A method for predicting mechanical properties of concrete specimens considering the heterogeneity of concrete
Through computed tomography and near-field dynamics methods, a detailed detailed model of concrete specimens was established, which solved the problem of insufficient prediction accuracy of concrete mechanical properties in the prior art, and achieved higher precision and adaptable mechanical properties prediction.
Patent Information
- Application Number
- CN202411817824.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-04-04
AI Technical Summary
The prior art is difficult to accurately predict the mechanical properties of concrete specimens, especially when taking into account the heterogeneous properties of concrete, the traditional simplified aggregate shape model cannot reflect the real structure, resulting in insufficient accuracy of the simulation results.
The two-dimensional structural section of the concrete specimen was obtained through computed tomography, binarization was performed, and the mortar and aggregate area were encoded, a meticulous calculation model was established, and the near-field dynamics method was used to simulate the failure process under uniaxial compression conditions, and mechanical properties were predicted.
It improves the accuracy and adaptability of the model, can more accurately reflect the heterogeneous properties of concrete, and enhances the accuracy of mechanical properties prediction.
Smart Images
Figure BDA0005182310560000032 
Figure BDA0005182310560000033 
Figure BDA0005182310560000034
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of material mechanics, and in particular relates to a method for predicting the mechanical properties of concrete specimens taking into account the heterogeneous characteristics of concrete. Background Art
[0002] As a heterogeneous multiphase composite material composed of aggregate, mortar, pores and microcracks, concrete has obvious multi-scale characteristics, and its macroscopic mechanical properties and behaviors are affected by the mesostructure. Previous studies have shown that the shape characteristics of aggregates have a significant impact on the mechanical properties and failure morphology of concrete. Therefore, how to accurately construct the concrete mesostructure is of great significance for predicting mechanical properties.
[0003] At present, the commonly used mesoscopic models often simplify the shape of aggregates into simple geometric shapes such as circles, ellipses, polygons, etc., and compile simplified aggregate random placement programs to construct random aggregate models. Although it has advantages in model construction and numerical simulation efficiency, the shapes of aggregates in real concrete structures are more complex and diverse. The simplified aggregate shapes cannot reflect the characteristics of concrete heterogeneity, which obviously affects the accuracy of simulation results. Therefore, with the continuous improvement of computer computing power, simple random aggregate models can no longer meet computing needs.
[0004] The prediction of the mechanical properties of concrete materials requires the description of their failure process under external loads, which involves the entire process of the initiation, expansion, and destruction of microcracks inside the structure. Traditional numerical simulation methods such as the finite element method are based on the theory of classical continuum mechanics. The spatial derivatives of the variables in their partial differential control equations have singularities at discontinuities such as cracks. Therefore, there is a bottleneck in the analysis of discontinuous deformation problems. It is often necessary to separate the control equations and discontinuity conditions, which makes the solution difficult. The introduction of the integral peridynamic theory provides a new solution for the analysis of discontinuous deformation and destruction problems of solids. Peridynamics can avoid the singularities of traditional local differential equations when solving discontinuous problems, and has advantages in simulating discontinuous deformation problems such as structural damage. Summary of the invention
[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for predicting the mechanical properties of concrete specimens taking into account the heterogeneous characteristics of concrete.
[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:
[0007] The present invention provides a method for predicting mechanical properties of concrete specimens taking into account the heterogeneous characteristics of concrete, comprising the following steps:
[0008] S1. Obtain a two-dimensional structural cross-section of a concrete specimen by computer tomography, perform binarization on the obtained two-dimensional cross-section, encode the mortar area and the aggregate area in the binarized two-dimensional structural cross-section using numbers, and mark the two-dimensional spatial coordinates;
[0009] S2, determining parameter information of the concrete specimen, and discretizing based on the parameter information to obtain a material point set;
[0010] S3. Based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points of each material component in the material point set are assigned corresponding material properties, and a mesoscopic calculation model considering the heterogeneous characteristics of concrete is established;
[0011] S4. The peridynamic method is used to simulate the failure process of the concrete mesoscopic model under uniaxial compression conditions, and its mechanical properties are predicted based on the overall stress-strain results.
[0012] Furthermore, in step S1, in the two-dimensional structural profile after binarization, the mortar area is encoded as 1, and the aggregate area is encoded as 0. Each pixel point in the two-dimensional structural profile is scanned as a two-dimensional space coordinate point, and the two-dimensional space coordinates of all mortar areas and aggregate areas are marked.
[0013] Furthermore, in step S2, the parameter information includes geometric dimensions and grid sizes of the concrete specimen, and the concrete specimen is discretized into a peridynamic lattice structure according to the geometric dimensions and grid sizes of the concrete specimen.
[0014] Furthermore, in step S3, based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points in the material point set are divided into mortar material points and aggregate material points in turn, and corresponding material properties are assigned to them, so as to establish a microscopic calculation model considering the heterogeneous characteristics of concrete.
[0015] Further, the step S4 includes:
[0016] S4.1. Set the initial conditions and boundary conditions of the model and initialize the calculation model;
[0017] S4.2, using an iterative method to solve the material point displacement information of each loading step, and update the force field and displacement field of the model;
[0018] S4.3. Based on the displacement field results, the critical elongation criterion is used to determine the fracture condition of the bonds between material points and calculate the damage results of the material points;
[0019] S4.4. Based on the force field and displacement field results obtained at each loading step, draw the stress-strain curve of the specified area, and predict the mechanical properties based on its stress-strain results.
[0020] Furthermore, in S4.1, the initialization parameters of the model are the near-field range δ, the critical elongation s0, the material point spacing Δx, the time step Δt, and the macroscopic physical parameters such as the density ρ of the mortar and aggregate, the Poisson's ratio ν, and the mixed elastic modulus E. The model uses displacement boundary conditions, and the displacement, velocity, etc. are directly applied to a certain volume of material points.
[0021] Furthermore, in S4.2, the method of using the iteration method to solve the material point displacement information of each loading step is as follows:
[0022] Assuming that at a certain time t, there is an interaction force f between any material point x in the domain and any other material point x′ within a certain size range with respect to the displacement field, then the peridynamic motion equation of the material point is:
[0023]
[0024] Where ρ is the material density, u is the material point displacement, b is the body density, H x is the near field range, dV x′ represents the volume element at the material point x′;
[0025] For a material point x i , discretize the equation of motion (1) into the following form:
[0026]
[0027] Where N represents the material point x i The number of material points within the near field, V j Represents the material point x j At the material point x i The volume occupied by the near field, V j =|Δx| 2 , |Δx| is the spacing of material points after discretization, and K is the stiffness matrix of material points;
[0028] The central difference format is used for time discretization, and the displacement increment and displacement in the period t→t+Δt are obtained as follows:
[0029]
[0030] Here, Δt is the time step.
[0031] Furthermore, in S4.3, the method of using the critical elongation criterion to judge the fracture state of the bond between material points is as follows: a scalar function μ with history dependence is used to describe the fracture behavior of the material at t′:
[0032]
[0033] In the formula, s is the elongation, which indicates the degree of relative displacement between material points. Where ξ is the relative position vector, η is the relative displacement vector, and s0 is the critical elongation;
[0034] Based on the failure criterion of critical elongation, the damage of a material point x inside the material at time t is obtained as:
[0035]
[0036] In the formula, Indicates that the material is not damaged. Indicates complete material damage.
[0037] Beneficial Effects
[0038] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:
[0039] (1) The model is constructed with high accuracy. The present invention uses computer tomography to obtain a two-dimensional structural cross-sectional image of a concrete specimen. Through binarization processing, the mortar area and the aggregate area are respectively coded with numbers, so that a two-dimensional concrete micro-geometric model based on the real aggregate morphology can be efficiently and accurately established.
[0040] (2) Strong adaptability. The present invention adopts the peridynamic method to simulate the destruction process of the concrete mesoscopic model under uniaxial compression conditions. It can adjust the loading quantity and loading form of the boundary particles to ensure that the simulation process is closer to the actual situation and enhance the accuracy of the model in predicting mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Figure 1 It is an overall flow chart of the concrete specimen mechanical property prediction method considering the concrete heterogeneity characteristics of the present invention;
[0042] Figure 2 It is a flow chart of the destruction process of a concrete mesoscopic model under uniaxial compression conditions simulated by the peridynamic method in the present invention;
[0043] Figure 3 is a flow chart of peridynamic modeling and solution of the present invention;
[0044] Figure 4 is a two-dimensional structural section of a concrete specimen obtained by computer tomography in an embodiment of the present invention;
[0045] Figure 5 In the embodiment of the present invention, based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points of each material component in the material point set are assigned corresponding material properties, and a mesoscopic calculation model considering the heterogeneous characteristics of concrete is established;
[0046] Figure 6is a diagram of the destruction process of a concrete mesoscopic model under uniaxial compression conditions simulated by a peridynamic method in an embodiment of the present invention;
[0047] Figure 7 It is the stress-strain curve of the concrete specimen predicted by the peridynamic method in the embodiment of the present invention. DETAILED DESCRIPTION
[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0049] Example 1
[0050] This embodiment provides a method for predicting the mechanical properties of concrete specimens taking into account the heterogeneous characteristics of concrete. Taking a concrete cube specimen with a side length of 150 mm as an example, the mesoscopic model considering the heterogeneous characteristics of concrete and the mechanical properties prediction method provided by the present invention are used to perform peridynamic modeling and analysis. The peridynamic modeling solution process is as follows: Figure 3 For the specific execution process, see Figure 1 As shown, Figure 1 The figure is a flow chart of the concrete mesoscopic model and the mechanical prediction simulation method thereof of the present invention, and the steps of the method include:
[0051] Step 1: Obtain the two-dimensional structural profile of the concrete specimen by computer tomography ( Figure 4 ), the obtained two-dimensional cross-section image is binarized, and in the binarized two-dimensional structural cross-section image, the mortar area and the aggregate area are respectively encoded with numbers, and the two-dimensional spatial coordinates are marked.
[0052] In the two-dimensional structural profile after binarization, the mortar area is coded as 1 and the aggregate area is coded as 0. Each pixel point in the two-dimensional structural profile is scanned as a two-dimensional space coordinate point, and the two-dimensional space coordinates of all mortar areas and aggregate areas are marked.
[0053] Step 2: Determine the parameter information of the concrete specimen, and discretize it based on the parameter information to obtain a set of material points.
[0054] The parameter information includes the geometrical size and mesh size of the concrete specimen. According to the geometrical size and mesh size of the concrete specimen, the concrete specimen is discretized into a lattice structure of peridynamics.
[0055] Step 3: Based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points of each material component in the material point set are assigned corresponding material properties, and a microscopic calculation model that considers the heterogeneous characteristics of concrete is established.
[0056] Based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points in the material point set are divided into mortar material points and aggregate material points in turn, and their corresponding material properties are assigned, such as Figure 5 As shown, a microscopic calculation model considering the heterogeneous characteristics of concrete is established.
[0057] Step 4: Use the peridynamic method to simulate the failure process of the concrete mesoscopic model under uniaxial compression ( Figure 2 ), and predict its mechanical properties based on the overall stress-strain results. The specific method is:
[0058] S1. Set the initial conditions and boundary conditions of the model and calculate the model initialization;
[0059] The initialization parameters of the model are the near-field range δ, the critical elongation s0, the material point spacing Δx, the time step Δt, and macroscopic physical parameters such as the density ρ of mortar and aggregate, Poisson’s ratio ν, and the elastic modulus E. The model uses displacement boundary conditions, and the displacement and velocity are directly applied to the material points of a certain volume.
[0060] S2, using the iterative method to solve the material point displacement information of each loading step, and update the force field and displacement field of the model;
[0061] The method of using the iteration method to solve the material point displacement information of each loading step is as follows:
[0062] Assuming that at a certain time t, there is an interaction force f between any material point x in the domain and any other material point x′ within a certain size range with respect to the displacement field, then the peridynamic motion equation of the material point is:
[0063]
[0064] Where ρ is the material density, u is the material point displacement, b is the body density, H x is the near field range, dV x′ represents the volume element at the material point x′;
[0065] For a material point x i , discretize the equation of motion (1) into the following form:
[0066]
[0067] Where N represents the material point x i The number of material points within the near field, V jRepresents the material point x j At the material point x i The volume occupied by the near field, V j =|Δx| 2 , |Δx| is the spacing of material points after discretization, and K is the stiffness matrix of material points;
[0068] The central difference format is used for time discretization, and the displacement increment and displacement in the period t→t+Δt are obtained as follows:
[0069]
[0070] Here, Δt is the time step.
[0071] S3. According to the displacement field results, the critical elongation criterion is used to judge the fracture condition of the bond between the material points and calculate the damage results of the material points;
[0072] The method of using the critical elongation criterion to judge the fracture state of the bond between material points is to use a scalar function μ with history dependence to describe the fracture behavior of the material at t′:
[0073]
[0074] In the formula, s is the elongation, which indicates the degree of relative displacement between material points. Where ξ is the relative position vector, η is the relative displacement vector, and s0 is the critical elongation;
[0075] Based on the failure criterion of critical elongation, the damage of a material point x inside the material at time t is obtained as:
[0076]
[0077] In the formula, Indicates that the material is not damaged. Indicates complete material damage.
[0078] according to Figure 3 The flowchart of the peridynamic method for simulating the failure process of the concrete mesoscopic model under uniaxial compression is shown in FIG. Figure 6 shown.
[0079] S4. According to the force field and displacement field results obtained at each loading step, the stress-strain curve of the specified area is drawn, and the mechanical properties are predicted based on the stress-strain results. The model stress-strain curve is drawn as follows: Figure 7 shown.
[0080] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.
Claims
1. A method for predicting the mechanical properties of concrete specimens taking into account the heterogeneous characteristics of concrete, characterized in that: The following steps are involved: S1. Obtain a two-dimensional structural cross-section of a concrete specimen by computer tomography, perform binarization on the obtained two-dimensional cross-section, encode the mortar area and the aggregate area in the binarized two-dimensional structural cross-section using numbers, and mark the two-dimensional spatial coordinates; S2, determining parameter information of the concrete specimen, and discretizing based on the parameter information to obtain a material point set; S3. Based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points of each material component in the material point set are assigned corresponding material properties, and a mesoscopic calculation model considering the heterogeneous characteristics of concrete is established; S4. The peridynamic method is used to simulate the failure process of the concrete mesoscopic model under uniaxial compression conditions, and its mechanical properties are predicted based on the overall stress-strain results.
2. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In step S1, in the two-dimensional structural cross-section image after binarization, the mortar area is coded as 1, and the aggregate area is coded as 0. Each pixel point in the two-dimensional structural cross-section image is scanned as a two-dimensional space coordinate point, and the two-dimensional space coordinates of all mortar areas and aggregate areas are marked.
3. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In the step S2, the parameter information includes the geometrical dimensions and the mesh size of the concrete specimen. According to the geometrical dimensions and the mesh size of the concrete specimen, the concrete specimen is discretized into a lattice structure of peridynamics.
4. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In step S3, based on the two-dimensional spatial coordinates of the mortar area and the aggregate area, the material points in the material point set are divided into mortar material points and aggregate material points in turn, and corresponding material properties are assigned to them, so as to establish a microscopic calculation model considering the heterogeneous characteristics of concrete.
5. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: The step S4 comprises: S4.
1. Set the initial conditions and boundary conditions of the model and initialize the calculation model; S4.2, using an iterative method to solve the material point displacement information of each loading step, and update the force field and displacement field of the model; S4.
3. Based on the displacement field results, the critical elongation criterion is used to determine the fracture condition of the bonds between material points and calculate the damage results of the material points; S4.
4. Based on the force field and displacement field results obtained at each loading step, draw the stress-strain curve of the specified area, and predict the mechanical properties based on its stress-strain results.
6. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In S4.1, the initialization parameters of the model are near-field range, critical elongation, material point spacing, time step, density of mortar and aggregate, Poisson's ratio and elastic modulus; the model uses displacement boundary conditions, and displacement and velocity are directly applied to a certain volume of material points.
7. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In S4.2, the method of using the iteration method to solve the material point displacement information of each loading step is as follows: Assuming that at a certain time t, there is an interaction force f between any material point x in the domain and any other material point x′ within a certain size range with respect to the displacement field, then the peridynamic motion equation of the material point is: Where ρ is the material density, u is the material point displacement, b is the body density, H x is the near field range, dV x′ represents the volume element at the material point x′; For a material point x i , discretize the equation of motion (1) into the following form: Where N represents the material point x i The number of material points within the near field, V j Represents the material point x j At the material point x i The volume occupied by the near field, V j =|Δx 2 , |Δx| is the spacing of material points after discretization, and K is the stiffness matrix of material points; The central difference format is used for time discretization, and the displacement increment and displacement in the period t→t+Δt are obtained as follows: Here, Δt is the time step.
8. The method for predicting mechanical properties of concrete specimens considering the heterogeneous characteristics of concrete according to claim 1, characterized in that: In S4.3, the method for judging the fracture condition of the bond between material points using the critical elongation criterion is as follows: The fracture behavior of the material at time t′ is described by a history-dependent scalar function μ: In the formula, s is the elongation, which indicates the degree of relative displacement between material points. Where ξ is the relative position vector, η is the relative displacement vector, and s0 is the critical elongation; Based on the failure criterion of critical elongation, the damage of a material point x inside the material at time t is obtained as: In the formula, Indicates that the material is not damaged. Indicates complete material damage.