CN116858888A - Coating sensor for orthotropic steel bridge deck - Google Patents

Abstract

The application discloses a coating sensor for orthotropic steel bridge deck plates, belonging to the technical field of crack detection and monitoring of key welding parts of steel bridges, wherein the coating sensor comprises a basal body insulating isolation layer, a crack damage sensing layer and a protective layer which are sequentially bonded and are all made of flexible materials; the crack damage sensing layer comprises a conductive nano coating, and a power interface and at least one detection probe point are arranged on the conductive nano coating. The coating sensor is made of flexible materials, so that the corresponding crack damage sensing layer is customized according to different cracking positions of the orthotropic steel bridge deck, the coating sensor can have higher response sensitivity in complex construction details, and can be suitable for crack detection and positioning of different cracking positions. The problems of difficulty in crack detection, low precision and difficulty in positioning at complex structural details of actual steel bridge space components are solved.

Description

Coating sensor for orthotropic steel bridge deck

Technical Field

The application relates to the technical field of crack detection and monitoring of key welding parts of steel bridges, in particular to a coating sensor for orthotropic steel bridge panels.

Background

At present, bridge engineering in China is in a key transformation period from construction to construction and restoration, newly-built bridges in recent years are rapidly increased in number, and the bridge engineering is expanded to regions with extremely complex environments such as offshore and hard mountain areas, and the like. Thus being widely applied. However, due to the characteristics of complex structure, multiple welding seams, large welding residual stress and the like of the orthotropic plate, the fatigue cracking problem is always a main factor for restricting the development of the orthotropic plate. Structural safety and service performance research of steel-structure bridges is urgently needed to be developed. The fatigue problem is still one of the key problems which restrict the sustainable development of the steel structure bridge for a period of time at present and in the future. The effective detection of the fatigue cracking is the key for effectively treating and avoiding the fatigue disease damage, but because the current high-tech detection technologies such as ultrasonic wave, infrared thermal imaging and the like are still immature and expensive, the current monitoring and detection technologies are still mainly based on manual inspection, intelligent application is not realized yet, effective detection and monitoring means are still lacking for the development of micro cracks which cannot be captured by naked eyes in the early stage of the expansion process and cracks of hidden complex structural detail parts in some bridges, such as the complex space structures of the joints of U ribs and top plates, the joints of U ribs and transverse baffles and the like, and the current detection method is difficult to realize accurate crack identification.

Disclosure of Invention

Aiming at the problem that fatigue cracking of an orthotropic steel bridge deck plate in the prior art lacks effective detection and monitoring means, the application provides a coating sensor for the orthotropic steel bridge deck plate, which aims at: the method lays a foundation for the real-time, visual and intelligent development and the complete construction of the health monitoring system of the steel structure bridge for the health monitoring and the safety evaluation of the steel structure bridge, and the long-term dynamic monitoring and the intelligent evaluation of the fatigue damage of the steel structure bridge are realized, so that the method has a wide application prospect.

The technical scheme adopted by the application is as follows: a coated sensor for orthotropic steel deck plates, the coated sensor comprising a base insulating isolation layer, a crack damage sensing layer and a protective layer, which are bonded in sequence and are all made of flexible materials; the crack damage sensing layer comprises a conductive nano coating, and a power interface and at least one detection probe point are arranged on the conductive nano coating.

According to the technical scheme, the problems of difficulty in detecting cracks, low precision and difficulty in positioning at complex structural details of an actual steel bridge deck are solved, numerical simulation and experimental research results show that the intelligent coating sensor can effectively detect fatigue cracks, has higher precision and stability for small-scale cracks, is low in cost of materials, simple and convenient in sensor manufacturing process, can customize different grid sensors according to different positions, is quick in layout process and simple in later result processing, provides a new thought for detecting the fatigue cracks of the steel bridge, establishes a foundation for long-term dynamic monitoring and intelligent evaluation of fatigue damage of the steel bridge, and has wide application prospects for real-time, visual and intelligent directional development and construction of a complete steel bridge health monitoring system for health monitoring and safety evaluation of the steel bridge.

The coating sensor is arranged on a possible crack propagation path, when a base steel structure is cracked, the coating sensor can also crack along with the steel structure, at the moment, the electric signal of the detection probe point on the coating sensor can be changed, and according to the electric potential change rule, whether the crack is developed or not and the crack length and the crack position can be deduced.

The beneficial effects of the application are as follows:

1. according to the application, by applying constant voltage to the crack damage sensing layer, the electrical signal changes of different measuring points before and after crack development are collected, so that the accurate detection of the base body crack is realized.

2. The coating sensor is made of flexible materials, so that the corresponding crack damage sensing layer is customized according to different cracking positions of the orthotropic steel bridge deck, the coating sensor can have higher response sensitivity in complex construction details, and can be suitable for crack detection and positioning of different cracking positions. The problems of difficulty in crack detection, low precision and difficulty in positioning at complex structural details of actual steel bridge space components are solved.

3. The material cost of the coating sensor is low, the sensor manufacturing process is simple and quick, the layout flow is simple and quick, the later data processing is simple, the result is visual, and the whole use cost is low.

Drawings

The application will now be described by way of example and with reference to the accompanying drawings in which:

FIG. 1 is a schematic and dimensional depiction of a coated sensor of the present application;

FIG. 2 is an enumeration of the coating sensor patterns when the substrate is planar;

FIG. 3 is an enumeration of coating sensor patterns where the base is U-ribbed and top plate weld construction details;

FIG. 4 is a graphical representation of a coated sensor pattern for a U-rib and diaphragm opening on a substrate, with the coating applied near the diaphragm opening;

FIG. 5 is a stylized listing of a coated sensor suitable for use in welded construction details where the base is a U-rib to diaphragm joint;

FIG. 6 is an alternative version of a coated sensor suitable for use in connection with U-ribs and diaphragms as the base, and with details of the welded construction;

FIG. 7 is a coated sensor model of example 1;

FIG. 8 is a finite element analysis diagram of example 1;

FIG. 9 is a graph showing the variation of the spot potential with crack growth in example 1;

FIG. 10 is a schematic diagram of the layer structure of a coating sensor in an embodiment, wherein: 8-a protective layer, 9-a crack damage sensing layer; 10-a matrix insulating barrier layer.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. The components of the embodiments of the present application generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the application, as presented in the figures, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present application.

The present application will be described in detail with reference to the accompanying drawings.

The existing method for detecting or monitoring fatigue cracking of the orthotropic steel bridge deck plate has the defect that accurate crack identification is difficult to achieve; the inventor finds that the conductive sensing material is adopted to sense the damage, has higher precision and stability, particularly aims at cracks with smaller dimensions, provides a new thought for detecting fatigue cracks of the steel structure bridge, lays a foundation for real-time, visual and intelligent directional development of health monitoring and safety evaluation of the steel structure bridge and construction of a complete steel structure bridge health monitoring system, realizes long-term dynamic monitoring and intelligent evaluation of the fatigue damage of the steel structure bridge, and has wide application prospect.

As shown in fig. 10, the present application provides a coated sensor for an orthotropic steel bridge deck, the coated sensor comprising a base insulating barrier layer 10, a crack damage sensing layer 9 and a protective layer 8, which are sequentially bonded and each made of a flexible material; the crack damage sensing layer 9 comprises a conductive nano-coating, and a power interface and at least one detection probe point are arranged on the conductive nano-coating.

In the application, one side close to the matrix steel structure is defined as the inner side, and one side far away from the matrix is defined as the outer side. The inner side is attached to the matrix, the matrix insulation isolation layer 10 is arranged on the outer side, the protection layer 8 is arranged on the outer side, and the crack damage sensing layer 9 is arranged between the inner side and the outer side.

Disposing a coating sensor on a possible crack propagation path; when the base steel structure is cracked, the coating sensor can also crack along with the steel structure, at the moment, the electric signal of the detection probe point on the coating sensor can be changed, and whether the crack is developed or not and the crack length and the crack position can be deduced according to the electric potential change rule.

In the application, the insulating isolating layer 2 is attached to the surface of the substrate and is a film with a specific shape, which is used for ensuring the mutual insulation between the crack damage sensing layer 9 and the substrate, so that the electrical signals of the substrate and the crack damage sensing layer 9 can be mutually separated, and interference is avoided. With the presence of the matrix insulating separator 10, crack propagation can be estimated by merely studying the change in the electrical signal in the area of the crack damage sensing layer 9, while the crack damage sensing layer 9 has good accompanying damage characteristics, and the matrix insulating separator 1 can crack together with the matrix cracking while transmitting such crack to the crack damage sensing layer 9 located thereon.

In the application, the crack damage sensing layer 9 has good accompanying damage characteristics and proper resistance characteristics, the accompanying damage characteristics enable the coating sensor to crack along with the cracking of the substrate and the substrate isolation insulating layer 3, and the proper resistance characteristics ensure that the resistance characteristics of the coating sensing layer change after the cracking, so that the output voltage signal changes, whether the substrate cracks or not is judged by monitoring the change of the voltage signal, and the cracking length and the orientation of the crack are positioned.

In one possible embodiment, the crack damage sensing layer 9 may be prepared by the steps of:

1. customizing and spraying a conductive nano coating;

2. a fixed power interface;

3. the position of the detection probe point is selected and fixed.

Wherein the conductive nano-coating is attached to the base insulating isolation layer 1.

In one possible embodiment, the arrangement range of the crack damage sensing layer 9 is smaller than the arrangement range of the insulating isolating layer 1, which is generally slightly smaller than the arrangement range, so that the purpose is to ensure that the crack damage sensing layer 9 is insulated from the steel structure substrate by 100%, and the electrical signals of the substrate and the crack damage sensing layer 9 are mutually separated, so that interference is avoided.

In one possible embodiment, the conductive nanocoating comprises at least 3 connection strips, at least 3 of the connection strips being in a grid-like distribution; the accuracy and stability of the detection can be further improved.

In one possible embodiment, two of at least 3 of the connecting strips are laterally distributed, the remaining connecting strips are longitudinally distributed and two ends of the remaining connecting strips are respectively bonded with the two laterally distributed connecting strips; the power interface and at least one detection probe point are arranged on the two connecting strips which are transversely distributed; the position and the size of the crack can be accurately determined by measuring the electric potentials at different positions.

In one possible embodiment, the thickness of the insulating base layer 10 is 20 to 40 μm, so that absolute insulation, adhesion and accompanying damage of the insulating base layer 10 are ensured.

In one possible embodiment, the thickness of the conductive nanocoating is 8-18 μm, thereby ensuring absolute adhesion, conductivity and attendant damage to the conductive nanocoating.

In one possible embodiment, the insulating base layer 10 is mainly made of a mixture of modified polyurethane resin, drier, leveling agent and environmentally friendly solvent oil.

The insulating and isolating layer 10 may be prepared by mixing the above materials to obtain slurry, coating the slurry on a substrate, and standing for 3 hours or maintaining at a constant temperature of 40 ℃ for 40 minutes. The coating may be applied in any manner that may be achieved, such as by spraying with a pneumatic spray gun.

In the application, the crack damage sensing layer 9 has good accompanying damage characteristics and proper resistance characteristics, the accompanying damage characteristics enable the sensing layer to crack along with the cracking of the matrix and the matrix isolating insulating layer 3, and the proper resistance characteristics ensure that the resistance characteristics of the crack damage sensing layer change after the cracking, so that the output voltage signal changes, whether the matrix cracks or not is judged by monitoring the change of the voltage signal, and the cracking length and the cracking direction of the crack are positioned.

In one possible embodiment, the conductive nanocoating is made mainly of conductive nanomaterials, coupling agents, adhesives, and adjuvants; preferably, the conductive nanomaterial is silver-plated copper powder; has good adhesion performance, conductivity and damage accompanying characteristics.

In one possible embodiment, the method for preparing the crack damage sensing layer 9 includes:

preparing a coupling agent hydrolysis solution, and then adding conductive nano materials into the coupling agent hydrolysis solution, and uniformly stirring to obtain a conductive filler;

mixing the adhesive, the conductive filler and deionized water, and adding an auxiliary agent to prepare slurry;

and coating the slurry to obtain the crack damage sensing layer.

In one possible embodiment, the detection probe points are formed by copper-plated tin connection terminals bonded to the conductive nanocoating through conductive glue.

In the application, the protective layer 8 is attached to the crack damage sensing layer 9, and has the functions of protecting the base insulating isolation layer 10 and the crack damage sensing layer 9 from the interference of external environment, improving the reliability of acquired data, avoiding external damage, prolonging the service life and the like, and the selected material is a protective material with corrosion resistance, high temperature resistance and water resistance, and uniformly covers the crack damage sensing layer by adopting a pneumatic spray gun spraying mode, wherein the range of the protective material is slightly larger than that of the crack damage sensing layer.

The application also discloses a preparation method of the coating sensor for the orthotropic steel bridge deck, which comprises the following 4 steps:

(1) Customizing a corresponding flexible sticker template according to the required detection part;

(2) Configuring a conductive material for manufacturing a conductive nano coating;

(3) Spraying by using a pneumatic spray gun;

(4) Standing and curing for 4 hours or curing for 1 hour at the constant temperature of 30 ℃.

In the step (1), corresponding flexible sticker templates are customized, and conductive nano coatings in different patterns can be further set according to different selected positions, as shown in fig. 1, a region 1 and a region 3 are transverse connecting strips, a region 2 is longitudinal connecting strips, the length a and the width b of the transverse connecting strips in the region 1 and the region 3 are adjustable, the length can be adjusted according to the size of a crack detection region, the resistance value of a conductive film can be changed by adjusting the width, and crack detection is more accurate; the number x of the longitudinal connecting strips in the region 2, the width cmm, the length dmm, the included angle f DEG between each connecting strip and the transverse connecting strip, the included angle between each connecting strip and the transverse connecting strip, and the like can be customized according to different crack monitoring positions, and the customization aims at enabling the coating sensor to be more suitable for a steel structure bridge substrate and enabling crack detection at complex non-planar structural details to be realized on the basis of meeting crack detection at general structures; specific detection sites that can be realized are listed below (the present application is only listed below, but not limited to the following list):

1. when the crack growth condition at the bridge deck top plate needs to be detected, the crack detection can be carried out by only arranging a planar single-strip or multi-strip coating sensor in the direction perpendicular to the cracking direction due to the planar structure, as shown in fig. 2;

2. when the crack propagation condition of the U-shaped rib and the welding construction detail of the top plate or the U-shaped hole periphery of the diaphragm plate needs to be detected, parallel multi-strip coating sensors which are bent in space are arranged in the direction perpendicular to the easy cracking direction, as shown in fig. 3;

3. when it is required to detect crack growth at the openings of the U-ribs and the diaphragm, a grid type coating sensor can be arranged in the hole Zhou Huanbao, as shown in fig. 4;

4. when the crack propagation condition of the welding structure detail of the U rib and the diaphragm plate needs to be detected, a plurality of strips of fan-shaped coating sensors are required to be arranged along the direction perpendicular to the cracking direction, and are bent along the matrix structure in the normal direction so as to be convenient for attaching to the matrix structure, and the crack detection precision is improved, as shown in fig. 5 and 6;

in the step (2), a conductive material is prepared, wherein the raw material of the conductive material is silver-plated copper powder, the conductive material is prepared by adopting a specific proportion, and the conductivity of the material is that the surface resistivity is approximately 2.5 multiplied by 10 ^-3 The size of the silver-plated copper powder particles is 8-25 mu m, the temperature stability is 0-90 ℃, the water resistance is weak, the piezoresistance effect is good, and the accompanying damage performance is good.

In the step (3), the air pressure sprayed by the spray gun is controlled to be 8-10 kg/cm ² The gun holding distance is 18-23 cm, the spraying width is controlled between 12-19 cm, the spraying amount of the coating is 160ml/min, the spraying width is 10cm, and the spraying thickness is controlled between 7-20 mu m.

The power interface is used for providing constant voltage for the conductive nano coating and driving the conductive nano coating to run, the connecting interface adopts a copper tin-plated connecting terminal, and the fixing mode is that ALTECOL-Z84 glue is adopted for quick adhesion, so that the operation is firm and quick.

The detection probe point is used for being connected with the data acquisition card and transmitting the electric signal to the data acquisition card so as to acquire the voltage change. When a crack on a certain part of the substrate starts to expand, the middle strip of the coating sensor is disconnected along with the expansion of the crack of the substrate, at the moment, the electric signal on the detection probe point is changed, whether the crack is developed or not and the development position of the crack can be determined by analyzing the change of the electric signal, the detection probe point is generally fixed on the transverse connecting strips at the two ends of the conductive nano coating, the specific position can be adjusted according to the different detection positions, and the materials and the fixing mode of the detection probe are the same as those of the power interface.

The application has the advantages of low cost of the used materials, simple and quick sensor manufacturing process, simple and quick layout flow, simple post data processing, visual result and lower overall use cost.

The crack damage sensing layer can be in a richer form aiming at the coating sensor arranged in the grid mode, so that the corresponding crack damage sensing layer can be customized according to different cracking positions of the orthotropic steel bridge deck, and the coating sensor can have higher response sensitivity at complex construction details, so that the coating sensor can be suitable for crack detection and positioning of different cracking positions, and the problems of difficult crack detection, low precision and difficult positioning at the complex construction details of an actual steel bridge space component are solved.

Example

In this example, the preparation flow of the coating sensor and the crack detection and positioning principle are mainly explained, and the adopted case is a preferred scheme, but the method is not limited by the application;

in this example, the steel deck top plate is simulated to crack, and for convenience in explaining the detection principle, this case adopts a three-strip grid type coating sensor to explain (the grid type sensor is not limited thereto).

The preparation process of the grid type coating sensor comprises the following steps:

1. firstly, manufacturing a basal body insulating isolation layer of a part to be detected, defining an insulating area as 100X 100mm, then preparing a specific insulating material, spraying by using a pneumatic spray gun, standing for 4 hours, and curing;

2. firstly, customizing a conductive nano coating, namely, a grid type conductive nano coating with three strips in the example, wherein the length of a connecting strip at two ends is 40mm and the width of a connecting strip at two ends is 5mm, the length of a connecting strip at the middle three longitudinal directions is 70mm and the width of a connecting strip is 6mm, customizing a template, then pasting the template on a manufactured base insulating layer, preparing a special conductive coating described in the specification, spraying by using a pneumatic spray gun, and standing and curing for 4 hours;

3. after maintenance is finished, preparing a power interface and detection probe points, respectively pasting and fixing the two power interfaces on the middle parts of an upper transverse connecting strip and a lower transverse connecting strip by using ALTECOL-Z84 glue, applying a 1V constant voltage source at a position indicated by 5 as shown in 5 and 6 in fig. 7, and fixing one detection probe point on each of two sides of the upper transverse connecting strip and the lower transverse connecting strip by adopting a 4-measuring-point mode in the detection, wherein the positions of cracks are convenient to position as shown in 1, 2, 3 and 4 in fig. 7, respectively connecting 4 detection probes to a data acquisition card, and acquiring electric signals;

4. finally, covering a protective coating with the range of 100X 100mm on the upper layer of the crack damage sensing layer to ensure that the sensor is not influenced by the outside, and finishing the preparation of the sensor.

Crack detection and positioning principle explanation:

as shown in FIG. 7, a constant voltage power supply of 1V is applied at the position indicated by 5, the finger position indicated by 6 is grounded, and then detection probe points are respectively arranged at positions 1, 2, 3 and 4 for connecting the data acquisition card to acquire the potential change condition of each measuring point, and U is respectively used for ₁ 、U ₂ 、U ₃ 、U ₄ To characterize the potential values of the corresponding points, and to simulate crack propagation at the position indicated by 7 for principle explanation.

Circuit description: the three strips of left (lines 51, 12, 26), middle (line 56) and right (lines 53, 34, 46) are connected in parallel, and the parallel voltages are equal everywhere, so the voltages of the three lines are all 1V, namely U _{Left side} ＝U _{In (a)} ＝U _{Right side} =1v, the current in the main path is equal to the sum of the current of the branches, i.e. _{Total (S)} ＝I _{Left side} +I _{In (a)} +I _{Right side} The method comprises the steps of carrying out a first treatment on the surface of the The left (lines 51, 12, 26) and right (lines 53, 34, 46) bands can be considered as series circuits on two branches, respectively, in which the total voltage across the series circuit is equal to the sum of the voltages across the series sections, i.e. U ₅ ＝U ₅₁ +U ₁₂ +U ₂₆ ＝U ₅₃ +U ₃₄ +U ₄₆ ；

When no crack is initiated: the potential of each point is U ₅ ＝U ₅₁ +U ₁₂ +U ₂₆ =1v (0 potential point at point 6 ground); u (U) ₁ ＝U ₅₆ -U ₅₁ ＝U ₃ ＝U ₅₆ -U ₅₃ X (x is the detection value of the acquisition card during monitoring), U ₂ 、U ₄ The values of (2) are also the detection values of the acquisition card.

When the crack develops from left to right:

as the crack progresses, the resistance R between the lines 12 ₁₂ Enlargement of

According to U _{Left side} ＝U ₅₁ +U ₁₂ +U ₂₆

U＝IR

So U is ₁₂ Increase U _{Left side} =1v is a fixed value, so U ₅₁ And U ₂₆ Reduction of

According to U ₁ ＝U ₅₆ -U ₅₁ So U is ₁ Increase in size

The results show that: the value of the detection probe point 1 becomes larger, the value of the detection probe point 2 becomes smaller, and the data acquisition result shows that the detection probe points 3 and 4 also have small amplitude changes but are far smaller than the changes of the detection probe points 1 and 2, so that the detection probe points can be used as the standard for distinguishing left and right side cracking.

From this it can be concluded that:

(1) The orthotropic steel deck plate has cracks;

(2) The crack is developed at the left strip of the sensor;

(3) The width of the crack can be determined based on the change in the data of the probe (the data of each crack changes, and the width of the crack can be determined based on the width of the strip)

When a crack splits two strips from left to right:

shunt in parallel, and as crack progresses, the resistance R of the left two strips increases

According to I _{Total (S)} ＝I _{Left side} +I _{In (a)} +I _{Right side}

I _{Left side} And I _{In (a)} Reduced, so I _{Right side} Increase in size

According to U _{Right side} ＝U ₅₃ +U ₃₄ +U ₄

U＝IR

So U is ₃₄ Increase U _{Right side} Is a fixed value, so U ₅₃ And U ₄₆ Reduction of

According to U ₃ ＝U ₅₆ -U ₅₃

So U is ₃ Increase in size

The results show that: when the crack propagates from left to right and has broken two, the detection probe point 1 approaches 1V, the detection probe point 2 approaches 0V, u ₃ Increase U ₄ Reduction of

From this it can be concluded that:

(1) The crack has propagated to the right

(2) Determination of crack length from strip length

Simulation was performed using finite element analysis software, and the potential distribution diagram when the crack was propagated to l=21 mm is shown in fig. 8; fig. 9 is a corresponding television change chart when the crack length is 0-40 mm, wherein the darkened blue area is the potential value when the crack passes through the sensor gate, and it can be seen that there is a significant change in the potential value, and the rest areas are the potential values when the crack passes through the sensor intermediate neutral area. The simulation results are consistent with the principle results of the coating sensor.

The above examples merely illustrate specific embodiments of the application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that it is possible for a person skilled in the art to make several variants and modifications without departing from the technical idea of the application, which fall within the scope of protection of the application.

Claims (10)

1. A coating sensor for orthotropic steel bridge deck plates, characterized in that the coating sensor comprises a basal body insulating isolation layer, a crack damage sensing layer and a protective layer which are sequentially bonded and are all made of flexible materials; the crack damage sensing layer comprises a conductive nano coating, and a power interface and at least one detection probe point are arranged on the conductive nano coating.

2. The coated sensor of claim 1, wherein the conductive nanocoating comprises at least 3 connection strips, at least 3 of the connection strips being in a grid-like distribution.

3. The coated sensor of claim 2, wherein two of at least 3 of the connection strips are laterally distributed, the remaining connection strips are longitudinally distributed and both ends thereof are respectively bonded with the two laterally distributed connection strips; the power interface and at least one detection probe point are arranged on the two connecting strips which are transversely distributed.

4. A coated sensor according to any one of claims 1-3, wherein the crack damage sensing layer is arranged in a range smaller than the range of the matrix insulating barrier layer.

5. The coated sensor of claim 1 wherein the thickness of the base insulating spacer layer is 20-40 μm.

6. The coated sensor of claim 1 wherein the conductive nanocoating has a thickness of 8-18 μm.

7. The coating sensor according to claim 1 or 5, wherein the substrate insulating isolation layer is mainly prepared by mixing modified polyurethane resin, a drier, a leveling agent and environment-friendly solvent oil.

8. A coated sensor according to any one of claims 1-3, wherein the conductive nanocoating is made mainly of conductive nanomaterials, coupling agents, adhesives and adjuvants; the conductive nano material is silver-plated copper powder.

9. The coated sensor of claim 8, wherein the method of preparing the crack damage sensing layer comprises:

preparing a coupling agent hydrolysis solution, and then adding conductive nano materials into the coupling agent hydrolysis solution, and uniformly stirring to obtain a conductive filler;

mixing the adhesive, the conductive filler and deionized water, and adding an auxiliary agent to prepare slurry;

and coating the slurry to obtain the crack damage sensing layer.

10. The coated sensor of claim 1, wherein the detection probe points are formed from copper-plated tin terminals bonded to the conductive nanocoating by conductive glue.