotropy unit.According to " GB/T19501-2004 Electron Back-Scattered Diffraction analytical approach general rule " national standard and " ISO24173 Electron Back-Scattered Diffraction Determination of Orientation general rule " international standard, in EBSD collection of illustrative plates, crystal grain is defined as the set of misorientation lower than the contiguous zone of a threshold angle.For example, threshold angle is 10 degree, and the angle that characterizes crystal orientation differs 10 degree and can be regarded as a crystal grain with interior oriented adjacent.As the important parameter of determining grain boundary and crystal grain position, the selection of threshold angle is very crucial.As shown in Figure 2, when threshold angle is less than 10 while spending, in white edge, be full of small-sized crystal grain, along with the increase of threshold angle, small-size grains is fewer and feweri, and when threshold angle reaches 30 while spending, crystal grain maximum in white edge is merged into same crystal grain with adjacent crystal grain.Therefore, threshold angle is less, and the crystal grain quantity in model is more, and average crystal grain diameter is less.On the contrary, when threshold angle is very large, can cause is not originally that the crystal grain of an orientation combines, and causes the crystal grain quantity of model to be less than material actual die quantity.By contrasting macroscopical metallograph Fig. 3, Taste threshold angle is that 20 patterns of model while spending are consistent with the macrostructure of material, as shown in Figure 4.

(4) determine after the grain contours line of model, the orientation in grain contours is unified, make each crystal grain only have unique crystal orientation.Utilize channel5 analysis software to count one group of maximum Eulerian angle of pixel number in each grain contours, correspondingly, the color of crystal grain is modified as to the corresponding color of main Eulerian angle, the final EBSD collection of illustrative plates being formed by 10 orientations or color that obtains;

(5) collection of illustrative plates is exported as to the picture that 2400 × 300 pixels form, in Photoshop software, open, 10 colors in former figure are arranged to corresponding gray-scale value, derive and preserve gray-scale map with PCX picture format, as shown in Figure 5.Eulerian angle corresponding to each gray scale refer to as table 1.Model is made up of 2400 × 300 different gray scale square node pixels, and size of mesh opening is 40 μ m, corresponding with scanning step.Each pixel is made up of a gray-scale value, meanwhile, each gray-scale value respectively corresponding one group represent grain-oriented Eulerian angle Φ,

Color, gray-scale value and Eulerian angle that table 1 different orientation region is corresponding

(6) utilize the Eulerian angle that crystal grain is corresponding Φ, try to achieve the direction cosine matrix R that represents crystal orientation, by 9 array element R in R ₁₁to R ₃₃can derive rotation matrix R _d, utilize R _dto this structure stiffness matrix, C is rotated, obtain elastic stiffness Matrix C under this grain orientation ', wherein, C is 6 × 6 matrixes, by 3 independently elastic constant form.

(7) by mode input in the ultrasonic numerical simulation program of Fdtd Method, upper, left and right is infinite boundary, lower end is solid-vacuum boundary.Mesh width is selected as 25pixel/mm, and corresponding with EBSD figure spectral resolution, whole model is made up of 2400 × 300 pixels.Select the ultrasonic loading of the single array element in 2mm aperture, respectively Analogue probe is placed on to model center position, center 2mm to the right, center 4mm to the right, center 2mm to the left, 4mm to the left position, center, as shown in Figure 6.Select 1MHz Gauss pulse matching waveform as sound source, waveform and the waveform that fits to 201 compositions according to actual sound source.In the following Fig. 7 of 1MHz matching waveform shown in (a), Fast Fourier Transform (FFT) (fast Fourier transform, FFT) its spectrum signature afterwards as (b) dominant frequency in Fig. 7 be 1.04MHz.Finally, utilize Fdtd Method solving wave equations to carry out transmission, reflection, the refraction behavior of accurate Calculation ultrasound wave on each propagation position and between anisotropic grain, obtain the time domain waveform as Fig. 8.Meanwhile, utilize 1MHz probe to gather the time domain waveform of the Z3CN20-09M sample of thickness 96mm, then this measured waveform and analog waveform are contrasted, as shown in Figure 8, two kinds of waveforms are substantially identical.And than CIVA software, do not rely on the anisotropy element number of model the computing time of FDTD simulated program, operation once only needs several minutes.

Claims (1)

1. the coarse grain material FDTD Ultrasonic Detection Building of Simulation Model method based on EBSD collection of illustrative plates, is characterized in that, comprises the steps:

(1) according to " GB/T19501-2004 Electron Back-Scattered Diffraction analytical approach general rule " national standard, to sample cut, the pre-service such as polishing, mechanical buffing, destressing electropolishing, select 40 μ m scanning steps to carry out EBSD analysis to sample to be tested;

(2) utilize EBSD device to scan the whole cross section of sample, each about 6mm ², then in order the zonule collection of illustrative plates obtaining is spliced to the final perfect crystal orientation collection of illustrative plates being spliced into by multiple collection of illustrative plates that obtains;

(3) according to the crystalline granular texture of real material, utilize channel5 analysis software to adjust the threshold angle in crystal orientation collection of illustrative plates, determine the grain contours of model, set it as the elastic anisotropy unit of model;

(4) utilize channel5 analysis software to count the color range value that in each unit, pixel quantity is maximum, be then this color range value by the color unification of all pixels in crystal grain, and write down Eulerian angle corresponding to this color range value;

(5) EBSD collection of illustrative plates is exported as to the picture of JPG form, then in Photoshop software, open, be converted into gray level image, the color range value of crystal grain is arranged to corresponding gray-scale value, derive and preserve gray-scale map with PCX picture format;

(6) utilize the Eulerian angle that crystal grain is corresponding Φ, try to achieve the direction cosine matrix R that represents crystal orientation,

By 9 array element R in R ₁₁to R ₃₃derive rotation matrix R _d,

$R_D=\left(\begin{array}{cccccc}{R}_{11}^2& R_{12}^2& R_{13}^2& 2R_{11}{R}_{12}& 2R_{11}{R}_{13}& 2R_{12}{R}_{13}\\ R_{21}^2& R_{22}^2& R_{32}^2& 2R_{21}{R}_{22}& 2R_{21}{R}_{23}& 2R_{22}{R}_{23}\\ R_{31}^2& R_{32}^2& R_{33}^2& 2R_{31}{R}_{32}& 2R_{31}{R}_{33}& 2R_{32}{R}_{33}\\ R_{11}{R}_{21}& R_{12}{R}_{22}& R_{13}{R}_{23}& R_{11}{R}_{22}+R_{12}{R}_{21}& R_{11}{R}_{23}+R_{13}{R}_{21}& R_{12}{R}_{23}+R_{13}{R}_{21}\\ R_{11}{R}_{31}& R_{12}{R}_{32}& R_{13}{R}_{33}& R_{11}{R}_{32}+R_{11}{R}_{31}& R_{11}{R}_{33}+R_{13}{R}_{31}& R_{11}{R}_{33}+R_{13}{R}_{31}\\ R_{21}{R}_{31}& R_{22}{R}_{32}& R_{23}{R}_{33}& R_{21}{R}_{32}+R_{22}{R}_{31}& R_{21}{R}_{33}+R_{23}{R}_{31}& R_{22}{R}_{23}+R_{23}{R}_{31}\end{array}\right)---\left(2\right)$

Utilize R _dto this structure stiffness matrix, C is rotated, obtain elastic stiffness Matrix C under this grain orientation ',

$C^{\′}=R_{D}C{R}_D^{-1}---\left(3\right)$

Wherein, C is 6 × 6 matrixes, by 3 independently elastic constant form,

$C=\left(\begin{array}{cccccc}{C}_{11}& C_{12}& C_{12}& 0& 0& 0\\ C_{12}& C_{11}& C_{12}& 0& 0& 0\\ C_{12}& C_{12}& C_{11}& 0& 0& 0\\ 0& 0& 0& C_{44}& 0& 0\\ 0& 0& 0& 0& C_{44}& 0\\ 0& 0& 0& 0& 0& C_{44}\end{array}\right)---\left(4\right)$

(7) mode input is arrived to the ultrasonic numerical simulation program of FDTD, the lower boundary of model is set to solid-vacuum interface, its excess-three border is set to infinite boundary, select Gauss pulse matching waveform as sound source, be placed on the diverse location of model, carry out numerical evaluation, finally analog result and experimental result are contrasted.