CN117704949A - Structure crack identification monitoring system and method based on wide-range strain sensing element - Google Patents
Structure crack identification monitoring system and method based on wide-range strain sensing element Download PDFInfo
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Abstract
The invention discloses a structural crack identification monitoring system and method based on a wide-range strain sensing element, which utilize the flexible characteristic of the strain sensing element to realize continuous monitoring of the whole process from micro strain to cracking of an engineering structure, and construct a crack identification analysis module based on the flexible strain sensing element according to the working characteristic and the change rule of an output signal in the process from continuous strain to crack occurrence and expansion of the engineering structure, so as to realize crack monitoring of the structure. The method can monitor the whole process of structural strain expansion and crack cracking, solves the problem of identifying and analyzing structural cracks by using the basic strain sensing element, and provides a corresponding solution for engineering structural crack monitoring.
Description
Technical Field
The invention relates to the technical field of concrete structure health monitoring, in particular to a structure crack identification monitoring system and method based on a wide-range strain sensing element.
Background
The existing concrete structure design and construction research is mature, and the research of the structure health monitoring technology still has great development space development in the aspect of prolonging the service life of the structure and improving the durability of the structure. In the research of damage to a concrete structure at present, cracks become the most common damage factor of the concrete structure, and are influenced by external environment and external load, microcracks in the concrete structure can gradually develop into macroscopic cracks which threaten structural safety and working performance, so in the technical field of structural health monitoring, crack monitoring is important for improving the durability and safety of engineering structures.
The traditional structural crack detection method is visual inspection or detection by using a ruler, a vernier caliper and a crack width measuring instrument, and has great limitation and low accuracy. The research of the current structural crack monitoring method is developed towards the directions of images, strain sensing, sound wave emission and the like, the most common modes of the strain sensing direction include resistance type, fiber bragg grating type and the like, and for a resistance type sensing element, a metal resistance type strain gauge is the most common, but the characteristics of limited range and easy damage cause the resistance type strain gauge to rapidly fail in crack monitoring, and the current crack monitoring function cannot be met.
Disclosure of Invention
In order to solve the technical problems that the existing crack measurement technology has obvious defects in real-time performance and accuracy, the invention provides a structural crack identification monitoring system and method based on a wide-range strain sensing element, which can identify, analyze, measure and early warn cracks in real time.
In order to achieve the technical purpose, the technical scheme of the invention is that,
a structural crack identification monitoring system based on a wide-range strain sensing element comprises a flexible strain sensing element, an electric signal acquisition instrument and an electric signal analysis module.
The flexible strain sensing element is arranged at the structure to be detected to monitor the strain deformation and crack of the structure.
The electric signal analysis module is in communication connection with the flexible strain sensing element through the electric signal acquisition instrument, and analyzes the input electric signal and judges the strain expansion degree of the structure and whether the crack exists or not according to the working characteristics and the output signal change rule of the structure to be detected in the continuous strain to crack occurrence and expansion process.
The structural crack identification monitoring system based on the wide-range strain sensing element is characterized in that the flexible strain sensing element is prepared by the following steps:
and mixing and drying the graphene-aqueous polyurethane conductive composite material with the mass fraction of 2-10% of graphene to obtain a sheet with the thickness of 0.15-0.55 mm, cutting the sheet with the side length of 100mm multiplied by 10mm, fixing copper foil electrodes at two ends of the sheet in the strain direction through conductive silver glue, and packaging to obtain the flexible strain sensing element. Wherein the shape of the flexible strain sensing element after encapsulation is matched with the shape of the structure to be tested. The flexible strain sensing element is adhered to the surface of the structure to be measured or is pre-buried in the structure to be measured.
The structural crack identification monitoring system based on the wide-range strain sensing element comprises an electrical signal analysis module, a power supply module and a power supply module.
The parameter input unit is used for inputting basic parameters and threshold control parameters.
The strain-crack monitoring unit is used for carrying out strain monitoring, crack capturing and crack width monitoring on the structure to be tested.
The signal output unit is used for outputting the strain information, the cracking time and the crack width monitoring information transmitted by the strain-crack monitoring unit to the upper computer.
The strain-crack monitoring unit monitors strain, and calculates and obtains strain information epsilon according to response electric signals generated by the flexible strain sensing element along with the strain of the structure to be measured before the structure cracks:
wherein R is 0 K is the initial resistance and sensitivity coefficient of the flexible strain sensing element, and ΔR is the difference between the current resistance and the initial resistance in the monitoring process.
The strain-crack monitoring unit captures cracks, namely when the strain rate is suddenly changed, namely the strain rate in a certain signal acquisition time step is simultaneously greater than the strain rate of a front acquisition time step and a rear acquisition time step, or the strain change in a short period is greater than a preset threshold, the suddenly changed strain is recorded as i=1, 2, …, n-time cracking is sequentially performed, early warning is performed, and the i-time suddenly changed instant strain epsilon is recorded simultaneously i Electric signal R i And electrical signals R before and after mutation i- And R is R i+ And the initial cracking width l of the crack is calculated according to the following formula wi ：
Wherein l 0 Is the initial length of the flexible strain sensing element.
The strain-crack monitoring unit monitors the crack width by subtracting the length l corresponding to the strain of the non-cracked section from the total length l calculated by the total strain epsilon of the flexible strain sensing element m Thereby obtaining the total length l of the crack area w Then subtracting the initial width l of the crack region wi Obtaining the crack width w i And (d)Crack development width x from i times of cracking to corresponding time before next cracking i ：
w 1 ＝0
Total crack width w at corresponding time after ith crack:
w＝x i +w i
wherein t is the stress relaxation coefficient of the structure to be measured.
When the output total crack width w is greater than the preset maximum crack threshold w max And sending out the maximum crack width early warning.
A structural crack identification monitoring method based on a wide-range strain sensing element comprises the following steps:
and step 1, measuring geometric parameters, sensitivity coefficients, structural stress relaxation coefficients and initial resistance of the flexible sensing element, and setting a crack width threshold value.
And 2, arranging the flexible sensing element at the position of the structure to be detected, and arranging electrodes at two ends of the flexible sensing element along the strain direction so as to acquire the strain generated by the structure to be detected.
And step 3, processing according to the electric signals generated and transmitted by the flexible sensing element due to the strain of the structure to be tested to obtain the strain information of the structure to be tested.
And step 4, capturing crack signals of the structure to be detected from the electric signals, marking the moment of crack cracking of each crack, and sending out crack cracking early warning.
And 5, outputting a total crack width signal, and sending out limit crack width early warning when the total crack width signal reaches a crack width threshold value.
In the step 1, the flexible strain sensing element is prepared by the following steps:
and mixing and drying the graphene-aqueous polyurethane conductive composite material with the mass fraction of 2-10% of graphene to obtain a sheet with the thickness of 0.15-0.55 mm, cutting the sheet with the side length of 100mm multiplied by 10mm, fixing copper foil electrodes at two ends of the sheet in the strain direction through conductive silver glue, and packaging to obtain the flexible strain sensing element. Wherein the shape of the flexible strain sensing element after encapsulation is matched with the shape of the structure to be tested.
In the step 2, the flexible sensing element is arranged at the position of the structure to be detected, and is adhered to the surface of the structure to be detected or pre-buried in the structure to be detected.
The method for identifying and monitoring structural cracks based on the wide-range strain sensing element comprises the following steps:
before the structure cracks, strain information epsilon is calculated and obtained according to response electric signals generated by the flexible strain sensing element along with the strain of the structure to be measured:
wherein R is 0 K is the initial resistance and sensitivity coefficient of the flexible strain sensing element, and ΔR is the difference between the current resistance and the initial resistance in the monitoring process.
The method for identifying and monitoring the structural cracks based on the wide-range strain sensing element comprises the following step 4:
when the strain rate is suddenly changed, namely the strain rate in a certain signal acquisition time step is simultaneously larger than the strain rates of the front acquisition time step and the rear acquisition time step, or the strain change in a short period is larger than a preset threshold, the suddenly changed strain is recorded as i=1, 2, …, n times of cracking and early warning are sequentially carried out, and the instant strain epsilon of the i time of suddenly changed strain is recorded at the same time i Electric signal R i And electrical signals R before and after mutation i- And R is R i+ And the initial cracking width l of the crack is calculated according to the following formula wi ：
Wherein l 0 Is the initial length of the flexible strain sensing element.
The method for identifying and monitoring the structural cracks based on the wide-range strain sensing element comprises the following steps:
total crack width w at corresponding time after ith crack:
w＝x i +w i
wherein t is the stress relaxation coefficient of the structure to be measured.
When the output total crack width w is greater than the preset maximum crack threshold w max And sending out the maximum crack width early warning.
The invention has the technical effects that by means of research of the nano high polymer conductive composite material, the continuous monitoring from strain to crack is realized by preparing the flexible strain sensing element which has wide range, is easy to shape and is not easy to damage, and by utilizing the characteristic of wide range of the flexible sensor, the crack identification is carried out by collecting the sudden change signals generated by the energy release and the structural strain relaxation at the moment of structural cracking. And analyzing continuous signal characteristics of crack extension and structural strain in a range output by the sensing element, so as to realize continuous monitoring of crack width. The method for monitoring and characterizing the cracks in real time is more accurate, reliable and practical for engineering structures.
Drawings
Fig. 1 is a schematic diagram of a system structure according to the present invention.
Fig. 2 is a schematic diagram of the crack monitoring principle of the present invention.
FIG. 3 is a diagram showing total strain before and after cracking of a structure to be tested and strain of an unbroken section.
Detailed Description
For a better understanding of the technical solutions of the present invention, reference will now be made to the accompanying drawings and examples, which are only a part of the examples of the present invention, it being apparent that the present invention is not limited to the scope of the detailed description. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1, a structural crack monitoring system based on a flexible strain sensor is provided in this embodiment. The device mainly comprises 3 parts of a flexible strain sensing element, an electric signal acquisition instrument and an electric signal analysis module.
The flexible strain sensing element is used for sensing the strain behavior of the structure and outputting the resistance change generated along with the deformation of the structure as an electric signal. The testing range of the flexible strain sensing element is more than 5%, the electric signal generated along with the deformation of the structure is continuously output in the testing range, and the stable electric signal can be continuously output after the crack of the structure occurs.
The flexible strain sensing element is used for strain monitoring by preparing the nano high polymer conductive composite material into a flexible functional membrane with good conductive performance, wherein the geometric shape of the flexible strain sensing element can be designed according to the requirement. In the embodiment, a graphene-based flexible strain sensing element is selected, a graphene-waterborne polyurethane conductive composite material with the mass fraction of 2-10% of graphene is mixed and dried to obtain a sheet with the thickness of 0.15-0.55 mm, a sheet with the thickness of 100mm multiplied by 10mm is cut from the sheet, copper foil electrodes are fixed at two ends of the sheet in the strain direction through conductive silver glue, and the flexible strain sensing element is obtained after packaging, and corresponding working parameters are obtained through testing. The flexible strain sensing element is adhered to the surface of the structure to be measured or is embedded in the structure to be measured, so that the strain and crack state of the structure surface in the adhered or embedded range are monitored.
An electric signal acquisition instrument: the signal input end is connected with the electrode of the flexible strain sensing element, and the signal output end is connected with the signal input end of the electric signal analysis module;
and the electric signal analysis module is used for: and analyzing the input electric signals and carrying out crack identification and crack width calculation according to the working characteristics and the change rule of the output signals in the process from continuous strain to crack occurrence and expansion of the engineering structure.
The electric signal analysis module comprises 3 parts of a parameter input unit, a strain-crack monitoring unit and a signal output unit:
the parameter input unit comprises basic parameters and threshold control parameters, wherein the basic parameters comprise geometric parameters of the flexible strain sensing element, initial resistance, sensitivity coefficient, initial temperature, relaxation coefficient of a structure to be tested and the like, and the threshold control parameters comprise a crack width control threshold, a crack strip number control threshold, an initial crack moment threshold and the like and can be set according to actual requirements.
Strain-crack monitoring unit: including strain monitoring, fracture trapping, and fracture width monitoring.
(I) Strain monitoring. Before the structure cracks, the sensing element is firmly adhered to the surface of the structure, and responds to an electric signal along with the structural strain, and the relation between the resistance change rate and the strain of the sensing element belongs to the general relation delta R/R 0 =k ε, where R 0 K is the initial resistance and sensitivity coefficient of the strain sensing element, and DeltaR is the difference between the test resistance and the initial resistance in the test process.
(II) crack trapping. After reaching a certain stress, the structure is strained from the elastic limit to initial cracking, the instantaneous release of energy causes the structural strain to generate mutation, the crack is captured by analyzing the collected strain information, the mutation is captured, and the capturing process of the mutation in the acquisition is as follows: when the strain rate is suddenly changed, that is, the strain rate generated in a certain acquisition step length is simultaneously larger than the strain rate delta epsilon/t of the front acquisition step length and the rear acquisition step length>Δε/t - And delta epsilon/t>Δε/t + That is, the strain of the middle section is larger than the strain of the two sides, or the strain change in a short period is larger than a certain value, a strain rate mutation signal is output, the point where the mutation is located is marked, the i=1, 2, … and n times of cracking are recorded in sequence and early warning is carried out, and the i time of mutation instant strain epsilon is recorded at the same time i Electric signal R i And electrical signals R before and after mutation i- And R is R i+ After conversion, the initial cracking width l of the crack is obtained wi ：
(III) crack width monitoring. Phase telecommunicationsThe measuring area of the flexible strain sensing element can be divided into a structure uncracked section and a cracked section after the structure is cracked, the sensing element of the structure uncracked section is always stuck on the surface of the structure, the corresponding length and the strain change along with the structure, the measurement of the width of the cracked area can be carried out by subtracting the length and the strain of the structure uncracked section from the total strain, the corresponding electric signal change is analyzed and converted, and finally the strain and the width corresponding to the crack are obtained, wherein one key item is the strain epsilon of the structure uncracked section m The ratio of the total strain epsilon' after cracking is compared with the total strain, and the relation is shown as follows: epsilon m T epsilon'. Certain stress relaxation can occur after the structure is cracked, so t is defined as the stress relaxation coefficient of the structure to be detected, and t can be obtained by carrying out cracking tests on different base materials to be detected, arranging a plurality of sensing elements and simultaneously measuring the total strain of the sensing elements after cracking and the strain of an uncleaved section. Subtracting the length l corresponding to the strain of the uncracked section from the total length l calculated by using the total strain epsilon m Obtain the total length l of the crack area w Subtracting the initial width l of the crack region wi Obtaining the crack width w i And crack development width x from the ith crack to the corresponding time before the next crack i ：
Total crack width w at corresponding time after ith crack:
w＝x i +w i
when the total crack width w is greater than or equal to w max And sending out the maximum crack width early warning.
The method for monitoring structural cracks based on the flexible strain sensing element provided by the embodiment corresponds to step 1: the flexible sensing element is stuck on the surface of the structure, electrodes at two ends conform to the changing direction and collect the strain information, so that the monitoring preparation work is finished.
After all the procedures, parameter input is carried out, and the specific implementation is as follows:
corresponding to step 2: parameters such as basic parameters of the flexible strain sensing element, stress relaxation coefficients of the matrix structure to be tested, crack width control threshold values and the like are input into the electric signal analysis module. And carrying out corresponding working performance test on the graphene-based strain sensing element of the embodiment to obtain a sensitivity coefficient k=9. The present example was carried out using a silicone rubber substrate, and the structural stress relaxation coefficient t=0.8 was measured by a test. Initial length l of strain gauge ranging 0 ＝100mm，R 0 =10kΩ. Crack width threshold w for early warning max =0.2 mm, set according to the three-stage crack control rating of the concrete structural design Specification GB 50010-2010.
After the parameter input is complete, a monitoring test is started, and the electric signal display unit outputs strain change information, and the method is implemented as follows:
step 3: the electric signals are input to the electric signal analysis module after being collected.
Step 4: the electric signal analysis module processes the electric signal obtained by the acquisition instrument, the electric signal display unit outputs the electric signal of the strain sensing element and the processed strain information, and fig. 2 and 3 are relations between the working characteristics of the sensing element and the output signal in the whole monitoring process. At limit strain ε 1 Previously, the output signal is structural strain information
At limit strain ε 1 Then, after cracking, the strain rate is suddenly changed, and the electric signal analysis module judges the strain rate (delta epsilon/t) in the acquisition step length>Δε/t - And delta epsilon/t>Δε/t + ) Record R at this time 1- 、R 1+ Limit strain epsilon 1 Instantaneous resistance R 1 。
Corresponding to step 5: the crack monitoring unit captures crack signals from the strain information, marks the moment of each crack, and records the moment of each crack as i=1, 2, …, and gives out early warning of crack occurrence.
Obtaining the initial width of the crack region after the conversion of the electric signals before and after capturing mutationWhen i cracks appear, the head is added>The transformation algorithm, at this time, the electric signal display unit outputs the crack width information, and is implemented as follows:
the acquired information is processed, the relationship of which is shown in fig. 3. Subtracting the length l corresponding to the strain of the uncracked section from the total length l calculated by using the total strain epsilon m Obtain the total length l of the crack area w Subtracting the initial width l of the crack region w1 Obtaining crack extension length:
after the deformation is further expanded, the crack expansion width x of the total crack width after the ith crack to the corresponding previous crack width i ：
Outputting the crack width w at the ith crack according to the input parameters and the crack catching part record data i ：
Width x of crack initiation after the ith crack and at the corresponding time before the next crack i ：
Total crack width w at corresponding time after ith crack:
w＝x i +w i
corresponding to step 6: output ofA total crack width signal, when the total crack width w is more than or equal to w max And when the preset crack width threshold is reached, sending out limit crack width early warning to complete crack monitoring.
The results of the crack measurements in this example are shown in Table 1.
TABLE 1 crack monitoring results
| Stretch deformation/mm | Strain/. Times.10 4 με | Crack width/mm | Outputting the result |
| 5.41667 | 0.02195 | -- | |
| 5.83333 | 0.02415 | -- | |
| 6.25 | 0.02635 | -- | 1 st crack |
| 6.66667 | 0.03089 | 0.02042 | |
| 7.08333 | 0.0354 | 0.08052 | |
| 7.5 | 0.03858 | 0.12283 | |
| 7.91667 | 0.0418 | 0.16566 | |
| 8.33333 | 0.04462 | 0.20316 | Maximum crack early warning |
| 8.75 | 0.04833 | 0.25248 | |
| 9.16667 | 0.05213 | 0.30314 | |
| 9.58333 | 0.05481 | 0.33873 | |
| 10 | 0.05872 | 0.39083 |
Compared with the measurement result of the artificial crack width measuring instrument, the relative error is within 10 percent, and the absolute error between the monitored crack width and the measured width of the crack width measuring instrument is not more than 0.04mm.
Therefore, the invention can realize the crack monitoring process accurately in real time, accords with a reliable and practical real-time crack monitoring and characterization method, can carry out corresponding crack monitoring on structural parts, and builds intelligent crack monitoring and processing equipment on the basis. The invention is suitable for monitoring and early warning the initial stage of the structural crack, and simultaneously provides a basic monitoring system and method for monitoring the structural crack by the flexible strain sensing element.
Claims (10)
1. The structural crack identification monitoring system based on the wide-range strain sensing element is characterized by comprising a flexible strain sensing element, an electric signal acquisition instrument and an electric signal analysis module;
the flexible strain sensing element is arranged at the structure to be detected to monitor the strain deformation and crack of the structure;
the electric signal analysis module is in communication connection with the flexible strain sensing element through the electric signal acquisition instrument, and analyzes the input electric signal and judges the strain expansion degree of the structure and whether the crack exists or not according to the working characteristics and the output signal change rule of the structure to be detected in the continuous strain to crack occurrence and expansion process.
2. The structural crack identification monitoring system based on a wide range strain sensing element of claim 1, wherein the flexible strain sensing element is prepared by:
mixing and drying graphene-aqueous polyurethane conductive composite materials with the mass fraction of 2-10% of graphene to obtain a sheet with the thickness of 0.15-0.55 mm, cutting out a sheet with the side length of 100mm multiplied by 10mm, fixing copper foil electrodes at two ends of the sheet in the strain direction through conductive silver glue, and packaging to obtain a flexible strain sensing element; wherein the shape of the flexible strain sensing element after encapsulation is matched with the shape of the structure to be detected; the flexible strain sensing element is adhered to the surface of the structure to be measured or is pre-buried in the structure to be measured.
3. The structural crack identification monitoring system based on the wide-range strain sensing element according to claim 1, wherein the electrical signal analysis module comprises a parameter input unit, a strain-crack monitoring unit and a signal output unit;
the parameter input unit is used for inputting basic parameters and threshold control parameters;
the strain-crack monitoring unit is used for carrying out strain monitoring, crack capturing and crack width monitoring on the structure to be tested;
the signal output unit is used for outputting the strain information, the cracking time and the crack width monitoring information transmitted by the strain-crack monitoring unit to the upper computer.
4. A structural crack identification monitoring system based on a wide-range strain sensing element according to claim 3, wherein the strain-crack monitoring unit performs strain monitoring by calculating and obtaining strain information epsilon according to response electric signals generated by the flexible strain sensing element along with the strain of the structure to be measured before the structure cracks:
wherein R is 0 K is the initial resistance and sensitivity coefficient of the flexible strain sensing element, and DeltaR is the difference value between the current resistance and the initial resistance in the monitoring process;
the strain-crack monitoring unit captures cracks, namely when the strain rate is suddenly changed, namely the strain rate in a certain signal acquisition time step is simultaneously greater than the strain rate of a front acquisition time step and a rear acquisition time step, or the strain change in a short period is greater than a preset threshold, the suddenly changed strain is recorded as i=1, 2, …, n-time cracking is sequentially performed, early warning is performed, and the i-time suddenly changed instant strain epsilon is recorded simultaneously i Electric signal R i And electrical signals R before and after mutation i- And R is R i+ And the initial cracking width l of the crack is calculated according to the following formula wi ：
Wherein l 0 An initial length of the flexible strain sensing element;
the strain-crack monitoring unit monitors the crack width by subtracting the length l corresponding to the strain of the non-cracked section from the total length l calculated by the total strain epsilon of the flexible strain sensing element m Thereby obtaining the total length l of the crack area w Then subtracting the initial width l of the crack region wi Obtaining the crack width w i And crack development width x from the ith crack to the corresponding time before the next crack i ：
w 1 ＝0
Total crack width w at corresponding time after ith crack:
w＝x i +w i
wherein t is the stress relaxation coefficient of the structure to be tested;
when the output total crack width w is greater than the preset maximum crack threshold w max And sending out the maximum crack width early warning.
5. The structural crack identification monitoring method based on the wide-range strain sensing element is characterized by comprising the following steps of:
step 1, measuring geometric parameters, sensitivity coefficients, structural stress relaxation coefficients and initial resistance of a flexible sensing element, and setting a crack width threshold value;
step 2, arranging the flexible sensing element at the position of the structure to be detected, and arranging electrodes at two ends of the flexible sensing element along the strain direction so as to acquire the strain generated by the structure to be detected;
step 3, processing to obtain strain information of the structure to be tested according to the electric signals generated and transmitted by the flexible sensing element due to the strain of the structure to be tested;
step 4, capturing crack signals of the structure to be detected from the electric signals, marking the moment of each crack, and sending out crack early warning;
and 5, outputting a total crack width signal, and sending out limit crack width early warning when the total crack width signal reaches a crack width threshold value.
6. The method for identifying and monitoring structural cracks based on a wide-range strain sensing element according to claim 5, wherein in the step 1, the flexible strain sensing element is prepared by the following steps:
mixing and drying graphene-aqueous polyurethane conductive composite materials with the mass fraction of 2-10% of graphene to obtain a sheet with the thickness of 0.15-0.55 mm, cutting out a sheet with the side length of 100mm multiplied by 10mm, fixing copper foil electrodes at two ends of the sheet in the strain direction through conductive silver glue, and packaging to obtain a flexible strain sensing element; wherein the shape of the flexible strain sensing element after encapsulation is matched with the shape of the structure to be tested.
7. The method for identifying and monitoring structural cracks based on wide-range strain sensing elements according to claim 5, wherein in the step 2, the flexible sensing elements are arranged at the position of the structure to be tested, and are adhered to the surface of the structure to be tested or are pre-buried in the structure to be tested.
8. The method for identifying and monitoring structural cracks based on a wide-range strain sensor according to claim 5, wherein the step 3 comprises:
before the structure cracks, strain information epsilon is calculated and obtained according to response electric signals generated by the flexible strain sensing element along with the strain of the structure to be measured:
wherein R is 0 K is the initial resistance and sensitivity coefficient of the flexible strain sensing element, and ΔR is the difference between the current resistance and the initial resistance in the monitoring process.
9. The method for identifying and monitoring structural cracks based on a wide-range strain sensing element according to claim 8, wherein the step 4 comprises:
when the strain rate is suddenly changed, namely the strain rate in a certain signal acquisition time step is simultaneously larger than the strain rates of the front acquisition time step and the rear acquisition time step, or the strain change in a short period is larger than a preset threshold, the suddenly changed strain is recorded as i=1, 2, …, n times of cracking and early warning are sequentially carried out, and the instant strain epsilon of the i time of suddenly changed strain is recorded at the same time i Electric signal R i And electrical signals R before and after mutation i- And R is R i+ And the initial cracking width l of the crack is calculated according to the following formula wi ：
Wherein l 0 Is the initial length of the flexible strain sensing element.
10. The method for identifying and monitoring structural cracks based on a wide-range strain sensing element according to claim 9, wherein the step 5 comprises:
total crack width w at corresponding time after ith crack:
w＝x i +w i
wherein t is the stress relaxation coefficient of the structure to be tested;
when the output total crack width w is greater than the preset maximum crack threshold w max And sending out the maximum crack width early warning.
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