Asphalt mixture fatigue damage normalization method

Abstract

The invention discloses an asphalt mixture fatigue damage normalization method, which belongs to the technical field of road engineering, and comprises the following steps: carrying out a fatigue loading cycle test on an asphalt mixture, and fitting a residual strength attenuation model by adopting a power function according to a test result; constructing a cumulative fatigue damage model according to the residual intensity attenuation model; representing the strength of the asphalt mixture on a tensile meridian and a compression meridian under different test conditions by using equivalent stress; calculating a fatigue stress ratio of the asphalt mixture in a three-dimensional stress state according to a strength yield surface theory, and constructing a fatigue normalization equation based on the fatigue stress ratio; and constructing an asphalt mixture fatigue damage normalization model based on the accumulative fatigue damage model and the fatigue normalization equation. According to the method, the problem that the fatigue damage change rule of the asphalt mixture in the three-dimensional stress state is difficult to objectively represent at present is solved by adopting a fatigue damage normalization method.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering, and in particular relates to a method for normalizing fatigue damage of asphalt mixture. Background Art

[0002] Asphalt pavement is a typical artificial strip three-dimensional structure that needs to be exposed to complex and changeable outdoor conditions for a long time. The service environment is harsh and it is mainly composed of asphalt mixture. Asphalt mixture is a viscoelastic-plastic material composed of asphalt and gravel. It is extremely sensitive to changes in traffic loads and humid and hot environments. Under the coupling of vehicle loads and environmental factors, microcracks will appear inside the pavement. The microcracks gradually evolve and eventually form macro cracks. The appearance of cracks will lead to a decrease in the service performance of the pavement and affect the service life of the pavement. At present, scientific preventive maintenance technology plays an important role in extending the service life of the pavement. The key to influencing maintenance technology lies in the evolution mechanism of the pavement service performance under multi-field coupling and its prediction model, that is, it is necessary to establish a nonlinear damage evolution model of the pavement material under complex service conditions throughout its life cycle.

[0003] The stress state and fatigue damage model used in the existing test methods for the research on fatigue damage of asphalt mixtures are not unified, and any point in the asphalt mixture structure is in a three-dimensional stress state. It is difficult to objectively characterize the fatigue damage change law of asphalt pavement under the three-dimensional stress state using a fatigue damage linear model under simple test conditions. Summary of the invention

[0004] The purpose of the present invention is to provide a method for normalizing fatigue damage of asphalt mixture, so as to solve the problem that it is currently difficult to objectively characterize the variation law of fatigue damage of asphalt mixture under a three-dimensional stress state.

[0005] The technical solution adopted by the present invention is a method for normalizing fatigue damage of asphalt mixture, comprising the following steps:

[0006] S1. Conduct fatigue loading cycle tests on asphalt mixtures under different stress states, temperatures, load frequencies, load levels, and cycle numbers, and use power functions to fit the residual strength attenuation model based on the test results;

[0007] S2. Constructing a cumulative fatigue damage model based on the residual strength attenuation model;

[0008] S3. Use equivalent stress to characterize the strength of asphalt mixture under different test conditions on the tensile meridian and compression meridian;

[0009] S4. Calculate the fatigue stress ratio of asphalt mixture under three-dimensional stress state according to the strength yield surface theory;

[0010] S5. construct fatigue normalization equation based on fatigue stress ratio;

[0011] S6. Construct a normalized fatigue damage model for asphalt mixture based on the cumulative fatigue damage model and the fatigue normalization equation.

[0012] Furthermore, in step S1, the stress state includes direct tension, uniaxial compression, and indirect tension.

[0013] Furthermore, in step S1, the residual strength attenuation model is:

[0014]

[0015] In the formula, S N is the residual strength of asphalt mixture after N fatigue loading cycles; S0 is the initial strength of asphalt mixture; N is the number of fatigue loading cycles; N f is the fatigue life of asphalt mixture, that is, the maximum number of cycles without damage or fracture; σ is the fatigue loading stress load; γ1 and γ2 are model parameters with no practical meaning and are obtained by power function fitting.

[0016] Furthermore, in step S2, the cumulative fatigue damage model is:

[0017]

[0018] Where D(N) is the accumulated fatigue damage of asphalt mixture.

[0019] Furthermore, in step S3, the equivalent stress on the stretch meridian and the compression meridian is:

[0020]

[0021] In the formula, σ e t is the equivalent stress on the tensile meridian, σ e c is the equivalent stress on the compression meridian, I1 is the first stress invariant, I1=σ1+σ2+σ3, σ1, σ2, σ3 are the first, second, and third principal stresses of a point respectively, R c is the uniaxial compression strength of asphalt mixture, a, b, and m are simplified parameters with no practical significance.

[0022] k1, k2, k3 are simplified parameters and have no practical significance. θ is the Lode angle, R T is the direct tensile strength of asphalt mixture, R IT It is the indirect tensile strength of asphalt mixture.

[0023] Further, in step S4, the fatigue stress ratio under the three-dimensional stress state is calculated as:

[0024]

[0025] In the formula, σ e (θ) is the equivalent stress under three-dimensional stress state, α, θ are the Lode angles, σ1, σ2, σ3 are the first, second, and third principal stresses of a point, respectively. Δ is the fatigue stress ratio of asphalt mixture under three-dimensional stress state. is the equivalent stress of fatigue cycle loading,

[0026] Furthermore, in step S5, the fatigue normalization equation is:

[0027] N f =Δ -n

[0028] Where n is a model parameter with no practical significance and is obtained by fitting a power function. There are boundary conditions: Δ = 1, N f =1.

[0029] Furthermore, in step S6, the fatigue damage normalization model is:

[0030]

[0031] The beneficial effects of the present invention are:

[0032] The present invention establishes a residual strength attenuation model for asphalt mixture, defines residual strength attenuation as a damage factor, comprehensively considers the fatigue damage variation law of asphalt mixture under various test conditions, establishes an asphalt mixture fatigue damage model, and derives a normalized model of fatigue damage for asphalt mixture based on the strength yield criterion of asphalt mixture under three-dimensional stress state and the fatigue normalization equation of asphalt mixture. The model has high correlation with actual test results and objectively characterizes the fatigue damage variation law of asphalt mixture, solves the problem of low correlation when evaluating fatigue damage of asphalt mixture under simple test conditions using a single test method in the prior art, and objectively characterizes the actual stress state of asphalt pavement by constructing the fatigue damage evolution law of asphalt mixture under complex stress state, thereby achieving a scientific evaluation of fatigue damage of asphalt mixture. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 is a schematic diagram of the envelope of the medium-effective stress in the π plane in Example 1 of the present invention;

[0035] Figure 2 is the fatigue damage curve under direct tensile stress in Example 1 of the present invention;

[0036] Figure 3 is the fatigue damage curve under uniaxial compressive stress state in Example 1 of the present invention;

[0037] Figure 4 is the fatigue damage curve under indirect tensile stress state in Example 1 of the present invention;

[0038] Figure 5 is the equivalent stress under direct tensile stress state in Example 1 of the present invention;

[0039] Figure 6 is the equivalent stress under uniaxial compressive stress state in Example 1 of the present invention;

[0040] Figure 7 is the equivalent stress under the indirect tensile stress state in Example 1 of the present invention;

[0041] Figure 8 is the fatigue normalized curve of the asphalt mixture in Example 1 of the present invention;

[0042] Fig. 9 It is the normalized curve of fatigue damage of asphalt mixture in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0044] The present invention provides a method for normalizing fatigue damage of asphalt mixture, comprising the following steps:

[0045] S1. Fatigue loading cycle tests of asphalt mixtures were conducted under different stress states, temperatures, load frequencies, load levels, and number of cycles. According to the test results, the power function was used to fit the residual strength attenuation model, which is:

[0046]

[0047] In the formula, S N is the residual strength of asphalt mixture after N fatigue loading cycles; S0 is the initial strength of asphalt mixture; N is the number of fatigue loading cycles; N f is the fatigue life of asphalt mixture, that is, the maximum number of cycles without damage or fracture; σ is the fatigue loading stress load; γ1 and γ2 are model parameters with no practical meaning and are obtained by power function fitting.

[0048] The stress state includes direct tension, uniaxial compression, and indirect tension.

[0049] S2. According to the residual strength attenuation model, the cumulative fatigue damage model is constructed as follows:

[0050]

[0051] Where D(N) is the accumulated fatigue damage of asphalt mixture.

[0052] S3. The equivalent stress is used to characterize the strength of asphalt mixture under different test conditions on the tensile meridian and the compression meridian:

[0053]

[0054] In the formula, σ e t is the equivalent stress on the tensile meridian, σ e c is the equivalent stress on the compression meridian, I1 is the first stress invariant, I1=σ1+σ2+σ3, σ1, σ2, σ3 are the first, second, and third principal stresses of a point respectively, R c is the uniaxial compression strength of asphalt mixture, a, b, and m are simplified parameters with no practical significance.

[0055] k1, k2, k3 are simplified parameters and have no practical significance. θ is the Lode angle, R T is the direct tensile strength of asphalt mixture, R IT It is the indirect tensile strength of asphalt mixture.

[0056] S4. According to the strength yield surface theory, the fatigue stress ratio of asphalt mixture under three-dimensional stress state is calculated as:

[0057]

[0058] In the formula, σ e (θ) is the equivalent stress under three-dimensional stress state, α, θ are the Lode angles, Δ is the fatigue stress ratio of asphalt mixture under three-dimensional stress state, is the equivalent stress of fatigue cycle loading,

[0059] S5. Based on the fatigue stress ratio, the fatigue normalization equation is constructed as follows:

[0060] N f =Δ -n

[0061] Where n is a model parameter with no practical significance and is obtained by fitting a power function. There are boundary conditions: Δ = 1, N f =1;

[0062] S6. Based on the cumulative fatigue damage model and the fatigue normalization equation, the fatigue damage normalization model of asphalt mixture is constructed as follows:

[0063]

[0064] In the formula, σ eN It is the residual strength of asphalt mixture after N fatigue loading cycles characterized by equivalent stress.

[0065] Example 1

[0066] In this embodiment, fatigue loading cycle test is performed on SMA (stone matrix asphalt), and the stress state is set to direct tension, uniaxial compression and indirect tension stress; the temperature is set to -15°C, 0°C, 15°C, 25°C; the load frequency is set to 0.1Hz, 1Hz, 10Hz, 20Hz; the direct tension and uniaxial compression load levels are set to 0.2kN, 0.25kN, 0.5kN, 1kN, 1.5kN, 2kN, 2.5kN, 3.5kN; the indirect tension load level is set to 6kN, 9kN, 10kN, 12kN, 15kN, 21kN, 25kN, 31kN, 40kN, 60kN; the number of cycles is set to 0, 20%N f 50%N f 、65%N f 、80%N f ;

[0067] Under the above test conditions, the residual strength of asphalt mixture was tested, and the residual strength attenuation model was fitted according to the residual strength. The results are as follows:

[0068] The direct tensile residual strength attenuation model is:

[0069] The residual strength attenuation model of uniaxial compression is:

[0070] The indirect tensile residual strength decay model is:

[0071] The cumulative fatigue damage model is constructed based on the residual strength attenuation model:

[0072] The direct tensile cumulative fatigue damage model is:

[0073] The uniaxial compression cumulative fatigue damage model is:

[0074] The indirect tensile cumulative fatigue damage model is:

[0075] Figure 2 is the fatigue damage curve under direct tensile stress state, Figure 3 is the fatigue damage curve under uniaxial compressive stress state, Figure 4 It is the fatigue damage curve under indirect tensile stress state.

[0076] The equivalent stress is used to characterize the strength of asphalt mixture on the tensile meridian and the compressive meridian. The equivalent stress envelope on the π plane is as follows: Figure 1 As shown, it is calculated according to the relationship shown in Table 1;

[0077] Table 1 Relationship between strength and equivalent stress under different stress states

[0078]

[0079] Figure 5 is the equivalent stress under direct tensile stress state, Figure 6 is the equivalent stress under uniaxial compressive stress state, Figure 7 is the equivalent stress under indirect tensile stress state.

[0080] According to the strength yield surface theory, the fatigue stress ratio of asphalt mixture under three-dimensional stress state is calculated as follows:

[0081]

[0082] Where Δ is the fatigue stress ratio of asphalt mixture under three-dimensional stress state, is the equivalent stress of fatigue cycle loading,

[0083] The fatigue normalization equation based on the fatigue stress ratio is:

[0084] N f =Δ -4.22

[0085] The fatigue normalization curve is as follows Figure 8 As shown, it can be seen that the correlation coefficient is 0.997;

[0086] Based on the cumulative fatigue damage model and fatigue normalization equation, the fatigue damage normalization model of asphalt mixture is established as follows:

[0087]

[0088] In the formula, σ eN It is the equivalent stress of asphalt mixture after N cycles of fatigue loading under stress state;

[0089] Substituting the above results into:

[0090]

[0091] The normalized fatigue damage curve of asphalt mixture is as follows: Fig. 9 As shown, according to the fitting results, the normalized model of fatigue damage of asphalt mixture of the present invention has a high correlation with the test data, and the correlation coefficient reaches 0.992, which proves that the derived normalized model of fatigue damage can better characterize the variation law of fatigue damage of asphalt mixture.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for normalizing fatigue damage of asphalt mixture, characterized in that: The following steps are involved: S1. Conduct fatigue loading cycle tests on asphalt mixtures under different stress states, temperatures, load frequencies, load levels, and cycle numbers, and use power functions to fit the residual strength attenuation model based on the test results; S2. Constructing a cumulative fatigue damage model based on the residual strength attenuation model; S3. Use equivalent stress to characterize the strength of asphalt mixture under different test conditions on the tensile meridian and compression meridian; S4. Calculate the fatigue stress ratio of asphalt mixture under three-dimensional stress state according to the strength yield surface theory; S5. construct fatigue normalization equation based on fatigue stress ratio; S6. Construct a normalized fatigue damage model for asphalt mixture based on the cumulative fatigue damage model and the fatigue normalization equation.

2. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S1, the stress state includes direct tension, uniaxial compression, and indirect tension.

3. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S1, the residual strength attenuation model is: In the formula, S N is the residual strength of asphalt mixture after N fatigue loading cycles; S0 is the initial strength of asphalt mixture; N is the number of fatigue loading cycles; N f is the fatigue life of asphalt mixture, that is, the maximum number of cycles without damage or fracture; σ is the fatigue loading stress load; γ1 and γ2 are model parameters with no practical meaning and are obtained by power function fitting.

4. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S2, the cumulative fatigue damage model is: Where D(N) is the accumulated fatigue damage of asphalt mixture, S N is the residual strength of asphalt mixture after N fatigue loading cycles, S0 is the initial strength of asphalt mixture, σ is the fatigue loading stress load, N is the number of fatigue loading cycles, N f is the fatigue life of asphalt mixture, γ1 and γ2 are model parameters with no practical meaning and are obtained by power function fitting.

5. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S3, the equivalent stress on the stretch meridian and the compression meridian is: In the formula, σ e t is the equivalent stress on the tensile meridian, σ e c is the equivalent stress on the compression meridian, I1 is the first stress invariant, I1=σ1+σ2+σ3, σ1, σ2, σ3 are the first, second, and third principal stresses of a point respectively, R c is the uniaxial compression strength of asphalt mixture, a, b, and m are simplified parameters with no practical significance. k1, k2, k3 are simplified parameters and have no practical significance. θ is the Lode angle, R T is the direct tensile strength of asphalt mixture, R IT It is the indirect tensile strength of asphalt mixture.

6. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S4, the fatigue stress ratio under the three-dimensional stress state is calculated as: In the formula, σ e (θ) is the equivalent stress under three-dimensional stress state, σ e t is the equivalent stress on the tensile meridian, σ e c is the equivalent stress on the compression meridian, α, θ are the Lode angles, σ1, σ2, and σ3 are the first, second, and third principal stresses of a point, respectively. Δ is the fatigue stress ratio of asphalt mixture under three-dimensional stress state. ei is the equivalent stress of fatigue cycle loading, 7. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S5, the fatigue normalization equation is: N f =D -n Where N f is the fatigue life of asphalt mixture, Δ is the fatigue stress ratio of asphalt mixture under three-dimensional stress state, n is a model parameter with no practical significance obtained by power function fitting, and there are boundary conditions: Δ=1, N f =1.

8. The asphalt mixture fatigue damage normalization method according to claim 1, characterized in that: In step S6, the fatigue damage normalization model is: Where D(N) is the cumulative fatigue damage of asphalt mixture, N is the number of fatigue loading cycles, is the equivalent stress of fatigue cycle loading, σ e (θ) is the equivalent stress under three-dimensional stress state, Δ is the fatigue stress ratio of asphalt mixture, n, γ1, γ2 are model parameters and have no practical meaning.

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