CN112098524B - A method for identifying the fracture process of asphalt concrete and quantifying microcracks based on acoustic emission - Google Patents
A method for identifying the fracture process of asphalt concrete and quantifying microcracks based on acoustic emission Download PDFInfo
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Abstract
本发明提供一种基于声发射识别沥青混凝土断裂过程及量化微裂纹的方法，其包括以下步骤：确定声发射信号参数，统计不同级配沥青混凝土断裂过程中力‑位移、声发射信号参数及表面裂纹图片数据，通过对各数据的分析，将沥青混凝土断裂过程分为弹性阶段、损伤累积阶段和裂纹扩展阶段并得到各阶段阈值，根据声发射信号参数与阈值的关系识别沥青混凝土的断裂过程；还构建了声发射能量‑微裂纹模型，根据模型得出不同级配沥青混凝土微裂纹情况判断表达式；根据表达式计算得到沥青混凝土的微裂纹密度，使沥青混凝土的微裂纹得到直观量化。本发明能够根据声发射振铃计数及能量对不同级配沥青混凝土断裂过程及断裂产生的微裂纹进行实时检测，工程适用性强。
The invention provides a method for identifying the fracture process of asphalt concrete and quantifying micro-cracks based on acoustic emission, which comprises the following steps: determining acoustic emission signal parameters, counting force-displacement, acoustic emission signal parameters and surface Crack image data, through the analysis of each data, the fracture process of asphalt concrete is divided into elastic stage, damage accumulation stage and crack propagation stage, and the thresholds of each stage are obtained, and the fracture process of asphalt concrete is identified according to the relationship between the acoustic emission signal parameters and the threshold; The acoustic emission energy-microcrack model is also constructed, and the expression for judging the microcracks of asphalt concrete with different grades is obtained according to the model; the microcrack density of asphalt concrete is calculated according to the expression, so that the microcrack of asphalt concrete can be directly quantified. The invention can perform real-time detection on the fracture process of asphalt concrete with different grades and the micro-cracks generated by the fracture according to the acoustic emission ringing count and energy, and has strong engineering applicability.
Description
Technical Field
The invention belongs to the technical field of nondestructive testing, and particularly relates to a method for identifying a bituminous concrete fracture process and quantifying microcracks based on acoustic emission.
Background
Asphalt concrete is widely applied to the field of roads due to the characteristics of comfortable driving, convenient maintenance and the like. When the asphalt concrete road is used, the asphalt concrete road is subjected to load and environmental action, and micro-cracks appear on the surface, which can affect the driving safety and bring expensive maintenance cost along with further expansion of the micro-cracks. Therefore, it is important to detect and identify the road cracks, but the traditional visual detection needs to consume a large amount of labor cost, has low reliability and does not have real-time detection performance. Therefore, it is important to develop a method for accurately identifying and monitoring the asphalt concrete fracture process and microcracks.
The acoustic emission is a form of transient elastic wave generated by energy released when a signal cracks due to a material, and is widely applied to the field of nondestructive testing because of the characteristics of instantaneity, sensitivity to defects and the like. The existing monitoring of asphalt concrete based on an acoustic emission technology mainly focuses on monitoring of low-temperature cracking temperature and macro cracks and trend prediction, but the existing monitoring method does not identify the cracking process of the asphalt concrete and detect and identify micro cracks, and the early identification of the micro cracks has important significance for reducing maintenance cost and prolonging the service life of roads. Therefore, corresponding method research is needed for real-time detection of the micro cracks of the asphalt concrete road based on the acoustic emission technology in actual use.
Disclosure of Invention
Aiming at the defects of the prior art, the invention establishes a method for dividing the asphalt concrete fracture process and quantitatively identifying microcracks under the action of three-point bending based on an acoustic emission technology. Analyzing to obtain the asphalt concrete fracture process according to acoustic emission signal parameters, mainly the change conditions of ringing count and accumulated energy in the concrete fracture process, and quantifying the size of the microcracks according to signal parameters when the microcracks appear on the surface of the asphalt concrete. The method simulates the mechanical change condition of the asphalt concrete under pressure in actual use, and divides the asphalt concrete fracture process and quantitatively identifies microcracks by analyzing the change of the acoustic emission signal parameters in the recorded bending process.
The invention discloses a method for identifying a bituminous concrete fracture process based on acoustic emission, which is characterized by comprising the following steps of: which comprises the following steps:
s1, determining acoustic emission signal parameters;
by analyzing the bending fracture failure process of the asphalt concrete with different grading, the acoustic emission signal parameters are determined as follows: amplitude, ringing count, energy, duration, and rise time; the energy is an acoustic emission time signal, the area under the envelope line reflects the intensity of an acoustic emission event, and the expression is as follows:
wherein E is energy, V (t) is recorded voltage, and t is acoustic emission signal duration;
the different-gradation asphalt concrete comprises a first type asphalt concrete, a second type asphalt concrete and a third type asphalt concrete used by an asphalt concrete pavement;
s2, counting force-displacement data, acoustic emission signal parameter data and microscopic observation surface crack picture data in the process of fracture of asphalt concrete with different grades under pressure;
s3, analyzing the data in the step S2 to divide the asphalt concrete fracture process into: an elastic stage, a damage accumulation stage and a crack propagation stage;
s4, identifying the asphalt concrete fracture process according to the acoustic emission signal parameters, which comprises the following steps,
s41, selecting key data in the acoustic emission signal parameter data;
determining key data of acoustic emission signals with strong correlation with the asphalt concrete fracture process as ringing count and energy through the change conditions of mechanical properties and acoustic emission signal parameter data in the asphalt concrete bending fracture process;
s42, determining stage thresholds of acoustic emission signal key data at different stages of the asphalt concrete fracture process;
by counting the acoustic emission cumulative ringing count and the cumulative energy in the process of the different-graded asphalt concrete fracture, the stage thresholds of the acoustic emission signal key data of the different-graded asphalt concrete fracture process in different stages are obtained, and are respectively the threshold W of the cumulative ringing count stageiOr accumulated energy phase threshold EiWherein i is the gradation of asphalt concrete, i is 1,2, 3;
threshold value W of accumulative ringing counting stage of key data of first type asphalt concrete acoustic emission signal1Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 10; the cumulative ringing count range during the damage accumulation phase is: 0<W1Less than or equal to 178; the cumulative ringing count range for the crack propagation stage is: w1>178；
The threshold value W of the accumulative ringing counting stage of the key data of the acoustic emission signal of the second type asphalt concrete2Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 20; the cumulative ringing count range during the damage accumulation phase is: 0<W2Less than or equal to 186; the cumulative ringing count range for the crack propagation stage is: w2>186；
Threshold value W of accumulative ringing counting stage of third type asphalt concrete acoustic emission signal key data3Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 30; the cumulative ringing count range during the damage accumulation phase is: 0<W3Less than or equal to 224; the cumulative ringing count range for the crack propagation stage is: w3>224；
Threshold value E of accumulated energy stage of key data of first type asphalt concrete acoustic emission signal1Comprises the following steps: the cumulative energy range for the elastic phase is: e 10; the cumulative energy range during the damage accumulation phase is: 0<E1Less than or equal to 0.0138; the cumulative energy range at the crack propagation stage is: e1>0.0138；
Cumulative energy stage threshold E of key data of acoustic emission signal of second type asphalt concrete2Comprises the following steps: the cumulative energy range for the elastic phase is: e 20; the cumulative energy range during the damage accumulation phase is: 0<E2Less than or equal to 0.0176; the cumulative energy range at the crack propagation stage is: e2>0.0176；
Threshold value E of accumulated energy stage of key data of third type asphalt concrete acoustic emission signal3Comprises the following steps: the cumulative energy range for the elastic phase is: e 30; the cumulative energy range during the damage accumulation phase is: 0<E3Less than or equal to 0.0238; the cumulative energy range at the crack propagation stage is: e3>0.0238；
S43, counting key data of acoustic emission signals of the asphalt concrete to be identified; and
and S44, comparing the key data of the acoustic emission signals obtained by statistics with a stage threshold value, and determining the fracture process of the asphalt concrete to be identified.
Preferably, the elastic phase in S3 means that the load linearly increases with displacement, during which no internal damage and no crack occurs, and no acoustic emission signal is generated.
Preferably, the damage accumulation stage in S3 is the period from the first occurrence of the acoustic emission signal to the beginning of the microcrack, and in the damage accumulation stage, the occurrence of the internal damage causes the acoustic emission signal to be generated, and the acoustic emission cumulative ringing count continuously increases.
Preferably, the crack propagation stage in S3 means that the acoustic emission signal continuously increases as the crack propagates, the cumulative ringing count gradually increases, and a sudden surge also occurs, and finally the acoustic emission signal tends to be stable.
Preferably, the ringing number is a number of oscillations of the crossing threshold signal.
A method of identifying and quantifying microcracks based on acoustic emissions, comprising the steps of;
p1, constructing an acoustic emission energy-microcrack model;
according to the nominal maximum grain diameter, the void ratio and the acoustic emission energy of the mixture in different gradation of the asphalt concrete, an acoustic emission energy-microcrack model is constructed, and the model is as follows:
where a is the microcrack density, E is the cumulative energy, biIs the nominal maximum grain diameter, c, of the mixture in different gradation of asphalt concreteiThe porosity of the mixture in different gradations of the asphalt concrete is shown, i is the gradation model of the asphalt concrete, and i is 1,2 and 3; b1、c1Corresponding to the coefficient of the first type asphalt concrete material; b2、c2Corresponding to the coefficient of the second type asphalt concrete material; b3、c3Corresponding to the coefficient of the third type asphalt concrete material;
p2, deducing to obtain a judgment expression (3) of the microcrack condition of the asphalt concrete with different gradation according to the constructed acoustic emission energy-microcrack model;
fitting the micro-crack density of the graded asphalt concrete with the acoustic emission accumulated energy before the micro-crack appears, and deducing to obtain a judgment expression of the micro-crack condition of the graded asphalt concrete, namely a relational expression of the acoustic emission accumulated energy and the micro-crack density, wherein the judgment expression is expressed as follows:
first type a-5.5022E1.2864
Type II, a is 0.2223E0.3598
Type III, a-0.9079E0.9032 (4)；
P3, statistically calculating the accumulated energy data of the acoustic emission signals of the asphalt concrete to be identified according to the expression (1);
p4, determining the grading type of the asphalt concrete to be identified;
and P5, substituting the accumulated energy data into the acoustic emission energy-microcrack model of the corresponding grading type, and calculating to obtain the density of the microcracks of the asphalt concrete so as to quantify the microcracks of the asphalt concrete.
The invention has the following beneficial effects:
1. the invention provides a method for dividing the fracture process of asphalt concrete according to acoustic emission ringing count and energy, which can judge the fracture process in the actual use of an asphalt road, can achieve the purpose of real-time detection, and has strong engineering applicability.
2. The invention provides a calculation method for quantifying asphalt concrete microcracks, which can analyze the size of the asphalt concrete surface cracks by calculating the acoustic emission accumulated energy.
3. The invention considers the fracture process and the micro-crack quantification of the asphalt concrete under various gradations, and can comprehensively reflect the fracture conditions under different conditions.
Drawings
FIG. 1 is a schematic flow chart of a method for identifying a bituminous concrete fracture process and quantifying microcracks based on acoustic emission according to the present invention;
FIG. 2a is a parameter trend chart of the first type graded asphalt concrete fracture process of the invention;
FIG. 2b is a graph showing the behavior of parameters in the second type graded asphalt concrete fracture process according to the present invention;
FIG. 2c is a graph of the parameter trend during the fracture of a third type of graded asphalt concrete according to the present invention; and
FIG. 3 is a schematic diagram of three grading asphalt concrete acoustic emission cumulative energy and microcrack size models of the present invention.
Detailed Description
The technical scheme and the specific embodiment of the invention are explained in detail below with reference to the accompanying drawings 1-3, and the method for identifying the asphalt concrete fracture process and quantifying the microcracks based on acoustic emission comprises the following steps:
s1: determining acoustic emission parameters:
the acoustic emission signal is a transient waveform generated in the asphalt concrete fracture process, and the received acoustic emission signal comprises several parameters: amplitude, ringing count, energy, duration, and rise time. The amplitude of the acoustic emission signal has a certain influence on energy, the larger the amplitude is, the higher the energy value is, the number of acoustic emission ringing times is the number of oscillation times of crossing the threshold signal, the energy is an acoustic emission time signal, and the area under the envelope line reflects the intensity of the acoustic emission event. The expression is as follows:
where E is the energy, V (t) is the recorded voltage, and t is the acoustic emission signal duration.
S2, counting force-displacement data, acoustic emission signal parameter data and microscopic observation surface crack picture data in the process of fracture of asphalt concrete with different grades under pressure;
the asphalt concrete gradation used by the current asphalt concrete pavement is mainly divided into three types: the first type is AC-13 type: continuous gradation mixture, the maximum nominal diameter is 13mm, the second type is AC-16 type: the maximum nominal diameter of the continuous graded mixture is 16mm, and the third type is SMA-13 type: the asphalt mastic mixture is prepared by mixing modified asphalt with fiber, wherein the first type AC-13 and the second type AC-16 belong to common dense-graded asphalt concrete used for a traditional asphalt concrete pavement layer, the third type SMA-13 belongs to an asphalt mastic macadam mixture commonly used for a high-performance pavement, and fiber and other materials are added.
The method comprises the following steps of obtaining force-displacement data, acoustic emission signal data and a microscope observation surface crack picture in the fracture process of asphalt concrete test pieces (AC-13, AC-16 and SMA-13 types), wherein the method comprises the following steps:
s21, loading the asphalt concrete test piece by using three-point bending to obtain force-displacement data in the fracture process, and simultaneously recording an acoustic emission signal in the pressing process and observing the initiation and the expansion of cracks on the surface of the test piece by using a microscope;
and S22, counting force-displacement data, acoustic emission signal data and microscope observation surface crack images in the fracture process of the asphalt concrete test pieces with different grades according to the asphalt concrete load, acoustic emission ringing count and microscope observation surface crack initiation and propagation conditions.
S3, analyzing the data in S2 to divide the asphalt concrete fracture process into: an elastic stage, a damage accumulation stage and a crack propagation stage;
the fracture process refers to the whole process from the beginning of damage to failure of the asphalt concrete from the inside; the mechanical property refers to the change process of the asphalt concrete along with the increasing load of deformation.
And analyzing the data in the S2, and dividing the asphalt concrete fracture process into: elastic phase, damage accumulation phase and crack propagation phase.
Preferably, the division of the damage accumulation phase is determined by recording the acoustic emission signal start time and the microcrack initiation time.
Preferably, the acoustic emission accumulated energy-microcrack model is obtained by fitting the microcrack density at the time when the microcracks appear in the plurality of groups of test pieces under various gradations and the calculated acoustic emission accumulated energy, and parameter values under different gradations are obtained.
Preferably, the division of the crack propagation phase is determined by the time of initiation of the microcracks and the time of final failure; the proportion of the crack propagation stage in the whole fracture process is calculated by the proportion of the acoustic emission ringing count in the crack propagation stage to the acoustic emission ringing count in the whole fracture process.
The acoustic emission ringing frequency and energy continuously rise in the stage when the crack is expanded after the crack appears. An elastic phase, during which no acoustic emission signal is generated due to no damage and no cracks occurring inside, the load increasing linearly with the displacement; in the damage accumulation stage, an acoustic emission signal is generated due to the occurrence of internal damage, and the acoustic emission accumulated ringing count continuously increases; in the crack propagation stage, the acoustic emission signal continuously increases along with the propagation of the crack, the cumulative ringing count also gradually increases, and a sudden surge also occurs in the crack rapid propagation stage, and finally the crack tends to be stable.
In the damage accumulation phase:
by analyzing the acoustic emission data of the asphalt concrete with different gradation under pressure and observing the surface crack picture by a microscope, in the process of asphalt mixture damage, the damage accumulation stage is a period from the initial occurrence of the acoustic emission signal to the initiation of the microcrack. Wherein, the asphalt mixture has microcrack after peak load, and the internal damage causes the reduction of bearing capacity. The damage accumulation phase can be distinguished by acoustic emission cumulative energy and acoustic emission count corresponding to the minimum microcracking. And the damage accumulation stages of the three graded asphalt concretes can be distinguished by the accumulated ringing times and the accumulated energy of the acoustic emission.
In the crack propagation stage:
after the asphalt concrete has microcracks, the asphalt concrete further expands to form macrocracks on the surface, the bearing capacity of the asphalt concrete is reduced, and the acoustic emission signals are continuously increased along with the expansion of the cracks. Towards the end of the fracture process, the slope of the acoustic emission cumulative ringing count increases significantly as macrocracks rapidly propagate and release more energy. And the crack propagation stages of the three graded asphalt concretes can be distinguished by sound emission accumulated ringing counts and analyzed in proportion in the whole fracture process.
S4, identifying the asphalt concrete fracture process according to the acoustic emission signal parameters, as shown in figure 1, the specific implementation steps are as follows:
s41, selecting key data in the acoustic emission signal parameter data;
by analyzing the asphalt concrete bending fracture failure process and analyzing the mechanical property and the change condition of the acoustic emission parameters in the fracture process, the key data in the acoustic emission signal parameter data which has stronger correlation with the cracks generated in the asphalt concrete fracture process are determined to be ringing count and energy.
S42, determining stage thresholds of acoustic emission signal key data at different stages of the asphalt concrete fracture process;
analyzing the asphalt concrete fracture process, carrying out a three-point bending test on an asphalt concrete test piece, adhering an acoustic emission sensor on the surface of the test piece for receiving an acoustic emission signal generated by fracture, and placing a microscope in front of the surface for observing the initiation and the propagation of cracks on the surface of the test piece. The force-displacement data and the acoustic emission signal data of the fracture process of the asphalt concrete with different gradation are counted, and the surface crack picture is observed by combining a microscope for analysis, so that the fracture process of the asphalt concrete with three gradation is respectively obtained, and the result shows that:
as shown in fig. 2a, for the first type AC-13 asphalt mixture, when the load reached about 81.1% of the maximum load (Fmax), the slope of the cumulative acoustic emission count curve rapidly increased, and no cracks were present on the surface of the test piece, which was associated with the accumulation of damage inside the test piece. After short-term stabilization, the slope of the cumulative acoustic emission count is again significantly increased, and microcracks occur simultaneously. The more acoustic emission activity means that more strain energy is suddenly released due to the formation of micro-cracks. As loading continues, the acoustic emission cumulative ringing count is still increasing. The intensity of the asphalt mixture test piece is reduced along with the expansion and accumulation of the large cracks, and the increase speed of the acoustic emission cumulative ringing count is reduced. The crack propagation path has certain influence on the detection of the acoustic emission signal, so that the increase rate of the actually measured acoustic emission cumulative ringing count is slightly reduced. When the load drops to 21.4% Fmax, the acoustic emission cumulative ringing count rises abruptly due to the generation of a high intensity acoustic emission signal as a result of the rapid propagation of macrocracks. Eventually, the sample completely destroyed and the acoustic emission cumulative ringing count rises sharply.
As shown in FIG. 2b, the load-displacement curve for the second type of AC-16 asphalt is similar to that for the AC-13 asphalt, and the trend of the acoustic emission cumulative ringing count is slightly different in number and time from that for the AC-13 asphalt. Similar to the AC-13 asphalt mixture, the load increases linearly with displacement at the initial stage of loading. When the load reaches 68.2% Fmax, the load continues to increase, but the slope decreases until a maximum value is reached. The maximum load of the AC-16 asphalt mixture is slightly higher than that of the AC-13 mixture. After the peak, the load decreases substantially with increasing displacement. Finally, the load is gradually reduced until the test piece breaks and fails. When the load rises to about 72.1% Fmax, the acoustic emission signal begins to be recorded. The acoustic emission cumulative ringing count increases sharply at 92.5% Fmax due to damage accumulation. Microcracking was observed at a load of 88.4% Fmax. The acoustic emission cumulative ringing count continues to increase, indicating that the macrocracks are stably propagating. When the load drops to 23.7% Fmax, the slope of the acoustic emission cumulative ringing count increases significantly as the macrocracks rapidly propagate releasing more energy. The trend of the final cumulative count tends to be flat until the test piece is completely broken.
The load-displacement curve for the third type of SMA-13, as shown in figure 2c, differs from the other two load-displacement curves in that the maximum load after the SMA-13 peak and the rate of load drop thereafter are both less than for the other two mixtures. The bearing capacity of the SMA-13 mixture is better than that of the other two mixtures after the maximum load is reached. This is because the SMA-13 mix uses modified bitumen as a binder and fibres are added to the material. The acoustic emission signal begins to be recorded when the load reaches 85% Fmax. As the load increased, the acoustic emission cumulative ringing count tended to rise slowly over a long period of time, with microcracking observed at 78.3% Fmax. Thereafter, the acoustic emission cumulative ringing count continues to slowly increase until it sharply increases at 36% Fmax due to unstable propagation of macrocracks. Eventually, the acoustic emission cumulative ringing count begins to slowly increase until a brief, sudden increase occurs when the specimen reaches a final failure state.
In the damage accumulation phase:
the threshold value distinction of the damage accumulation stages of the three graded asphalt concretes is obtained by counting the acoustic emission accumulated ringing count and the energy in the damage accumulation stages of the different graded asphalt concretes: the acoustic emission accumulated ringing counting ranges of the AC-13, the AC-16 and the SMA-13 in the damage accumulation stage are respectively as follows: 0 to 178, 0 to 186, 0 to 224; the cumulative energy of acoustic emission is respectively: 0j to 0.0138pj, 0j to 0.0176pj, and 0j to 0.0238 pj.
In the crack propagation stage:
the characteristics of the three asphalt concrete crack propagation stages and the ratio in the whole fracture process are obtained by counting the acoustic emission cumulative ringing count and the time of the asphalt concrete crack propagation stages with different grading. Wherein, the acoustic emission cumulative ringing count ranges of the crack propagation stages of AC-13, AC-16 and SMA-13 are respectively as follows: 178-786, 186-656, 224-584; the proportion of the acoustic emission cumulative ringing count in the crack propagation stage of the AC-13, AC-16 and SMA-13 in the whole fracture process is as follows: 77.4%, 71.6%, 61.6%; the proportion of the crack propagation stage time in the fracture process is as follows: 48.9%, 51.6% and 44.8%.
The method comprises the steps of obtaining stage thresholds of key data of acoustic emission signals of different stages in the cracking process of the different-gradation asphalt concrete by counting acoustic emission cumulative ringing counts and cumulative energy in the cracking process of the different-gradation asphalt concrete, wherein the stage thresholds are cumulative ringing count stage thresholds Wi or cumulative energy stage thresholds Ei respectively, wherein i is the gradation type of the asphalt concrete, and i is 1,2 or 3;
threshold value W of accumulated ringing counting stage of first type asphalt concrete acoustic emission signal key data1Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 10; the cumulative ringing count range during the damage accumulation phase is: 0<W1Less than or equal to 178; the cumulative ringing count ranges at the crack propagation stage are: w1>178；
Cumulative ringing count stage threshold value W of second type asphalt concrete acoustic emission signal key data2Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 20; the cumulative ringing count range during the damage accumulation phase is: 0<W2Less than or equal to 186; the cumulative ringing count ranges at the crack propagation stage are: w2>186；
Threshold value W of third type asphalt concrete acoustic emission signal key data in accumulative ringing counting stage3Comprises the following steps: the cumulative ringing count range for the elastic phase is: w 30; the cumulative ringing count range during the damage accumulation phase is: 0<W3Less than or equal to 224; the cumulative ringing count ranges at the crack propagation stage are: w3>224；
Cumulative energy stage threshold E of first type asphalt concrete acoustic emission signal key data1Comprises the following steps: the cumulative energy range for the elastic phase is: e 10; the cumulative energy range during the damage accumulation phase is: 0<E1Less than or equal to 0.0138; the cumulative energy ranges at the crack propagation stage are: e1>0.0138；
Cumulative energy stage threshold E of second type asphalt concrete acoustic emission signal key data2Comprises the following steps: the cumulative energy range for the elastic phase is: e 20; the cumulative energy range during the damage accumulation phase is: 0<E2Less than or equal to 0.0176; the cumulative energy ranges at the crack propagation stage are: e2>0.0176；
Cumulative energy stage threshold E of third-type asphalt concrete acoustic emission signal key data3Comprises the following steps: the cumulative energy range for the elastic phase is: e 30; the cumulative energy range during the damage accumulation phase is: 0<E3Less than or equal to 0.0238; the cumulative energy ranges at the crack propagation stage are: e3>0.0238；
S43, counting key data of acoustic emission signals of the asphalt concrete to be identified;
and S44, comparing the key data of the acoustic emission signals obtained by statistics with a stage threshold value, and determining the fracture process of the asphalt concrete to be identified.
A method for identifying and quantifying microcracks based on acoustic emissions, comprising the steps of:
p1, constructing an acoustic emission energy-microcrack model;
and observing the microcracks on the surfaces of the three graded asphalt concretes under the compression condition according to a microscope, and recording the cumulative energy of acoustic emission. The parametric expression for quantifying microcracks is as follows:
wherein A is the size of the micrograph, lmThe length of the mth crack is m, and m is a positive integer;
regression analysis is carried out on crack density and acoustic emission accumulated energy, an acoustic emission energy-microcrack model is constructed according to the nominal maximum grain diameter, the void ratio and the acoustic emission energy of the mixture in different gradations of the asphalt concrete, and the acoustic emission accumulated energy-microcrack model is established as follows:
where a is the microcrack density, E is the cumulative energy, biIs the nominal maximum grain diameter, c, of the mixture in different gradation of asphalt concreteiThe porosity of the mixture in different gradations of the asphalt concrete, i is the gradation of the asphalt concrete, and i is 1,2 and 3; b1、c1Corresponding to the coefficient of the first type asphalt concrete material; b2、c2Corresponding to the coefficient of the second type asphalt concrete material; b3、c3Corresponding to the coefficient of the third type asphalt concrete material;
the acoustic emission cumulative energy-microcrack model means: the crack density and the acoustic emission energy are in an exponential relationship, and different materials have different coefficients;
p2, deducing to obtain a judgment expression (4) of the microcrack condition of the asphalt concrete with different gradation according to the constructed acoustic emission energy-microcrack model;
the nominal maximum grain sizes of the first type AC-13, the second type AC-16 and the third type SMA-13 in the coefficients related to the nominal maximum grain sizes and the void ratios of the mixture in different gradation of the asphalt concrete are respectively as follows: 13. 16, 13; the void ratios of the first type AC-13, the second type AC-16 and the third type SMA-13 are respectively as follows: 4.32%, 4.79%, 3.27%.
Fitting the micro-crack density of the graded asphalt concrete with the acoustic emission accumulated energy before the micro-crack appears, and deducing to obtain a judgment expression of the micro-crack condition of the graded asphalt concrete, namely a relational expression of the acoustic emission accumulated energy and the micro-crack density, wherein the judgment expression is expressed as follows:
first type a-5.5022E1.2864
Type II, a is 0.2223E0.3598
Type III, a-0.9079E0.9032 (4)；
Wherein the fitted curve is shown in figure 3. The results show that the SMA-13 asphalt mixture has a greater dispersion of data points, mainly due to the non-uniformity of the fiber distribution in the mixture. As the cumulative energy of acoustic emission increases, the growth rate of the AC-13 asphalt micro-cracks is higher than that of the SMA-13 asphalt micro-cracks. The main reasons are that the void ratio of SMA-13 asphalt mixture is lower than that of AC-13 asphalt mixture, and the fiber structure hinders the crack from expanding. In the three asphalt mixtures, the AC-16 asphalt mixture microcracks grow at the slowest speed along with the increase of the cumulative energy of acoustic emission. This is because cracks in the asphalt mixture grow at the interface between the asphalt and the aggregate, the aggregate particle size of the AC-16 asphalt mixture is largest, and the presence of large aggregates prevents the cracks from growing.
P3, statistically calculating the accumulated energy data of the acoustic emission signals of the asphalt concrete to be identified according to the expression (1);
p4, determining the grading type of the asphalt concrete to be identified;
and P5, substituting the accumulated energy data into the acoustic emission energy-microcrack model of the corresponding grading type, and calculating to obtain the density of the microcracks of the asphalt concrete so as to quantify the microcracks of the asphalt concrete.
The method is further tested by combining a specific asphalt concrete trabecula test piece so as to verify the actual effect of the method.
In the experiment, a three-point bending test is carried out on an asphalt concrete trabecula specimen, numerical data of accumulated ringing times and accumulated energy of acoustic emission signals in the experiment are randomly extracted, an acoustic emission sensor is pasted on the surface of the specimen for receiving the acoustic emission signals generated by fracture, a microscope is arranged in front of the surface for observing the initiation and the propagation of cracks on the surface of the specimen, the effectiveness of the method is verified according to the display of the observation result of the microscope, and the judgment result and the actual observation result of the microscope of the randomly extracted numerical values of the accumulated ringing times and the accumulated energy according to the observation result of the microscope are shown in the following table:
the results are consistent with the expectation according to the observation results of a microscope, and the method is proved to be effective.
According to the results, the asphalt concrete fracture process can be divided into an elastic stage, a damage accumulation stage and a crack propagation stage, wherein the acoustic emission signals begin to appear in the damage accumulation stage, the acoustic emission accumulated ringing count continuously increases, and the acoustic emission accumulated ringing count can show a trend of sharp increase in the crack rapid increase stage in the crack propagation stage and finally tends to be stable. The acoustic emission technology can be applied to actual asphalt road detection, the fracture stages (damage accumulation stage and crack propagation stage) of asphalt concrete are judged through acoustic emission accumulated ringing counting and energy, and the size of cracks on the current pavement is quantified according to the size of the received acoustic emission energy, so that the purpose of monitoring the pavement damage condition in real time on line is achieved, early maintenance is facilitated, maintenance cost is reduced, and the service life of the pavement is prolonged.
Meanwhile, the result shows that the method has better identification performance on the asphalt concrete with different proportions, can identify the damage condition by applying a corresponding acoustic emission accumulated energy-microcrack model according to the asphalt concrete with a certain proportion adopted in actual use, and has wider application range and strong applicability because the asphalt concrete researched by the method basically covers the gradation used by the asphalt pavement.
Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and are not limited thereto; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
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