A method for identifying the initiation, propagation and fracture failure of asphalt fatigue cracks

Abstract

The present invention discloses a method for identifying the initiation, expansion, and fracture failure of asphalt fatigue cracks. The present invention uses a dynamic shear rheometer to perform a scanning test on an asphalt sample, collects torque T and deflection angle #imgabs0# data, and sequentially obtains the asphalt fatigue crack length a and the energy release rate G during the asphalt fatigue crack growth process. Finally, based on the evolution relationship between the asphalt fatigue crack length a and the number of cyclic loading cycles N, the dividing point between the fatigue crack initiation process and the expansion process is calculated, and the peak point of the energy release rate G is used as the critical point of asphalt fatigue failure. The present invention systematically solves the current problems of dividing asphalt into different fatigue stages under dynamic shear fatigue loads and determining the critical point of fatigue failure, and can finely analyze the fatigue process and behavioral characteristics of asphalt materials.

Description

Technical Field

[0001] The present invention specifically relates to an identification method for judging the initiation, expansion and fracture failure of asphalt fatigue cracks. Background Art

[0002] Under the repeated effects of vehicle loads, asphalt pavements inevitably develop fatigue cracking. The presence of fatigue cracks seriously affects the service life and driving comfort of asphalt pavements. Asphalt pavement's resistance to fatigue cracking is largely constrained by the fatigue properties of the asphalt material. Therefore, a deep understanding of the development and evolution of microscopic defects within asphalt materials is necessary to scientifically evaluate and differentiate the fatigue resistance of different asphalt materials. Existing asphalt material fatigue performance characterization methods analyze the combined effects of various microscopic defects on fatigue strength or life through macroscopic analysis using "fatigue equations" or "damage variables." These methods do not address the mechanical mechanisms of asphalt fatigue and fracture, nor the crack nucleation process. Consequently, they lack a detailed understanding and characterization of the fatigue fracture process. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention provides a method for identifying asphalt fatigue crack initiation, propagation, and fracture failure. This method distinguishes the initiation and propagation stages of fatigue cracks during scanning (fatigue) testing of asphalt, identifying and determining the critical point at which fatigue failure occurs. This allows for quantitative comparison of the crack initiation and propagation lifespans of different asphalt materials under dynamic shear loading.

[0004] The specific identification method of the present invention comprises the following steps:

[0005] (1) Use a dynamic shear rheometer to perform a scanning test on the asphalt sample and collect the torque T and deflection angle data;

[0006] (2) According to the collected torque T and deflection angle The fatigue crack length a of asphalt is calculated according to formula (1).

[0007]

[0008] Where T is the torque; Deflection angle; r0 is the initial radius of the sample, 4 mm; h is the height of the sample, 2 mm;

[0009] (3) According to formula (2), the energy release rate G during the growth of asphalt fatigue crack is further calculated.

[0010]

[0011] Where, |G*| is the dynamic shear modulus; e is the base of the natural logarithm; c is the correction coefficient of the crack tip plastic zone;

[0012] (4) The dividing point between the fatigue crack initiation process and the expansion process is calculated based on the evolution relationship between the asphalt fatigue crack length a and the number of cyclic loading times N, and the peak point of the energy release rate G is taken as the critical point of asphalt fatigue failure.

[0013] Preferably, the scanning test of the present invention is a strain-controlled time scanning test (traditional fatigue test) or a linear amplitude scanning test (accelerated fatigue test).

[0014] Further preferably, the strain-controlled time sweep test is a strain-controlled time sweep test on a parallel plate asphalt specimen using a dynamic shear rheometer, with a parallel plate diameter of 8 mm and a parallel plate gap of 2 mm; the strain level is 1%-10%, the test loading frequency is fixed at 10 Hz, the test temperature is 20°C, and the test is stopped when the dynamic shear modulus of the asphalt specimen decays to 10% of the initial value, and two parallel tests are performed on each group of samples.

[0015] Further preferably, the linear amplitude scanning test is a linear amplitude scanning test on a parallel plate asphalt sample using a dynamic shear rheometer, the parallel plate diameter is 8 mm, the parallel plate gap is 2 mm, the scanning range of the dynamic strain amplitude increases linearly from 0.1% to 30%, the test loading frequency is fixed at 10 Hz, the test temperature is 20°C, and the scanning time is designed to be 5 minutes, 10 minutes or 15 minutes.

[0016] Preferably, when a linear amplitude sweep test is used, step (4) is to obtain the crack growth rate da / dN according to formula (3), and calculate the dividing point between the crack initiation process and the growth process according to the evolution relationship between the asphalt crack growth rate da / dN and the energy release rate G, and use the peak point of the energy release rate G as the critical point of asphalt fatigue failure.

[0017]

[0018] Preferably, when a strain-controlled time sweep test is used, step (4) is to plot the crack growth curve in a plane rectangular coordinate system with the number of cyclic loading N as the abscissa and the fatigue crack length a as the ordinate. The turning point of the crack growth curve is defined as the demarcation point between the initiation and propagation of fatigue cracks in the asphalt; and the peak point of the energy release rate G is taken as the critical point of fatigue failure of the asphalt when the number of cyclic loading N is as the abscissa and the energy release rate G as the ordinate.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides an identification method for judging the initiation, expansion and fracture failure of asphalt fatigue cracks. The method is based on the theory of fracture mechanics, and calculates key indicators such as fatigue crack length and energy release rate of asphalt through dynamic mechanical response parameters in time scanning (traditional fatigue test) and linear amplitude scanning (accelerated fatigue test) to quantitatively analyze and characterize the damage evolution process inside the asphalt material. The method distinguishes and judges the initiation and expansion process of asphalt fatigue cracks by analyzing the evolution process of the crack growth curve in the traditional fatigue test and the evolution process of the crack expansion characteristic curve in the accelerated fatigue test, and proposes to use the peak point of the energy release rate as the criterion for fatigue failure of asphalt. The present invention systematically solves the current problems of dividing different fatigue stages of asphalt under dynamic shear fatigue load and determining the critical point of fatigue failure, and can finely study and judge the fatigue process and behavioral characteristics of asphalt materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the division of asphalt fatigue crack initiation and growth stages in asphalt time sweep test;

[0022] Figure 2 is the evolution of energy release rate in the asphalt time sweep test;

[0023] Figure 3 This is a schematic diagram of the division of asphalt fatigue crack initiation and growth stages in asphalt linear amplitude sweep test;

[0024] Figure 4 It is the evolution of the energy release rate of asphalt in the asphalt linear amplitude sweep test;

[0025] Figure 5 is the fatigue life of the matrix asphalt under different strain levels (the strain amplitude applied to the asphalt sample in the strain-controlled time sweep test)

[0026] Figure 6 The fatigue life of SBS modified asphalt (SBS modifier added to base asphalt) under different strain levels in time sweep test

[0027] Figure 7 The crack initiation and growth life of different asphalts at the same strain level in time sweep tests

[0028] Figure 8 The fatigue life of the matrix asphalt and SBS modified asphalt under three loading rates of linear amplitude sweep test

[0029] Figure 9 Crack initiation and growth life of matrix asphalt and SBS modified asphalt in a linear amplitude sweep test with a scanning time of 5 minutes DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] A method for identifying asphalt fatigue crack initiation, growth, and fracture failure, specifically operates as follows:

[0033] (1) Use a dynamic shear rheometer to perform a strain-controlled time sweep test (traditional fatigue test) on the asphalt sample to collect torque T and deflection angle Data: In the specific scanning test, the parallel plate diameter was 8 mm, the parallel plate gap was 2 mm, the strain level was 1%-10%, the test loading frequency was fixed at 10 Hz, the test temperature was 20°C, and the test was stopped when the dynamic shear modulus of the asphalt sample decayed to 10% of the initial value. Two parallel tests were performed on each group of samples.

[0034] (2) According to the collected torque T and deflection angle The fatigue crack length a of asphalt is calculated according to formula (1).

[0035]

[0036] Where T is the torque; Deflection angle; r0 is the initial radius of the sample, 4 mm; h is the height of the sample, 2 mm;

[0037] (3) According to formula (2), the energy release rate G during the growth of asphalt fatigue crack is further calculated.

[0038]

[0039] Where, |G*| is the dynamic shear modulus; e is the base of the natural logarithm; c is the correction coefficient of the crack tip plastic zone;

[0040] (4) According to the evolution relationship between the asphalt fatigue crack length a and the number of cyclic loading N, the dividing point between the fatigue crack initiation process and the expansion process is calculated, and the peak point of the energy release rate G is used as the critical point of asphalt fatigue failure. The specific operation is to draw a plot in a plane rectangular coordinate system with the number of cyclic loading N as the horizontal coordinate and the fatigue crack length a as the vertical coordinate to obtain the crack growth curve (such as Figure 1 The turning point of the crack growth curve is defined as the dividing point between the initiation and expansion of asphalt fatigue cracks; the number of cyclic loading N is used as the horizontal coordinate and the energy release rate G is used as the vertical coordinate in the plane rectangular coordinate system (as shown in Figure 2). Figure 2 The peak point of energy release rate G is taken as the critical point of fatigue failure of asphalt.

[0041] Since the fatigue failure process of asphalt in the time sweep test can be further divided into the crack initiation stage and the crack propagation stage, the corresponding fatigue life (N f ) is also determined by the crack initiation life (N i ) and crack growth life (N p ) composition, crack growth life (N p ) is calculated as follows:

[0042] N p =N f -N i

[0043] Example 2

[0044] A method for identifying asphalt fatigue crack initiation, growth, and fracture failure, specifically operates as follows:

[0045] (1) Use a dynamic shear rheometer to perform a linear amplitude sweep test (accelerated fatigue test) on the asphalt sample and collect the torque T and deflection angle Data; In the specific scanning test, the parallel plate diameter is 8 mm, the parallel plate gap is 2 mm, the dynamic strain amplitude scanning range increases linearly from 0.1% to 30%, the test loading frequency is fixed at 10 Hz, the test temperature is 20°C, and the scanning time is designed to be 5 minutes, 10 minutes, or 15 minutes;

[0046] (2) According to the collected torque T and deflection angle The fatigue crack length a of asphalt is calculated according to formula (1).

[0047]

[0048] Where T is the torque; Deflection angle; r0 is the initial radius of the sample, 4 mm; h is the height of the sample, 2 mm;

[0049] (3) According to formula (2), the energy release rate G during the growth of asphalt fatigue crack is further calculated.

[0050]

[0051] Where, |G*| is the dynamic shear modulus; e is the base of the natural logarithm; c is the correction coefficient of the crack tip plastic zone;

[0052] (4) is to obtain the crack growth rate da / dN according to formula (3), and calculate the dividing point between the crack initiation process and the expansion process according to the evolution relationship between the asphalt crack growth rate da / dN and the energy release rate G, and use the peak point of the energy release rate G as the critical point of asphalt fatigue failure. The specific operation is to draw the crack growth characteristic curve with the energy release rate G as the horizontal coordinate and the crack growth rate da / dN as the vertical coordinate, and take the first inflection point of the crack growth characteristic curve as the dividing point between the initiation and expansion of asphalt fatigue cracks. In order to accurately divide the different fatigue stages of asphalt under dynamic shear load, the secant method is used to calculate the dividing point. The number of cyclic loading times N corresponding to this point is the crack initiation life of the asphalt material (N i ),like Figure 3 As shown in the figure, the number of cyclic loading N is used as the horizontal axis and the energy release rate G is used as the vertical axis. The peak point of the energy release rate G is taken as the critical point of fatigue failure of the asphalt. The fatigue life of the asphalt sample at this specific temperature, loading frequency and loading rate can be determined (N f ),like Figure 4 shown.

[0053]

[0054] According to the above implementation method, the crack initiation life (N) of different asphalts was determined. i ), crack growth life (N p ) and the total fatigue life (N f ).from Figure 5-Figure 9 It can be seen that with the increase of strain level in the time sweep test, the fatigue life of asphalt (N f ) gradually decreases; with the extension of the scanning time in the linear amplitude sweep test, the fatigue life of the asphalt (N f ) gradually increases. Compared with different types of asphalt, the crack initiation life of SBS modified asphalt (N i ) and crack growth life (N p ) are significantly higher than those of the matrix asphalt, so the addition of modifiers can significantly improve the fatigue life of asphalt (N f ); Compared with the crack initiation life (N i ), Modifier effect on crack growth life (N p ) has a more significant improvement effect.

[0055] It should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and may have other variations. All variations directly or indirectly derived from the present disclosure by those skilled in the art should be considered to be within the scope of protection of the present invention.

Claims

1. A method for identifying the initiation, expansion and fracture failure of asphalt fatigue cracks, characterized in that: The following steps are involved: (1) Use a dynamic shear rheometer to perform a scanning test on the asphalt sample and collect the torque T and deflection angle data; (2) According to the collected torque T and deflection angle The fatigue crack length a of asphalt is calculated according to formula (1). Where T is the torque; Deflection angle; r0 is the initial radius of the sample, 4 mm; h is the height of the sample, 2 mm; (3) According to formula (2), the energy release rate G during the growth of asphalt fatigue crack is further calculated. Where, |G*| is the dynamic shear modulus; e is the base of the natural logarithm; c is the correction coefficient of the crack tip plastic zone; (4) The dividing point between the fatigue crack initiation process and the expansion process is calculated based on the evolution relationship between the asphalt fatigue crack length a and the number of cyclic loading times N, and the peak point of the energy release rate G is used as the critical point of asphalt fatigue failure; When the linear amplitude sweep test is used, step (4) is to obtain the crack growth rate da / dN according to formula (3), and calculate the dividing point between the crack initiation process and the growth process according to the evolution relationship between the asphalt crack growth rate da / dN and the energy release rate G, and take the peak point of the energy release rate G as the critical point of asphalt fatigue failure. When a strain-controlled time sweep test is used, step (4) is to plot the number of cyclic loading N as the horizontal coordinate and the fatigue crack length a as the vertical coordinate in a plane rectangular coordinate system to obtain a crack growth curve, and define the turning point of the crack growth curve as the dividing point between the initiation and extension of asphalt fatigue cracks; and to plot the number of cyclic loading N as the horizontal coordinate and the energy release rate G as the vertical coordinate in a plane rectangular coordinate system, and take the peak point of the energy release rate G as the critical point of fatigue failure of asphalt.

2. The method for identifying asphalt fatigue crack initiation, expansion and fracture failure according to claim 1, characterized in that: The scanning test is a strain-controlled time scanning test or a linear amplitude scanning test.

3. The identification method for judging the initiation, expansion and fracture failure of asphalt fatigue cracks according to claim 2 is characterized in that: The strain-controlled time sweep test is a strain-controlled time sweep test performed on parallel plate asphalt specimens using a dynamic shear rheometer, with a parallel plate diameter of 8 mm and a parallel plate gap of 2 mm; the strain level is 1%-10%, the test loading frequency is fixed at 10 Hz, the test temperature is 20°C, and the test is stopped when the dynamic shear modulus of the asphalt specimen decays to 10% of the initial value. Two parallel tests are performed on each group of samples.

4. The identification method for judging the initiation, expansion and fracture failure of asphalt fatigue cracks according to claim 2 is characterized in that: The linear amplitude sweep test is a linear amplitude sweep test performed on a parallel plate asphalt sample using a dynamic shear rheometer. The parallel plate diameter is 8 mm, the parallel plate gap is 2 mm, the dynamic strain amplitude sweep range increases linearly from 0.1% to 30%, the test loading frequency is fixed at 10 Hz, the test temperature is 20°C, and the sweep time is designed to be 5 minutes, 10 minutes or 15 minutes.

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