A simulation method for loading reversal behavior of granular materials based on stress trial

Abstract

The present application relates to a kind of particle material loading reversal behavior simulation method based on stress probe, comprising: the evolution of strain response envelope in loading reversal process is captured;Plastic modulus, plastic flow direction and shear dilatancy coefficient are derived through response envelope;Boundary surface framework is introduced, and the constitutive model under loading reversal condition is constructed;Define the projection center that can migrate and mapping rule, link current stress with boundary surface, and at least one projection center repositioning strategy is used;The response of different projection center repositioning strategies is verified, the performance of the model corresponding to different projection center repositioning strategies is compared, and the prediction effect of the model corresponding to different projection center repositioning strategies is evaluated.The beneficial effects of the present application are: the present application can effectively capture the strain response of particle sample under different direction stress increment through discrete element stress probe test, and accurately simulate the mechanical behavior in loading reversal process.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and more specifically, to a method for simulating the loading reversal behavior of granular materials based on stress testing. Background Technology

[0002] In practical geotechnical engineering, soil elements often undergo complex stress paths involving loading reversal; however, existing technologies have significant shortcomings in several aspects. At the experimental equipment level, traditional experimental studies are often limited by laboratory equipment, making it difficult to accurately capture the mechanical behavior of granular materials during loading reversal. Furthermore, the initial structure of granular materials (such as void ratio and particle arrangement) significantly affects mechanical behavior, but artificially prepared samples cannot guarantee microstructural consistency, leading to discrete experimental results and severely hindering the study and understanding of the mechanical behavior of granular materials.

[0003] Existing constitutive models and numerical simulation techniques also have shortcomings. Constitutive models are mostly based on macroscopic phenomenological assumptions, neglecting microscopic mechanisms and failing to directly link particle-scale contact force chain evolution with macroscopic mechanical responses, thus providing insufficient explanation for the physical mechanisms of loading reversal behavior. Most models also lack direction dependence, assuming the plastic flow direction is consistent with the loading direction, failing to capture the flow direction shift caused by anisotropy due to particle rearrangement during actual loading reversal. Furthermore, the expressions for shear dilatation coefficient and plastic modulus largely rely on empirical formulas, failing to fully couple state parameters (such as void ratio and critical state) with real-time changes in stress paths. In numerical simulation, high-precision discrete element method (DEM) simulations require a large number of particles and fine time steps, resulting in extremely high computational costs and making them difficult to apply to multi-condition analysis at the practical engineering scale. Therefore, to address the above problems, a simulation method for the loading reversal behavior of granular materials based on stress testing is proposed. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for simulating the loading reversal behavior of granular materials based on stress testing.

[0005] Firstly, a method for simulating the loading reversal behavior of granular materials based on stress testing is provided, including:

[0006] S1. By conducting discrete element stress detection tests on specimens at different loading and unloading stages, the evolution of the strain response envelope during the loading reversal process is captured; the plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope.

[0007] S2. Introduce a boundary surface framework to construct a constitutive model under loading inversion conditions;

[0008] S3. Define transferable projection centers and mapping rules, associate the current stress with the boundary surface, and adopt at least one projection center repositioning strategy.

[0009] S4. Verify the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

[0010] Preferably, S1 includes:

[0011] S101. Apply multiple stress increments of equal magnitude but different directions to obtain the incremental stress-strain response of the particulate material;

[0012] S102. Conduct trial tests to obtain the total strain increment and elastic strain increment; the plastic strain increment is the difference between the total strain increment and the elastic strain increment.

[0013] S103. Derive the plastic modulus, plastic flow direction, and shear dilatation coefficient from the response envelope.

[0014] Preferably, in S101, the components of the stress increment are expressed as:

[0015] dσ 11 =dσ r cos(α dσ );

[0016] in, Indicates the magnitude of the stress increment; α dσ Indicates the direction of stress testing.

[0017] Preferably, in S103, the plastic strain increment is expressed as:

[0018]

[0019] Among them, dε p For plastic strain increment tensors, it represents the irreversible strain changes that occur in a material during loading; To load the activation condition, use Macauley brackets to indicate: ① If dL > 0, then =dL, plastic deformation occurs; ② If dL≤0, then =0, only elastic deformation; χ represents the direction of plastic flow, including the biased part n and the volumetric part. I is a second-order unit tensor, representing the isotropic nature of the volume change; dL = ||de p || is the loading exponent, n = de p / ||de p || is the unit norm partial tensor, specifying the partial plastic strain increment de. p Size and orientation; It is the shear dilatation coefficient.

[0020] Preferably, S2 includes:

[0021] S201. Introduce a boundary surface frame, wherein the boundary surface frame adopts a tapered boundary surface;

[0022] S202, Construct an expression for loading and reversing the direction of plastic flow;

[0023] S203, Construct the loading inversion plastic modulus K p The expression;

[0024] S204. Construct an expression for the loading inverse shear dilatation coefficient D.

[0025] Preferably, in S201, the expression for the boundary surface frame is:

[0026]

[0027] in, and These are the image stresses on the boundary surface F. Two invariants; H is a hardening parameter that defines the magnitude of F, set to the maximum value of R / g(θ) experienced by the material;

[0028] In S202, the expression for reversing the plastic flow direction is:

[0029]

[0030] Where F is the boundary surface function, representing the plastic response boundary of the material in stress space; r is the stress ratio tensor; is the gradient of the boundary surface with respect to the stress ratio; I is the second-order unit tensor used to represent the direction of isotropic volume change; m represents the loading direction; n represents the plastic flow direction, m = n, the loading direction is consistent with the plastic flow direction.

[0031] Preferably, in S203, the inverted plastic modulus K is applied. p The expression is:

[0032]

[0033] h = [h1exp(-h2e)](p / pa) β

[0034]

[0035] Where h1, h2, n, α, β, and λ are model parameters, R is the stress ratio invariant, α is the stress ratio power parameter used to adjust the influence of R on the plastic modulus, h is the hardening function, e is the void ratio, p is the effective stress, and p a Atm, M c The critical stress ratio, ρ and These represent the distances from the current stress and the image stress to the projection center, respectively. For interpolation function, Let θ be the Lode angle and c be the material constant.

[0036] In S204, the expression for the loading inverse shear dilatation coefficient D is:

[0037]

[0038] Where m is the state parameter coupling coefficient, which adjusts the effect of ψ; d0 is the basic dilatation coefficient; λ is the decay exponent; M c The critical stress ratio; ρ and These represent the distances from the current stress and the image stress to the projection center, respectively. It is an interpolation function; and This indicates stress based on the current image rather than calculated stress; ψ is a state parameter, ψ = ee c e c =e-[e Γ -λ c (p / pa) ξ ], ψ represents the parameter e Γ ,λ c The critical void ratio composed of ξ; It is an interpolation function.

[0039] Preferably, in S3, the projection center repositioning strategy includes an immediate projection center repositioning strategy, an elastic range projection center adjustment strategy based on yield surface constraints, and a dynamic adjustment strategy for the projection center as the stress ratio evolves.

[0040] In a second aspect, a stress-testing-based simulation system for reversing loading behavior of granular materials is provided for performing any of the methods described in the first aspect, including:

[0041] The experimental module is used to capture the evolution of the strain response envelope during loading reversal by performing discrete element stress probing tests on specimens at different loading and unloading stages; the plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope.

[0042] The building block is used to introduce the boundary surface framework and construct the constitutive model under the loading inversion condition;

[0043] The definition module is used to define transferable projection centers and mapping rules, associate the current stress with the boundary surface, and adopt at least one projection center repositioning strategy.

[0044] The validation module is used to validate the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

[0045] Thirdly, a computer storage medium is provided, wherein a computer program is stored therein; when the computer program is run on a computer, the computer causes the computer to perform any of the methods described in the first aspect.

[0046] The beneficial effects of this invention are:

[0047] 1. This invention, through discrete element stress testing, can effectively capture the strain response of particle samples under stress increments in different directions and accurately simulate the mechanical behavior during loading reversal.

[0048] 2. This invention proposes three models (A, B, C) to simulate the mechanical behavior of particle samples under loading reversal conditions, providing a powerful tool for the study of the mechanical behavior of granular materials in geotechnical engineering. Attached Figure Description

[0049] Figure 1 Typical strain response envelope diagram provided by the present invention;

[0050] Figure 2 The boundary surface and mapping rules provided for this invention;

[0051] Figure 3 Three strategies for repositioning the projection center are provided by this invention;

[0052] Figure 4 A comparison diagram of the experimental results under different stage conditions and the strain response envelope prediction results of Model A provided for this invention;

[0053] Figure 5 A comparison chart of the test results of plastic modulus and shear dilatation coefficient during the loading and unloading phases of the present invention, and the prediction results of model B and model C.

[0054] Figure 6 A comparison chart of the experimental data of the loading reversal stage trial provided by the present invention with the predictions of model B and model C. Detailed Implementation

[0055] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0056] Example 1:

[0057] As one embodiment, the present invention provides a method for simulating the loading reversal behavior of granular materials (such as sand) based on stress testing, comprising:

[0058] S1. By conducting discrete element stress detection tests on specimens at different loading and unloading stages, the evolution of the strain response envelope during the loading reversal process is captured; the plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope.

[0059] S1 includes:

[0060] S101. Apply multiple stress increments of equal magnitude but different directions to obtain the incremental stress-strain response of the granular material. In S101, the components of the stress increment are represented as:

[0061] dσ 11 =dσ r cos(α dσ );

[0062] in, Indicates the magnitude of the stress increment; α dσ Indicates the direction of stress testing.

[0063] S102, at μ = 0.5 and μ = 1 × 10 9 Experiments were conducted on two sets of samples to obtain the total strain increment and the elastic strain increment; the plastic strain increment is the difference between the total strain increment and the elastic strain increment, i.e., dε. p =dε-dε e .

[0064] S103. The plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope, which are the components of the constitutive model.

[0065] In S103, the plastic strain increment is expressed as:

[0066]

[0067] Where, dε p For plastic strain increment tensors, it represents the irreversible strain changes that occur in a material during loading; To load the activation condition, use Macauley brackets to indicate: ① If dL > 0, then =dL, plastic deformation occurs; ② If dL≤0, then =0, only elastic deformation; χ represents the direction of plastic flow, including the biased part n and the volumetric part. I is a second-order unit tensor, representing the isotropic nature of the volume change; dL = | |de p | | is the loading index, n = de p / ||de p | | is the unit norm partial tensor, specifying the partial plastic strain increment de. p Size and orientation; It is the shear dilatation coefficient.

[0068] Combination Figure 1 From OA in (b), it can be seen that the plastic strain increment formula is calculated according to the following formulas for the biased plastic flow direction n and the shear dilatation coefficient D:

[0069]

[0070] In the formula, dε OA The strain increment specified by OA, de OA It is its biased part.

[0071] The loading exponent dL is calculated based on the consistency condition as follows:

[0072] dω+K p dL = 0

[0073] In the formula, f is the yield surface. K represents the normal direction of the yield surface at σ; p It is the plastic modulus. According to this formula, when K p When the magnitude of dσ is known, and the direction of the stress increment dσ is... When the stress is constant, dL reaches its maximum value, and the stress test direction is perpendicular to the normal vector of the yield surface. Therefore, the normal direction of the yield surface can be defined based on the stress test direction, such as... Figure 1 The vector OA' in (a) is:

[0074]

[0075] Where, dσ OA' This represents the stress increment specified by the vector OA'.

[0076] Furthermore, based on the formula for calculating the loading exponent dL using the consistency condition, the plastic modulus K... p Represented as:

[0077]

[0078] Using the above formulas, we can obtain the plastic flow direction, plastic modulus, and shear dilatation coefficient of the sand sample under loading reversal conditions based on the response envelope.

[0079] S2. Introduce the boundary surface framework and construct the constitutive model under the loading inversion condition.

[0080] S2 includes:

[0081] S201. Introduce a boundary surface frame, wherein the boundary surface frame adopts a conical boundary surface.

[0082] In S201, the expression for the boundary surface frame is:

[0083]

[0084] in, and These are the image stresses on the boundary surface F. Two invariants; H is a hardening parameter that defines the magnitude of F, set to the maximum value of R / g(θ) experienced by the material.

[0085] S202. Construct an expression for loading and reversing the direction of plastic flow.

[0086] In S202, the expression for reversing the plastic flow direction is:

[0087]

[0088] Where F is the boundary surface function, representing the plastic response boundary of the material in stress space; r is the stress ratio tensor; is the gradient of the boundary surface with respect to the stress ratio; I is the second-order unit tensor used to represent the direction of isotropic volume change; m represents the loading direction; n represents the plastic flow direction, m = n, the loading direction is consistent with the plastic flow direction.

[0089] S203, Construct the loading inversion plastic modulus K p The expression.

[0090] In S203, the inverted plastic modulus K is applied. p The expression is:

[0091]

[0092] h = [h1exp(-h2e)](p / pa) β

[0093]

[0094] Where h1, h2, n, α, β, and λ are model parameters, R is the stress ratio invariant, α is the stress ratio power parameter used to adjust the influence of R on the plastic modulus, h is the hardening function, e is the void ratio, p is the effective stress, and p a Atm, M c The critical stress ratio, ρ and These represent the distances from the current stress and the image stress to the projection center, respectively. For interpolation function, Let θ be the Lode angle and c be the material constant.

[0095] S204. Construct an expression for the loading inverse shear dilatation coefficient D.

[0096] In S204, the expression for the loading inverse shear dilatation coefficient D is:

[0097]

[0098] Where, m is the state parameter coupling coefficient, which adjusts the effect of ψ; d0 is the basic dilatation coefficient; λ is the decay exponent; M c The critical stress ratio; ρ and These represent the distances from the current stress and the image stress to the projection center, respectively. It is an interpolation function; and This indicates stress based on the current image rather than calculated stress; ψ is a state parameter, ψ = ee c e c =e-[e Γ -λ c (p / pa) ξ ], ψ represents the parameter e Γ ,λ c The critical void ratio composed of ξ; It is an interpolation function.

[0099] S3. Define the transferable projection center and mapping rules, see Figure 2 As shown, the current stress is associated with the boundary surface, and at least one projection center repositioning strategy is employed.

[0100] The specific principle is as follows:

[0101] The image stress on the interface surface can be obtained by projecting a line from the projection center α through the current stress σ. Figure 3 (a) and (b) show the evolution of the projection center α, where r1 to r 11 Represents the stress state at different loading and unloading stages, α1 to α 11 This represents the corresponding projection center. During the loading phase, the projection center is fixed at the initial stress state. When the stress evolves from r1 to r4, and a loading reversal occurs at point r4, the projection center may immediately move to the reversal point, i.e., jump from r1 to r4. This leads to an increase in the plastic modulus and a change in the direction of plastic flow. However, during unloading and immediate reloading, the repositioning of the projection center may cause the stress-strain curve to unrealistically exceed the continuation of the previous curve.

[0102] Specifically, this application proposes three projection center repositioning strategies, including immediate projection center repositioning (Model A), a model with an elastic range (Model B), and a model with an evolving projection center (Model C). In Model B, a yield surface is introduced to simulate the mechanical behavior during the loading reversal process. In Model C, it is assumed that the projection center evolves with the stress ratio, thus proposing an evolution rule.

[0103] S4. Verify the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

[0104] Example 2:

[0105] Based on Example 1, Example 2 of this application provides a more specific method for simulating the loading reversal behavior of granular materials based on stress testing, including:

[0106] S1. By conducting discrete element stress detection tests on specimens at different loading and unloading stages, the evolution of the strain response envelope during the loading reversal process is captured; the plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope.

[0107] S2. Introduce the boundary surface framework and construct the constitutive model under the loading inversion condition.

[0108] S3. Define transferable projection centers and mapping rules, associate the current stress with the boundary surface, and adopt at least one projection center repositioning strategy.

[0109] In S3, the projection center repositioning strategies include an immediate projection center repositioning strategy (Model A), an elastic range projection center adjustment strategy based on yield surface constraints (Model B), and a dynamic adjustment strategy for the projection center as the stress ratio evolves (Model C). The three projection center repositioning strategies are described in [link to relevant documentation]. Figure 3 As shown, a yield surface is introduced in model B to simulate the mechanical behavior during the loading reversal process, and in model C, it is assumed that the projection center evolves with the change of stress ratio, thus proposing an evolution rule. Figure 3 Model A(a,b) indicates that when the load is reversed, the projection center is immediately repositioned to the current stress; Model B(c,d) indicates that when the stress is within the yield surface, the projection center remains in its original position, and when the stress reaches the boundary of the yield surface and moves outward, it is repositioned to the current stress; Model C(e,f) indicates that after the load is reversed, the projection center gradually evolves towards the stress reversal point.

[0110] Specifically as follows:

[0111] (1) The evolution of the strain response envelope during loading, loading reversal and unloading is simulated using the model formula obtained in S2.

[0112] (2) Introduce a yield surface in model B to simulate the mechanical behavior during the loading reversal process.

[0113] A yield surface is introduced in model B, within which the purely elastic response is predicted, with the projection center remaining unchanged. See [reference needed]. Figure 3 (c) and (d), and define a circular yield surface in the deviatoric stress plane, the expression of which is:

[0114]

[0115] Where c represents the center of the yield surface, r f Here, r is a model parameter representing the radius of the yield surface; in this invention, r... f Take 0.01. When the stress state is inside the yield surface, the model predicts no plastic strain and the position of the projection center remains unchanged. If the stress state reaches the boundary of the yield surface and moves outward, then c should evolve to ensure that the stress does not exceed the yield surface.

[0116] Assuming that α evolves towards r during plastic hardening, its evolution rule can be expressed as:

[0117]

[0118] Among them, h α It is the appropriate modulus; v represents the direction of evolution of α; h(dL) indicates that α remains constant when the stress is inside the yield surface. Since the change in the radius of the yield surface during kinematic hardening is neglected, we have dr f =0 and v:dr=v:dα, thus obtaining h α =v:dr.

[0119] (3) In model C, it is assumed that the projection center evolves with the change of stress ratio, and the following evolution rule is proposed:

[0120] After loading and reversing, a gradually evolving projection center is used, such as... Figure 3 (e) and Figure 3 As shown in (f), after the stress reverses at r4, the projection center gradually evolves from α4 to α7 as the stress transitions from r4 to r7.

[0121] This invention assumes that the projection center evolves with the change of stress ratio, and proposes the following evolution rule:

[0122] α i+1 =φα i +(1-φ)r in ;

[0123] Where, α i and α i+1 Let r represent the projection centers of the i-th and (i+1)-th loading segments, respectively. in χ1 and χ2 are the stresses during loading reversal, and are model parameters controlling the evolution rate and nonlinearity. According to equation (17), at r in After loading and reversing, the projection center α i+1 With gradual from α i Evolved to r in Finally in ||rr in The target value r is reached when ||≥χ1. in In this invention, χ1 is 0.9 - 0.885 = 0.015, and χ2 is 0.1.

[0124] S4. Verify the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

[0125] The specific process is as follows:

[0126] (1) Performance evaluation of Model A

[0127] Figure 4 The simulation results of the response envelope predicted by model A under the same conditions as the trial experiment are shown. Figure 4 In the diagram, (a, b, c, d) represent experimental data, and (e, f, g, h) represent the strain response envelope prediction results of Model A. Specifically, (a, e) represent the experimental results and Model A prediction results during the loading phase; (b, f) represent the experimental results and Model A prediction results during the loading reversal phase; and (c, d and g, h) represent the experimental results and Model A prediction results during the unloading phase, respectively. Figure 4 It can be seen that the simulation results of Model A are in good agreement with the experimental results, indicating that Model A can reasonably capture the incremental stress-strain response during the loading and unloading stages. The simulated plastic strain amplitude gradually increases during loading, decreases to a very small value when loading reverses, and finally increases again in the new loading segment.

[0128] Figure 5 The evolution of plastic modulus (a, b) and shear dilatation coefficient (c, d) during loading and unloading is given, where (a, b) are experimental data and (c, d) are prediction results from model A. Figure 5 (c) and (d) further demonstrate Model A's predictions for the evolution of plastic modulus and shear dilatation coefficient during the loading and unloading stages. (Comparison) Figure 5 As shown in (a) and (c), the simulated plastic modulus agrees well with the DEM test results. This indicates that the loading-reversed plastic modulus K proposed in this invention... p The expression reasonably reflects the phenomenon that the plastic modulus decreases during loading and increases during the loading reversal process. (Comparison) Figure 5 As shown in (b) and (d), the prediction effect of the dilatation coefficient in the expression for loading the inverse dilatation coefficient D is poor.

[0129] (2) Performance evaluation of Model B and Model C

[0130] Figure 6 In the diagram, (a, c, e) represent the strain response envelope; (b, d, f) represent the relationship between plastic strain and the direction of stress increment; where (a, b) are experimental results; (c, d) are prediction results from model B; and (e, f) are prediction results from model C. Figure 6 (c) demonstrates that Model B accurately captures the phenomenon that the plastic flow direction remains essentially unchanged during the initial unloading stage. In this stage, the stress remains within the yield surface, and the positions of the projection center and projected stress remain constant, thus the plastic flow direction of the model also remains unchanged. In contrast, Model C fails to reflect this phenomenon, such as... Figure 6 As shown in (e), due to the evolution of α, after the loading is reversed, the projection center and stress gradually change, which leads to a significant change in the shear dilatation coefficient D calculated according to the expression of the loading reversal shear dilatation coefficient D. Figure 6 (b), (d), and (f) compare the experimental results and model predictions of plastic strain with the stress increment direction α. dσ The relationship between them. Through Figure 6 (b) It can be seen that when η = 0.9, the direction of the stress increment is in α dσ Plastic strain occurs between 60° and 240°. As η decreases, the direction of the stress increment causing plastic strain also decreases. When η ≤ 0.855, plastic strain almost completely disappears. Figure 6 As shown in (d), the comparison shows that Model B can more accurately simulate the mechanical behavior during the loading and reversal process compared to Model A and Model C.

[0131] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 1 can be referred to each other, and will not be repeated in this application.

[0132] Example 3:

[0133] Based on Example 2, Example 3 of this application provides a simulation system for the loading reversal behavior of granular materials based on stress testing, comprising:

[0134] The experimental module is used to capture the evolution of the strain response envelope during loading reversal by performing discrete element stress probing tests on specimens at different loading and unloading stages; the plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope.

[0135] The building block is used to introduce the boundary surface framework and construct the constitutive model under the loading inversion condition;

[0136] The definition module is used to define transferable projection centers and mapping rules, associate the current stress with the boundary surface, and adopt at least one projection center repositioning strategy.

[0137] The validation module is used to validate the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

[0138] It should be noted that the system provided in this embodiment is the system corresponding to the method provided in embodiment 2. Therefore, the parts in this embodiment that are the same as or similar to those in embodiment 2 can be referred to each other, and will not be described again in this application.

Claims

1. A method for simulating the loading reversal behavior of granular materials based on stress testing, characterized in that, include: S1. By conducting discrete element stress detection tests on specimens at different loading and unloading stages, the evolution of the strain response envelope during the loading reversal process is captured. The plastic modulus, plastic flow direction, and shear dilatation coefficient are derived from the response envelope. S2. Introduce a boundary surface framework to construct a constitutive model under loading inversion conditions; S2 includes: S201. Introduce a boundary surface frame, wherein the boundary surface frame adopts a tapered boundary surface; S202, Construct an expression for loading and reversing the direction of plastic flow; S203, Constructing the loading inversion plastic modulus The expression; S204. Construct an expression for the loading of the inverse shear dilatation coefficient D; In S201, the expression for the boundary surface frame is: in, and These are the image stresses on the boundary surface F. Two invariants; H is the hardening parameter defining the magnitude of F, set to the material's hardening process. The maximum value; It is an interpolation function; In S202, the expression for reversing the plastic flow direction is: Where F is the boundary surface function, representing the plastic response boundary of the material in stress space; The stress ratio tensor; denoted as the gradient of the boundary surface with respect to the stress ratio; I is the second-order unit tensor used to represent the direction of isotropic volume change; m represents the loading direction; n represents the plastic flow direction. This indicates that the loading direction is consistent with the plastic flow direction; S3. Define transferable projection centers and mapping rules, link the current stress with the boundary surface, and adopt multiple projection center repositioning strategies. S4. Verify the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

2. The method for simulating the loading reversal behavior of granular materials based on stress testing according to claim 1, characterized in that, S1 includes: S101. Apply multiple stress increments of equal magnitude but different directions to obtain the incremental stress-strain response of the particulate material; S102. Conduct trial tests to obtain the total strain increment and elastic strain increment; The plastic strain increment is the difference between the total strain increment and the elastic strain increment; S103. Derive the plastic modulus, plastic flow direction, and shear dilatation coefficient from the response envelope.

3. The method for simulating the loading reversal behavior of granular materials based on stress testing according to claim 2, characterized in that, In S101, the components of the stress increment are expressed as: in, Indicates the magnitude of the stress increment; Indicates the direction of stress testing.

4. The method for simulating the loading reversal behavior of granular materials based on stress testing according to claim 2, characterized in that, In S103, the plastic strain increment is expressed as: in, For plastic strain increment tensors, it represents the irreversible strain changes that occur in a material during loading; To load activation conditions, use Macaulay brackets to indicate: ① If ,but Plastic deformation occurs; ② If ,but Only elastic deformation; Indicates the direction of plastic flow, including the deviatoric component q and the volumetric component. I is a second-order unit tensor, representing the isotropic nature of the volume change; It is the loading index. These are unit-norm deviator tensors, specifying the deviatoric plastic strain increments respectively. Size and orientation; It is the shear dilatation coefficient.

5. The method for simulating the loading reversal behavior of granular materials based on stress testing according to claim 2, characterized in that, In S203, the inverted plastic modulus is applied. The expression is: in, , ,z, , , These are model parameters. As the stress ratio invariant, This is a power-law parameter for stress ratio, used to adjust... The influence of strength on plastic modulus, where h is the hardening function, e is the void ratio, and p is the effective stress. Atmospheric pressure The critical stress ratio. and These represent the distances from the current stress and the image stress to the projection center, respectively. For interpolation functions, Let θ be the Lode angle and c be the material constant. In S204, the expression for the loading of the inverse shear dilatation coefficient is: Where k is the state parameter coupling coefficient, and the adjustment... The impact; The basic shear dilatation coefficient; The decay index; The critical stress ratio; and These represent the distances from the current stress and the image stress to the projection center, respectively. It is an interpolation function; , , Indicates by parameters , and The critical void ratio of the composition.

6. The method for simulating the loading reversal behavior of granular materials based on stress testing according to claim 3, characterized in that, In S3, the projection center repositioning strategy includes an immediate projection center repositioning strategy, an elastic range projection center adjustment strategy based on yield surface constraints, and a dynamic adjustment strategy for the projection center as the stress ratio evolves.

7. A simulation system for the loading reversal behavior of granular materials based on stress testing, characterized in that, For performing the method according to any one of claims 1 to 6, comprising: The test module is used to capture the evolution of the strain response envelope during loading reversal by performing discrete element stress detection tests on specimens at different loading and unloading stages; and to derive the plastic modulus, plastic flow direction and shear dilatation coefficient from the response envelope. The building block is used to introduce the boundary surface framework and construct the constitutive model under the loading inversion condition; The definition module is used to define transferable projection centers and mapping rules, associate the current stress with the boundary surface, and adopt various projection center repositioning strategies. The validation module is used to validate the response of different projection center repositioning strategies, compare the performance of the models corresponding to different projection center repositioning strategies, and evaluate the prediction effect of the models corresponding to different projection center repositioning strategies.

8. A computer storage medium, characterized in that, The computer storage medium stores a computer program; when the computer program is run on the computer, it causes the computer to perform the method described in any one of claims 1 to 6.

Images