Method for predicting microscopic fracture performance of interface transition area of asphalt mixture

Abstract

The invention relates to the field of road engineering, in particular to an asphalt mixture interface transition zone microscopic fracture performance prediction method, which comprises the following steps: carrying out a nanoindentation test on an asphalt mortar-aggregate interface transition zone in a test piece to obtain an indentation load-depth curve of each test point; according to the indentation load-depth curve of each measuring point, elastic modulus data and indentation hardness data of each measuring point are obtained; according to the critical energy release rate generated by the sample crack, the fracture toughness of each measuring point is calculated through an energy analysis method; through linear regression analysis, a relation formula between the fracture toughness and the elastic modulus and a relation formula between the fracture toughness and the indentation hardness are determined; and substituting the elastic modulus and the indentation hardness of each measuring point into the relation formula to obtain the predicted fracture toughness of each measuring point. The prediction method provided by the invention has low requirements on test design, can establish a fracture toughness prediction model only by carrying out a nanoindentation test, has good operability, improves the calculation efficiency, and is convenient for engineering application and popularization.

Description

Technical Field

[0001] The present invention relates to the field of road engineering, and particularly relates to a method for predicting the microscopic fracture performance of the interface transition zone of asphalt mixtures. Background Art

[0002] During the mixing and compaction process of asphalt mixtures, the asphalt mortar wraps the aggregates, and physical and chemical reactions and mechanical interlocking effects occur between them, forming a narrow area around the aggregate particles, which is called the interface transition zone. Its microscopic structure and mechanical properties are closely related to the interface debonding behavior and adhesion index inside the mixture, and play a crucial role in the overall performance of asphalt mixtures.

[0003] In the prior art, the aggregates and asphalt mortar in asphalt mixtures are two materials with different moduli. The interface transition zone formed by the two has an obvious mechanical behavior change trend as the weak link of asphalt mixtures. Under the action of load and environment, high stress concentration is likely to occur in the interface transition zone, resulting in the initiation of cracks in the interface transition zone, becoming the crack initiation point, and it is extremely easy to occur interface failure and damage.

[0004] With the development of microscopic testing methods, it provides an effective method for characterizing the asphalt mortar-aggregate interface transition zone and its traditional mechanical parameters, but there is still a lack of further analysis of the microscopic fracture characteristics of the interface transition zone. Microscopic fracture parameters are crucial for the internal stress transfer, crack initiation state and propagation of asphalt mixtures, and to a certain extent determine the strength, crack resistance and durability of the mixtures. The fracture toughness (also known as the critical stress intensity factor) is an important mechanical parameter characterizing the crack propagation resistance and is often used to evaluate the fracture characteristics of materials.

[0005] However, it is difficult to measure the fracture toughness of asphalt mixtures, and it is also rarely seen in the literature, while the elastic modulus information of materials is very easy to obtain. Therefore, carrying out research on the microscopic mechanical properties of the interface transition zone of asphalt mixtures and establishing a prediction method for the fracture toughness of the interface transition zone of asphalt mixtures can provide a potential method for estimating the fracture toughness of asphalt mixtures without conducting large-scale tests and calculations, thus obtaining more benefits. Summary of the Invention

[0006] In view of the above technical problem that it is difficult to measure the fracture toughness of asphalt mixtures, a method for predicting the microscopic fracture performance of the interface transition zone of asphalt mixtures is provided. The present invention mainly uses the elastic modulus and indentation hardness as fitting parameters, and establishes a fracture toughness prediction model through nanoindentation tests, thereby providing a potential method for estimating the fracture toughness of asphalt mixtures without conducting large-scale tests and calculations.

[0007] The technical means adopted by the present invention are as follows:

[0008] A method for predicting the microscopic fracture performance of the interface transition zone of asphalt mixture, the steps include:

[0009] S1. Prepare Marshall specimens of asphalt mixture, cut the specimens with a metallographic cutting machine, and polish the cut specimens with a polishing cloth and polishing fluid to obtain polished specimens. The polished specimens include the asphalt mortar-aggregate interface transition zone;

[0010] S2. Select the asphalt mortar-aggregate interface transition zone in the polished specimens under a microscope, divide the test area according to the asphalt mortar-aggregate interface transition zone in the specimens, and conduct nano-indentation tests on the specimens in the test area to obtain the change trend of the indentation depth data of each measuring point with the applied indentation force;

[0011] S3. Draw the indentation load-depth curve of each measuring point according to the change trend of the indentation depth data of each measuring point with the applied indentation force;

[0012] S4. Obtain the elastic modulus data and indentation hardness data of each measuring point according to the indentation load-depth curve of each measuring point. Based on the elastic modulus data and indentation hardness data of each measuring point, draw the elastic modulus distribution map of the specimen and the indentation hardness distribution map of the specimen;

[0013] S5. Measure the thickness of the asphalt mortar-aggregate interface transition zone according to the elastic modulus distribution map of the specimen and the indentation hardness distribution map of the specimen;

[0014] S6. According to the total test energy obtained from the nano-indentation testing machine, calculate the test pure plastic performance through energy analysis method. According to the total test energy, test elastic energy and test pure plastic performance, calculate the test fracture energy, and according to the test fracture energy, calculate the critical energy release rate of specimen crack generation;

[0015] S7. Calculate the fracture toughness of each measuring point through energy analysis method according to the critical energy release rate of specimen crack generation. Draw the fracture toughness distribution map of the specimen according to the fracture toughness of each measuring point;

[0016] S8. Through linear regression analysis, according to the fracture toughness and elastic modulus of each measuring point, determine the relationship formula between the fracture toughness of each measuring point and the elastic modulus of each measuring point, and generate the first prediction formula. Through linear regression analysis, according to the fracture toughness and indentation hardness of each measuring point, determine the relationship formula between the fracture toughness of each measuring point and the indentation hardness of each measuring point, and generate the second prediction formula;

[0017] S9. Substitute the elastic modulus of each measuring point into the first prediction formula, and substitute the indentation hardness of each measuring point into the second prediction formula to obtain the predicted fracture toughness of each measuring point.

[0018] Further, according to the indentation load-depth curves of each measurement point, elastic modulus data and indentation hardness data of each measurement point are obtained, including:

[0019] According to the indentation load-depth curves of each measurement point, the slope at the top of the unloading section of the indentation load-depth curve of each measurement point is calculated. The calculation formula for the slope at the top of the unloading section of the indentation load-depth curve of each measurement point is as follows:

[0020]

[0021] Among them, S is the slope at the top of the unloading section of the indentation load-depth curve of each measurement point,

[0022] According to the slope at the top of the unloading section of the indentation load-depth curve of each measurement point, the calculation formula for the elastic modulus of each measurement point is as follows:

[0023]

[0024] Among them, E r is the elastic modulus of each measurement point, β is the indenter geometry correction factor, S is the slope at the top of the unloading section of the indentation load-depth curve of each measurement point, and A is the projected contact area of the indenter tip under the maximum load at the indentation.

[0025] According to the indentation load-depth curves of each measurement point, mechanical parameters of the test specimen are obtained. The mechanical parameters of the test specimen include the maximum load at the indentation, the indentation depth at the peak load, the residual indentation depth after complete unloading, and the indentation contact depth. According to the maximum load at the indentation and the indentation depth at the peak load, the indentation contact depth is calculated. The calculation formula for the indentation contact depth is as follows:

[0026]

[0027] Among them, h max is the indentation depth at the peak load, h c is the indentation contact depth, P max is the maximum load at the indentation, and ε is the indenter-related parameter.

[0028] According to the indentation contact depth, the projected contact area of the indenter tip under the maximum load at the indentation is calculated. The calculation formula for the projected contact area of the indenter tip under the maximum load at the indentation is as follows:

[0029]

[0030] Among them, A is the projected contact area of the indenter tip under the maximum load at the indentation, h c is the indentation contact depth,

[0031] According to the projected contact area of the indentation tip under the maximum load at the indentation and the maximum load at the indentation, calculate the indentation hardness of each measurement point. The calculation formula for the indentation hardness of each measurement point is as follows:

[0032]

[0033] Among them, P max is the maximum load at the indentation, H is the indentation hardness of each measurement point, and A is the projected contact area of the indentation tip under the maximum load at the indentation.

[0034] Furthermore, according to the total test energy obtained from the nano-indentation testing machine, calculate the test pure plastic performance through energy analysis. According to the total test energy, test elastic energy, and test pure plastic performance, calculate the test fracture energy. According to the test fracture energy, calculate the critical energy release rate for the generation of specimen cracks, including:

[0035]

[0036] Among them, U t is the total test energy, U p is the test plastic energy, h f is the residual indentation depth after complete unloading, h max is the indentation depth at the peak load,

[0037] The calculation formula for the test fracture energy is as follows:

[0038] U c =U t -U e -U p

[0039] Among them, U t is the total test energy, U c is the test fracture energy, U e is the test elastic energy, U p is the test plastic energy,

[0040] According to the test fracture energy, calculate the critical energy release rate for crack generation. The formula for the critical energy release rate for crack generation is as follows:

[0041]

[0042] Among them, U c is the test fracture energy, A max is the contact area at the maximum indentation depth, G c is the critical energy release rate for crack generation, h max is the indentation depth at the peak load.

[0043] Furthermore, the calculation formula for the fracture toughness of each measurement point is as follows:

[0044]

[0045] Among them, K IC is the fracture toughness of each measuring point, E r is the elastic modulus of each measuring point, and G c is the critical energy release rate for crack generation.

[0046] Furthermore, the first prediction formula is as follows:

[0047] K IC = α1E r + β1

[0048] Among them, K IC is the fracture toughness of each measuring point, E r is the elastic modulus of each measuring point, α1 is the fitting parameter related to the elastic modulus, and β1 is the intercept term fitting parameter related to the elastic modulus.

[0049] The second prediction formula is as follows:

[0050] K IC = α2H + β2

[0051] Among them, K IC is the fracture toughness of each measuring point, H is the indentation hardness of each measuring point, α2 is the fitting parameter related to the elastic modulus, and β2 is the intercept term fitting parameter related to the elastic modulus.

[0052] Furthermore, the indenter geometry correction factor is 1.034.

[0053] Compared with the prior art, the present invention has the following advantages:

[0054] 1. By performing nano-indentation tests on Marshall specimens of asphalt mixtures, the present invention obtains the change trend of the indentation depth data with the applied indentation force, and then plots the indentation load-depth curve to obtain the elastic modulus data and indentation hardness data of each measuring point, and finally establishes a fracture toughness prediction model. Since only nano-indentation tests are required, the requirements for test operations are relatively low, and it has good operability, which is convenient for popularization and application in different laboratories or engineering sites.

[0055] 2. By selecting the asphalt mortar-aggregate interfacial transition zone on the polished specimen under a microscope, dividing the test area and performing nano-indentation tests and other operations, the present invention focuses on the weakest link of the asphalt mixture interfacial transition zone. Thus, it can observe and predict the occurrence and expansion of microcracks inside the asphalt mixture, provide a more accurate basis for the performance evaluation and service life prediction of the asphalt mixture, and help take corresponding measures in advance to improve its performance or prevent damage.

[0056] 3. The present invention uses elastic modulus and indentation hardness as fitting parameters to characterize fracture toughness respectively. The elastic modulus data and indentation hardness data obtained through nano-indentation tests can more accurately reflect the microscopic fracture properties of the interfacial transition zone of asphalt mixtures. The discreteness of the results is small and the correlation is high, which improves the reliability and accuracy of the prediction model and provides a more accurate analysis method for the study of the microscopic fracture properties of asphalt mixtures.

[0057] 4. The present invention analyzes the indentation load-depth curves of each measuring point, calculates the experimental fracture energy and the critical energy release rate of specimen crack generation, and then calculates the fracture toughness of each measuring point and draws the fracture toughness distribution map. Its model has few parameters and the calculation process of parameters is simple, which greatly improves the calculation efficiency, facilitates rapid application and promotion in practical engineering, and can provide timely and effective technical support for the design, construction and quality control of asphalt mixtures.

[0058] Based on the above reasons, the present invention can be widely promoted in the fields of road engineering and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0060] Figure 1 It is a schematic flow chart of the method for predicting the microscopic fracture properties of the interfacial transition zone of the asphalt mixture of the present invention.

[0061] Figure 2 It is the grading curve of the AC-16 asphalt mixture in the present invention.

[0062] Figure 3 It is the indentation load-depth (P-h) curve in the present invention.

[0063] Figure 4 It is the elastic modulus distribution map in the present invention.

[0064] Figure 5 It is the indentation hardness distribution map in the present invention.

[0065] Figure 6 It is the fracture toughness and standard deviation in the present invention.

[0066] Figure 7 It is the fracture toughness distribution map in the present invention.

[0067] Figure 8It is a diagram of the fracture toughness prediction model based on elastic modulus in the present invention.

[0068] Figure 9 It is a diagram of the fracture toughness prediction model based on indentation hardness in the present invention.

[0069] Figure 10 It is a schematic diagram for calculating the slope at the top of the unloading section of the indentation load-depth curve at each measuring point of the present invention. Detailed implementation manners

[0070] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0071] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily need to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0072] As Figures 1 - 10 shown, the present invention provides a method for predicting the microscopic fracture performance of the interface transition zone of asphalt mixture, and the specific steps are as follows:

[0073] S1. Prepare Marshall specimens of asphalt mixture, cut the specimens with a metallographic cutting machine, and polish the cut specimens with a polishing cloth and polishing liquid to obtain polished specimens. The polished specimens include the asphalt mortar-aggregate interface transition zone.

[0074] First, as Figure 2As shown in the figure, the mix design of asphalt mixture was carried out by the Marshall test method. The test sample was selected as AC-16 type asphalt mixture. Two types of asphalt were selected, namely 90# base asphalt and SBS modified asphalt, and two types of aggregates were selected, namely limestone and basalt aggregates. According to the relevant regulations of the "Technical Specification for Highway Engineering Construction", the mix ratio range was determined, and thus four standard Marshall specimens of base asphalt-limestone asphalt mixture, base asphalt-basalt asphalt mixture, SBS modified asphalt-limestone asphalt mixture, and SBS modified asphalt-basalt asphalt mixture were prepared and formed.

[0075] Finally, a metallographic cutting machine was used to cut the four types of standard Marshall specimens. Then, a metallographic grinding machine was used in combination with 240, 400, 800, and 1200 mesh metallographic sandpapers to grind the specimens successively under water-cooled conditions until the surface was flat. The grinding time for each mesh of sandpaper was 2 minutes. After grinding and cleaning, a polishing cloth was used for polishing treatment. The particle size of the polishing liquid used was W2.5, and nano-indentation test specimens with dimensions of 15 mm × 15 mm × 10 mm were obtained.

[0076] S2. In the microscope, select the asphalt mortar-aggregate interfacial transition zone in the polished specimen. According to the asphalt mortar-aggregate interfacial transition zone in the specimen, divide the test area, and conduct nano-indentation tests on the specimens in the test area to obtain the change trend of the indentation depth data of each measuring point with the applied indentation force.

[0077] Specifically, fix the test sample on the test platform of the nano-indentation instrument. Select a clear and flat interface area between the asphalt mortar and the aggregate under the microscope, and delimit the test area as 40 μm × 20 μm; arrange a measuring point matrix from the edge of the aggregate phase to the asphalt mortar phase direction, with a distance of 10 μm between adjacent points, and conduct nano-indentation tests in the displacement control mode.

[0078] S3. As Figure 3 shown in the figure, according to the change trend of the indentation depth data of each measuring point with the applied indentation force, draw the indentation load-depth curve of each measuring point, and distinguish the three different regions of the aggregate, asphalt mortar, and their interfacial transition zone according to the response load.

[0079] S4. According to the indentation load-depth curve of each measuring point, obtain the elastic modulus data and indentation hardness data of each measuring point. Based on the elastic modulus data and indentation hardness data of each measuring point, as Figure 4 and Figure 5 shown in the figure, draw the elastic modulus distribution map of the test sample and the indentation hardness distribution map of the test sample.

[0080] Specifically, according to the indentation load-depth curve of each measuring point, calculate the slope at the top of the unloading section of the indentation load-depth curve of each measuring point, as Figure 10As shown, the calculation formula for the slope at the top of the unloading section of the indentation load-depth curve at each measurement point is as follows:

[0081]

[0082] Among them, S is the slope at the top of the unloading section of the indentation load-depth curve at each measurement point.

[0083] According to the slope at the top of the unloading section of the indentation load-depth curve at each measurement point, calculate the elastic modulus, i.e., the reduced elastic modulus, of each measurement point. The calculation formula is as follows:

[0084]

[0085] Among them, E r is the elastic modulus of each measurement point, β is the indenter geometry correction factor, β = 1.034, S is the slope at the top of the unloading section of the indentation load-depth curve at each measurement point, and A is the projected contact area of the indenter tip under the maximum load at the indentation.

[0086] According to the indentation load-depth curve at each measurement point, obtain the mechanical parameters of the specimen to be tested. The mechanical parameters of the specimen to be tested include the maximum load at the indentation, the indentation depth at the peak load, the residual indentation depth after complete unloading, and the indentation contact depth. Calculate the indentation contact depth according to the maximum load at the indentation and the indentation depth at the peak load. The calculation formula for the indentation contact depth is as follows:

[0087]

[0088] Among them, h max is the indentation depth at the peak load, h c is the indentation contact depth, P max is the maximum load at the indentation, and ε is the indenter-related parameter.

[0089] Calculate the projected contact area of the indenter tip under the maximum load at the indentation. The calculation formula for the projected contact area of the indenter tip under the maximum load at the indentation is as follows:

[0090]

[0091] Among them, according to the Oliver-Pharr calculation model, A is related to the contact depth between the indenter and the specimen, h c and the parameters of the indenter. A = ah c 2 , a is the parameter related to the indenter shape. For the Berkovich indenter, a = 24.56, ε is the parameter related to the indenter, taking 0.75 for the Berkovich indenter, and h c is the indentation contact depth.

[0092] The calculation formula for the indentation hardness at each measurement point is as follows:

[0093]

[0094] Among them, P max is the maximum load at the indentation, H is the indentation hardness at each measurement point, and A is the projected contact area of the indentation tip under the maximum load at the indentation.

[0095] During the unloading process, the recovery of the indentation depth is determined by the true elastic modulus Es of the specimen. Assuming that the elastic modulus of the indenter is known, the true elastic modulus of the specimen can be determined by the following formula:

[0096]

[0097] Among them, E s is the true elastic modulus of the specimen, υ s is the Poisson's ratio of the specimen, E r is the reduced elastic modulus, υ i is the Poisson's ratio of the indenter, and E i is the elastic modulus of the indenter.

[0098] S5. According to the elastic modulus distribution map of the test sample and the indentation hardness distribution map of the test sample, measure the thickness of the asphalt mortar-aggregate interfacial transition zone.

[0099] Specifically, by calculating the elastic modulus and indentation hardness of the tested specimen through the change trend curve of the indentation depth data at each measurement point with the applied indentation force, the range of the interfacial transition zone of different types of asphalt mixtures is obtained. Among them, the asphalt type has a relatively small influence on it, while the aggregate has a more obvious influence. Therefore, the thickness of the interfacial transition zone of limestone asphalt mixture is 10μm - 18μm, and the thickness of the interfacial transition zone of basalt asphalt mixture is 6μm - 12μm. The results show that the thickness and hardness of the interfacial transition zone of asphalt mixture mainly depend on the aggregate characteristics, while the elastic modulus is jointly affected by the asphalt mortar and the aggregate. As Figure 7 shown, by using the elastic modulus and indentation hardness as evaluation indexes respectively to identify the interfacial transition zone of different kinds of asphalt mixtures, the same range of interfacial transition zone thickness can be obtained.

[0100] S6. According to the total test energy obtained from the nano-indentation testing machine, calculate the test pure plastic performance through energy analysis method. According to the total test energy, test elastic energy and test pure plastic performance, calculate the test fracture energy, and according to the test fracture energy, calculate the critical energy release rate for the generation of specimen cracks.

[0101] Specifically, the nanoindentation tester will display the total test energy and the elastic performance of the test, and record them for calculating the pure plastic performance of the test. According to the residual indentation depth after complete unloading, the total test energy, and the indentation depth at the peak load, the pure plastic performance of the test is calculated. The calculation formula for the pure plastic performance of the test is as follows:

[0102]

[0103] Among them, U t is the total test energy, U p is the plastic performance of the test, h f is the residual indentation depth after complete unloading, h max is the indentation depth at the peak load.

[0104] Based on the total test energy and the elastic performance of the test obtained from the testing machine, and the calculated pure plastic performance of the test, the fracture energy of the test is jointly calculated. The calculation formula for the fracture energy of the test is as follows:

[0105] U c = U t - U e - U p

[0106] Among them, U t is the total test energy, U c is the fracture energy of the test, U e is the elastic performance of the test, U p is the plastic performance of the test.

[0107] Based on the fracture energy of the test and the contact area between the indenter and the specimen at the maximum indentation depth, the critical energy release rate for crack generation is jointly calculated. The formula for the critical energy release rate for crack generation is as follows:

[0108]

[0109] A max = 24.56h 2 max

[0110] Among them, U c is the fracture energy of the test, A max is the contact area at the maximum indentation depth, G c is the critical energy release rate for crack generation, h max is the indentation depth at the peak load.

[0111] S7. According to the critical energy release rate for crack generation of the specimen, the fracture toughness of each measuring point is calculated by the energy analysis method. Based on the fracture toughness of each measuring point, the fracture toughness distribution map of the specimen is drawn

[0112] Specifically, the calculation formula for the fracture toughness of each measurement point is as follows:

[0113]

[0114] Among them, K IC is the fracture toughness of each measurement point, E r is the elastic modulus of each measurement point, and G c is the critical energy release rate for crack generation.

[0115] According to the energy input during the nano-indentation test, the fracture toughness of the test sample is calculated using the energy analysis method to obtain the average fracture toughness and standard deviation. Among the four interfacial transition zones, the interfacial transition zone of SBS modified asphalt-limestone has the largest K IC , which is 0.919 MPa·m 0.5 , and the interfacial transition zone of matrix asphalt-basalt has the smallest K IC , which is 0.711 MPa·m 0.5 . It is reflected that the interfacial transition zone of SBS modified asphalt mixture has a higher elastic modulus, and the formed interfacial transition zone is more stable; more asphalt is adsorbed on the surface of limestone, and the formed interfacial transition zone is thicker, so the fracture toughness is greater, the performance of the interfacial transition zone to resist crack propagation is better, and the overall mechanical properties are more stable. The thickness of the asphalt mortar-aggregate interfacial transition zone is used for comparative analysis to explain the subjective correlation between the thickness of the interfacial transition zone and its fracture resistance performance.

[0116] Furthermore, the fracture toughness distribution map of the test sample is drawn, and it is found that the distribution trend of the fracture toughness is consistent with both the elastic modulus and the indentation hardness. The fracture toughness of the interfacial transition zone close to the asphalt mortar is less than that of the interfacial transition zone close to the aggregate. The higher the fracture toughness value of the interfacial transition zone, the greater the critical stress required for the unstable crack propagation. Therefore, stress concentration is more likely to occur at the junction of the interfacial transition zone and the asphalt mortar in the asphalt mixture, resulting in brittle fracture.

[0117] S8. Through linear regression analysis, based on the fracture toughness and elastic modulus of each measurement point, the relationship formula between the fracture toughness of each measurement point and the elastic modulus of each measurement point is determined to generate the first prediction formula. Through linear regression analysis, based on the fracture toughness and indentation hardness of each measurement point, the relationship formula between the fracture toughness of each measurement point and the indentation hardness of each measurement point is determined to generate the second prediction formula.

[0118] Specifically, the first prediction formula is as follows:

[0119] K IC =α1E r +β1

[0120] Among them, K IC is the fracture toughness of each measurement point, E r$E$ is the elastic modulus of each measuring point, $\alpha_1$ is the fitting parameter related to the elastic modulus, and $\beta_1$ is the intercept term fitting parameter related to the elastic modulus.

[0121] Specifically, the second prediction formula is as follows:

[0122] $K$ IC $=\alpha_2H + \beta_2$

[0123] where $K$ IC is the fracture toughness of each measuring point, $H$ is the indentation hardness of each measuring point, $\alpha_2$ is the fitting parameter related to the elastic modulus, and $\beta_2$ is the intercept term fitting parameter related to the elastic modulus.

[0124] As Figure 8 and Figure 9 shown, based on the elastic modulus and indentation hardness to predict the fracture toughness, linear regression fitting is performed on the nano-scale mechanical parameters of four asphalt mixture test samples respectively, and the fracture toughness prediction model and correlation coefficient are obtained. There is a good positive correlation between the elastic modulus and indentation hardness obtained from the nano-indentation test and the fracture toughness. The correlation coefficient $R$ 2 is greater than 0.91 for all, and among them, the correlation between the elastic modulus and the fracture toughness is higher, and $R$ 2 is greater than 0.95 for all. The prediction model shows that as the elastic modulus increases, the fracture toughness also increases. This is because the increase in the elastic modulus can improve the ultimate fracture strength, thereby enhancing the material's anti-fracture and crack instability propagation capabilities.

[0125] S9. Substitute the elastic modulus of each measuring point into the first prediction formula, and substitute the indentation hardness of each measuring point into the second prediction formula to obtain the predicted fracture toughness of each measuring point.

[0126] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the microscopic fracture performance of the interface transition zone of asphalt mixture, characterized in that the steps Including: S1. Prepare Marshall specimens of asphalt mixture, cut the specimens using a metallographic cutting machine, and polish the cut specimens using a polishing cloth and polishing fluid to obtain polished specimens. The polished specimens include the asphalt mortar-aggregate interface transition zone; S2. Select the asphalt mortar-aggregate interface transition zone in the polished specimens under a microscope, divide the test area according to the asphalt mortar-aggregate interface transition zone in the specimens, and conduct nanoindentation tests on the specimens in the test area to obtain the variation trend of the indentation depth data at each measurement point with the applied indentation force; S3. Draw the indentation load-depth curve of each measurement point according to the variation trend of the indentation depth data at each measurement point with the applied indentation force; S4. Obtain the elastic modulus data and indentation hardness data of each measurement point according to the indentation load-depth curve of each measurement point. Based on the elastic modulus data and indentation hardness data of each measurement point, draw the elastic modulus distribution map of the specimen and the indentation hardness distribution map of the specimen; S5. Measure the thickness of the asphalt mortar-aggregate interface transition zone according to the elastic modulus distribution map of the specimen and the indentation hardness distribution map of the specimen; S6. Calculate the pure plastic performance of the test through energy analysis according to the total test energy obtained from the nanoindentation testing machine. Calculate the fracture energy of the test according to the total test energy, the elastic energy of the test, and the pure plastic performance of the test. Calculate the critical energy release rate of specimen crack generation according to the fracture energy of the test; S7. Calculate the fracture toughness of each measurement point through energy analysis according to the critical energy release rate of specimen crack generation. Draw the fracture toughness distribution map of the specimen according to the fracture toughness of each measurement point; S8. Through linear regression analysis, determine the relationship formula between the fracture toughness of each measurement point and the elastic modulus of each measurement point according to the fracture toughness and elastic modulus of each measurement point, and generate the first prediction formula. Through linear regression analysis, determine the relationship formula between the fracture toughness of each measurement point and the indentation hardness of each measurement point according to the fracture toughness and indentation hardness of each measurement point, and generate the second prediction formula; S9. Substitute the elastic modulus of each measurement point into the first prediction formula, and substitute the indentation hardness of each measurement point into the second prediction formula to obtain the predicted fracture toughness of each measurement point.

2. The method for predicting the microscopic fracture properties of the asphalt mixture interface transition zone according to claim 1, characterized in that, According to the indentation load-depth curve of each measurement point, obtain the elastic modulus data and indentation hardness data of each measurement point, including: According to the indentation load-depth curve of each measurement point, calculate the slope at the top of the unloading section of the indentation load-depth curve of each measurement point. The calculation formula for the slope at the top of the unloading section of the indentation load-depth curve of each measurement point is as follows: where S is the slope at the top of the unloading section of the indentation load-depth curve of each measurement point; According to the slope at the top of the unloading section of the indentation load-depth curve of each measurement point, the calculation formula for the elastic modulus of each measurement point is as follows: Among them, E r is the elastic modulus of each measurement point, β is the indenter geometry correction factor, S is the slope at the top of the unloading section of the indentation load-depth curve of each measurement point, and A is the projected contact area of the indentation tip under the maximum load at the indentation According to the indentation load-depth curve of each measurement point, obtain the mechanical parameters of the specimen to be tested. The mechanical parameters of the specimen to be tested include the maximum load at the indentation, the indentation depth at the peak load, the residual indentation depth after complete unloading, and the indentation contact depth. Calculate the indentation contact depth according to the maximum load at the indentation and the indentation depth at the peak load. The calculation formula for the indentation contact depth is as follows: where h max is the indentation depth at peak load, h c is the indentation contact depth, P max is the maximum load at the indentation, and ε is an indenter-related parameter Calculate the projected contact area of the indentation tip under the maximum load at the indentation according to the indentation contact depth. The calculation formula for the projected contact area of the indentation tip under the maximum load at the indentation is as follows: where A is the projected contact area of the indentation tip under the maximum load at the indentation, and h c is the indentation contact depth Calculate the indentation hardness of each measurement point according to the projected contact area of the indentation tip under the maximum load at the indentation and the maximum load at the indentation. The calculation formula for the indentation hardness of each measurement point is as follows: Among them, P max is the maximum load at the indentation, H is the indentation hardness of each measuring point, and A is the projected contact area of the indentation tip under the maximum load at the indentation.

3. The method for predicting the microscopic fracture performance of the asphalt mixture interface transition zone according to any one of claims 1-2, characterized in that According to the total test energy obtained from the nano-indentation testing machine, calculate the test pure plastic performance through energy analysis. According to the total test energy, test elastic energy, and test pure plastic performance, calculate the test fracture energy. According to the test fracture energy, calculate the critical energy release rate for crack generation in the specimen, including: Calculate the test pure plastic energy according to the residual indentation depth after complete unloading, the total test energy, and the indentation depth at the peak load. The calculation formula for the test pure plastic performance is as follows: Among them, U t is the total test energy, U p is the plastic energy of the test, h f is the residual indentation depth after complete unloading, h max is the indentation depth at the peak load The calculation formula for the test fracture energy is as follows: U c = U t - U e - U p Among them, U t is the total test energy, U c is the test fracture energy, U e is the test elastic energy, U p is the test plastic energy According to the test fracture energy, calculate the critical energy release rate for crack generation. The formula for the critical energy release rate for crack generation is as follows: Among them, U c is the experimental fracture energy, A max is the contact area at the maximum indentation depth, G c is the critical energy release rate for crack generation, h max is the indentation depth at the peak load.

4. The microscopic fracture property prediction method for the asphalt mixture interface transition zone according to claim 1, characterized in that The calculation formula for the fracture toughness of each measurement point is as follows: Among them, K IC is the fracture toughness of each measuring point, E r is the elastic modulus of each measuring point, and G c is the critical energy release rate for crack generation.

5. The method for predicting the microscopic fracture performance of the asphalt mixture interface transition zone according to claim 1, characterized in that The first prediction formula is as follows: K IC = α1E r + β1 Among them, K IC is the fracture toughness of each measurement point, E r is the elastic modulus of each measurement point, α1 is the fitting parameter related to the elastic modulus, and β1 is the intercept term fitting parameter related to the elastic modulus. The second prediction formula is as follows: K IC = α2H + β2 Among them, K IC is the fracture toughness of each measuring point, H is the indentation hardness of each measuring point, α2 is the fitting parameter related to the elastic modulus, and β2 is the intercept term fitting parameter related to the elastic modulus.

6. The method for predicting the microscopic fracture performance of the asphalt mixture interface transition zone according to claim 2, wherein, The indenter geometry correction factor is 1.034.

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