A numerical characterization method for granite mesoscopic crack structure

Abstract

To address the problem that current numerical simulations of granite fail to consider the effects of material heterogeneity, intragranular cracks, and grain boundary cracks in granite, this paper provides a numerical characterization method for granite's mesoscopic crack structure. The method comprises the following steps: 1) randomly generating grains; 2) assigning material numbers to the grains; 3) randomly selecting several grains and cropping their grain boundaries to generate grain boundary cracks; 4) using numerical simulation software to assign material models corresponding to the material numbers of the cropped grains, and then combining the cropped grains through Boolean operations to generate a granite model containing grain boundary cracks; 5) randomly generating intragranular cracks based on the set intragranular crack length and orientation, and segmenting the grains; 6) segmenting the granite model based on the intragranular cracks using sketch cutting, and assigning intragranular crack properties. 7) establishing a crack contact model to obtain a numerical representation of the granite mesoscopic crack width.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering acoustic wave detection, and particularly relates to a numerical characterization method for granite mesoscopic crack structure. Background Art

[0002] As a common geological material, the mechanical properties of granite have an important impact on geological engineering and rock and soil blasting engineering, and the speed of sound is an important manifestation of its mechanical properties.

[0003] Granite often appears as a continuous, dense rock on a macroscopic scale, but internally it contains a wealth of microstructures. Granite contains various grains of quartz, feldspar, and mica, each with numerous microcracks at and within the grain boundaries. Different granites have varying amounts of each type of grain, as well as the presence and width of grain boundary and intragranular cracks. When sound waves propagate through rock media like granite, they encounter microstructures such as cracks, causing transmission, reflection, and diffraction. This in turn affects the macroscopic sound velocity and sound transmission coefficient, which serve as the basis for evaluating rock quality using sound waves. By developing a mesoscopic numerical model of granite containing internal microcracks and using numerical simulation to deeply analyze the sound wave propagation mechanism in granite, this approach can provide a basis for engineering quality evaluation based on sound wave detection.

[0004] Current numerical simulation studies often treat granite as a continuous medium or a polycrystalline material that only considers material heterogeneity. There is still a lack of numerical modeling methods that can simultaneously consider material heterogeneity, intragranular cracks, and grain boundary cracks in granite. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that the current research on numerical simulation of granite cannot take into account the influence of material heterogeneity, intragranular cracks and grain boundary cracks in granite, and to provide a numerical characterization method for the mesoscopic crack structure of granite.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A numerical characterization method for the microscopic crack structure of granite, which is special in that it includes the following steps: Step 1), randomly generating grains

[0008] N seeds are randomly placed in the target area, which is equal to the number of granite grains to be generated. The target area is divided into n polygonal sub-areas using the Thiessen polygon segmentation method. Each polygonal sub-area is regarded as a grain. Each grain contains one seed. The sequence numbers of the n grains are S1, S2, S3, ..., S k …,S n , n≥k≥1, and n is a positive integer;

[0009] Step 2) Assign the grain material number

[0010] Assign material number M to each of the n grains i , different numbers represent different types of grains; where i = 1, 2, 3, ..., m, m is the number of grain types, m ≥ 2;

[0011] Step 3) Randomly select several grains and cut their grain boundaries to generate a width of d deta grain boundary cracks;

[0012] Step 4), using a numerical simulation software pre-processing module to assign a material model corresponding to the material number of each grain in step 2) to the grains cut in step 3), and then combining the cut grains through Boolean operations to generate a granite model containing grain boundary cracks;

[0013] Step 5) Set the length and orientation of the intracrystalline crack and randomly generate a crack with a width of d in the grains cut in step 3). inner Intragranular cracks are detected, and the grains are divided by intragranular crack segments, and intragranular crack sets are established;

[0014] Step 6) segmenting the granite model obtained in step 4) according to the intracrystalline cracks in the intracrystalline crack set in step 5) by means of sketch cutting, and assigning corresponding crack attributes in the numerical simulation software to the intracrystalline cracks;

[0015] Step 7) Establish a crack contact model and obtain the numerical representation of the granite microcrack width: d outer =d inner +d deta .

[0016] Furthermore, step 3) is specifically as follows:

[0017] 3.1. Calculate the total length of grain boundary cracks: L outer =ρ outer ×A granite , where ρ outer represents the distribution density of grain boundary cracks, A granite represents the total area of the granite model;

[0018] 3.2. Randomly select a grain with any sequence number, cut part of its grain boundary, and mark the midpoint of the cut grain boundary;

[0019] 3.3. Create a trimmed grain boundary sequence set and store the first selected grain. At the same time, create a trimmed grain boundary midpoint set and store the midpoint of the trimmed grain boundary of the first grain.

[0020] 3.4. Randomly select a sequence number S k The grains are judged by the grain Sk Is it in the set of trimmed grain sequences? If so, go to step 3.5; if not, go to step 3.6;

[0021] 3.5. Return to step 3.4 and reselect the grains;

[0022] 3.6. Determine the grain S in turn k 1st to Eth i Whether the midpoint of the stripe grain boundary is within the set of midpoints of the trimmed grain boundary, where E i The value is less than or equal to the grain S k If yes, keep the original grain boundary; if no, trim the grain boundary inwards. deta Width, after cutting, the grain S k Store the trimmed grain boundary sequence set and store the grain S k The midpoint of the cropped grain boundary is stored in the midpoint set of the cropped grain boundary; the center position of the cropped grain boundary is stored in the cropped grain boundary array to prevent repeated cropping of two grain boundaries at the same position, which will cause the width of the grain boundary crack to double;

[0023] 3.7. Calculate the total length of the cut grain boundary cracks. If the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer , then the completed width is d deta Otherwise, return to step 3.4 until the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer .

[0024] Furthermore, step 5) is specifically as follows:

[0025] 5.1. Setting the average crack length l within the grain inner , crack length variation range Δl, crack inclination θ and crack inclination variation range Δθ, and calculate the total crack length in the grain: L inner =ρ inner ×A grain , where ρ inner Indicates the density of intragranular crack distribution, A grain represents the area of the grain;

[0026] 5.2. Randomly select a point (x i ,y i ) as the starting point of the first crack, establish an intragranular crack starting point set and store the starting point of the first crack;

[0027] 5.3. Calculate the length l of the first crack in the crystal c and the inclination angle θ c , l c =l inner +α*Δl,θc =θ+β*Δθ, where α represents the crack length variation coefficient, -0.5≤α≤0.5; β represents the crack inclination variation coefficient, -0.5≤β≤0.5

[0028] 5.4. Determine the end point of the first crack (x i +l c *cosθ c ,y i +l c *sinθ c ) is within the grain, if so, the generated width is d inner If there is an intragranular crack, create an intragranular crack set and save the first crack; if not, return to step 5.3 and adjust the value of α, keeping the value of β unchanged until the end point is inside the grain and a crack with a width of d is generated. inner Intragranular cracks, create an intragranular crack set and store the first crack;

[0029] 5.5. Randomly select a crack starting point within the grain and determine whether it coincides with a starting point in the set of intragranular crack starting points. If so, proceed to step 5.6; if not, proceed to step 5.7.

[0030] 5.6. Return to step 5.5 and reselect the crack starting point;

[0031] 5.7. Calculate the crack length and inclination angle using the same method as in steps 5.3 and 5.4, and determine whether the crack to be generated intersects with an existing crack in the intracrystalline crack set. If so, discard the crack; if not, generate a crack and store it in the intracrystalline crack set.

[0032] 5.8. Calculate the total crack length of all cracks in the intragranular crack set. If the total crack length of all cracks reaches the total intragranular crack length L inner , then the generation of intragranular cracks is completed, otherwise, return to step 5.5 until the total crack length of all cracks reaches the total crack length L within the grain. inner .

[0033] Furthermore, in step 7), the relationship between the contact stress and the crack closure amount in the crack contact model is specifically as follows: the crack closure amount reaches the intracrystalline crack width d inner Before, the contact stiffness is a small amount that tends to zero; the crack closure amount reaches the intragranular crack width d inner Afterwards, when the crack is completely closed, the contact stiffness gradually increases to a larger value that tends to infinity.

[0034] Furthermore, in step 2), the types of grains in the granite include quartz, mica and feldspar, and m=3.

[0035] Furthermore, in step 5) and step 3), dinner and d deta Both are 0.5μm.

[0036] Compared with the prior art, the present invention has the following beneficial technical effects:

[0037] 1. The numerical characterization method for the mesoscopic crack structure of granite provided by the present invention is based on Thiessen polygon segmentation (Voronoi space topology method). It establishes a two-dimensional mesoscopic numerical model that can simultaneously characterize the granite grain type, grain material properties, intragranular cracks and grain boundary cracks, providing a basis for the study of dynamic mechanical properties such as granite acoustic wave properties.

[0038] 2. Using the numerical characterization method for the microscopic crack structure of granite provided by the present invention, parameters such as the intracrystalline crack distribution density, intracrystalline crack tendency, grain boundary crack density, and grain boundary crack distribution morphology are controllable, and have good similarity with the microscopic morphology and statistical parameters of the granite sample.

[0039] 3. The numerical characterization method for granite meso-crack structure provided by this invention can be easily applied to large-scale, general-purpose commercial finite element software. For example, in Abaqus (numerical simulation software), a commonly used large-scale nonlinear computing platform, intragranular crack simulation can be achieved by segmenting the grain model using crack segments from the intragranular crack set through sketch cutting and assigning seam properties to these segments.

[0040] 4. The granite mesoscopic model established in the numerical characterization method of granite mesoscopic crack structure provided by the present invention can realize the numerical characterization of cracks of different widths within the grain and at the grain boundary. By assigning the global universal contact to the "crack contact model", the width d inner Intragranular crack simulation; the actual physical width of the grain boundary crack is d deta , plus the numerical width d inner , then the width of the grain boundary crack represented is d outer =d inner +d deta At room temperature, the width of the intragranular crack of granite is about 0.5μm, and the width of the grain boundary crack is about 1μm. inner and d deta Just set it to 0.5μm.

[0041] 5. The mesoscopic numerical model established in the numerical characterization method of granite mesoscopic crack structure provided by the present invention can be further used to characterize jointed rock mass. The joints of actual jointed rock mass are often distributed in groups, which is similar to intracrystalline cracks. When actually modeling, it is only necessary to enlarge the model according to the actual size of the jointed rock mass and the distribution density of the intracrystalline cracks ρ innerThe density of the joints is the same as the actual distribution density, the tendency of the intragranular crack is the same as the actual tendency of the joints, and the contact model d inner It can be the same as the joint width. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of random points in a target area and sub-areas segmented based on the Voronoi algorithm in an embodiment of a numerical characterization method for granite meso-crack structure of the present invention;

[0043] Figure 2 Schematic diagram of grains assigned different material models in an embodiment of the present invention;

[0044] Figure 3 Schematic diagram of the process of generating grain boundary cracks in an embodiment of the present invention; (a) to (f) are respectively the processes of cutting different grain boundaries;

[0045] Figure 4 Schematic diagram of the process of generating intracrystalline cracks in an embodiment of the present invention; wherein (a) to (f) are the processes of generating intracrystalline cracks respectively;

[0046] Figure 5 Schematic diagram of granite model with different material grains, grain boundary cracks, and intragranular cracks in an embodiment of the present invention;

[0047] Figure 6 Comparison diagrams of the microscopic model of a granite slice and the model generated using the present invention; (a1), (b1), and (c1) are the microscopic model of the granite slice and the extracted intragranular and grain boundary model diagrams, respectively; (a2), (b2), and (c2) are schematic diagrams of the grains, grain boundary cracks, and intragranular cracks, respectively, generated using the present invention;

[0048] Figure 7 A relationship diagram between contact stress and crack closure amount in an interface contact model generated in an embodiment of the present invention;

[0049] Reference numerals:

[0050] 1-grain, 2-continuous grain boundary, 3-intragranular crack, 4-grain boundary crack. DETAILED DESCRIPTION

[0051] To further clarify the objectives, advantages, and features of the present invention, the numerical characterization method for the microscopic crack structure of granite proposed in the present invention is further described in detail below with reference to the accompanying drawings and specific examples. Those skilled in the art should understand that these embodiments are merely intended to illustrate the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0052] The present invention proposes a numerical characterization method for the mesoscopic crack structure of granite, which specifically includes the following steps:

[0053] Step 1) Randomly generate grains

[0054] N seeds are randomly placed in the target area, which is equal to the number of granite grains to be generated. The target area is divided into n polygonal sub-areas using the Thiessen polygon segmentation method. Each polygonal sub-area is regarded as a grain. Each grain contains one seed. The sequence numbers of the n grains are S1, S2, S3, ..., S k …,S n , n≥k≥1, and n is a positive integer.

[0055] Step 2) Assign the grain material number

[0056] Assign material number M to each of the n grains i (i=1,2,3,...,m, m is the number of grain types, m≥2), different numbers represent different grain types, such as quartz, mica, feldspar, etc. commonly found in granite.

[0057] Step 3) Generate grain boundary cracks

[0058] 3.1. Calculate the total length of grain boundary cracks: L outer =ρ outer ×A granite , where ρ outer represents the distribution density of grain boundary cracks, A granite represents the total area of the granite model;

[0059] 3.2. Randomly select a grain with any sequence number, cut part of its grain boundary, and mark the midpoint of the cut grain boundary;

[0060] 3.3. Create a trimmed grain boundary sequence set and store the first selected grain. At the same time, create a trimmed grain boundary midpoint set and store the midpoint of the trimmed grain boundary of the first grain.

[0061] 3.4. Randomly select a sequence number S k The grains are judged by the grain S k Is it in the set of trimmed grain sequences? If so, go to step 3.5; if not, go to step 3.6;

[0062] 3.5. Return to step 3.4 and reselect the sequence number S k of grains;

[0063] 3.6. Determine the grain S in turn k 1st to Eth i Whether the midpoint of the stripe grain boundary is within the set of midpoints of the trimmed grain boundary (where E i The value is less than or equal to the grain Sk If yes, the original grain boundary is retained. If no, the grain boundary is cut inwards to a certain width d. deta , after cutting, the grain S k Store the trimmed grain boundary sequence set and store the grain S k The midpoint of the cropped grain boundary is stored in the midpoint set of the cropped grain boundary; the center position of the cropped grain boundary is stored in the cropped grain boundary array to prevent repeated cropping of two grain boundaries at the same position, which will cause the width of the grain boundary crack to double;

[0064] 3.7. Calculate the total length of the cut grain boundary cracks. If the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer , the generation of grain boundary cracks is completed, otherwise, return to repeat steps 3.4-3.6 until the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer .

[0065] Step 4) using a numerical simulation software pre-processing module to assign a material model corresponding to the material number of each grain in step 2) to the grains cut in step 3), and then combining the cut grains through Boolean operations to generate a granite model containing grain boundary cracks.

[0066] Step 5) Generate intracrystalline cracks

[0067] According to the set intragranular crack length and orientation, intragranular crack line segments with certain orientations are randomly generated in each grain. These intragranular crack line segments are used to segment the grains and establish an intragranular crack set.

[0068] 5.1. Setting the average crack length l within the grain inner , crack length variation range Δl, crack inclination θ and crack inclination variation range Δθ, and calculate the total crack length in the grain: L inner =ρ inner ×A grain , where ρ inner Indicates the density of intragranular crack distribution, A grain represents the area of the grain;

[0069] The set values are based on the model parameters to be generated. The model parameters can refer to the actual granite microstructure or be adjusted by yourself.

[0070] 5.2. Randomly select a point (x i ,y i ) as the starting point of the first crack, establish an intragranular crack starting point set and store the starting point of the first crack;

[0071] 5.3. Calculate the length l of the first crack in the crystal c and the inclination angle θ c, l c =l inner +α*Δl,θ c =θ+β*Δθ, where α represents the crack length variation coefficient, -0.5≤α≤0.5; β represents the crack inclination variation coefficient, -0.5≤β≤0.5

[0072] 5.4. Determine the end point of the first crack (x i +l c *cosθ c ,y i +l c *sinθ c ) is within the grain, if so, the generated width is d inner If there is an intragranular crack, create an intragranular crack set and save the first crack; if not, return to step 5.3 and adjust the value of α, keeping the value of β unchanged until the end point is inside the grain and a crack with a width of d is generated. inner Intragranular cracks, create an intragranular crack set and store the first crack;

[0073] 5.5. Randomly select a crack starting point within the grain and determine whether it coincides with a starting point in the set of intragranular crack starting points. If so, proceed to step 5.6; if not, proceed to step 5.7.

[0074] 5.6. Return to step 5.5 and reselect the crack starting point;

[0075] 5.7. Calculate the crack length and inclination angle using the same method as in steps 5.3 and 5.4, and determine whether the crack to be generated intersects with an existing crack in the intracrystalline crack set. If so, discard the crack; if not, generate a crack and store it in the intracrystalline crack set.

[0076] 5.8. Calculate the total crack length of all cracks in the intragranular crack set. If the total crack length of all cracks reaches the total intragranular crack length L inner , the generation of intragranular cracks is completed, otherwise, return to repeat steps 5.5-5.7 until the total crack length of all cracks reaches the total intragranular crack length L inner .

[0077] Step 6) By means of sketch cutting, the granite model is segmented according to the intracrystalline cracks in the intracrystalline crack set in step 5), and the intracrystalline cracks are given seam attributes.

[0078] Step 7) Establish a crack contact model and obtain the numerical representation of the granite microcrack width: d outer =d inner +d deta .

[0079] The relationship between the contact stress and crack closure in the crack contact model is as follows: when the crack closure reaches the crack width d inner Before, the contact stiffness is a small amount that tends to zero; when the crack closure reaches the crack width d inner Afterwards, when the crack is completely closed, the contact stiffness gradually increases to a larger value that tends to infinity.

[0080] The present invention is described below with a specific example. According to the size of granite grains, it is planned to generate 100 grains in a square area of 1 cm×1 cm.

[0081] Step 1), such as Figure 1 As shown in FIG, 100 seeds are randomly placed in a target area of 1 cm × 1 cm, and the target area is divided into 100 polygonal sub-areas using the Voronoi method, that is, 100 grains are generated.

[0082] Step 2) Set the material properties of each grain according to the type and content of the granite grains. Figure 2 As shown, assuming that the granite in this embodiment is composed of three components: quartz, feldspar, and mica, and the content of each component is equal, 1 / 3 of the grains are randomly selected to be assigned quartz material properties, 1 / 3 are assigned feldspar material properties, and 1 / 3 are assigned mica material properties.

[0083] Step 3), generate grain boundary cracks,

[0084] 3.1. Calculate the total length of grain boundary cracks, L outer =ρ outer ×A granite =7cm,ρ outer Indicates the distribution density of grain boundary cracks, with a value of 7cm / cm 2 , A granite Indicates the total area of the granite model, with a value of 1cm 2 .

[0085] 3.2. Select the grain with sequence number S1, trim part of its grain boundary, and mark the midpoint of the trimmed grain boundary;

[0086] 3.3. Establish a trimmed grain boundary sequence set and store the selected grain S1 therein. At the same time, establish a trimmed grain boundary midpoint set and store the midpoint of the trimmed grain boundary of grain S1 therein.

[0087] 3.4. Randomly select sequence number S k grains, if the grain S k Not in the set of trimmed grain sequence, grain S k Store the trimmed grain boundary sequence set. If the grain S k In the cropped die sequence set, reselect the die.

[0088] 3.5. Determine the grain S in sequence k 1st to Eth i (E i Less than or equal to S k The total number of sides of each grain is determined by the number of grains. The midpoint of the grain boundary is within the set of midpoints of the trimmed grain boundary. If not, trim it inwards by 0.5 μm. Otherwise, retain the original grain boundary. Record the center position of the trimmed grain boundary and store it in the array of trimmed grain boundaries to prevent repeated trimming of two grain boundaries at the same position, which would double the width of the grain boundary crack. Figure 3 (a) to (f) show the grain boundary trimming process of a single grain.

[0089] 3.6. Count the number of trimmed grain boundaries into the set of trimmed grain boundaries and calculate the total length of the currently trimmed grain boundary cracks. If the total length of the grain boundary cracks reaches the set total grain boundary crack length of 7 cm, the grain boundary cracks are established. Otherwise, repeat steps 3.4 to 3.6 until the total length of the grain boundary cracks reaches the set total grain boundary crack length of 7 cm.

[0090] In step 4), the grains cut in step 3) are assigned a material model corresponding to the material number of each grain in step 2) by using the Python secondary development function of Abaqus software, and then the cut grains are combined through Boolean operations to generate a granite model containing grain boundary cracks.

[0091] Step 5) Generate intracrystalline cracks.

[0092] According to the set intragranular crack length and orientation, intragranular crack segments with a certain orientation are randomly generated inside each grain, and these intragranular crack segments are used to divide the grains.

[0093] like Figure 4 As shown in (a) to (f), the generation method of a single intragranular crack is:

[0094] 5.1. Set the average crack length l in the current grain inner , crack length variation range Δl, crack inclination θ and crack inclination variation range Δθ, and calculate the total crack length L in the current grain inner :L inner =ρ inner ×A grain ,ρ inner Indicates the density of intracrystalline crack distribution, with a value of 100 cm / cm 2 , A grain Indicates the area of the current grain;

[0095] 5.2. Randomly select a point (x i ,y i) as the starting point of the first crack, establish an intragranular crack starting point set and store the starting point of the first crack;

[0096] 5.3. Calculate the length l of the first crack in the crystal c and the inclination angle θ c , l c =l inner +α*Δl,θ c =θ+β*Δθ, where α represents the crack length variation coefficient, -0.5≤α≤0.5; β represents the crack inclination variation coefficient, -0.5≤β≤0.5, l inner The value is the equivalent radius of the current grain;

[0097] 5.4. Determine the end point of the first crack (x i +l c *cosθ c ,y i +l c *sinθ c ) is within the grain, if so, the generated width is d inner If there is an intragranular crack, create an intragranular crack set and save the first crack; if not, return to step 5.3 and adjust the value of α, keeping the value of β unchanged until the end point is inside the grain and a crack with a width of d is generated. inner Intragranular cracks, create an intragranular crack set and store the first crack;

[0098] 5.5. Randomly select a crack starting point within the grain and determine whether it coincides with a starting point in the set of intragranular crack starting points. If so, reselect a crack starting point. If not, proceed to step 5.7.

[0099] 5.6. Return to step 5.5 and reselect the crack starting point;

[0100] 5.7. Calculate the crack length and inclination angle, and determine whether the crack to be generated intersects with the existing cracks in the intracrystalline crack set. If so, discard the crack; if not, generate the crack and store it in the intracrystalline crack set.

[0101] 5.8. Calculate the total crack length of all cracks in the intragranular crack set. If the total crack length of all cracks reaches the total intragranular crack length L inner , the generation of intragranular cracks is completed, otherwise, repeat steps 5.5 to 5.7 until the total crack length of all cracks reaches the total intragranular crack length L inner

[0102] Step 6) By means of sketch cutting, the granite model is segmented according to the intracrystalline cracks in the intracrystalline crack set in step 5), and the intracrystalline crack seam attributes are assigned, such as Figure 5As shown, the generated model covers the grains, grain boundary cracks and intragranular cracks of different materials.

[0103] Figure 6 (a1), (b1) and (c1) are the microscopic model of the granite slice, the extracted intragranular and grain boundary models respectively (reference: MHB Nasseri, A. Schubnel, RP Young, Coupled evolutions of fracture toughness and elastic wave velocities at high crack density in therma [J]. International Journal of Rock Mechanics and Mining Sciences, 2006.). Figure 6 (a2), (b2) and (c2) are schematic diagrams of the grains, grain boundary cracks and intragranular cracks of the model generated using the above steps. Comparison shows that the grain shape, intragranular crack distribution and grain boundary crack distribution of the constructed model are highly similar to the actual granite microstructure.

[0104] Step 7) Establish a crack contact model, such as Figure 7 shown.

[0105] The relationship between contact stress and crack closure in the crack contact model: Before the crack closure reaches a crack width of 0.5 μm, the contact stiffness is a small value approaching zero. When the crack closure reaches a crack width of 0.5 μm, that is, the crack is completely closed, the contact stiffness gradually increases to a large value approaching infinity. At this time, the width of the intragranular crack represented is 0.5 μm, and the width of the grain boundary crack is 1 μm.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A numerical characterization method for granite meso-crack structure, characterized in that: The following steps are involved: Step 1) Randomly generate grains N seeds are randomly placed in the target area, which is equal to the number of granite grains to be generated. The target area is divided into n polygonal sub-areas using the Thiessen polygon segmentation method. Each polygonal sub-area is regarded as a grain. Each grain contains one seed. The sequence numbers of the n grains are S1, S2, S3, ..., S k …,S n , n≥k≥1, and n is a positive integer; Step 2) Assign the grain material number Assign material number M to each of the n grains i , different numbers represent different types of grains; where i = 1, 2, 3, ..., m, m is the number of grain types, m ≥ 2; Step 3) Randomly select several grains and cut their grain boundaries to generate a width of d deta Grain boundary cracks; specifically: 3.1) Calculate the total length of grain boundary cracks: L outer =ρ outer ×A granite , where ρ outer represents the grain boundary crack distribution density, A granite represents the total area of the granite model; 3.2) Randomly select a grain with any sequence number, cut part of its grain boundary, and mark the midpoint of the cut grain boundary; 3.3) Establish a trimmed grain boundary sequence set and store the first selected grain in it, and at the same time establish a trimmed grain boundary midpoint set and store the midpoint of the trimmed grain boundary of the first grain in it; 3.4) Randomly select a sequence number S k The grains are judged by the grain S k Is it in the set of trimmed grain sequences? If so, go to step 3.5); if not, go to step 3.6; 3.5) Return to step 3.4) and reselect the grains; 3.6) Determine the grain S in turn k 1st to Eth i Whether the midpoint of the grain boundary is within the set of midpoints of the trimmed grain boundary, where E i The value is less than or equal to the grain S k If yes, keep the original grain boundary; if no, trim the grain boundary inwards. deta Width, after cutting, the grain S k Store the trimmed grain boundary sequence set and store the grain S k The midpoint of the cropped grain boundary is stored in the midpoint set of the cropped grain boundary; the center position of the cropped grain boundary is stored in the cropped grain boundary array to prevent repeated cropping of two grain boundaries at the same position, which will cause the width of the grain boundary crack to double; 3.7) Calculate the total length of the cut grain boundary cracks. If the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer , then the completed width is d deta Otherwise, return to step 3.4) until the total length of the cut grain boundary cracks reaches the set total grain boundary crack length L outer Step 4), using a numerical simulation software pre-processing module to assign a material model corresponding to the material number of each grain in step 2) to the grains cut in step 3), and then combining the cut grains through Boolean operations to generate a granite model containing grain boundary cracks; Step 5) Set the length and orientation of the intracrystalline crack and randomly generate a crack with a width of d in the grains cut in step 3). inner The intragranular cracks are detected, the grains are divided by intragranular crack segments, and an intragranular crack set is established; specifically: 5.1) Set the average crack length l within the grain inner , crack length variation range Δl, crack inclination θ and crack inclination variation range Δθ, and calculate the total crack length in the grain: L inner =ρ inner ×A grain , where ρ inner Indicates the density of intragranular crack distribution, A grain represents the area of the grain; 5.2) Randomly select a point (x i ,y i ) as the starting point of the first crack, establish an intragranular crack starting point set and store the starting point of the first crack; 5.3) Calculate the length of the first crack in the crystal l c and the inclination angle θ c , l c =l inner +α*Δl,θ c =θ+β*Δθ, where α represents the crack length variation coefficient, -0.5≤α≤0.5; β represents the crack inclination variation coefficient, -0.5≤β≤0.5 5.4) Determine the end point of the first crack (x i +l c *cosθ c ,y i +l c *sinθ c ) is within the grain, if so, the generated width is d inner If there is an intragranular crack, create an intragranular crack set and store the first crack; if not, return to step 5.3) and adjust the value of α, keeping the value of β unchanged until the end point is inside the grain, generating a crack with a width of d inner Intragranular cracks, create an intragranular crack set and store the first crack; 5.5) Randomly select a crack starting point within the grain and determine whether it coincides with a starting point in the set of intragranular crack starting points. If so, proceed to step 5.6); if not, proceed to step 5.7); 5.6) Return to step 5.5) and reselect the crack starting point; 5.7) Calculate the crack length and inclination angle in the same way as in steps 5.3) and 5.4) to determine whether the crack to be generated intersects with an existing crack in the intracrystalline crack set. If so, discard the crack; if not, generate a crack and store it in the intracrystalline crack set. 5.8) Calculate the total crack length of all cracks in the intragranular crack set. If the total crack length of all cracks reaches the total intragranular crack length L inner , the generation of intragranular cracks is completed, otherwise, return to step 5.5) until the total crack length of all cracks reaches the total intragranular crack length L inner Step 6) segmenting the granite model obtained in step 4) according to the intracrystalline cracks in the intracrystalline crack set in step 5) by means of sketch cutting, and assigning corresponding crack attributes in the numerical simulation software to the intracrystalline cracks; Step 7) Establish a crack contact model and obtain the numerical representation of the granite microcrack width: d outer =d inner +d deta .

2. The numerical characterization method for granite meso-crack structure according to claim 1, characterized in that: In step 7), the relationship between the contact stress and the crack closure amount in the crack contact model is specifically: the crack closure amount reaches the intracrystalline crack width d inner Before, the contact stiffness is a small amount that tends to zero; the crack closure amount reaches the intragranular crack width d inner Afterwards, when the crack is completely closed, the contact stiffness gradually increases to a value that approaches infinity.

3. The numerical characterization method for granite meso-crack structure according to claim 1 or 2, characterized in that: In step 2), the types of grains in the granite include quartz, mica and feldspar, that is, m=3.

4. The numerical characterization method for granite meso-crack structure according to claim 3, characterized in that: Step 5) d in step 3) inner and d deta Both are 0.5μm.

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