阅读说明：本技术 一种处理Laue衍射图片的方法及系统 (Method and system for processing Laue diffraction picture ) 是由 施奇伟 钟鸿儒 张丰果 钟圣怡 陈哲 王浩伟 于 2021-01-20 设计创作，主要内容包括：本发明提供了一种处理Laue衍射图片的方法及系统,包括：步骤M1：基于Laue实验测得衍射观测图案；步骤M2：对衍射观测图案进行预处理,得到预处理后的衍射观测图案；步骤M3：基于预设弹性变形梯度张量采用全局集成数字图像相干技术配准衍射参考图案和预处理后的衍射观测图案,得到配准后的被衍射区域的弹性变形梯度张量；步骤M4：基于得到的配准后被衍射区域的弹性变形梯度张量,得到衍射样品中的弹性应力；本发明通过将全局集成数字图像相干技术和Laue衍射实验相结合,提升了Laue衍射实验测量局部应变和应力的精度。(The invention provides a method and a system for processing Laue diffraction pictures, which comprise the following steps: step M1: measuring a diffraction observation pattern based on a Laue experiment; step M2: preprocessing the diffraction observation pattern to obtain a preprocessed diffraction observation pattern; step M3: registering a diffraction reference pattern and a preprocessed diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area; step M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region; according to the invention, the global integrated digital image coherence technology is combined with the Laue diffraction experiment, so that the accuracy of the Laue diffraction experiment for measuring local strain and stress is improved.)

1. A method for processing Laue diffraction pictures, which is characterized by comprising the following steps:

step M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

step M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

step M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

step M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

2. The method for processing Laue diffraction picture according to claim 1, wherein the step M2 includes:

step M2.1: adjusting the brightness of the diffraction observation pattern to ensure that the average value and the variance of the pixel gray values of the diffraction reference pattern and the diffraction observation pattern are the same to obtain the processed diffraction observation pattern;

step M2.2: calculating residual errors of the diffraction reference pattern and the processed diffraction observation pattern, and calculating the distribution of a plurality of pattern residual error fields based on the calculated residual errors to obtain the standard deviation of the noise of the diffraction reference pattern and the diffraction observation pattern;

step M2.3: and dividing the diffraction reference pattern and the diffraction observation pattern by the standard deviation to obtain the preprocessed diffraction reference pattern and the preprocessed diffraction observation pattern.

3. The method for processing Laue diffraction picture as claimed in claim 1, wherein the residual error in the step M2.2 comprises:

r＝f(x)-g[x+u(F^e,x)] (1)

wherein r represents the residual; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under action.

4. The method for processing Laue diffraction picture according to claim 1, wherein the step M3 includes: setting the difference between the diffraction reference pattern and the diffraction observation pattern after characterization preprocessing as a target function, and registering the diffraction reference pattern and the diffraction observation pattern after preprocessing by adopting a global integrated digital image coherence technique based on a preset elastic deformation gradient tensor until the target function is converged.

5. The method of processing Laue diffraction picture according to claim 4, wherein the objective function comprises:

θ＝∑_ROI(f(x)-g[x+u(F^e,x)])² (1)

wherein, ROI represents a computational domain; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under influence; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern;

using the fluorescent screen as a reference system, examining the action region S of the X-ray beam and the sample, wherein the action region S of the sample is the center of the Laue diffraction pattern, and the coordinate position is defined as (X)^＊,y^＊,-z^＊) And then:

wherein u represents a displacement; p represents a projection vector; p' represents the projected vector after elastic deformation, and the subscript z represents the vector F^eThe component of p in the z-direction;

wherein X represents the position vector of any material point in the sample under the condition of no deformation; the position vector of the object point in the undeformed state is represented by coordinates X, Y, Z in space; x is the number of^eThe position vector of the deformed object point is represented by the coordinate x in space^e、y^e、z^eRepresents; the superscript e indicates that the nature of the deformation is elastic.

6. The method of processing Laue diffraction picture according to claim 4, wherein the objective function convergence comprises: and correcting the elastic deformation gradient tensor parameters by adopting a Newton algorithm, and gradually reducing the target function to be convergent to obtain the elastic deformation gradient tensor of the registered diffracted area.

7. The method of processing Laue diffraction picture as claimed in claim 6, wherein the Newton's algorithm modifying elastic deformation gradient tensor parameters comprises:

step N1: based on Hessian matrix [ M ]]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eJudging an elastic deformation gradient tensor parameter (delta F)^eAs elastic deformation gradient tensor parameter { δ F }^eWhen the value is larger than the preset value, the value is based on { F }^e,n}＝{F^e,n-1}+{δF^eUpdating the elastic deformation gradient tensor;

step N2: calculating displacement based on the updated elastic deformation gradient tensor;

step N3: calculating an objective function according to the displacement;

step N4: updating Hessian matrix [ M ] based on objective function and updated elastic deformation gradient tensor]And a second term { γ }; repeating the steps N1 to N4 until the Hessian matrix [ M ] is based]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eAnd when the mean value is less than or equal to a preset value, obtaining the elastic deformation gradient tensor of the registered diffracted area.

8. The method for processing Laue diffraction picture according to claim 7, wherein the step N1 includes:

[M]{δF^e}＝{γ}

wherein M is_ijRepresents the Hessian matrix [ M ]]Component of row i and column j, gamma_iAn ith component representing a second term { γ }; f_i ^eTensor F representing deformation gradient^eThe ith component of (a);tensor F representing deformation gradient^eThe jth component of (a);a gradient tensor representing the function f (x); Ψ (x, F)^e) Denotes u with respect to F^eThe ith component of (a) is expressed asg(x+u(x,F^e) Is according to u (x, F)^e) A corrected diffraction observation pattern.

9. The method for processing Laue diffraction picture according to claim 1, wherein the step M4 includes: based on the elastic deformation gradient tensor, the elastic strain tensor is obtained through the ball decomposition, and the elastic stress is obtained by utilizing the elastic strain tensor and based on the Hooke's law.

10. A system for processing Laue diffraction pictures, comprising:

module M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

module M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

module M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

module M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

Technical Field

The invention relates to the field of crystal material characterization and particle diffraction, in particular to a method and a system for processing Laue diffraction pictures.

Background

Particle diffraction techniques include X-ray diffraction, backscattered electron diffraction, neutron diffraction, and the like. Various diffraction techniques have found wide application in various engineering materials and academia in terms of their non-destructive, easy to automate, high resolution, high speed and rich observations. The Laue technology relies on high-energy X-rays, has high resolution and good transmission performance, can quickly give information such as grain size, deformation degree and the like, and is widely applied to the fields of materials, geology and the like.

In the Laue diffraction technology, high-energy X-rays are converged and emitted to the surface of a sample, and finally, part of the X-rays are emitted out of the surface of the sample under the complex action of atoms forming with the sample, and the emitting angle and the crystal face spacing of the sample conform to a Bragg diffraction equation, so that characteristic Laue diffraction spots, also called Laue diffraction patterns, are formed on a screen. If the sample is deformed, the position of the Laue diffraction pattern is correspondingly changed, the sample can be regarded as being undeformed, the corresponding Laue diffraction pattern is taken as a reference pattern, and the relative displacement field between the reference pattern and the analysis pattern is related to the experimental geometric parameters and the local deformation of the sample. At present, the local image tracking method is generally adopted in the industry to analyze the Laue diffraction picture, and the method is difficult to determine a calculation domain (Region of Interest) and has a large error. Therefore, a simple, easy and accurate method for analyzing the Laue diffraction pattern is urgently needed.

Patent document CN105136361A (application number: 201510563598.X) discloses a method for measuring stress of cubic single crystal material by using X-ray diffraction, and relates to a method for measuring stress of cubic single crystal material. The invention aims to solve the problem that the reliability of the measurement result of the existing single crystal material stress measurement method is not high. The invention firstly utilizes a pole figure technology to accurately determine the direction of the crystal; obtaining a polar diagram of the processed sample by utilizing an X-ray diffraction technology, and further obtaining an azimuth angle and psi through polar diagram analysis; then establishing a relation coordinate system and carrying out single crystal orientation; obtaining 2 theta-2 theta 0 (A1 sigma 11+ A2 sigma 12+ A3 sigma 22) according to the relation of the relation coordinate system and the elastic mechanical stress strain, then obtaining A1, A2 and A3 by changing the azimuth angle psi and respectively obtaining A1, A2 and A3, substituting the formula 2 theta-2 theta 0 (A1 sigma 11+ A2 sigma 12+ A3 sigma 22), and further obtaining sigma 11, sigma 12 and sigma 22.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method and a system for processing a Laue diffraction picture.

The method for processing the Laue diffraction picture comprises the following steps:

step M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

step M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

step M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

step M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

Preferably, the step M2 includes:

step M2.1: adjusting the brightness of the diffraction observation pattern to ensure that the average value and the variance of the pixel gray values of the diffraction reference pattern and the diffraction observation pattern are the same to obtain the processed diffraction observation pattern;

step M2.2: calculating residual errors of the diffraction reference pattern and the processed diffraction observation pattern, and calculating the distribution of a plurality of pattern residual error fields based on the calculated residual errors to obtain the standard deviation of the noise of the diffraction reference pattern and the diffraction observation pattern;

step M2.3: and dividing the diffraction reference pattern and the diffraction observation pattern by the standard deviation to obtain the preprocessed diffraction reference pattern and the preprocessed diffraction observation pattern.

Preferably, the residual error in step M2.2 comprises:

r＝f(x)-g[x+u(F^e,x)] (1)

wherein r represents the residual; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under action.

Preferably, the step M3 includes: setting the difference between the diffraction reference pattern and the diffraction observation pattern after characterization preprocessing as a target function, and registering the diffraction reference pattern and the diffraction observation pattern after preprocessing by adopting a global integrated digital image coherence technique based on a preset elastic deformation gradient tensor until the target function is converged.

Preferably, the objective function comprises:

θ＝∑_ROI(f(x)-g[x+u(F^e,x)])² (1)

wherein, ROI represents a computational domain; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under influence; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern;

using the fluorescent screen as a reference system, examining the action region S of the X-ray beam and the sample, wherein the action region S of the sample is the center of the Laue diffraction pattern, and the coordinate position is defined as (X)^＊,y^＊,-z^＊) And then:

wherein u represents a displacement; p represents a projection vector; p' represents a projection vector after elastic deformationThe subscript z denotes the vector F^eThe component of p in the z-direction;

wherein X represents the position vector of any material point in the sample under the condition of no deformation; the position vector of the object point in the undeformed state is represented by coordinates X, Y, Z in space; x is the number of^eThe position vector of the deformed object point is represented by the coordinate x in space^e、y^e、z^eRepresents; the superscript e indicates that the nature of the deformation is elastic.

Preferably, the objective function convergence comprises: and correcting the elastic deformation gradient tensor parameters by adopting a Newton algorithm, and gradually reducing the target function to be convergent to obtain the elastic deformation gradient tensor of the registered diffracted area.

Preferably, the newton's algorithm modifying the elastic deformation gradient tensor parameters comprises:

step N1: based on Hessian matrix [ M ]]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eJudging an elastic deformation gradient tensor parameter (delta F)^eAs elastic deformation gradient tensor parameter { δ F }^eWhen the value is larger than the preset value, the value is based on { F }^e,n}＝{F^e,n-1}+{δF^eUpdating the elastic deformation gradient tensor;

step N2: calculating displacement based on the updated elastic deformation gradient tensor;

step N3: calculating an objective function according to the displacement;

step N4: updating Hessian matrix [ M ] based on objective function and updated elastic deformation gradient tensor]And a second term { γ }; repeating the steps N1 to N4 until the Hessian matrix [ M ] is based]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eAnd when the mean value is less than or equal to a preset value, obtaining the elastic deformation gradient tensor of the registered diffracted area.

Preferably, the step N1 includes:

[M]{δF^e}＝{γ}

wherein M is_ijRepresents the Hessian matrix [ M ]]Component of row i and column j, gamma_iAn ith component representing a second term { γ }; f_i ^eTensor F representing deformation gradient^eThe ith component of (a);tensor F representing deformation gradient^eThe jth component of (a);a gradient tensor representing the function f (x); Ψ (x, F)^e) Denotes u with respect to F^eThe ith component of (a) is expressed asg(x+u(x,F^e) Is according to u (x, F)^e) A corrected diffraction observation pattern.

Preferably, the step M4 includes: based on the elastic deformation gradient tensor, the elastic strain tensor is obtained through the ball decomposition, and the elastic stress is obtained by utilizing the elastic strain tensor and based on the Hooke's law.

The system for processing the Laue diffraction picture comprises the following steps:

module M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

module M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

module M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

module M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, the global integrated digital image coherence technology is combined with the Laue diffraction experiment, so that the accuracy of measuring local strain and stress in the Laue diffraction experiment is improved, and the experiment proves that the strain accuracy obtained by the method is 10^-6The magnitude is far higher than that of a local image tracking method generally adopted in the industry at present;

2. the Laue diffraction pattern data processing method has the characteristics of simple writing and high calculation speed, and is convenient to use and accurate;

3. the invention selects the whole picture for analysis at one time without extracting some specific spots in the picture;

4. the method adopts a global integrated DIC method to minimize the difference between two types of pictures, only eight parameters of the elastic deflection gradient tensor are used as unknowns, and the eight parameters are corrected to register the pictures;

5. according to the method, firstly, a plurality of Laue diffraction images are registered, so that the noise distribution of the images is calculated, and then a more accurate reference pattern after noise reduction is reconstructed, so that the calculation precision is improved;

6. and (3) adopting a more accurate reference pattern, dividing the more accurate reference pattern by the standard deviation of noise of each part, and registering all experimental diffraction patterns and the reference pattern so as to more accurately measure the stress strain of the sample.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a projection of Laue diffraction spot displacement versus local elastic strain of a sample;

FIG. 2 is a sample experimental Laue diffraction pattern;

FIG. 3 is ux with respect to F^eEight gradient fields psi_xi；

FIG. 4 shows the four-point bending experiment of single crystal iron and the measurement of elastic strain;

FIG. 5 is a Laue picture noise standard difference layout;

FIG. 6 is the gradient field of Laue picture before and after noise reduction, which shows that the gradient field is significantly reduced after noise reduction;

FIG. 7 is a flow chart of a method of processing Laue diffraction pictures.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

Example 1

The method for processing the Laue diffraction picture comprises the following steps:

step M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

step M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

step M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

step M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

Specifically, the step M2 includes:

step M2.1: adjusting the brightness of the diffraction observation pattern to ensure that the average value and the variance of the pixel gray values of the diffraction reference pattern and the diffraction observation pattern are the same to obtain the processed diffraction observation pattern;

step M2.2: calculating residual errors of the diffraction reference pattern and the processed diffraction observation pattern, and calculating the distribution of a plurality of pattern residual error fields based on the calculated residual errors to obtain the standard deviation of the noise of the diffraction reference pattern and the diffraction observation pattern;

step M2.3: and dividing the diffraction reference pattern and the diffraction observation pattern by the standard deviation to obtain the preprocessed diffraction reference pattern and the preprocessed diffraction observation pattern.

Specifically, the residual error in the step M2.2 includes:

r＝f(x)-g[x+u(F^e,x)] (1)

wherein r represents the residual; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under action.

Specifically, the step M3 includes: setting the difference between the diffraction reference pattern and the diffraction observation pattern after characterization preprocessing as a target function, and registering the diffraction reference pattern and the diffraction observation pattern after preprocessing by adopting a global integrated digital image coherence technique based on a preset elastic deformation gradient tensor until the target function is converged.

Specifically, the objective function includes:

θ＝∑_ROI(f(x)-g[x+u(F^e,x)])² (1)

wherein, ROI represents a computational domain; u (F)^eX) denotes the gradient tensor F in elastic deformation^eDisplacement at x under influence; (x) denotes a diffraction reference pattern; g (x) represents a diffraction observation pattern;

using the fluorescent screen as a reference system, examining the action region S of the X-ray beam and the sample, wherein the action region S of the sample is the center of the Laue diffraction pattern, and the coordinate position is defined as (X)^＊,y^＊,-z^＊) And then:

wherein u represents a displacement; p represents a projection vector; p' represents the projected vector after elastic deformation, and the subscript z represents the vector F^eThe component of p in the z-direction;

wherein X represents the position vector of any material point in the sample under the condition of no deformation; the position vector of the object point in the undeformed state is represented by coordinates X, Y, Z in space; x is the number of^eThe position vector of the deformed object point is represented by the coordinate x in space^e、y^e、z^eRepresents; the superscript e indicates that the nature of the deformation is elastic.

Specifically, the objective function convergence includes: and correcting the elastic deformation gradient tensor parameters by adopting a Newton algorithm, and gradually reducing the target function to be convergent to obtain the elastic deformation gradient tensor of the registered diffracted area.

Specifically, the newton algorithm modifying the elastic deformation gradient tensor parameters includes:

step N1: based on Hessian matrix [ M ]]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eJudging an elastic deformation gradient tensor parameter (delta F)^eAs elastic deformation gradient tensor parameter { δ F }^eWhen it is larger than the preset value, thenIn { F^e,n}＝{F^e,n-1}+{δF^eUpdating the elastic deformation gradient tensor;

step N2: calculating displacement based on the updated elastic deformation gradient tensor;

step N3: calculating an objective function according to the displacement;

step N4: updating Hessian matrix [ M ] based on objective function and updated elastic deformation gradient tensor]And a second term { γ }; repeating the steps N1 to N4 until the Hessian matrix [ M ] is based]And the second term [ gamma ] calculates the elastic deformation gradient tensor parameter [ delta F ]^eAnd when the mean value is less than or equal to a preset value, obtaining the elastic deformation gradient tensor of the registered diffracted area.

Specifically, the step N1 includes:

[M]{δF^e}＝{γ}

wherein M is_ijRepresents the Hessian matrix [ M ]]Component of row i and column j, gamma_iAn ith component representing a second term { γ }; f_i ^eTensor F representing deformation gradient^eThe ith component of (a);tensor F representing deformation gradient^eThe jth component of (a);a gradient tensor representing the function f (x); Ψ (x, F)^e) Denotes u with respect to F^eThe ith component of (a) is expressed asg(x+u(x,F^e) Is according to u (x, F)^e) Modified diffractionAnd observing the pattern.

Specifically, the step M4 includes: based on the elastic deformation gradient tensor, the elastic strain tensor is obtained through the ball decomposition, and the elastic stress is obtained by utilizing the elastic strain tensor and based on the Hooke's law.

The system for processing the Laue diffraction picture comprises the following steps:

module M1: measuring a diffraction observation pattern and a diffraction reference pattern based on a Laue experiment;

module M2: preprocessing the diffraction reference pattern and the diffraction observation pattern to obtain a preprocessed diffraction observation pattern and a preprocessed diffraction reference pattern;

module M3: registering the preprocessed diffraction reference pattern and the diffraction observation pattern by adopting a global integrated digital image coherent technology based on a preset elastic deformation gradient tensor to obtain an elastic deformation gradient tensor of a registered diffracted area;

module M4: obtaining elastic stress in the diffraction sample based on the obtained elastic deformation gradient tensor of the registered diffraction region;

the Laue diffraction observation pattern is a spotted diffraction pattern formed by diffraction of X-rays with composite wavelengths in a crystal material;

the diffraction reference pattern is a pattern which is selected from observation patterns of Laue experiments and has no deformation or the deformation degree is within a preset range and is used as the diffraction reference pattern.

Example 2

Example 2 is a modification of example 1

The present invention relates to a method for extracting local stress strain of a sample from Laue diffraction patterns, as shown in FIG. 7, and is suitable for all Laue diffraction experiments. The invention adopts the global Integrated Digital Image Correlation technique (Integrated Digital Image Correlation) to register the reference pattern and the observation pattern based on the diffraction pattern (Laue experiment). An objective function is established in the registration process to represent the difference between the two pictures, an elastic deflection gradient tensor (elastic deformation gradient tensor) is used as 8 sought parameters, a Newton algorithm is adopted to correct the parameters, and the objective function is gradually reduced until convergence, so that the local stress strain of the sample is obtained. The invention has the advantages of simple code compiling, high convergence speed and high precision, and can be conveniently transplanted to other diffraction experiment fields.

The experimental principle of the Laue diffraction experiment is shown in FIG. 1, and high-energy X-rays are emitted at an angle according with the Bragg equation after being incident into a crystal sample, so that a light spot pattern is formed on a fluorescent screen, as shown in FIG. 2. The Laue diffraction technique requires at least 4 spots to be formed on the phosphor screen and a series of Laue diffraction pictures should be taken. Let Laue diffraction reference pattern be f (x), Laue diffraction observation pattern be g (x), and relative displacement field between the two figures be u. The brightness of the observation pattern is adjusted so that the average and variance of the two are the same.

The core variable of Laue diffraction stress strain measurement technology is elastic deformation gradient tensor

Where X represents the location vector of any particle of the substance in the sample without deformation, which may be represented by three coordinates X, Y, Z in space; x is the number of^eRepresenting the position vector of the object point after deformation, which can be represented by three coordinates x in space^e、y^e、z^e(ii) a The superscript e indicates that the nature of the deformation is elastic.

The X-ray beam and the action region S of the sample, namely the center of the Laue diffraction pattern, are examined by taking the fluorescent screen as a reference system, and the coordinate positions of the X-ray beam and the action region S are (X, y, -z). Assuming that there is a perfect lattice without residual stress, within which there is a direction vector Δ X, which is projected at point P (X, y,0) on the screen, the projection vector SP is expressed here as P for convenience of expression. In this case, the projection vector is { X-X, y-y, z } - [ α Δ X ], and α is the projection scale. When the crystal sample has residual elastic strain, the elastic deformation tensor Fe acts on the direction vector Delta X of the backscattered electrons, and the electron spot projected on the fluorescent screen generates displacement u, and the displacement can be expressed as:

wherein the subscript z represents the vector F^eThe component of p in the z direction.

The above equation relates the elastic deformation gradient tensor to the relative displacement of two Laue diffraction patterns, which is the basic principle of the present invention. Analysis of the above formula shows that if Fe is multiplied by any constant, u does not change. Thus this method can only achieve up to 8 degrees of freedom in Fe, the remaining one being provided by the complementary setting, usually assuming that the normal stress of the sample normal to the surface is zero.

The goal of DIC is to measure u (x) as accurately and at high resolution as possible. Therefore, the invention adopts a global integrated DIC algorithm, and substitutes all pixels of two Laue diffraction patterns into calculation at one time to minimize an objective function theta:

wherein ROI represents the Region of Interest (Region of Interest), u (F)^eX) is represented by^eDisplacement at x under influence;

a relative displacement field is searched in the calculation field to correct the observation pattern to be as close as possible to the reference Laue diffraction pattern.

u can be expressed in various ways, and the global integrated DIC means that u is directly expressed by the searched physical quantity, namely u and F^eDirect contact: u-u (F)^e,x)。

The connection between the various components of u (x) and Fe is established by a first order taylor expansion:

wherein, δ F^eIndicating a slight variation in Fe, the index i indicates the ith component,is represented by δ F^eThe ith component of (a). The einstein summation convention is applied to the right side of the above equation. ψ is the gradient field of u with respect to Fe:

eight psi_xiThe gradient field distribution is shown in FIG. 3, and the appropriate u can be obtained by linearly combining the gradient fields by modifying the eight parameters_xDisplacement field, u_yAnd in the same way, the two experimental pictures are accurately registered.

Therefore, eight parameters can be adjusted to minimize the objective function, and the method adopts a Newton algorithm to minimize the objective function, and the specific process is as follows:

[M]{δF^e}＝{γ}

{F^e,n}＝{F^e,n-1}+{δF^e}

{δF^eis the amount of change in eight parameters per iteration, below a set value (e.g., 10)^-6) And (4) when the calculation is finished, finding the most appropriate elastic deflection gradient tensor, and otherwise, carrying out the next iteration. Hessian matrix [ M ]]Size 8X 8, and expression of each element thereof

The expression of the second term [ gamma ] is

It can be seen that each term in the newton algorithm has a definite expression about the sought elastic deformation tensor, so that the newton algorithm can quickly find the optimal solution, and the method is remarkably superior to the local DIC-based optimization algorithm in speed and precision.

The core achievement of the invention is elastic deformation gradient tensor F^eThe elastic strain tensor can be obtained by sphere Decomposition (Polar Decomposition) (see fig. 4), and then multiplied by the elastic coefficient matrix (hooke's modulus)Law) to obtain the elastic stress of the sample.

Another important result of the invention is the residual r between the two pictures after registration.

r＝f(x)-g[x+u(F^e,x)]

The residual field is linearly related to the noise of the experimental picture, and the distribution of several residual fields is calculated to obtain the standard deviation (std (r)) of the picture noise, as shown in fig. 5.

According to the statistical theory, the Laue diffraction picture is divided by the noise standard deviation (f/std (r), g/std (r)), namely different weights are added to the gray values of all parts of the picture, the part with high noise has low weight, the part with low noise has high weight, and the error can be effectively reduced.

By adopting a plurality of residual error pictures and averaging the residual errors, the accidental error of the Laue picture can be effectively reduced, a more accurate reference picture after noise reduction is obtained, and the measurement precision can be improved. Fig. 6 shows a comparison of Laue pictures before and after noise reduction.

Through experimental data verification, the accurate elastic deflection gradient tensor can be obtained through 20 iterations. The calculation results of the Laue diffraction pattern with 2400 x 2600 resolution show that the strain accuracy obtained by the invention is 10^-6Magnitude.

Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.