CN111695283A - Method for obtaining microscopic deterioration mechanism of England rock in freeze-thaw cycle process - Google Patents

Method for obtaining microscopic deterioration mechanism of England rock in freeze-thaw cycle process Download PDF

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CN111695283A
CN111695283A CN202010544005.6A CN202010544005A CN111695283A CN 111695283 A CN111695283 A CN 111695283A CN 202010544005 A CN202010544005 A CN 202010544005A CN 111695283 A CN111695283 A CN 111695283A
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郑达
汪鑫
姚青
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Chengdu Univeristy of Technology
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Abstract

The application provides a method for obtaining a microscopic deterioration mechanism of England rock in a freeze-thaw cycle process, and relates to the technical field of freeze-thaw rock. The development rule of the microscopic damage of the rock in the freeze-thaw cycle is obtained by a digital image numerical method on the basis of microscopic change of the rock damage expansion evolution, and the comprehensive damage rule of the freeze-thaw Enhan rock under the action of freeze-thaw cycle load is obtained from the microscopic scale and the macroscopic scale. The method mainly comprises the steps of establishing a finite element grid model by using a microscopic structure image of the Enhan rock slice, carrying out instantaneous cooling temperature field simulation, stress field freeze-thaw cycle simulation and displacement field freeze-thaw cycle simulation on the finite element grid model to obtain a plurality of temperature change distribution diagrams, a plurality of shear stress cloud diagrams, a plurality of tensile stress cloud diagrams and a plurality of displacement vector diagrams, and analyzing the plurality of temperature change distribution diagrams, the plurality of shear stress cloud diagrams, the plurality of tensile stress cloud diagrams and the plurality of displacement vector diagrams to obtain a microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle process.

Description

Method for obtaining microscopic deterioration mechanism of England rock in freeze-thaw cycle process
Technical Field
The application relates to the technical field of freeze-thaw rocks, in particular to a method for obtaining a microscopic deterioration mechanism of England rock in a freeze-thaw cycle process.
Background
The areas of various frozen soil areas on the earth account for about 50 percent of the land area of the earth, the frozen soil areas are mainly distributed in two poles of the earth, nearby zones and high-altitude areas, 75 percent of the land area of China is in a cold area, belongs to frozen soil and is in periodic change of winter freezing and summer thawing (freezing and thawing action).
The deterioration of rocks in frozen earth in cold regions under the freeze-thaw action creates a number of geotechnical problems: for example, uneven settlement of buildings caused by repeated freezing and thawing of foundations, frost heaving and cracking of underground oil pipelines and tunnel surrounding rocks in high and cold mountain areas, slope instability of rock slopes caused by weathering and degradation, and long-term abnormal operation of the national roads 217, 314 and 318 due to freezing and thawing disasters, so that the influence of freezing and thawing on the stability of rocks is mainly considered for engineering construction in cold areas, and the obtained degradation mechanism of the frozen and thawed rocks has important significance for engineering construction in cold areas.
Currently, the research on freezing and thawing rocks mainly has the following 3 problems:
1. there is a lack of methodology and theory for the investigation of the freeze-thaw rock problem. A large number of natural defects such as pores, cracks and the like exist in the rock, while the soil is a weathered product of the rock, and the structural difference between the two appears as different mechanical constitutive relations. Therefore, the frozen and thawed rock is researched by adopting a frozen soil mechanics method, so that the result difference is large.
2. The microscopic frost heaving mechanism of the rock is not sufficiently researched. The theory and experimental research on the physical and mechanical properties of the freeze-thaw rock mainly focuses on the aspects of macroscopic damage mechanical theory and macroscopic fracture mechanical theory. The influence of the freeze-thaw action on the microcracks, pores and mineral grain composition inside the rock mass is less considered.
3. The mesoscopic structural characteristics of rock and soil mass are not considered in numerical simulation of frozen soil and frozen rock. Based on a traditional macroscopic continuous medium thermodynamic model and corresponding theoretical analysis, the internal structural characteristics of the material are ignored, so that the microscopic behavior change among different groups in the material under the action of freeze-thaw cycle is difficult to describe.
Disclosure of Invention
In view of the above problems, the application provides a method for obtaining a microscopic deterioration mechanism of the Endoconcha in a freeze-thaw cycle process, which simulates the microscopic heat-force behavior of the low-temperature freeze-thaw rock based on microscopic changes of the damage and expansion evolution of the rock, obtains a development rule of the microscopic damage of the rock in the freeze-thaw cycle based on a digital image numerical method, and comprehensively obtains a deterioration rule of the Endoconcha under the action of repeated freeze-thaw cycle load from a microscopic scale and a macroscopic scale.
The embodiment of the application provides a method for obtaining a mesoscopic degradation mechanism of England rock in a freeze-thaw cycle process, which comprises the following steps: acquiring a microscopic structure image of the England rock slice by using a scanning electron microscope;
performing edge detection on the mesoscopic structure image to obtain a closed interface pixel point in the mesoscopic structure image; connecting the closed interface pixel points in the microscopic structure image to obtain an initial damage distribution image of the England rock slice; establishing a finite element mesh model according to the initial damage distribution image; carrying out instantaneous cooling temperature field simulation on the finite element mesh model to generate a plurality of temperature change distribution maps of the finite element mesh model in a target temperature range; performing stress field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of shear stress cloud pictures and a plurality of tensile stress cloud pictures in the stress field freeze-thaw cycle simulation; performing displacement field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of displacement vector diagrams in the displacement field freeze-thaw cycle simulation; and respectively obtaining a mesoscopic degradation mechanism of the Enhan rock slice in a freeze-thaw cycle according to the temperature change distribution maps, the shear stress cloud maps, the tensile stress cloud maps and the displacement vector maps.
Optionally, performing edge detection on the mesoscopic structure image to obtain a closed interface pixel point in the mesoscopic structure image, including:
running a Canny operator by using MATLAB to obtain a binary image of the mesoscopic structure image;
connecting first pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the first pixel points are pixel points corresponding to holes in the England rock slice;
connecting second pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the second pixel points are pixel points corresponding to micro cracks in the Enhan rock slice;
connecting a third pixel point with the gray level of 1 in the binary image to obtain a pixel point of the closed interface; and the third pixel point is a pixel point corresponding to a pore in the Enhan rock slice.
Optionally, the method further comprises:
measuring the chemical element content of the Enhan rock slice by using a scanning electron microscope and an X-ray energy spectrometer to obtain the mass percentage of various chemical elements contained in the Enhan rock slice;
obtaining the mineral contents of various mineral components contained in the Enhan rock slice according to the mass percentages of various chemical elements contained in the Enhan rock slice;
respectively establishing corresponding relations between the mineral content of each mineral component and the mechanical parameters of the Enhan rock model;
carrying out correlation and partial correlation analysis on the mineral content of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice, and obtaining the corresponding relation between the correlation and partial correlation of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice;
determining target mineral components influencing the mechanical properties of the Enhan rock slices according to the partial correlation corresponding relation and the correlation analysis;
connecting the second pixel points with the gray scale of 1 in the binary image to obtain the pixel points of the closed interface, including:
determining a cementing surface pixel point of a cementing surface of a crystal structure corresponding to the target mineral component in the binary image;
and determining pixel points corresponding to the crystal cracks in the cementing surface pixel points as the closed interface pixel points.
Optionally, establishing a finite element mesh model according to the initial damage distribution image includes:
converting the connected closed interface pixel points in the initial damage distribution image into a plurality of closed polygons to form a vector diagram of the initial damage of the Enhan rock slice;
screening the plurality of closed polygons, and removing interference data in the vector diagram of the initial damage;
and importing the vector diagram of the initial damage after the interference data is removed into finite element analysis software, and establishing the finite element mesh model.
Optionally, the method further comprises:
establishing a comparison finite element grid model of the nondestructive Enhan rock;
carrying out instantaneous temperature field simulation on the comparison finite element mesh model to generate a plurality of comparison temperature change distribution maps of the comparison finite element mesh model in the target temperature range;
obtaining a mesoscopic deterioration mechanism of the England rock slices in a freeze-thaw cycle according to the plurality of temperature change distribution maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
and comparing the plurality of temperature change distribution maps with the plurality of control temperature change distribution maps to obtain the mesoscopic degradation mechanism of the England rock slice in the freeze-thaw cycle.
Optionally, the method further comprises:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
carrying out instantaneous cooling temperature field simulation on the finite element mesh model, wherein the simulation comprises the following steps:
performing instantaneous cooling temperature field simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
obtaining a mesoscopic deterioration mechanism of the England rock slices in a freeze-thaw cycle according to the plurality of temperature change distribution maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
determining a first corresponding position of the closed interface pixel point in the plurality of temperature change distribution graphs;
and obtaining a mesoscopic deterioration mechanism of the England rock slice in the freeze-thaw cycle according to the relationship between the temperature distribution in the temperature change distribution maps and the first corresponding position.
Optionally, the method further comprises:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
performing stress field freeze-thaw cycle simulation on the finite element mesh model, wherein the stress field freeze-thaw cycle simulation comprises the following steps:
performing stress field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation; the cycle period of the freeze-thaw cycle simulation is 12 hours;
obtaining a microscopic degradation mechanism of the England rock slice in a freeze-thaw cycle according to the plurality of shear stress cloud pictures and the plurality of tensile stress cloud pictures, wherein the microscopic degradation mechanism comprises the following steps:
respectively obtaining a shear stress cloud picture and a tensile stress cloud picture after the 1 st freeze-thaw cycle simulation, a shear stress cloud picture and a tensile stress cloud picture after the 5 th freeze-thaw cycle simulation, and a shear stress cloud picture and a tensile stress cloud picture after the 10 th freeze-thaw cycle simulation;
according to the shear stress cloud chart and the tensile stress cloud chart which are obtained after the three times of freeze-thaw cycle simulation, the influence of water-ice phase change generated in the rock on the microscopic damage degradation of the rock is obtained, and further the microscopic degradation mechanism of the England rock slice in the freeze-thaw cycle is obtained.
Optionally, the method further comprises:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
performing displacement field freeze-thaw cycle simulation on the finite element mesh model, wherein the displacement field freeze-thaw cycle simulation comprises the following steps:
performing displacement field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
obtaining a mesoscopic deterioration mechanism of the Endothia rock slices in a freeze-thaw cycle according to the plurality of displacement vector maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
respectively obtaining a displacement vector diagram after the 1 st freeze-thaw cycle simulation, a displacement vector diagram after the 5 th freeze-thaw cycle simulation and a displacement vector diagram after the 10 th freeze-thaw cycle simulation;
determining a second corresponding position of the closed interface pixel point in a displacement vector diagram obtained three times after freeze-thaw cycle simulation;
and obtaining the displacement of the degradation of the microscopic damage in the rock according to the second corresponding position in the displacement vector diagram obtained after the three times of freeze-thaw cycle simulation, thereby obtaining the microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle.
Optionally, the method further comprises:
setting an initial boundary condition and a convection boundary condition;
determining a boundary mesh corresponding to a surface boundary of the England rock slice in the finite element mesh model;
determining an initial temperature of the boundary grid using the initial boundary condition;
constraining temperature changes of the boundary grid using the convective boundary conditions;
and utilizing the temperature control equation to perform instantaneous cooling temperature field simulation on the finite element grid model in the range of 20 ℃ to-30 ℃, wherein the simulation comprises the following steps:
and controlling the finite element mesh model to change from the initial temperature of the boundary mesh by using the temperature control equation according to the constraint of the convection boundary condition on the temperature change of the boundary mesh until the finite element mesh model completes the simulation of the instantaneous cooling temperature field of 20 ℃ to-30 ℃.
Optionally, the initial boundary condition is: t is1＝T1(x, y, z, t); where x, y, z are the coordinates of the bounding grid, t1Is the operating time of the finite element mesh model;
the convection boundary conditions are: q ″ ═ h (T)S-TB) And
Figure BDA0002540053900000061
wherein q "is the heat flux density of the Enhan rock model and h is the thermal convection coefficient of the Enhan rock model and the indoor air; t issIs the temperature, T, of the England rock modelBIs the temperature of the indoor air; s is the area of the boundary mesh;
the temperature control equation is
Figure BDA0002540053900000062
Figure BDA0002540053900000063
Wherein, CrIs the specific heat, r, of the England rock slicerIs the density, k, of the Enhan rock slicerIs the thermal conductivity of the England rock slice; k is a radical ofiIs the thermal conductivity of ice; ciIs the specific heat of ice; r isiIs the density of ice.
According to the method for obtaining the microscopic degradation mechanism of the England in the freeze-thaw cycle process, the position (the cementing surface of quartz and plagioclase feldspar crystals) where the England is most prone to fission in the freeze-thaw cycle is obtained by performing correlation analysis on the mineral content and mechanical parameters of the England, and the position is used as a concerned area. And then obtaining an electron microscope scanning picture of the Enhan rock slice, obtaining a microscopic structure of the Enhan rock, determining an attention region in the microscopic structure, taking initial damages such as micro cracks, pores and cavities in the attention region as closed interface pixel points in an edge detection mode, obtaining a microscopic structure image of the Enhan rock with a key attention region (closed interface pixel points), and taking the image as a basic image (initial damage image) for establishing a finite element grid model, so that the finite element grid model not only can clearly show the real microscopic structure of the Enhan rock, but also can show the structure position of the microscopic structure which is possibly further degraded in a freeze-thaw cycle.
After the finite element grid model is obtained, the instant cooling temperature field simulation is carried out on the finite element grid model, the influence of original damages such as microcracks, pores and cavities in the Enhan rock on the temperature distribution is analyzed, and then the rule of deterioration of the Enhan rock caused by the fact that the temperature distribution is uneven in the freeze thawing of the Enhan rock is obtained. The finite element grid model is subjected to stress field freeze-thaw cycle simulation and displacement field freeze-thaw cycle simulation to obtain a water-ice phase change of water contained in the initial damages such as micro-cracks, pores and cavities in the Enhan rock in the freeze-thaw process, a stress influence rule of the initial damages such as the micro-cracks, the pores and the cavities and a degradation extension rule of the initial damages such as the micro-cracks, the pores and the cavities on the basis of stress, so that a microscopic degradation mechanism of the Enhan rock slices in the freeze-thaw cycle is obtained.
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In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive exercise.
FIG. 1 is a flow chart of the steps proposed in the present application to obtain a mesoscopic degradation mechanism of England rock during a freeze-thaw cycle;
FIG. 2 is a flowchart illustrating edge detection on a mesoscopic structure image according to an embodiment of the present application;
FIG. 3 is a binary image of an initial lesion distribution image obtained in an embodiment of the present application;
FIG. 4 is a flowchart of steps for determining a pixel point of a closed interface according to an embodiment of the present disclosure.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, fig. 1 is a flow chart of the steps proposed in the present application to obtain a mesoscopic degradation mechanism of the imperial rock during a freeze-thaw cycle. The method for obtaining the mesoscopic degradation mechanism of the England rock in the freeze-thaw cycle process comprises the following steps of:
step S11: acquiring a microscopic structure image of the England rock slice by using a scanning electron microscope;
based on a macroscopic angle, the natural defects in the rock mass comprise cracks, joints and the like; based on the microscopic view, the natural defects in the rock mass include cavities, pores, particle interfaces, microcracks and the like which cannot be seen by naked eyes. The thermal and mechanical properties of the rock under the low-temperature action are mainly influenced by the composition and structural morphology of the microscopic medium in the rock, so that the damage degradation research of the freeze-thaw rock is carried out on the basis of the microscopic scale, and the degradation rule of the freeze-thaw rock under the microscopic scale is analyzed.
After a whole block of the Enhance rock is collected in a cold soil area, a diamond saw blade is used for cutting an undecorated part of the Enhance rock into Enhance rock samples with proper sizes conforming to a cover glass, the samples conforming to the cover glass are ground and glued, a slice cutting machine is used for cutting the samples into the thickness of 0.5mm, and finally a slice grinding disc is used for grinding the samples with the thickness of 0.5mm to the thickness of 0.03mm by utilizing the vacuum principle, so that an Enhane rock slice is obtained.
The microscopic structure of the Enhan rock slice, such as microcracks, cavities, pores and the like, can be clearly observed by magnifying 2000 times the microscopic structure image obtained by scanning the Enhan rock slice by a Scanning Electron Microscope (SEM).
Step S12: performing edge detection on the mesoscopic structure image to obtain a closed interface pixel point in the mesoscopic structure image;
the closed interface pixel points are initial damages such as microcracks, cavities, pores and the like corresponding to the England rock slices in the microscopic structure image. The boundary can be seen as the outermost rock surface in the mesoscopic structure image corresponding to the imperial rock slice. The set of corresponding pixel points of the micro cracks, the holes and the pores in the microscopic structure image is a closed interface, the closed interface is a surface part in contact with air under the condition that the Enhan rock slice is dry, the closed interface is a contact surface with water inside the Enhan rock slice under the state that the Enhan rock slice is saturated with water, and the pixel points of the micro cracks, the holes and the pores in the microscopic structure image are closed interface pixel points.
Step S13: connecting the closed interface pixel points in the microscopic structure image to obtain an initial damage distribution image of the England rock slice;
after the microscopic structure of the Enhan rock slice is analyzed, the pixel points corresponding to the same microcrack are connected into a closed area, the pixel points corresponding to the same cavity are connected into a closed area, and the pixel points corresponding to the same pore are connected into a closed area. Because the Enhan rock slices are naturally damaged differently, for example, the Enhan rock slices have a plurality of microcracks, cavities or pores with different sizes, more than one closed area is formed by connecting pixel points corresponding to the microcracks, cavities or pores.
Step S14: establishing a finite element mesh model according to the initial damage distribution image;
the finite element grid model is a numerical analysis (computational mathematics) tool and can simulate an actual structure, the finite element grid model is established based on a microscopic structure of the Enhan rock, and then the finite element grid model is used for carrying out instantaneous cooling temperature field simulation, stress field freeze-thaw cycle simulation and displacement field freeze-thaw cycle simulation, so that transition from the microscopic scale to the macroscopic scale of the Enhan rock is realized, and the degradation mechanism of the freeze-thaw Enhan rock under the action of freeze-thaw cycle load is comprehensively obtained.
Another embodiment of the present application provides a method for processing an initial damage distribution image, which performs geometric vectorization on the initial damage distribution image, so as to avoid the problem of excessive calculation amount caused by directly using an image obtained by an SEM. If a finite element mesh model is generated based on a microscopic structure image or an initial damage distribution image obtained by scanning of an SEM, a node needs to be generated according to each pixel point in the image, so that the generation of the finite element mesh model is too intensive, and finally, the generation of the finite element mesh model is difficult due to too large calculation amount.
Step S14-1: converting the connected closed interface pixel points in the initial damage distribution image into a plurality of closed polygons to form a vector diagram of the initial damage of the Enhan rock slice;
and (3) converting the connecting lines (closed regions) corresponding to the microcracks, cavities, pores and boundaries of the Enhan rock in the initial damage distribution image into vector space distribution consisting of closed polygons by adopting plane design software (CorelDraw), and further converting the initial damage distribution image into a vector diagram.
Step S14-2: screening the plurality of closed polygons, and removing interference data in the vector diagram of the initial damage;
the disturbance data refers to a small pore and closed polygon group corresponding to particles in a vector diagram of an initial damage distribution image.
Step S14-3: and importing the vector diagram of the initial damage after the interference data is removed into finite element analysis software, and establishing the finite element mesh model.
And (3) the vector diagram of the initial damage after the interference data are removed is the vector space distribution formed by the finally obtained closed polygon, and the vector space distribution is imported into the finite element analysis software (ANSYS) to establish a finite element grid model.
Step S15: carrying out instantaneous cooling temperature field simulation on the finite element mesh model to generate a plurality of temperature change distribution maps of the finite element mesh model in a target temperature range;
because the finite element grid model is established based on the microscopic structure of the Enhan rock slice, particularly, the finite element grid model restores the distribution and damage forms of the initial damage such as microcracks, pores and cavities in the Enhan rock slice, an instantaneous temperature-reducing temperature field is carried out on the finite element grid model, the influence of temperature difference on the damage development (for example, the influence of the temperature difference of the microcracks on the stress position of the frost heaving force generated in the finite element grid model is influenced so as to influence the development position of the microcracks) is analyzed, and the influence rule of the temperature on the deterioration in the Enhan rock is obtained.
The temperature change distribution map is a temperature distribution map corresponding to the finite element mesh model. Assuming that a temperature change distribution map is obtained every 1 hour in the process of performing six-hour instantaneous cooling temperature field simulation on the finite element grid model, the temperature corresponding to different regions in the Enhan rock at each moment can be obtained according to the temperature change distribution maps obtained 6 times, and particularly the difference distribution relation between the temperature of the damaged part (microcrack, pore and cavity) in the Enhan rock and the temperature of the damaged region in the Enhan rock can be obtained.
Step S16: performing stress field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of shear stress cloud pictures and a plurality of tensile stress cloud pictures in the stress field freeze-thaw cycle simulation;
according to the shear stress cloud chart and the tensile stress cloud chart obtained by performing freeze-thaw cycle on the finite element grid model, the influence of the water ice phase change in freeze-thaw on the interior of the Enhan rock can be simulated, particularly the shear stress and the tensile stress of the area corresponding to the closed interface pixel point in the finite element grid model are obtained, the stress influence of the water ice phase change on the damage parts such as microcracks, pores and cavities in the Enhan rock in the freeze-thaw cycle can be obtained, and further the degradation mechanism of the Enhan rock in the freeze-thaw cycle is obtained.
Step S17: performing displacement field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of displacement vector diagrams in the displacement field freeze-thaw cycle simulation;
according to a displacement vector diagram obtained by carrying out freeze-thaw cycling on the finite element grid model, the expansion condition of initial damage (microcracks, pores and cavities) of the internal structure of the Enhan rock caused by water ice phase change in freeze thawing can be simulated, and then the degradation mechanism of the Enhan rock in the freeze-thaw cycling is obtained.
Step S18: and respectively obtaining a mesoscopic degradation mechanism of the Enhan rock slice in a freeze-thaw cycle according to the temperature change distribution maps, the shear stress cloud maps, the tensile stress cloud maps and the displacement vector maps.
Another embodiment of the present application provides a method for edge detection of a mesoscopic structure image.
Step S12-1: running a Canny operator by using MATLAB to obtain a binary image of the mesoscopic structure image;
and (3) carrying out edge detection on the mesoscopic structure image obtained by scanning the England rock slice by the SEM by using a Canny operator, wherein the edge detection mainly distinguishes the edge of the image from the information around the image. Typically including four parts of filtering, enhancement, edge detection and localization. As shown in fig. 2, fig. 2 is a flowchart of performing edge detection on a mesoscopic structure image according to an embodiment of the present application.
The first step is to preprocess the microscopic structure image, including converting the image format and removing the image impurity.
And secondly, performing gradient calculation on the microscopic structure image:
the strength of the edge of the mesostructure image is represented by the magnitude of the gradient, the direction in which the edge goes perpendicular is the direction of the gradient, and for a continuous mesostructure image f (x, y), the gradient of the image midpoint (x, y) is defined as the following vector:
Figure BDA0002540053900000111
wherein (x, y) represents coordinates of a pixel point in the mesoscopic structure image,
Figure BDA0002540053900000112
representing the magnitude of the image gradient, and T' is the transition sign of the matrix.
Formula for the magnitude of the gradient:
Figure BDA0002540053900000113
the magnitude of the gradient is typically expressed approximately in absolute terms as:
Figure BDA0002540053900000114
the direction of the gradient is defined as
Figure BDA0002540053900000115
Where θ (x, y) is the angle between the detected edge of the image and the horizontal direction, the first derivative is replaced by a first difference:
fx(x,y)＝f(x,y)-f(x-1,y)
fy(x,y)＝f(x,y)-f(x,y-1)
substituting the convolution template into the gradient magnitude formula, two different convolution templates are:
fx(x,y)＝[1 -1]
Figure BDA0002540053900000121
and thirdly, carrying out non-maximum suppression on the mesoscopic structure image.
Binarizing the gradient to obtain an edge image g (x, y), and selecting a threshold value F of the amplitude of the gradient to obtain:
Figure BDA0002540053900000122
f is obtained by Canny operator detection, and A is a numerical value which is greater than or equal to 0 and less than or equal to 255. When the magnitude of the gradient is greater than the threshold F, the edge image g (x, y) is equal to a value obtained by calculating the magnitude formula of the gradient, and when the magnitude of the gradient is less than the threshold F, the edge image g (x, y) is equal to 0.
And fourthly, carrying out double-threshold detection on the mesoscopic structure image. The MATLAB program runs Canny to construct a detector using two mathematical templates (two different convolution templates shown in the above formula) and then combines the two into one Canny detector.
The Canny operator is a multi-scale spatial edge detection operator that determines image edges by finding local maxima of the image gradient.
An initial damage distribution image of the Enhance rock, which is detected by running a Canny operator by utilizing an MATLAB program, is a binary image (an image consisting of 0-value pixel points and 1-value pixel points), and the boundaries of damages such as cracks, cavities, pores and the like and the Enhance rock are formed by connecting pixel points with the gray level of 1. The edge of the SEM image is extracted to obtain an initial damage distribution image based on the micro-structure image of the England rock, the initial damage distribution image reflects the actual distribution condition of the initial damage such as holes, pores, microcracks and the like in the England rock, and a real micro-structure image in the England rock is provided.
Step S12-2: connecting first pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the first pixel points are pixel points corresponding to holes in the England rock slice;
step S12-3: connecting second pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the second pixel points are pixel points corresponding to micro cracks in the Enhan rock slice;
step S12-4: connecting a third pixel point with the gray level of 1 in the binary image to obtain a pixel point of the closed interface; and the third pixel point is a pixel point corresponding to a pore in the Enhan rock slice.
The first pixel point, the second pixel point and the third pixel point are all pixel points with the gray level of 1 in a binary image obtained by calculating a microscopic structure image (initial damage distribution image) through a Canny operator. According to the different characteristic information of the hole, the microcrack and the boundary, the pixel points corresponding to the hole, the microcrack and the boundary and the positions of the pixel points in the image of the mesoscopic structure can be found in the image of the mesoscopic structure, so that the positions corresponding to the hole, the microcrack and the boundary can also be confirmed by a binary image obtained after the image of the mesoscopic structure is calculated by a Canny operator.
Referring to fig. 3, fig. 3 is a binary image of an initial lesion distribution image obtained in an embodiment of the present application. The binary image provides a true microscopic structure inside the England rock slice.
The square frame boundary of fig. 3 corresponds to an imperial rock slice boundary, the area surrounded by the black lines in fig. 3 corresponds to initial damages such as microcracks, pores and cavities in the imperial rock, and specific damages can be distinguished according to the forms of different types of damages.
Another embodiment of the application provides a method for determining a pixel point of a closed interface. Referring to fig. 4, fig. 4 is a flowchart illustrating steps of determining pixels in a closed interface according to an embodiment of the present disclosure.
Step S21: measuring the chemical element content of the Enhan rock slice by using a scanning electron microscope and an X-ray energy spectrometer to obtain the mass percentage of various chemical elements contained in the Enhan rock slice;
step S22: obtaining the mineral contents of various mineral components contained in the Enhan rock slice according to the mass percentages of various chemical elements contained in the Enhan rock slice;
the SEM-EDS technology combining a Scanning Electron Microscope (SEM) and an X-ray energy spectrometer can give the content of various chemical elements forming the Enhan rock slice based on the structural connection characteristics of the Enhan rock slice on the structural level and structural element connection, then the relation between the oxide in the Enhan rock and the mineral content of mineral components is analyzed by adopting a multiple regression analysis method to obtain a mineral content calculation formula, and the mineral content calculation formula is solved by utilizing a non-negative linear least square method to obtain the mineral content of various mineral components contained in the Enhan rock slice.
Illustratively, after performing site-specific analysis on the Enhance rock slices using SEM-EDS techniques, the Enhance rock slices contain the following main elements and the corresponding content percentages: na-1.76%, Mg-1.18%, Al-6.24%, Si-25.76%, K-0.28%, Ca-3.14%, Fe-1.47%. Converting the chemical elements into corresponding oxide forms according to the mass conservation law of the chemical elements: SiO 22-58.21、Al2O3-16.51、Fe2O3-2.16、FeO-3.05、MgO-2.26、CaO-5.19、Na2O-2.98、K2O-1.40。
Supplementing pyroxene, montmorillonite and pyrite based on the mineral components detected by SEM to obtain mineral components of the England rock slice, wherein the mineral components of the England rock slice comprise: quartz, plagioclase, pyroxene, biotite, amphibole, kaolinite, chlorite, montmorillonite, calcite, pyrite, and magnetite, and substituting the characteristic oxide conversion coefficients of the above various mineral components by using a theoretical method and average chemical components to obtain a mineral characteristic oxide conversion coefficient matrix (relationship between oxides in the imperial rock and mineral contents of the mineral components):
Figure BDA0002540053900000141
the characteristic oxide means an oxide (SiO) contained in a specific mineral component (e.g., quartz)2) I.e. the characteristic oxide of quartz.
Substituting the 11 mineral components and 8 characteristic oxides into a mineral content calculation formula.
The mineral content calculation formula is:
C11X1+C12X2+……+C1nXn＝P1
C21X1+C22X2+……+C2nXn＝P2
……
Cm1X1+Cm2X2+……+CmnXn＝Pm
wherein, CmnDenotes the content percentage of the m-th oxide in the n-th mineral component, XnDenotes the mineral content of the n-th mineral component, PmIs a partial component of the m-th oxide. PmCan be obtained from the existing data, let x1、x2、x3、x4、x5、x6、x7、x8、x9、x10、x11Respectively the mass percentage of quartz, plagioclase, pyroxene, biotite, hornblende, kaolinite, chlorite, montmorillonite, calcite, pyrite and magnetite, P1、P2、P3、P4、P5、P6、P7、P8Are respectively SiO2、Al2O3、Fe2O3、FeO、MgO、CaO、Na2O、K2Mass partial component of O. CmnCan be obtained according to the mineral characteristic oxide conversion coefficient matrix of the Enhan rock slice, and then X can be obtained by calculationnNamely the mass percentage of mineral components: 18 percent of quartz, 24.39 percent of plagioclase, 0 percent of pyroxene, 15.2 percent of biotite, 3.86 percent of hornblende, 15.83 percent of kaolinite, 0 percent of chlorite, 15.53 percent of montmorillonite, 7.55 percent of calcite, 0 percent of pyrite and 0.52 percent of magnetite.
Carrying out correlation and partial correlation analysis on the mineral content of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice, and obtaining the corresponding relation between the correlation and partial correlation of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice;
generally, the corresponding relation between the mineral content of mineral components and the mechanical parameters of the Enhan rock slices is established by carrying out uniaxial compression and triaxial compression on the Enhan rock.
The corresponding relation between the mechanical parameters and the mineral content comprises the following steps: the corresponding relation between the mineral components and the elastic modulus and the corresponding relation between the mineral components and the compressive strength.
Step S23: performing correlation analysis on the mineral content of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice, and obtaining a partial correlation corresponding relation between each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice;
step S24: determining target mineral components influencing the mechanical properties of the Enhan rock slices according to the partial correlation corresponding relation and the correlation analysis;
examples of the correspondence relationship: when the content of the mineral component quartz in the Enhance rock is within the range of 17.01-18.76%, the correlation coefficient of the quartz is 0.67, the content of the mineral component plagioclase is within the range of 23.95-25.16%, and the correlation coefficient of the plagioclase is 0.6. And performing correlation analysis according to the corresponding relation to obtain that: the compressive strength and the elastic modulus of the Endonax slice are in an increasing trend along with the increase of the content of the quartz and the plagioclase feldspar, and the compressive strength and the elastic modulus of the Endonax are strongly related to the content and the existence of the quartz and the plagioclase minerals contained in the Endonax. When the content of the mineral component silimanite is in the range of 3.11 to 4.79%, the correlation between the compressive strength and the elastic modulus of the Enhan rock slice is weaker as the content of the silimanite increases.
From this it can be determined that the mineral components affecting the mechanical properties of the andesite slices are non-clay minerals such as plagioclase and quartz, the target mineral component being a non-clay mineral.
Determining the mechanical failure mode of the England rock supported by the target mineral component influencing the mechanical property of the England rock slice as brittle failure, determining the closed interface pixel points on the basis of the cementing surface of the target mineral component, and ensuring that the finite element grid model research is simulated natural failure (brittle failure) of the England rock.
Performing partial correlation analysis on mineral components, and controlling variables: the coefficient of correlation of the content of non-clay minerals (quartz, plagioclase, biotite, amphibole, calcite, magnetite) with the compressive strength of Enantion rock and the coefficient of correlation of the content of non-clay minerals with the elastic modulus of Enantion rock were analyzed by SPSS. Obtaining partial correlation coefficients, and under the condition that the total amount of the clay minerals is constant, the partial correlation coefficients of various non-clay minerals are shown in the following table:
Figure BDA0002540053900000161
the total amount of clay mineral in the above table is a controlled constant amount.
From the above-described partial correlation coefficient table, it can be determined that the target mineral components are quartz and plagioclase.
Further, the microcracks, cavities, pores and the like of the cementing surface of the target mineral component are determined as closed interface pixel points, namely the corresponding pixel points of the microcracks, cavities, pores and the like of the cementing surface in the microscopic structure image are determined as initial damage simulated by the finite element grid model, and then the real freeze-thaw damage process of the England rock is simulated better.
Specifically, step S25: determining a cementing surface pixel point of a cementing surface of a crystal structure corresponding to the target mineral component in the binary image; step S26: and determining pixel points corresponding to the crystal cracks in the cementing surface pixel points as the closed interface pixel points.
The anorthite crystal damage and the quartz crystal damage are both expressed as a large number of crystal cracks, and the pixel points corresponding to the crystal cracks in the microscopic structure image are used as the closed interface pixel points for constructing an initial damage distribution image, so that the natural deterioration position of the Enhan rock slice can be restored.
Intergranular cracks are a particular manifestation of microcracking. Classifying the microcracks according to the morphology of the microcrack fractures, comprising: intergranular cracks, transgranular fractures and intergranular and transgranular coupled fractures.
Determining a cementing surface and a position of a crystal crack of the cementing surface in a binary image, ensuring that an initial damage distribution image can more pertinently reduce initial damage influencing the deterioration and development of the Enhan rock, further ensuring that a finite element grid model generated based on the initial damage distribution image can pertinently reduce the initial position of the Enhan rock deterioration, and carrying out cooling field simulation and freeze-thaw cycle simulation on the finite element grid model can pertinently simulate the water-ice phase change of an initial damage part influencing the deterioration and development of the Enhan rock and the pressure influence (shear stress and tensile stress) of the water-ice phase change on the initial damage part of the Enhan rock.
Micro cracks in a microscopic structure image obtained by scanning the Enhan rock slice by the SEM are extracted, and pixels with similar properties can be gathered to form a region expected to be segmented by using a region growing algorithm. Specifically, one or more seed pixels are determined in each micro-crack region to be segmented and are used as the growth starting points of the micro-cracks, then 8 neighborhood pixels of the seed points are compared with the seed points, and pixels with similar properties to the seed points are merged into the region where the seed pixels are located, so that the micro-crack regions are gradually grown.
Another embodiment of the present application provides a method for performing an instantaneous cooling temperature field simulation on the finite element mesh model.
Establishing a comparison finite element grid model of the nondestructive Enhan rock;
carrying out instantaneous temperature field simulation on the comparison finite element mesh model to generate a plurality of comparison temperature change distribution maps of the comparison finite element mesh model in the target temperature range;
and determining the temperature change of the positions of microcracks, cavities, pores and the like in the Enhan rock by comparing the control finite element grid model without damaging the Enhan rock with the temperature change distribution diagram of the finite element grid model established based on the initial damage distribution image.
And comparing the plurality of temperature change distribution maps with the plurality of control temperature change distribution maps to obtain the mesoscopic degradation mechanism of the England rock slice in the freeze-thaw cycle.
Before the finite element grid model is subjected to instantaneous cooling temperature field simulation, stress field freeze-thaw cycle simulation and displacement field freeze-thaw cycle simulation, condition limitation is carried out on the Enhan rock slices, and a temperature control equation of the finite element grid model is set according to the condition limitation.
Setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
the rock system of the Enhan rock where the Enhan rock slices are located can be used as the Enhan rock system, and the rock system of the Enhan rock in any nature can be used as the Enhan rock system, and the environment where the Enhan rock of the rock system is located is the environment where the Enhan rock is located. Assuming that the rock system of the Enhance A is used as the rock system of the Enhance on which the temperature control equation is set, the environment of the Enhance A is the same as the environment of the Enhance.
The following assumptions were made for the section of Enhance rock studied, with conditional definitions:
(1) the rock system of the Enhan rock slice is an anisotropic pore medium;
(2) the Enhance rock slice is completely saturated, the pores are filled with water, and the water (ice) in the sample is completely frozen at the negative temperature without considering the seepage influence of the water;
(3) the Enhan rock simulated by the finite element grid model is placed in a constant-temperature indoor environment and only exchanges heat with air;
(4) the thermal conductivity and specific heat of ice change over time.
Based on the above conditions, in the heat conduction process between the rock system of the Enhan rock slice and the indoor air, the temperature change of the rock sample and the ice is mainly caused by the air temperature change, and the temperature control equation is set as follows:
Figure BDA0002540053900000181
wherein, CrIs the specific heat, r, of the England rock slicerIs the density, k, of the Enhan rock slicerIs the thermal conductivity of the England rock slice; k is a radical ofiIs the thermal conductivity of ice; ciIs the specific heat of ice; r isiIs the density of ice. T is the temperature of the mesh in the finite element mesh model corresponding to the interior of the England rock slice.
Performing instantaneous cooling temperature field simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
the method comprises the steps of utilizing a temperature control equation to cool a grid corresponding to an Enhant rock boundary in a finite element grid model, wherein the finite element grid model is established according to an initial damage distribution image, and determining the position of a closed interface pixel point in the initial damage distribution image, in other words, determining the position of an initial damage (micro-crack, pore and cavity) in the initial damage distribution image, so that the position of the rock boundary of an Enhan rock slice can be determined in the finite element grid model, carrying out instantaneous cooling temperature field simulation on the finite element grid model, and setting the grid temperature corresponding to the Enhan rock boundary in the finite element grid model as a target temperature from the position corresponding to the rock boundary of the Enhan rock slice.
Setting an initial boundary condition and a convection boundary condition;
determining a boundary grid corresponding to the surface boundary of the England rock model in the finite element grid model, and determining the initial temperature of the boundary grid by using the initial boundary condition;
constraining temperature changes of the boundary grid using the convective boundary conditions;
after the boundary grid temperature corresponding to the rock boundary in the finite element grid model is set, the temperature of the grid corresponding to the boundary of the Enhant rock model in the finite element grid model is obtained according to the energy conservation principle and by combining the initial boundary condition and the convection boundary condition. The surface boundary is the area near the boundary of the England rock slice.
The Enhan rock model refers to an integral model of the integral Enhan rock where the Enhan rock slices are located and obtained by reduction according to the Enhan rock slices.
Four sides of the microscopic structure image obtained by scanning by the SEM can be directly determined as the surface boundary of the England rock slice, and then the four sides are used as the boundary grid of the finite element grid model.
The target temperature is a value in the temperature range of 20 ℃ to-30 ℃. Generally, the mesh corresponding to the boundary of the England rock in the finite element mesh model is set to a continuously decreasing temperature at intervals starting at a maximum temperature of 20 ℃ until a minimum temperature of-30 ℃.
The initial boundary conditions are: t is1＝T1(x,y,z,t1)；
Where x, y, z are the coordinates of the bounding grid, t1Is the operating time of the finite element mesh model; t is1＝T1(x, y, z, t) is a temperature function set in the digital image numerical analysis software that controls the temperature of the boundary mesh of the finite element mesh model; t is1The grid node temperature corresponding to the England rock boundary in the set finite element grid model; t is1Is a known function of temperature.
The convection boundary conditions are: q ″ ═ h (T)S-TB) And
Figure BDA0002540053900000201
the room air is the air in the environment in which the England rock slice is located.
Figure BDA0002540053900000202
Is the unit of h (thermal convection coefficient).
Wherein q "is the heat flux density of the Enhan rock model and h is the thermal convection coefficient of the Enhan rock model and the indoor air; t issIs the temperature of the England rock model, i.e. the temperature of the grid corresponding to the rock surface in the finite element grid model, TBIs the temperature of the indoor air;
after the temperature of the grid corresponding to the Enhant rock boundary in the finite element grid model is obtained, the temperature change of the part corresponding to the rock inside the Enhant rock slice inside the finite element grid model is controlled by using a temperature control equation, namely the process that the temperature is changed from the position of the finite element grid model corresponding to the Enhant rock slice boundary to the position of the finite element grid model corresponding to the Enhant rock slice inside the finite element grid model is controlled, and then the distribution condition of the temperature in the finite element grid model is obtained.
And then the specific steps of utilizing the temperature control equation to carry out instantaneous cooling temperature field simulation on the finite element mesh model within the range of 20 ℃ to-30 ℃ comprise:
and controlling the finite element mesh model to change from the initial temperature of the boundary mesh by using the temperature control equation according to the constraint of the convection boundary condition on the temperature change of the boundary mesh until the finite element mesh model completes the simulation of the instantaneous cooling temperature field of 20 ℃ to-30 ℃. It can be seen that the temperature control equation is a temperature function that controls the temperature of the mesh within the finite element mesh model.
The control finite element mesh model and the finite element mesh model containing the initial damage are 162mm long in the X-axis direction and 142mm long in the Y-axis direction. The cycle of 20 ℃ to-30 ℃ was set to 6 hours, and the temperature field change during the cooling process at 20 ℃ to-30 ℃ was analyzed.
And controlling the finite element grid model to change from the initial temperature of the boundary grid until the finite element grid model completes the simulation of the instantaneous cooling temperature field of 20 ℃ to-30 ℃, wherein the temperature change of the grid corresponding to the interior of the Enhan rock slice in the finite element grid model is restrained by utilizing a temperature control equation.
Obtaining a mesoscopic degradation mechanism of the Enhan rock slices in a freeze-thaw cycle according to a temperature change distribution map, firstly performing instantaneous temperature-reducing temperature field simulation by contrasting a finite element grid model to obtain a contrasting temperature change distribution map, then performing instantaneous temperature-reducing temperature field simulation on the finite element grid model to obtain a temperature change distribution map, comparing the contrasting temperature change distribution map and the temperature change distribution map at the same time, and correspondingly comparing the different temperatures of the same position of the Enhan rock slices, and further simulating the influence of initial damage (microcracks, pores and cavities) of the Enhan rock on the Enhan rock in the temperature change process so as to obtain the mesoscopic degradation mechanism of the Enhan rock slices in the freeze-thaw cycle.
Obtaining a mesoscopic deterioration mechanism of the England rock slices in a freeze-thaw cycle according to the plurality of temperature change distribution maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
determining a first corresponding position of the closed interface pixel point in the plurality of temperature change distribution graphs;
and obtaining a mesoscopic deterioration mechanism of the England rock slice in the freeze-thaw cycle according to the relationship between the temperature distribution in the temperature change distribution maps and the first corresponding position.
The first position refers to the position of microcracks, pores and cavities corresponding to the England rock slices in the temperature change distribution map.
The stress field freeze-thaw cycle simulation and the displacement field freeze-thaw cycle simulation both perform 10 times of freeze-thaw simulation on the finite element grid model within the range of-30 ℃ to 20 ℃, wherein the cycle period of one time is 12 hours, and the influence of water-ice phase change on initial damage (microcracks, pores and cavities) in freeze-thaw cycle inside Enhan rock is simulated.
Because the rock is a poor thermal conductor, the surface and the inside of the rock cannot expand and contract simultaneously under the temperature difference change between day and night and seasons, so that tension is induced on the surface layer and the inside of the rock, and cracks parallel to and perpendicular to the surface layer of the rock are easily generated under the repeated action of the tension, so that the rock is broken. Therefore, the stress condition of the initial damage part of the Enhan rock slice in the freeze-thaw cycle can be obtained through the shear stress cloud picture and the tensile stress cloud picture, and further the influence rule of the frost heaving force generated by water-ice phase change on the Enhan rock in the freeze-thaw cycle is obtained, so that the microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle is obtained.
Performing stress field freeze-thaw cycle simulation on the finite element mesh model, wherein the stress field freeze-thaw cycle simulation comprises the following steps:
performing stress field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation; the cycle period of the freeze-thaw cycle simulation is 12 hours;
obtaining a microscopic degradation mechanism of the England rock slice in a freeze-thaw cycle according to the plurality of shear stress cloud pictures and the plurality of tensile stress cloud pictures, wherein the microscopic degradation mechanism comprises the following steps:
respectively obtaining a shear stress cloud picture and a tensile stress cloud picture after the 1 st freeze-thaw cycle simulation, a shear stress cloud picture and a tensile stress cloud picture after the 5 th freeze-thaw cycle simulation, and a shear stress cloud picture and a tensile stress cloud picture after the 10 th freeze-thaw cycle simulation;
according to the shear stress cloud chart and the tensile stress cloud chart which are obtained after the three times of freeze-thaw cycle simulation, the influence of water-ice phase change generated in the England rock on the degradation of the microscopic damage of the rock is obtained, and further the microscopic degradation mechanism of the England rock slice in the freeze-thaw cycle is obtained.
Through a displacement vector diagram, the development conditions of the damage position and the damage size of the initial damage (microcracks, pores and cavities) of the Enhan rock slice in the freeze-thaw cycle can be obtained, and the expansion condition of the initial damage of the Enhan rock slice in the freeze-thaw cycle is further simulated, so that the microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle is obtained.
Performing displacement field freeze-thaw cycle simulation on the finite element mesh model, wherein the displacement field freeze-thaw cycle simulation comprises the following steps:
performing displacement field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
obtaining a mesoscopic deterioration mechanism of the Endothia rock slices in a freeze-thaw cycle according to the plurality of displacement vector maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
respectively obtaining a displacement vector diagram after the 1 st freeze-thaw cycle simulation, a displacement vector diagram after the 5 th freeze-thaw cycle simulation and a displacement vector diagram after the 10 th freeze-thaw cycle simulation;
determining a second corresponding position of the closed interface pixel point in a displacement vector diagram obtained three times after freeze-thaw cycle simulation;
and obtaining the displacement of the degradation of the microscopic damage in the rock according to the second corresponding position in the displacement vector diagram obtained after the three times of freeze-thaw cycle simulation, thereby obtaining the microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle.
The second position refers to the position of the boundary, microcrack, pore and cavity corresponding to the England rock slice in the displacement vector diagram.
The method for obtaining the microscopic degradation mechanism of the Enhan rock in the freeze-thaw cycle process obtains key minerals (quartz and plagioclase feldspar crystals) influencing the mechanical properties of the Enhan rock by analyzing the correlation between the mineral content and mechanical parameters of the Enhan rock, further obtains a region needing attention in the freeze-thaw cycle of the Enhan rock, namely the position of the key mineral (the position of the cementing surface of the quartz and plagioclase feldspar crystals), scans pictures through an electronic microscope of Enhan rock slices to obtain the microscopic structure of the Enhan rock, determines the attention region (corresponding pixel points of the cementing surface of the quartz and plagioclase feldspar crystals in the microscopic structure image) in the microscopic structure, and takes the initial damages such as micro cracks, pores, cavities and the like in the attention region as closed interface points by means of edge detection, particularly takes the micro cracks, micro pores, cavities and the like of the cementing surface of the quartz and placlase feldspar crystals as closed interface points, Initial damages such as pores and cavities are used as closed interface pixel points to obtain a mesoscopic structure image of the England rock with a key concern area (closed interface pixel points), and the image is used as a basic image (initial damage image) for establishing a finite element grid model, so that the finite element grid model not only can clearly show the real mesoscopic structure of the England rock, but also can show the structure position of the mesoscopic structure which is possibly further degraded in the freeze-thaw cycle.
After the finite element grid model is obtained, the instant cooling temperature field simulation is carried out on the finite element grid model, the influence of original damages such as microcracks, pores and cavities in the Enhan rock on the temperature distribution is analyzed, and then the rule of deterioration of the Enhan rock caused by the fact that the temperature distribution is uneven in the freeze thawing of the Enhan rock is obtained. The finite element grid model is subjected to stress field freeze-thaw cycle simulation and displacement field freeze-thaw cycle simulation to obtain a water-ice phase change of water contained in the initial damages such as micro-cracks, pores and cavities in the Enhan rock in the freeze-thaw process, a stress influence rule of the initial damages such as the micro-cracks, the pores and the cavities and a degradation extension rule of the initial damages such as the micro-cracks, the pores and the cavities on the basis of stress, so that a microscopic degradation mechanism of the Enhan rock slices in the freeze-thaw cycle is obtained.
The embodiments in the present specification are described in a progressive or descriptive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
While preferred embodiments of the present application have been described, additional variations and modifications of these embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred embodiment and all such alterations and modifications as fall within the true scope of the embodiments of the application.
It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or terminal that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or terminal. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or terminal that comprises the element.
The method for obtaining the mesoscopic degradation mechanism of the England rock in the freeze-thaw cycle process provided by the application is described in detail above, and the description of the above embodiment is only used to help understand the method and the core idea of the application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.

Claims (10)

1. A method of obtaining a mesoscopic degradation mechanism of imperial rock during a freeze-thaw cycle, the method comprising:
acquiring a microscopic structure image of the England rock slice by using a scanning electron microscope;
performing edge detection on the mesoscopic structure image to obtain a closed interface pixel point in the mesoscopic structure image;
connecting the closed interface pixel points in the microscopic structure image to obtain an initial damage distribution image of the England rock slice;
establishing a finite element mesh model according to the initial damage distribution image;
carrying out instantaneous cooling temperature field simulation on the finite element mesh model to generate a plurality of temperature change distribution maps of the finite element mesh model in a target temperature range;
performing stress field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of shear stress cloud pictures and a plurality of tensile stress cloud pictures in the stress field freeze-thaw cycle simulation;
performing displacement field freeze-thaw cycle simulation on the finite element mesh model to generate a plurality of displacement vector diagrams in the displacement field freeze-thaw cycle simulation;
and respectively obtaining a mesoscopic degradation mechanism of the Enhan rock slice in a freeze-thaw cycle according to the temperature change distribution maps, the shear stress cloud maps, the tensile stress cloud maps and the displacement vector maps.
2. The method of claim 1, wherein performing edge detection on the mesoscopic structure image to obtain a closed interface pixel point in the mesoscopic structure image comprises:
running a Canny operator by using MATLAB to obtain a binary image of the mesoscopic structure image;
connecting first pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the first pixel points are pixel points corresponding to holes in the England rock slice;
connecting second pixel points with the gray scale of 1 in the binary image to obtain pixel points of the closed interface; the second pixel points are pixel points corresponding to micro cracks in the Enhan rock slice;
connecting a third pixel point with the gray level of 1 in the binary image to obtain a pixel point of the closed interface; and the third pixel point is a pixel point corresponding to a pore in the Enhan rock slice.
3. The method of claim 2, further comprising:
measuring the chemical element content of the Enhan rock slice by using a scanning electron microscope and an X-ray energy spectrometer to obtain the mass percentage of various chemical elements contained in the Enhan rock slice;
obtaining the mineral contents of various mineral components contained in the Enhan rock slice according to the mass percentages of various chemical elements contained in the Enhan rock slice;
carrying out correlation and partial correlation analysis on the mineral content of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice, and obtaining the corresponding relation between the correlation and partial correlation of each mineral component in the Enhan rock slice and the mechanical parameters of the Enhan rock slice;
determining target mineral components influencing the mechanical properties of the Enhan rock slices according to the partial correlation corresponding relation and the correlation analysis;
connecting the second pixel points with the gray scale of 1 in the binary image to obtain the pixel points of the closed interface, including:
determining a cementing surface pixel point of a cementing surface of a crystal structure corresponding to the target mineral component in the binary image;
and determining pixel points corresponding to the crystal cracks in the cementing surface pixel points as the closed interface pixel points.
4. The method of claim 1, wherein building a finite element mesh model from the initial lesion distribution image comprises:
converting the connected closed interface pixel points in the initial damage distribution image into a plurality of closed polygons to form a vector diagram of the initial damage of the Enhan rock slice;
screening the plurality of closed polygons, and removing interference data in the vector diagram of the initial damage;
and importing the vector diagram of the initial damage after the interference data is removed into finite element analysis software, and establishing the finite element mesh model.
5. The method of claim 1, further comprising:
establishing a comparison finite element grid model of the nondestructive Enhan rock;
carrying out instantaneous temperature field simulation on the comparison finite element mesh model to generate a plurality of comparison temperature change distribution maps of the comparison finite element mesh model in the target temperature range;
obtaining a mesoscopic deterioration mechanism of the England rock slices in a freeze-thaw cycle according to the plurality of temperature change distribution maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
and comparing the plurality of temperature change distribution maps with the plurality of control temperature change distribution maps to obtain the mesoscopic degradation mechanism of the England rock slice in the freeze-thaw cycle.
6. The method of claim 1, further comprising:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
carrying out instantaneous cooling temperature field simulation on the finite element mesh model, wherein the simulation comprises the following steps:
performing instantaneous cooling temperature field simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
obtaining a mesoscopic deterioration mechanism of the England rock slices in a freeze-thaw cycle according to the plurality of temperature change distribution maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
determining a first corresponding position of the closed interface pixel point in the plurality of temperature change distribution graphs;
and obtaining a mesoscopic deterioration mechanism of the England rock slice in the freeze-thaw cycle according to the relationship between the temperature distribution in the temperature change distribution maps and the first corresponding position.
7. The method of claim 1, further comprising:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
performing stress field freeze-thaw cycle simulation on the finite element mesh model, wherein the stress field freeze-thaw cycle simulation comprises the following steps:
performing stress field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation; the cycle period of the freeze-thaw cycle simulation is 12 hours;
obtaining a microscopic degradation mechanism of the England rock slice in a freeze-thaw cycle according to the plurality of shear stress cloud pictures and the plurality of tensile stress cloud pictures, wherein the microscopic degradation mechanism comprises the following steps:
respectively obtaining a shear stress cloud picture and a tensile stress cloud picture after the 1 st freeze-thaw cycle simulation, a shear stress cloud picture and a tensile stress cloud picture after the 5 th freeze-thaw cycle simulation, and a shear stress cloud picture and a tensile stress cloud picture after the 10 th freeze-thaw cycle simulation;
according to the shear stress cloud chart and the tensile stress cloud chart which are obtained after the three times of freeze-thaw cycle simulation, the influence of water-ice phase change generated in the rock on the microscopic damage degradation of the rock is obtained, and further the microscopic degradation mechanism of the England rock slice in the freeze-thaw cycle is obtained.
8. The method of claim 1, further comprising:
setting a temperature control equation according to the rule of heat conduction of the Enhan rock system and air in the environment where the Enhan rock is located;
performing displacement field freeze-thaw cycle simulation on the finite element mesh model, wherein the displacement field freeze-thaw cycle simulation comprises the following steps:
performing displacement field freeze-thaw cycle simulation on the finite element grid model within the range of 20 ℃ to-30 ℃ by using the temperature control equation;
obtaining a mesoscopic deterioration mechanism of the Endothia rock slices in a freeze-thaw cycle according to the plurality of displacement vector maps, wherein the mesoscopic deterioration mechanism comprises the following steps:
respectively obtaining a displacement vector diagram after the 1 st freeze-thaw cycle simulation, a displacement vector diagram after the 5 th freeze-thaw cycle simulation and a displacement vector diagram after the 10 th freeze-thaw cycle simulation;
determining a second corresponding position of the closed interface pixel point in a displacement vector diagram obtained three times after freeze-thaw cycle simulation;
and obtaining the displacement of the degradation of the microscopic damage in the rock according to the second corresponding position in the displacement vector diagram obtained after the three times of freeze-thaw cycle simulation, thereby obtaining the microscopic degradation mechanism of the Enhan rock slice in the freeze-thaw cycle.
9. The method of claim 6, further comprising:
setting an initial boundary condition and a convection boundary condition;
determining a surface boundary in the finite element network model corresponding to the contact of the England rock slice and indoor air;
determining an initial temperature of the surface boundary using the initial boundary condition;
constraining a temperature change of the surface boundary using the convection boundary condition;
and utilizing the temperature control equation to perform instantaneous cooling temperature field simulation on the finite element network model in the range of 20 ℃ to-30 ℃, wherein the simulation comprises the following steps:
and controlling the finite element network model to change from the initial temperature of the surface boundary by using the temperature control equation according to the constraint of the convection boundary condition on the temperature change of the surface boundary until the finite element network model completes the simulation of the instantaneous cooling temperature field of 20 ℃ to-30 ℃.
10. The method of claim 9, wherein the initial boundary conditions are: t is1＝T1(x,y,z,t1) (ii) a Where x, y, z are the coordinates of the bounding grid, t1Is the operating time of the finite element mesh model;
the convection boundary conditions are: q ″ ═ h (T)S-TB) And
Figure FDA0002540053890000051
wherein q "is the heat flux density of the Enhan rock model and h is the thermal convection coefficient of the Enhan rock model and the indoor air; t issIs the temperature, T, of the England rock modelBIs the temperature of the indoor air;
the temperature control equation is
Figure FDA0002540053890000052
Figure FDA0002540053890000053
Wherein, CrIs the specific heat, r, of the England rock slicerIs said Ying anDensity of rock section, krIs the thermal conductivity of the England rock slice; k is a radical ofiIs the thermal conductivity of ice; ciIs the specific heat of ice; r isiIs the density of ice.
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