Cement stabilized material micro crack simulation method

Abstract

The present application belongs to the technical field of model simulation, and relates to a cement stabilized material micro-crack simulation method, comprising: 1) obtaining a two-dimensional slice image inside the cement stabilized material, performing micro-defect quantitative analysis, obtaining a micro-crack defect geometry analysis information database and water-stable mortar average porosity; 2) using the water-stable mortar average porosity to construct a cement stabilized material basic model; 3) using the micro-crack defect geometry analysis information database to establish a simulation micro-crack geometry parameter stochastic construction model, determine the geometry parameter of the micro-crack, and form a simulation micro-crack template; 4) according to the simulation micro-crack template, stochastically constructing a micro-crack, performing micro-crack quantitative random throwing in the cement stabilized material basic model, and completing micro-crack simulation. The present application can quantitatively realize random generation and throwing of micro-cracks, the constructed water-stable material mesoscopic fracture model is more accurate, and can reflect crack propagation behavior and fracture mechanism of the water-stable material from a mesoscopic level.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of model simulation, and relates to a cement stabilized material micro-crack simulation method. BACKGROUND

[0002] For cement stabilized materials, due to the differences in mechanical properties of aggregates and mortar, cement hydration and dry shrinkage, micro-pores and micro-cracks will inevitably be generated in the structure of cement stabilized materials; in addition, fatigue damage will also generate micro-cracks in the internal structure of cement stabilized materials during operation. These small defects usually exist in the cement mortar matrix and the interface between mortar and aggregate. Unlike micro-pores, micro-cracks are a finite linear segment in space, and have connectivity between cracks. These micro-cracks will further evolve under cyclic loading, leading to structural fracture; in addition, micro-cracks increase the quasi-brittleness of cement-based materials, making them different from the sudden fracture of brittle materials, but there is a relative crack stable propagation process. The existence of micro-cracks has an important influence on the cracking behavior of cement stabilized materials, so in the fracture failure analysis research, the effect of this crack initial defect on the development of structural damage cannot be ignored.

[0003] At present, researchers have used micro-analysis techniques such as impact echo method, scanning electron microscope, mercury intrusion test, vacuum fluorescent epoxy impregnation method, X-ray CT method to explore the initial defects in concrete, studied the relationship between internal micro-cracks of concrete and compressive strength, splitting tensile strength, frost resistance and chloride ion permeability, and pointed out that the micro-crack density is an intuitive indicator reflecting the internal damage of concrete; however, due to the fact that the size of micro-cracks is mostly below 50 μm, and the environment humidity during observation and the cutting, polishing and other disturbances in the sample preparation process are relatively sensitive, it is difficult to accurately obtain micro-crack information. Therefore, in order to facilitate analysis, the existence of micro-cracks is mostly ignored in the previous fracture research of cement stabilized materials, and the mortar material is treated as a macro-continuum, and the role of micro-cracks in the fracture research of cement stabilized materials needs to be further explored.

[0004] However, for most engineering materials, due to the characteristics of various types, various geometric shapes and complex mechanical environment of micro-cracks inside the material, the conventional testing methods cannot establish the connection between the mesostructure and the macroscopic mechanical properties, and the traditional mechanics theory is also difficult to obtain mathematical analytical solution. Under this background, with the development of computer simulation technology, mesoscale fracture simulation has become an important means to reveal the cracking mechanism of composite materials. In the current numerical simulation method, the finite element method is often used to simulate the simulation of micro-cracks, but there are the following problems: it cannot well solve the problem of large deformation of discontinuous system, cannot effectively simulate the slip and cracking of medium and other non-continuous phenomena, resulting in low accuracy of the micro-crack defect model constructed; the existing method is difficult to realize the quantitative and controllable operation of the micro-crack when the micro-crack is randomly placed, and cannot truly reflect the meso-heterogeneous characteristics of the cement stabilized material, so it is difficult to obtain the influence mechanism of micro-defects on the meso-cracking behavior of the structure. SUMMARY

[0005] In view of the technical problems of low modeling efficiency and difficulty in quantitative and controllable random placement of micro-cracks in the existing simulation method, the cement stabilized material micro-crack simulation method can quantitatively realize the random generation and placement of micro-cracks, and the constructed meso-fracture model of the cement stabilized material is more accurate, which can reflect the crack propagation behavior and fracture mechanism of the cement stabilized material from the meso-level.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0007] A cement stabilized material micro-crack simulation method, comprising the following steps:

[0008] 1) Obtain the two-dimensional slice image inside the cement stabilized material, perform micro-defect quantitative analysis on the cement stabilized material, obtain the micro-crack defect geometric shape analysis information database and the average porosity of the cement stabilized mortar;

[0009] 2) Use the average porosity of the cement stabilized mortar in step 1) to construct a cement stabilized material basic model;

[0010] 3) Use the micro-crack defect geometric shape analysis information database in step 1) to establish a simulation micro-crack geometric parameter random construction model, determine the geometric parameters of the micro-crack, and form a simulation micro-crack template;

[0011] 4) According to the simulation micro-crack template, construct the micro-crack, and quantitatively and randomly place the micro-crack in the cement stabilized material basic model, and complete the micro-crack simulation.

[0012] Further, the step 1) is specifically:

[0013] 1.1) Obtain the two-dimensional slice image inside the cement stabilized material;

[0014] 1.2) Processing the two-dimensional slice images to identify each target defect area inside the cement stabilized material, traversing each target defect area, dividing all target defect areas into vein defects and hole defects, and obtaining the two-dimensional distribution geometric shape parameters corresponding to each microcrack defect;

[0015] 1.3) Extracting the two-dimensional distribution geometric shape parameters corresponding to each microcrack defect in step 1.2) to obtain a microcrack defect geometric shape analysis information database and an average porosity of the cement stabilized sand mortar.

[0016] Further, the step 1.2) includes the following steps:

[0017] 1.2.1) Using VGStudio Max software to process the two-dimensional slice images, using different gray values to represent the aggregate, cement stabilized sand mortar and defects in the cement stabilized material;

[0018] 1.2.2) Continue to import the two-dimensional slice images into Image J, and identify the target defect area by setting the gray threshold value;

[0019] 1.2.3) Set the measurement parameters and execute the "Analyze Particles" operation to solve the minimum circumscribed rectangle frame wrapping the target defect area;

[0020] 1.2.4) Traversing each target defect area, identifying the actual coverage area of each target defect area, and using the area equivalent method to obtain the equivalent rectangle frame from the minimum circumscribed rectangle frame, i.e. the two-dimensional distribution shape of each target defect area;

[0021] 1.2.5) Calculate the equivalent length, equivalent width and equivalent area of the equivalent rectangle frame of each target defect area, i.e. the two-dimensional distribution geometric shape parameters; and calculate the aspect ratio of the equivalent rectangle frame, and divide the target defect area into vein defects and hole defects according to the aspect ratio.

[0022] Further, in the step 1.3), the average porosity P of the cement stabilized sand mortar 0 is calculated according to the following formula:

[0023]

[0024] wherein: A i is the equivalent rectangle frame area of the i-th vein defect, Bj is the equivalent rectangle frame area of the j-th hole defect, Q n is the area of the cement stabilized sand mortar on the n-th two-dimensional slice image, I is the number of vein defects on the two-dimensional slice image; J is the number of hole defects on the two-dimensional slice image, and N is the number of two-dimensional slice images.

[0025] Further, the specific process of the step 2) is:

[0026] 2.1) Generate boundary wall by "wall" command in PFC2D software, form closed model boundary area, and randomly fill the granular system composed of aggregate and cement mortar in the model boundary area;

[0027] 2.2) According to the average porosity size, randomly delete part of the cement mortar particles from the granular system in step 2.1) to construct the target porosity, form a numerical specimen composed of aggregate, cement mortar and pore;

[0028] 2.3) Assign the corresponding contact model to the unit particles inside the aggregate, the unit particles inside the cement mortar, and the unit particles at the interface of the aggregate and the cement mortar, set the model mesoscopic parameters of each phase material, and form the basic model of cement stabilized material.

[0029] Further, the specific process of step 3) is:

[0030] 3.1) According to the microcrack defect geometric shape analysis information database in step 1), obtain the length distribution function, inclination distribution function and center position distribution function of each microcrack;

[0031] 3.2) According to the length distribution function, inclination distribution function and center position distribution function of the simulation microcrack of each microcrack, determine the random construction model of the microcrack geometric parameters, that is, the microcrack length L i , the microcrack inclination θ i , and the microcrack center coordinate C i (x i , y i ) parameters;

[0032] 3.3) Convert the above microcrack length L i , microcrack inclination θ i , microcrack center coordinate C i (x i , y i ) to obtain the simulation microcrack template.

[0033] Further, in step 3.3), the calculation formulas of θ i , x i and y i are as follows:

[0034] θ i = 360 × u

[0035] x i = x min + (x max - x min )u

[0036] yi = y min + (y max - y min )u

[0037] wherein: x min is the minimum value of the horizontal coordinate in the micro-crack distribution area; x max is the maximum value of the horizontal coordinate in the micro-crack distribution area; y min is the minimum value of the vertical coordinate in the micro-crack distribution area; y max is the maximum value of the vertical coordinate in the micro-crack distribution area; u is a random number subject to uniform distribution, u ~ U(0, 1).

[0038] Further, the step 4) specifically comprises:

[0039] 4.1) obtaining the number of cement mortar particles from the cement stabilized material base model in step 2), calculating the area of the micro-crack distribution area and the total length of the required micro-crack distribution;

[0040] 4.2) generating micro-cracks in the mortar particles of the cement stabilized material by using a self-identification algorithm for the simulation micro-crack template of step 3), and recording the total length of the completed simulation micro-cracks;

[0041] 4.3) repeating step 4.2) until the total length of the completed simulation micro-cracks reaches the total length of the required micro-crack distribution calculated in step 4.1), completing the quantitative random distribution of all simulation micro-cracks;

[0042] 4.4) setting the tensile strength of the range on both sides of all the distributed simulation micro-cracks to 0, completing the micro-crack simulation.

[0043] Further, the specific process of step 4.1) is: taking the mortar of the cement stabilized material as the distribution area of the simulation micro-cracks, calculating the area S of the simulation micro-crack distribution area according to the number of cement stabilized mortar particle units in the cement stabilized material base model of step 2), and calculating the total length T of the required micro-crack distribution according to the set micro-crack density D as follows:

[0044] T = S x D

[0045] wherein: T, unit m; S, unit m 2 ; D is the total length of micro-cracks per unit area, unit m / m 2 .

[0046] Further, the specific process of step 4.2) is:

[0047] 4.2.1) Randomly generating a single simulation micro-crack according to the simulation micro-crack template, determining the two end point coordinates of the simulation micro-crack, the two end points are A end point and B end point respectively, and the specific calculation formula is as follows:

[0048]

[0049]

[0050] In the formula, L i is the length of the i-th micro-crack; θ i is the inclination angle of the i-th micro-crack defect; x i , y i is the center point coordinate of the i-th micro-crack; x (1) , y (1) is the A end point coordinate; x (2) , y (2) is the B end point coordinate;

[0051] 4.2.2) Determine whether the two end points of the simulation micro-crack are in the cement stabilized material base model;

[0052] If both end point coordinates meet the requirements, a single random drop is performed;

[0053] If any end point exceeds the model boundary region or is in the aggregate particle unit region, a new micro-crack inclination angle is generated according to the single rotation angle of the micro-crack inclination angle, and the maximum number of trials is set;

[0054] The calculation formula of the single rotation angle of the micro-crack inclination angle is as follows:

[0055] Δθ=360 / t

[0056] In the formula, Δθ is the single rotation angle of the micro-crack inclination angle; t is the maximum number of trials;

[0057] Within the range of the set maximum number of trials, the two end point coordinates of the new micro-crack are recalculated until the end point coordinates of the generated micro-crack meet the requirements; if the maximum number of trials is reached, the A end point coordinate and the B end point coordinate of the generated new micro-crack still do not meet the set conditions, then the micro-crack generation is abandoned, and the next round of micro-crack random construction is started.

[0058] The beneficial effects of the present application are:

[0059] 1) The micro-crack simulation method of the cement stabilized material provided by the present application can realize quantitative and random drop of micro-cracks in the cement stabilized mortar matrix, and is used for constructing a more accurate micro-fracture model of the cement stabilized material.

[0060] 2、The application adopts X-ray CT scanning equipment and digital image processing technology, realizes extraction and analysis of crack defect shape parameters through self-defined algorithm, and obtains real and reliable micro crack defect distribution data, so as to guide to build a more accurate micro crack defect model.

[0061] 3、The application can automatically control random micro crack feeding operation through a self-identification algorithm, and is quantitatively controllable, so that the modeling efficiency and accuracy are greatly improved.

[0062] 4、The discrete element model of the cement stabilized material established in the application is a five-phase composite model containing aggregate, mortar, interface, pore and crack, can more realistically represent the mesoscopic heterogeneous characteristics of the cement stabilized composite material, can be used for mesoscopic fracture simulation analysis of the cement stabilized composite material, and provides practical verification and technical reference for mesoscopic model construction research of heterogeneous multi-phase composite materials. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 A flowchart for simulating random micro crack feeding;

[0064] Figure 2 A two-dimensional CT slice image;

[0065] Figure 3 A two-dimensional defect shape quantification characterization method schematic diagram;

[0066] Figure 4 A crack feeding position schematic diagram;

[0067] Figure 5 A two-dimensional discrete element model example (D=40m / m 2 , dist=0.15mm) containing micro cracks. DETAILED DESCRIPTION

[0068] The technical solutions of the application will be described in detail in combination with the drawings and examples.

[0069] The application adopts the discrete element method to construct a mesoscale fracture model containing micro crack defects, realizes simulation of micro cracks of the cement stabilized material, can well solve the problem of large deformation movement of a discontinuous system, obtain the overall movement state of the discontinuous body, and effectively simulate the slip and cracking of the medium and other discontinuous phenomena. The cracking behavior of the cement stabilized material is researched from the mesoscale, and then the cumulative damage and damage mechanism of the micro and mesoscale medium of the cement stabilized material under complex conditions are revealed.

[0070] The cement stabilized material micro crack simulation method provided by the application includes the following steps.

[0071] 1) Obtain the two-dimensional slice image inside the cement stabilized material, and perform microscopic defect quantitative analysis on the cement stabilized material to obtain the geometric shape analysis information database of the micro-crack defects and the average porosity of the cement stabilized material.

[0072] The purpose of this step is to perform microscopic defect quantitative analysis on the selected cement stabilized material, obtain the two-dimensional shape parameter distribution information of the length and width of the internal microscopic defects of the cement stabilized mortar, and form the crack defect geometric shape analysis information database of the cement stabilized mortar matrix. Specifically, the following steps are included.

[0073] 1.1) Obtain the two-dimensional slice image inside the cement stabilized material.

[0074] In implementation, a cement stabilized material observation test sample is prepared.

[0075] The cement stabilized material observation test sample can be a field core sample or an indoor molded sample, which can be a cylindrical sample or a cuboid sample; the size of the observation test sample is determined according to the X-ray CT scanning equipment.

[0076] Set the slice interval, and use the X-ray CT scanning equipment to obtain the two-dimensional slice image inside the cement stabilized material observation test sample.

[0077] 1.2) Process the two-dimensional slice image, identify each target defect area inside the cement stabilized material, traverse each target defect area, divide all target defect areas into crack defects and hole defects, and obtain the two-dimensional distribution geometric shape parameters corresponding to each micro-crack defect.

[0078] Step 1.2) includes the following steps:

[0079] 1.2.1) Use VGStudio Max software to process the two-dimensional slice image, and use different gray values to represent the aggregate, cement stabilized mortar and defect phases inside the cement stabilized material. The defect phase includes single-point hole and irregular line segment micro-crack.

[0080] After the two-dimensional slice image is processed by the VGStudio Max software, according to the different gray values, the brightest part is the aggregate particles, the middle gray area is the mortar phase, and the darkest black area is the defect.

[0081] 1.2.2) Continue to import the two-dimensional slice image into Image J, identify the target defect area by setting the gray threshold; import the two-dimensional slice image into Image J, identify the target defect area by setting the gray threshold, use a rectangular frame to equivalent the defect area on the two-dimensional plane, and according to the distribution area of the defect, solve the minimum circumscribed rectangle that can wrap the defect area, and take the longer side as the length direction of the defect and the shorter side as the width direction of the defect.

[0082] 1.2.3) Set the measurement parameters and perform the "Analyze Particles" operation to solve the minimum circumscribed rectangle frame that can wrap the target defect area.

[0083] The actual operation is: import the two-dimensional slice image into Image J to convert it into an 8-bit image (gray value 0-255), identify the target defect area by setting the gray threshold, and the gray value range corresponding to the defect is 0-37. Then, set the measurement parameters as "Bounding Rectangle" and "Area", regard each independent defect area as a "Particle", and perform the "Analyze Particles" operation to solve the minimum circumscribed rectangle frame that can wrap the defect area, thereby realizing the one-by-one calculation and extraction of the long axis, short axis and area of the defect, and taking the longer side to represent the length direction of the defect and the shorter side to represent the width direction of the defect.

[0084] 1.2.4) Traverse each target defect area to identify the actual coverage area of each target defect area, and use the area equivalence method to obtain the equivalent rectangular frame of each target defect area from the minimum circumscribed rectangle frame, i.e. the two-dimensional distribution shape of each target defect area.

[0085] Traverse each defect area to identify the actual coverage area of each defect area, and use the area equivalence method to scale the size of the minimum circumscribed rectangle frame while keeping the length of the long side unchanged to obtain the equivalent rectangular frame. The equivalent rectangular frame is consistent with the two-dimensional projection area of the actual defect, and during scaling, the two long sides are moved synchronously and oppositely into the minimum circumscribed rectangle frame to ensure that the position of the equivalent rectangular frame after scaling does not deviate much from the position of the defect core area.

[0086] 1.2.5) Calculate the equivalent length, equivalent width and equivalent area of the equivalent rectangular frame corresponding to each target defect area, i.e. the two-dimensional distribution geometric shape parameters; and calculate the aspect ratio of the equivalent rectangular frame to divide the target defect area into line gap defects and hole defects.

[0087] Take the equivalent rectangular frame as the distribution shape of the two-dimensional defect, and determine the type of the defect according to the distribution shape parameters of the defect to divide the hole defects and the line gap defects.

[0088] Take the aspect ratio as the determination condition, set the determination threshold, and take the defect area with an aspect ratio greater than the determination threshold as a line gap defect, and take the defect area with an aspect ratio less than or equal to the determination threshold as a hole defect.

[0089] For line gap defects, the equivalent length l i , the equivalent width w i , and the equivalent rectangular frame area A iparameters, and aggregate records; for hole defects, the equivalent rectangular frame area B of each hole defect is extracted j .

[0090] The calculation formula of the equivalent rectangular frame area is as follows:

[0091] A i = l i *w i

[0092] B j = e j *h j

[0093] In the formula, A i is the equivalent rectangular frame area of the i-th groove defect; l i is the equivalent length of the i-th groove defect; w i is the equivalent width of the i-th groove defect; B i is the equivalent rectangular frame area of the j-th hole defect; e j is the equivalent length of the j-th hole defect; h j is the equivalent width of the j-th hole defect.

[0094] 1.3) Extract the two-dimensional distribution geometry parameter corresponding to each micro-crack defect in step 1.2), obtain the micro-crack defect geometry analysis information database and the average porosity of the water-stable mortar.

[0095] According to the extracted two-dimensional shape parameter distribution information of the length and width of the internal micro-crack defects of the water-stable mortar on each two-dimensional slice, a crack defect geometry analysis information database of the water-stable mortar matrix is formed, and the average porosity of the water-stable mortar is calculated.

[0096] The area information of the internal groove defects and hole defects of the water-stable mortar on each two-dimensional slice is extracted, the defect area in the unit area of the water-stable mortar matrix is averaged and calculated, and the average porosity P of the water-stable mortar is formed 0 .

[0097] The porosity of the water-stable mortar refers to the defect area on the unit area of the water-stable mortar matrix. First, the total defect area and the water-stable mortar matrix area on a single two-dimensional slice are calculated, and the ratio of the total defect area to the water-stable mortar matrix area is taken as the porosity of the corresponding two-dimensional slice. The average porosity of the cement stabilized material water-stable mortar matrix is obtained by averaging the porosities of each two-dimensional slice.

[0098]

[0099] In the formula, A i is the equivalent rectangular frame area of the i-th groove defect, B jQ is the area of the equivalent rectangular frame of the jth hole defect n I is the area of the water-stable mortar material on the nth two-dimensional slice image, I is the number of linear defects on the two-dimensional slice image; J is the number of hole defects on the two-dimensional slice image, and N is the number of two-dimensional slice images.

[0100] It is particularly pointed out that, since the width of the microcrack in the cement stabilized material is generally small, the length of the microcrack represented by the long side of the rectangle and the result of using the diagonal line are not much different, so the long side of the rectangular frame can be directly used to approximate the length value of the microcrack.

[0101] It is particularly pointed out that, by using the rectangular frame, the shape of the complex microcrack defect is greatly simplified, and the microcrack length and microcrack width measured based on this are also an equivalent result, which can accurately reflect the shape of the two-dimensional microcrack defect to a certain extent.

[0102] 2) Using the average porosity of the cement stabilized material in step 1), a basic model of the cement stabilized material is constructed.

[0103] Using PFC2D software and the average porosity of the water-stable mortar in step 1), a basic model of the cement stabilized material is formed, and the specific process of step 2) of the present application is as follows.

[0104] 2.1) Use the "wall" command in PFC2D software to generate a boundary wall to form a closed model boundary area, and randomly fill the particle system composed of aggregate and water-stable mortar in the model boundary area.

[0105] Specifically, the "wall" command in PFC2D software is used to generate a boundary wall according to the proposed virtual specimen size and shape to form a closed model boundary area, and randomly fill the particle system composed of aggregate and water-stable mortar in the model boundary area; and in this area, "ball" particles with a diameter of d are arranged regularly, the "ball" particles belonging to the aggregate area are determined according to the particle size and shape distribution information of the aggregate, and are attributed to "aggregate ball" and assigned to the "aggregate" group name, and the remaining "ball" particles not assigned to the "aggregate" group name are attributed to "water-stable mortar ball" and assigned to the "mortar" group name.

[0106] Further, in this step, the shape and size of the model boundary area refer to the shape and size of the discrete element virtual specimen.

[0107] Further, the aggregate and cement mortar particle systems in this step are both composed of regularly arranged "balls", each "ball" has the same diameter, and according to the different attribution of each "ball", it is defined as "aggregate ball" and "cement mortar ball", that is, the aggregate particle is composed of several "aggregate balls" bonded together, and the cement mortar matrix is composed of several "cement mortar balls" bonded together.

[0108] In this step, the regular arrangement of "ball" particles can adopt one of "cubic" and "hexagonal".

[0109] In this step, the particle size and shape of each aggregate can be defined by the user. The aggregate particle size range is preferably 1.18mm-19mm.

[0110] It is particularly pointed out that in order to achieve the purpose of mesoscopic simulation, the diameter of "ball" in this step is preferably 0.3mm, and in order to improve the calculation efficiency, the aggregate with particle size less than 1.18mm is regarded as cement mortar material.

[0111] 2.2) According to the average porosity value, randomly delete part of the cement mortar particles from the particle system of step 2.1) to construct the target porosity, and form a numerical test piece composed of aggregate, cement mortar and pores.

[0112] Specifically, this step is to construct the target porosity P by randomly deleting a certain number of cement mortar particle units through Fish function according to the average porosity of cement mortar, and form a numerical test piece composed of aggregate, cement mortar and pores.

[0113] The Fish function for constructing the target porosity P is written as follows:

[0114]

[0115] 2.3) Assign the corresponding contact model to the unit particles inside the aggregate, the unit particles inside the cement mortar and the unit particles at the interface between the aggregate and the cement mortar, set the model mesoscopic parameters of each phase material, and form the basic model of cement stabilized material.

[0116] The step is specifically, traversing each contact in the numerical specimen of step 2.2), judging the properties of each contact, if the adjacent "ball" particles connected at both ends of the contact belong to the "aggregate" group name, the contact is judged as a unit particle inside the aggregate, and the contact model of the aggregate is assigned to the contact; if the adjacent "ball" particles connected at both ends of the contact belong to the "mortar" group name, the contact is judged as a unit particle inside the stabilized sand mortar, and the contact model of the stabilized sand mortar is assigned to the contact; if the adjacent "ball" particles connected at both ends of the contact belong to the "aggregate" group name and the "mortar" group name respectively, the contact is judged as a unit particle at the interface between the aggregate and the stabilized sand mortar, and the contact model of the interface is assigned to the contact; the model microscopic parameters of each phase material are calculated by inverse analysis based on the macroscopic mechanical test and simulation test of single-phase materials, the microscopic parameters of each contact model in the model are set, and the basic model of the cement stabilized material is formed.

[0117] In the basic model of the cement stabilized material, the contact model of the unit particle inside the aggregate is preferably a linear contact bond model, and the contact model of the unit particle inside the stabilized sand mortar and the contact model of the unit particle at the interface between the aggregate and the stabilized sand mortar are preferably parallel bond models.

[0118] 3) Using the micro-crack defect geometric shape analysis information database of step 1), a random construction model of micro-crack geometric parameters is established, the geometric parameters of the micro-crack (including micro-crack length, micro-crack inclination angle and micro-crack center position) are determined, and a simulation micro-crack template is formed.

[0119] The purpose of this step is to determine the distribution function of the geometric parameters of the simulation micro-crack according to the micro-crack defect geometric shape analysis information database of step 1), establish a random construction model of the geometric parameters of the simulation micro-crack, determine the geometric parameters of the micro-crack, and form a simulation micro-crack template.

[0120] The specific process of this step is as follows.

[0121] 3.1) According to the micro-crack defect geometric shape analysis information database of step 1), the length distribution function, the inclination angle distribution function and the center position distribution function of each micro-crack are obtained.

[0122] The center position C i and the inclination angle θ i of the two-dimensional crack defect are regarded as obeying uniform distribution, and the distribution functions of the inclination angle and the center position of the simulation micro-crack are established.

[0123] 3.2) According to the length distribution function, the inclination angle distribution function and the center position distribution function of the simulation micro-crack of each micro-crack, the random construction model of the geometric parameters of the micro-crack is determined, and the micro-crack length L i , the micro-crack inclination angle θ iCoordinates of the microcrack center C i (x i y i )parameter.

[0124] Center position C i and tilt angle θ i The distribution function is expressed as follows:

[0125] θ i =360×u

[0126] x i =x min +(x max -x min )u

[0127] y i =y min +(y max -y min )u

[0128] In the formula, α i x is the angle of inclination of the i-th crack defect; i Center position C i x-coordinate; y i Center position C i The ordinate; x min x represents the minimum x-coordinate of the coordinate region. max The x-coordinate of the coordinate region is the maximum value; y min The minimum value of the ordinate in the coordinate region; y max is the maximum value of the ordinate of the coordinate region; u is a random number that follows a uniform distribution, u ~ U(0, 1).

[0129] In this invention, the coordinate region refers to the distribution area of ​​the microcracks. Within the slice, it is the area range of the slice, and within the model, it is the range of the wall.

[0130] 3.3) The above microcrack length L i Microcrack inclination angle θ i and the coordinates C of the microcrack center i (x i y i ), which is converted to obtain a simulated microcrack template.

[0131] Based on the results of the crack defect geometry analysis database of the water-stabilized mortar material in step 1, the distribution functions of the geometric parameters of the simulated microcrack length, microcrack inclination angle, and microcrack center position are determined, and a stochastic construction model of the geometric parameters of the microcrack length, microcrack inclination angle, and microcrack center position is established; according to the stochastic construction model of the microcrack geometric parameters, that is, based on the microcrack length L... i Microcrack inclination angle θi and micro crack center coordinates C i (x i , y i ), the geometric parameters of each micro crack are generated according to the simulation micro crack template, and the micro crack geometric parameters are converted into corresponding micro crack templates by the "dfn template create" command.

[0132] 4) According to the simulation micro crack template, the micro crack is generated and the crack quantitative random placement is carried out in the cement stabilized material base model, and the micro crack simulation is completed.

[0133] Step 4) specifically includes:

[0134] 4.1) The number of cement mortar particles is obtained from the cement stabilized material base model in step 2), the area of the micro crack placement area is calculated, and the total length of the micro crack to be placed is calculated.

[0135] The specific process of step 4.1) is: the cement mortar of the cement stabilized material is taken as the placement area of the simulation micro crack, the area S of the simulation micro crack placement area is calculated according to the number of cement stabilized mortar particle units in the cement stabilized material base model in step 2), and the total length T of the micro crack to be placed is calculated according to the set micro crack density D:

[0136] T = S x D

[0137] Where: T, unit m; S, unit m 2 ; D is the total length of the micro crack per unit area, unit m / m 2 .

[0138] 4.2) The simulation micro crack template in step 3) is generated by using self-identification algorithm to generate micro crack, and the total length of the simulation micro crack to be placed is recorded.

[0139] In this step, according to the simulation micro crack template, a single simulation micro crack is randomly generated, and the two endpoints of the simulation micro crack are set as A endpoint and B endpoint, the coordinates of the two endpoints are calculated, and it is judged whether the simulation micro crack is in the cement stabilized material base model.

[0140] The coordinates of the two endpoints of the micro crack are calculated according to the following formula, and the two endpoints are A endpoint and B endpoint respectively, and the specific calculation formula is as follows:

[0141]

[0142]

[0143] In the formula, L i is the length of the i-th micro crack; θi is the inclination angle of the ith micro crack; x, y are the coordinates of the micro crack center point; x (1) , y (1) is the A endpoint coordinate; x (2) , y (2) is the B endpoint coordinate.

[0144] If both endpoint coordinates meet the requirements, proceed to the next operation; if either endpoint exceeds the model boundary area or is in the aggregate particle unit area, generate a new micro crack inclination angle according to the single rotation angle of the micro crack inclination angle, and set the maximum number of trials.

[0145] Within the range of the set maximum number of trials, recalculate the two endpoint coordinates of the new micro crack according to step 3), until the endpoint coordinates of the micro crack meet the requirements; if the maximum number of trials is reached, the A endpoint coordinate and the B endpoint coordinate of the new micro crack still do not meet the set conditions, then abandon this micro crack generation and start the next round of micro crack random construction.

[0146] The calculation formula of the single rotation angle of the micro crack inclination angle is as follows:

[0147] Δθ = 360 / t

[0148] In the formula, Δθ is the single rotation angle of the micro crack inclination angle; t is the maximum number of trials.

[0149] It is particularly noted that, in order to ensure the calculation efficiency, the maximum number of trials in step 4.2) is preferably 10 times, and the single rotation angle of the micro crack inclination angle is set to 18°, that is, the micro crack inclination angle is increased by 18° based on the last inclination angle angle when it is generated again, so that it can complete a 360° rotation after 10 maximum number of trials.

[0150] 4.3) Repeat step 4.2) until the total length of the simulation micro crack that has been completed reaches the total length of the required crack calculated in step 4.1), complete the quantitative random placement of all simulation micro cracks;

[0151] 4.4) Set the tensile strength of the two sides of all the placed simulation micro cracks to 0, complete the micro crack simulation.

[0152] Specifically, the influence range of the micro crack is set through the "dist" keyword, and the contact model and related contact parameters between the particle units in the specified range on both sides of the micro crack are set through the "dfn property" command, to complete the installation of the micro crack.

[0153] In actual operation, the parameter value specified by "dist" is half of the actual width of the micro crack, and the actual width of the micro crack is determined by the crack defect quantification result in step 1).

[0154] Further, in this step, it is generally assumed that the "ball" particles in the micro-crack influence range are completely disconnected, i.e., the contact model type is kept unchanged, the tensile strength parameter is set to 0, and other model parameters are kept unchanged.

[0155] The application is further illustrated below with specific examples.

[0156] Taking a two-dimensional circular specimen of cement stabilized macadam material as an example, the implementation steps of the application are described in detail in combination with the drawings, and the diameter of the two-dimensional circular specimen is selected as 100 mm.

[0157] The specific process of the micro-crack simulation of the cement stabilized material provided in this example is as follows.

[0158] Step 1) Form a 100 mm diameter cement stabilized macadam cylinder specimen in a laboratory.

[0159] Step 2) Set a slice interval of 0.2 mm, and use an X-ray CT scanning device to obtain internal two-dimensional slice images of the cement stabilized material observation sample (see Figure 2 ).

[0160] Step 3) Use VGStudio Max software to process the two-dimensional slice images, use different gray values to represent different cement stabilized material compositions, and distinguish aggregate, cement stabilized mortar and defect phases, wherein the brightest part is the aggregate particle, the middle gray area is the mortar phase, and the darkest black area is the defect.

[0161] Step 4) Import the two-dimensional slice images into Image J to convert them into 8-bit images (gray value is 0-255), and set the area with a gray value of 0-37 as the target defect area, with 0.01 mm 2 as the minimum threshold for defect extraction, to extract the defect. Then, set the measurement parameters as "Bounding Rectangle" and "Area", regard each independent defect area as a "Particle", and execute the "Analyze Particles" operation to solve the minimum circumscribed rectangle that can wrap the defect area, realize the one-by-one calculation and extraction of the long axis, short axis and area of the defect, and express the length direction of the defect with the longer side and the width direction of the defect with the shorter side.

[0162] Step 5) Traverse each defect area, identify the actual coverage area of each defect area, keep the length of the long side unchanged, and simultaneously move the two long sides towards the inside of the rectangle frame, so that the area of the scaled rectangle frame is consistent with the two-dimensional projection area of the actual defect, to obtain an equivalent rectangle frame (see Figure 3 ).

[0163] Step 6) Taking 3 as the length-width ratio threshold, the defect area with a length-width ratio greater than 3 is regarded as a groove defect, and the defect area with a length-width ratio less than or equal to 3 is regarded as a hole defect.

[0164] Step 7) For groove defects, the equivalent length l i , equivalent width w i , and equivalent rectangular frame area A i of each two-dimensional groove defect are extracted, respectively, and recorded; for hole defects, the equivalent rectangular frame area B j of each hole defect is extracted.

[0165] Step 8) Taking the center of the two-dimensional slice image as the coordinate origin, according to the two-dimensional shape parameter distribution information of the length and width of the micro-crack defects on each two-dimensional slice, the crack defect geometry analysis information database of the water stable mortar matrix is formed, the distribution function of the length L i of the simulated micro-crack is established, and the center position C i and the inclination angle θ i of the two-dimensional crack defect are regarded as subject to uniform distribution, and the distribution functions of the inclination angle and the center position of the simulated micro-crack are established; the distribution functions of the geometric parameters are as follows:

[0166] L i = 0.3 + 2.7u

[0167] θ i = 360xu

[0168] x i = -50 + 100u

[0169] y i = -50 + 100u

[0170] In the formula, u is a random number subject to uniform distribution, u ~ U(0, 1), and the unit is mm. According to the area information of the micro-crack defects and hole defects in the water stable mortar on each two-dimensional slice, the average defect area per unit area of the water stable mortar matrix is calculated by averaging, and the average porosity of the water stable mortar is 4%.

[0171] The length distribution function is the basis for determining the length of the micro-crack, which is uniformly distributed, the minimum value of the micro-crack length is 0.3, the maximum value of the micro-crack length is 3, and the difference between the maximum value and the minimum value is 2.7. Then, according to the above micro-crack length formula, a micro-crack length can be randomly generated and fall within the maximum value and the minimum value.

[0172] Step 9) Taking the center of the model as the coordinate origin, a circular boundary wall with a diameter of 100 mm is generated by using the "wall" command in the PFC2D software, and a "cubic" way is used to regularly arrange the "ball" with a diameter of 0.3 mm in the circular boundary wall area. The particle size range is set to 1.18 mm-19 mm, the two-dimensional aggregate is regarded as an irregular polygon with 4-10 sides, and the aggregate polygon area "geometry" is randomly generated in the circular boundary wall area according to the design gradation in Table 1. The "ball" particles covered by the aggregate polygon area "geometry" are divided into "aggregate ball", and the "aggregate" group name is given. The "ball" particles outside the aggregate polygon area "geometry" belong to the "mortar ball", and the "mortar" group name is given.

[0173] Table 1 Aggregate design gradation of virtual test piece

[0174]

[0175] Step 10) A certain number of "ball" particles in the "mortar" group name are randomly deleted by a Fish function to construct a target porosity of 4%, and a numerical test piece composed of aggregate, water-stable mortar and pore is formed.

[0176] The Fish function for constructing a target porosity of 4% is written as follows:

[0177]

[0178]

[0179] Step 11) Each contact in the numerical test piece is traversed, and the properties of each contact are judged. If the adjacent "ball" particles connected at both ends of the contact belong to the "aggregate" group name, the contact is judged as a unit particle inside the aggregate, and the contact is given a linear contact bond model. If the adjacent "ball" particles connected at both ends of the contact belong to the "mortar" group name, the contact is judged as a unit particle inside the water-stable mortar, and the contact is given a parallel bond model. If the adjacent "ball" particles connected at both ends of the contact belong to the "aggregate" group name and the "mortar" group name respectively, the contact is judged as a unit particle at the interface between the aggregate and the water-stable mortar, and the contact is given a parallel bond model. The model micro parameters of each phase material are calculated by inverse analysis based on the macroscopic mechanical test and simulation test of single-phase materials, the micro parameters of each contact model in the model are set, and a basic model of cement stabilized material is formed.

[0180] Step 12) A finite line segment is used to represent the geometric morphology of microcracks in a two-dimensional discrete element model, and is represented by length, inclination, center position and influence width. According to the distribution function of the geometric parameters such as the length, inclination and center position of the simulated microcracks, a geometric parameter random construction model of the length, inclination and center position of the microcracks in the discrete element model is established, and the Fish command stream is represented as follows:

[0181] Microcrack length: local L = 0.3 + 2.7 * math.random.uniform

[0182] Microcrack inclination: localjiaodu = 360 * math.random.uniform

[0183] Horizontal coordinate of center position: local x = -50 + 100 * math.random.uniform

[0184] Vertical coordinate of center position: local y = -50 + 100 * math.random.uniform

[0185] Step 13) The water-stable mortar matrix part is taken as the microcrack placement area, and the total length of the microcracks required to be placed in the microcrack placement area is calculated according to the area of the microcrack placement area, 40 m / m 2

[0186] Step 14) According to the Fish command stream of the microcrack center position geometric parameter random construction model provided in step 12), a center position coordinate C i (x i , y i ) of a pre-placed microcrack is generated, and it is judged whether it is located in the water-stable mortar matrix. If the microcrack center position belongs to the water-stable mortar area, the next step of microcrack construction work can be carried out, otherwise the microcrack center position coordinate needs to be regenerated until the microcrack center position is within the water-stable mortar matrix range.

[0187] Step 15) According to the Fish command stream of the microcrack length geometric parameter random construction model provided in step 12), a microcrack length parameter L is generated.

[0188] Step 16) According to the Fish command stream of the microcrack inclination geometric parameter construction model provided in step 12), the microcrack inclination angle θ i is set.

[0189] Step 17) According to the microcrack center position coordinate C i (x i , y i ​), the micro crack length L in step 15), the micro crack inclination angle θ in step 16) i , the position coordinates of the two end points A and B of the micro crack are calculated (see Figure 4 ).

[0190] Step 18) judge whether the coordinate positions of the two end points A and B of the micro crack in step 17) are both in the closed area surrounded by the boundary wall and in the range of the water stable mortar matrix, if the coordinates of the end points A and B both meet the requirements, then proceed to the next step; if any end point exceeds the model boundary or is in the aggregate area, then generate a new micro crack inclination angle according to the single rotation angle of the micro crack inclination angle, and calculate the new end point position coordinates of the micro crack according to step 17); wherein the maximum number of trials is set to 10, and the single rotation angle of the micro crack inclination angle corresponding thereto is set to 18°.

[0191] Step 19) repeat step 18) within the range of the set maximum number of trials 10 times, until the end point position coordinates of the micro crack meet the requirements; if the maximum number of trials 10 is reached, the end point position coordinates of the micro crack still cannot meet the set conditions, then give up this micro crack generation, and re-execute step 12) to start the next round of micro crack construction operation.

[0192] Step 20) under the condition that the set conditions are all met, convert the micro crack geometric parameters into the corresponding micro crack template through the "dfn template create" command, generate the micro crack template according to the generated micro crack template, run the "dfn generate" command to randomly put the micro crack in the water stable mortar, and record the total length of the cracks that have been put.

[0193] Step 21) repeat steps 14) to 20) until the total length of the micro cracks that have been put reaches the required total length of the cracks 0.157m in step 13), that is, the pre-fabrication and putting of all micro cracks are completed (see Figure 1 ).

[0194] Step 22) set the influence range of the micro crack to 0.15mm through the "dist" keyword, and set the tensile strength between the "ball" particles in the specified range on both sides of the micro crack to 0 through the "dfnproperty" command, to complete the simulation of the micro crack (see Figure 5 ).

[0195] It is particularly pointed out that the influence range of each micro crack can be individually set according to user needs, or can be uniformly set after all micro cracks are put in with the same value.

[0196] The above merely describes the preferred embodiments of the present application, and it should be pointed out that any technical improvement, replacement and decoration made by those skilled in the art without departing from the principles of the present application shall also fall within the protection scope of the present application.

Claims

1. A method for simulating microcracks in cement-stabilized materials, characterized in that, Includes the following steps: 1) Obtain two-dimensional slice images of the interior of cement-stabilized materials, perform quantitative analysis of micro-defects in cement-stabilized materials, and obtain a database of microcrack defect geometry analysis information and the average porosity of water-stabilized mortar. Step 1) specifically involves: 1.1) Obtain two-dimensional slice images of the interior of cement-stabilized materials; 1.2) Process the two-dimensional slice image to identify each target defect area inside the cement stabilized material. Traverse each target defect area and divide all target defect areas into crevice defects and pore defects, and obtain the two-dimensional distribution geometric shape parameters corresponding to each microcrack defect. 1.3) Extract the two-dimensional distribution geometric shape parameters corresponding to each microcrack defect in step 1.2) to obtain the microcrack defect geometric shape analysis information database and the average porosity of water-stabilized mortar; 2) Using the average porosity of the water-stabilized mortar in step 1), construct a basic model of the cement-stabilized material; The specific process of step 2) is as follows: 2.1) Use the "wall" command in PFC2D software to generate boundary walls, forming a closed model boundary area, and randomly fill the model boundary area with a particle system composed of aggregates and water-stabilized mortar; 2.2) Based on the average porosity of the water-stabilized mortar, randomly remove some water-stabilized mortar particles from the particle system in step 2.1) to construct the target porosity, forming a numerical specimen composed of aggregate, water-stabilized mortar and pores. 2.3) Assign corresponding contact models to the unit particles inside the aggregate, the unit particles inside the water-stabilized mortar, and the unit particles at the interface between the aggregate and the water-stabilized mortar, set the model micro-parameters of each phase material, and form a basic model of cement-stabilized material. 3) Using the microcrack defect geometry analysis information database from step 1), establish a random construction model of simulated microcrack geometry parameters, determine the geometric parameters of the microcrack, and form a simulated microcrack template; The specific process of step 3) is as follows: 3.1) Based on the microcrack defect geometry analysis information database from step 1), obtain the length distribution function, tilt angle distribution function, and center position distribution function of each microcrack; 3.2) Based on the simulated microcrack length distribution function, tilt angle distribution function, and center position distribution function, a stochastic construction model of the microcrack geometric parameters is determined, namely, the microcrack length L. i Microcrack inclination angle θ i Coordinates of the microcrack center C i (x i y i )parameter; 3.3) The above microcrack length L i Microcrack inclination angle θ i Coordinates of the microcrack center C i (x i y i ), which is converted to obtain a simulated microcrack template; 4) Construct microcracks randomly according to the simulated microcrack template, and quantitatively and randomly place microcracks in the cement-stabilized material basic model to complete the microcrack simulation; Step 4) specifically includes: 4.1) Obtain the number of cement mortar particles from the cement-stabilized material base model in step 2), calculate the area of ​​the microcrack placement region and the total length of the microcracks to be placed; 4.2) For the simulated microcrack template in step 3), a self-identification algorithm is used to generate microcracks, which are randomly placed into the mortar particles of cement-stabilized material, and the total length of the simulated microcracks that have been placed is recorded. 4.3) Repeat step 4.2) until the total length of the simulated microcracks that have been deployed reaches the total length of the microcracks to be deployed calculated in step 4.1), thus completing the quantitative random deployment of all simulated microcracks; 4.4) Set the tensile strength of all simulated microcracks within both sides to 0 to complete the microcrack simulation.

2. The microcrack simulation method for cement-stabilized materials according to claim 1, characterized in that, Step 1.2) includes the following steps: 1.2.1) The two-dimensional slice images were processed using VGStudio Max software, and different gray values ​​were used to characterize the aggregates, water-stabilized mortar and defect phases in the cement-stabilized material; 1.2.2) Continue importing the two-dimensional slice image into ImageJ, and identify the target defect area by setting the grayscale threshold; 1.2.3) Set the measurement parameters and execute the "Analyze Particles" operation to solve for the minimum bounding rectangle that encloses the target defect area; 1.2.4) Traverse each target defect area, identify the actual coverage area of ​​each target defect area, and use the area equivalence method to obtain the equivalent rectangle from the minimum bounding rectangle, that is, the two-dimensional distribution shape of each target defect area. 1.2.5) Calculate the equivalent length, equivalent width, and equivalent area of ​​the equivalent rectangular frame for each target defect area, i.e., the two-dimensional distribution geometric shape parameters; and calculate the aspect ratio of the equivalent rectangular frame, and divide the target defect area into crevice defects and hole defects according to the aspect ratio.

3. The microcrack simulation method for cement-stabilized materials according to claim 2, characterized in that, In step 1.3), the average porosity P of the water-stabilized mortar 0 Calculate according to the following formula: Among them: A i Let B be the equivalent rectangular area of ​​the i-th crease defect. j Let Q be the area of ​​the equivalent rectangular frame of the j-th hole defect. n Let I represent the area of ​​the water-stabilized mortar material on the nth two-dimensional slice image, I represent the number of cracks and defects on the two-dimensional slice image, J represent the number of pores and defects on the two-dimensional slice image, and N represent the number of two-dimensional slice images.

4. The microcrack simulation method for cement-stabilized materials according to claim 3, characterized in that, In step 3.3), θ i x i and y i The calculation formula is as follows: i i =360×u x i =x min +(x max -x min )u and i / and min +(and max -and min )or Where: x min x represents the minimum value of the abscissa within the microcrack distribution area; max The maximum value of the abscissa within the microcrack distribution area; y min y represents the minimum value of the ordinate within the microcrack distribution area; max denoted as the maximum value of the ordinate within the microcrack distribution region; u is a random number following a uniform distribution, u ~ U(0,1).

5. The microcrack simulation method for cement-stabilized materials according to claim 4, characterized in that, The specific process of step 4.1) is as follows: The cement-stabilized mortar is used as the area for simulating microcracks. Based on the number of cement-stabilized mortar particle units in the cement-stabilized material base model from step 2), the area S of the microcrack placement area is calculated. And based on the set microcrack density D, the total length T of the required microcracks is calculated as follows: T = S × D Where: T is in meters (m); S is in meters (m). 2 D represents the total length of microcracks per unit area, in m / m. 2 .

6. The microcrack simulation method for cement-stabilized materials according to claim 5, characterized in that, The specific process of step 4.2) is as follows: 4.2.1) Randomly generate a single simulated microcrack based on the simulated microcrack template, and determine the coordinates of the two endpoints of the simulated microcrack, namely endpoint A and endpoint B. The specific calculation formula is as follows: A endpoint coordinates B endpoint coordinates In the formula, L i Let θ be the length of the i-th microcrack; i Let x be the inclination angle of the i-th microcrack; i y i x represents the coordinates of the center point of the i-th microcrack; (1) y (1) x represents the coordinates of endpoint A; (2) y (2) Let B be the coordinates of the endpoint. 4.2.2) Determine whether the two endpoints of the simulated microcrack are located within the cement-stabilized material base model; If the coordinates of both endpoints meet the requirements, then a single random delivery will be performed; If any endpoint exceeds the model boundary region or is within the aggregate particle unit region, a new microcrack inclination angle is generated based on the single rotation angle of the microcrack inclination angle, and the maximum number of trial calculations is set at the same time. The formula for calculating the single rotation angle of the microcrack tilt angle is as follows: Δθ=360 / t In the formula, Δθ is the single rotation angle of the microcrack inclination angle; t is the maximum number of trials. Within the set maximum number of trial calculations, the coordinates of the two endpoints of the new microcrack are recalculated until the endpoint coordinates of the generated microcrack meet the requirements. If the maximum number of trial calculations is reached and the coordinates of endpoints A and B of the generated new microcrack still do not meet the set conditions, the generation of this microcrack is abandoned and the next round of random microcrack construction is restarted.

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