Intelligent concrete stress damage detection method using 3D printing technology

Abstract

The invention provides an intelligent concrete stress damage detection method using a 3D printing technology, and particularly relates to the technical field of building structure stress damage detection. The method specifically comprises the following steps: preparing a high-resistivity intelligent concrete substrate; a low-resistivity intelligent concrete linear strip, a point electrode and an annular strip are printed on the intelligent concrete substrate through 3D printing and connected with a copper wire; preparing an intelligent concrete detection device and calibrating initial parameters and sensitivity values; preparing a to-be-detected concrete member containing an intelligent concrete detection device, and obtaining the actual strain on three dimensions; external force is applied to the to-be-detected concrete member, the damage state of the intelligent concrete base and the volume deformation condition of the annular strip are analyzed, and then the overall stress damage condition of the to-be-detected concrete member is obtained. According to the invention, the spatial characteristics of the 3D printing technology are utilized, and the high sensitivity of the intelligent concrete material is combined, so that the accurate monitoring of the damage, strain stress and volume deformation of the structure can be realized at the same time.

Description

Technical Field

[0001] The patent of this invention relates to the technical field of stress damage detection of building structures, and specifically to an intelligent concrete stress damage detection method using 3D printing technology. Background Art

[0002] With the development of the construction industry and science and technology, more and more concrete structures with huge volume, complex structure and diverse functions have emerged, such as super-long span bridges, large water conservancy projects, offshore platform structures, nuclear power plant buildings, etc. These structures are often of high importance, long service life, complex loads and forces, and once they fail, the cost is huge. Therefore, in order to ensure the safety of these structures, effective means are often needed to conduct tests and monitor the health of the structures. Accurately grasping the distribution characteristics of the internal forces, deformations and damages of the key parts of these complex structures, especially the multi-dimensional strain characteristics, has become an important research hotspot in the field of building structures.

[0003] The so-called smart concrete is a piezoresistive sensor formed by adding conductive particles to concrete. It can not only monitor the strain of concrete, but also monitor its damage. According to the corresponding relationship between the resistance change rate and strain of this type of smart material, it can be used to detect the strain and damage of concrete; however, the detection effect is often affected by the uniformity of smart concrete, multi-axis stress state, stability, etc. Therefore, the smart concrete material prepared by conventional casting methods has problems such as insufficient precision and unstable intelligent characteristics. 3D printing is a rapid prototyping technology. With its advantages of high precision, low cost and good repeatability, it has become a new and promising process in the field of electronic product preparation. It is based on digital model files and constructs three-dimensional objects by extruding concrete materials with certain fluidity and plasticity layer by layer.

[0004] Therefore, in order to solve the above problems, the present invention provides an intelligent concrete stress damage detection method using 3D printing technology. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art and solve the problem that the smart concrete material prepared by the conventional casting method has insufficient uniformity, insufficient precision, and unstable intelligent characteristics, which in turn affects the detection results, the present invention provides a smart concrete stress damage detection method using 3D printing technology, and the specific technical scheme is as follows:

[0006] An intelligent concrete stress damage detection method using 3D printing technology specifically comprises the following steps:

[0007] S1. Cast two high-resistivity smart concrete substrates;

[0008] S2. Use a 3D printer to print low-resistivity smart concrete linear strips along the X, Y, and Z directions on the top of one of the smart concrete substrates; and print two low-resistivity smart concrete point electrodes and a smart concrete annular strip on the top and bottom of another smart concrete substrate;

[0009] S3. Insert copper wires into the smart concrete straight strip, smart concrete point electrode, and smart concrete ring strip in S2 before solidification and mark them;

[0010] S4. The two smart concrete bases in S3 are stacked, and one side of the smart concrete straight strip is set back to the other side of the smart concrete annular strip;

[0011] S5. Pour ordinary concrete encapsulation layer on one side of the smart concrete straight strip and one side of the smart concrete ring strip, and obtain the smart concrete detection device after solidification; keep the lead ends of several copper wires exposed on the surface of the smart concrete detection device;

[0012] S6. Apply external force to the smart concrete detection device, measure the resistivity change law between the copper wires on the three smart concrete straight strips under different external forces, calibrate the initial parameters of the relationship between the resistance of the smart concrete straight strip and the external force; calculate the initial resistivity values ​​of the smart concrete point electrode and the smart concrete ring strip, and obtain the sensitivity value of the smart concrete detection device;

[0013] S7 pouring the concrete member to be inspected, and the smart concrete detection device obtained in S5 is placed in the concrete member to be inspected, keeping the lead ends of several copper wires exposed to the surface of the concrete member to be inspected;

[0014] S8. Calculate the actual stress magnitude of the entire concrete component to be inspected in the three directions of X, Y, and Z through the initial parameters and sensitivity values ​​of the smart concrete straight strip;

[0015] By applying external forces of different directions and magnitudes to the concrete components to be inspected, measuring the resistivity change law of the smart concrete point electrode under different external forces, analyzing the damage state of the smart concrete base, and then obtaining the overall damage state of the concrete components to be inspected;

[0016] By applying external forces of different directions and magnitudes to the concrete component to be inspected, measuring the resistivity variation of the smart concrete annular strip under different external forces, analyzing the volume deformation of the area inside the smart concrete annular strip, and then obtaining the overall volume deformation of the concrete component to be inspected;

[0017] S9. Collect measurement parameters and data based on the measurement results obtained in S8, and issue early warnings and take structural maintenance measures in a timely manner.

[0018] Preferably, the high resistivity has a value range of >10000Ω·m; the low resistivity has a value range of ≤10000Ω·m.

[0019] Preferably, the material ratio of the smart concrete substrate described in S1 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.0025-0.01: 0.0025-0.01; the material ratio of the smart concrete straight strips, smart concrete point electrodes and smart concrete annular strips described in S2 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.03-0.08: 0.03-0.08.

[0020] Preferably, the specific insertion position of the copper wire in S3 is as follows:

[0021] Take six copper wires, insert one copper wire at each end of each smart concrete straight strip, and lead out the other end of the copper wire; regard the two copper wires on each smart concrete straight strip as a group, and number the three groups of copper wires A, B, and C respectively;

[0022] Take two copper wires, insert one copper wire into each smart concrete point electrode, and lead out the other end of the copper wire; regard the copper wires on the two smart concrete point electrodes as a group, numbered D;

[0023] Take two more copper wires, select two points at the intersection of any diameter and the arc on the smart concrete ring strip, insert a copper wire at each point, and lead out the other end of the copper wire; regard the two copper wires on the smart concrete ring strip as a group, numbered E.

[0024] Preferably, the method for measuring the resistivity variation law between copper wires on the smart concrete straight strip in S6 is as follows:

[0025] External forces of different directions and magnitudes are applied to the smart concrete detection device through a press, and the resistance values ​​between the pairs of copper wires in groups A, B, and C corresponding to different external forces are measured respectively. The variation law of the resistivity of the smart concrete straight strips in three directions with the change of external forces is obtained, and then the initial parameter value of the relationship between the resistance of each smart concrete straight strip and the external force it is subjected to is calculated.

[0026] Preferably, the specific conversion method of the actual stress magnitude of the entire concrete component to be inspected in the three directions of X, Y, and Z in S8 is as follows:

[0027] According to the relationship between resistance and stress:

[0028] S = aR + b;

[0029] Where R is the resistance value of the concrete component to be tested, a and b are the initial parameter values ​​obtained in S6, and S is the stress;

[0030] Combined with the sensitivity value obtained in S6, the specific values ​​of the actual stresses on the concrete component to be inspected along the three directions of X, Y, and Z can be calculated.

[0031] Also preferably, the method for measuring the resistivity variation law between the copper wires of the intelligent concrete point electrodes in S8 is as follows:

[0032] The press machine applies external forces of different directions and magnitudes to the concrete component to be inspected in S7, and measures the resistance values ​​between the paired copper wires in D corresponding to different external forces, thereby obtaining the variation law of the resistivity of the smart concrete point electrode with the change of external force.

[0033] Further preferably, the damage state of the entire concrete component to be inspected in S8 is divided into the following three situations:

[0034] If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 is within ±0.1%, it indicates that the smart concrete substrate is not damaged, that is, the concrete component to be inspected is in a non-damaged stage;

[0035] If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 varies by more than 0.1% and less than or equal to 5%, it indicates that the smart concrete substrate has slight damage, that is, the concrete component to be inspected is in the damage stage;

[0036] If the resistivity between the two copper wires on the smart concrete point electrode varies by more than 5% from the initial value of the resistivity of the smart concrete point electrode obtained in S6, it indicates that the smart concrete substrate is seriously damaged or even cracked, that is, the concrete component to be inspected is in the destruction stage.

[0037] Still further preferably, the method for measuring the resistivity variation law between the copper wires on the smart concrete annular strip in S8 is as follows:

[0038] External forces of different directions and magnitudes are applied to the concrete component to be inspected in S7 by a press, and the resistance values ​​between the paired copper wires numbered E corresponding to different external forces are measured, thereby obtaining the variation law of the resistivity of the smart concrete annular strip with the change of external force.

[0039] More preferably, the volume deformation state of the entire concrete component to be inspected in S8 is divided into the following three situations:

[0040] Case 1: If the resistivity between the two copper wires on the smart concrete ring strip gradually decreases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip shrinks, and further indicates that the volume of the concrete component to be inspected shrinks;

[0041] Case 2: If the resistivity between the two copper wires on the smart concrete ring strip gradually increases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip has expanded, and further indicates that the volume of the concrete component to be inspected has expanded;

[0042] Case 3: If the resistivity between the two copper wires on the smart concrete annular strip varies by more than 5% from the initial resistivity value of the smart concrete annular strip obtained in S6, it indicates that cracks appear in the inner area of ​​the smart concrete annular strip, which further indicates that the volume of the concrete component to be inspected has further expanded compared to the state in Case 2.

[0043] The beneficial effects of the present invention are:

[0044] The present invention intends to use high-resistivity smart concrete as a matrix, and combine a low-resistivity smart concrete structure with a high-resistivity smart concrete matrix through 3D printing technology. Compared with traditional cast-type test pieces, the present invention utilizes the spatial characteristics of 3D printing technology to obtain X, Y, and Z multi-dimensional structural detection of the test piece; in addition, the present invention uses smart concrete materials, which have higher measurement sensitivity and accuracy than ordinary concrete materials, and can simultaneously realize comprehensive monitoring of structural damage, strain stress, and volume deformation; it provides an effective basis for improving the safety of civil engineering facilities, reasonably guiding maintenance plans for structural health, and extending the service life of structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The drawings constituting the specification of this application are used to provide further understanding of this application and do not constitute improper limitations on this application.

[0046] Figure 1 This is a schematic diagram of the production of the smart concrete substrate in the present invention;

[0047] Figure 2 It is a schematic diagram of the intelligent concrete base in the concrete component to be inspected in the present invention;

[0048] Figure 3 The change law of resistivity between point electrodes of smart concrete with stress state;

[0049] Figure 4 The resistivity of the smart concrete straight strip in the X direction changes with the stress state;

[0050] Figure 5 The resistivity of the smart concrete straight strip in the Y direction changes with the stress state;

[0051] Figure 6 The resistivity of the smart concrete straight strip in the Z direction changes with the stress state;

[0052] Figure 7 The resistivity of the smart concrete ring strip varies with the stress state;

[0053] In the figure, 1-3D printer; 11-extrusion nozzle; 2-intelligent concrete base; 21-intelligent concrete straight strip; 22-intelligent concrete point electrode; 23-intelligent concrete annular strip; 3-packaging layer; 4-concrete component to be inspected. DETAILED DESCRIPTION

[0054] The specific implementation of an intelligent concrete stress damage detection method using 3D printing technology provided by the present invention is further described in conjunction with the accompanying drawings and embodiments.

[0055] like Figure 1-2 As shown, a smart concrete stress damage detection method using 3D printing technology specifically includes the following steps:

[0056] S1. Cast two high-resistivity smart concrete substrates; wherein the high-resistivity smart concrete has smart features for rough damage state detection.

[0057] S2. Use a 3D printer to print low-resistivity smart concrete straight strips along the X, Y, and Z directions on the top of one of the smart concrete bases; print two low-resistivity smart concrete point electrodes and a smart concrete annular strip on the top and bottom of another smart concrete base; among them, the low-resistivity smart concrete has higher sensitivity and more accurate stress and resistivity change laws, which is used for strain detection.

[0058] The high resistivity has a value range of >100,000 Ω·m; the low resistivity has a value range of ≤10,000 Ω·m.

[0059] Preferably, the material ratio of the smart concrete substrate in S1 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.0025-0.01: 0.0025-0.01;

[0060] Preferably, the material ratio of the smart concrete straight strip, the smart concrete point electrode and the smart concrete annular strip in S2 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.03-0.08: 0.03-0.08.

[0061] S3. Insert copper wires into the smart concrete straight strip, smart concrete point electrode, and smart concrete ring strip in S2 before solidification and mark them;

[0062] Preferably, the specific insertion position of the copper wire in S3 is as follows:

[0063] Take six copper wires, insert one copper wire at each end of each smart concrete straight strip, and lead out the other end of the copper wire; regard the two copper wires on each smart concrete straight strip as a group, and number the three groups of copper wires A, B, and C respectively;

[0064] Take two copper wires, insert one copper wire into each smart concrete point electrode, and lead out the other end of the copper wire; regard the copper wires on the two smart concrete point electrodes as a group, numbered D;

[0065] Take two more copper wires, select two points at the intersection of any diameter and the arc on the smart concrete ring strip, insert a copper wire at each point, and lead out the other end of the copper wire; regard the two copper wires on the smart concrete ring strip as a group, numbered E.

[0066] S4. The two smart concrete bases in S3 are stacked, and one side of the smart concrete straight strip is set back to the other side of the smart concrete annular strip;

[0067] S5. Pour ordinary concrete encapsulation layer on one side of the smart concrete straight strip and one side of the smart concrete ring strip, and obtain the smart concrete detection device after solidification; keep the lead ends of several copper wires exposed on the surface of the smart concrete detection device;

[0068] S6. Apply external force to the smart concrete detection device, measure the resistivity change law between the copper wires on the smart concrete straight strip under different external forces, and calibrate the initial parameters of the relationship between the resistance of the smart concrete straight strip and the external force; calculate the initial resistivity values ​​of the smart concrete point electrode and the smart concrete ring strip, and obtain the sensitivity value of the smart concrete detection device;

[0069] S7. Cast the concrete member to be tested, and place the intelligent concrete detection device obtained in S5 in the concrete member to be tested, keeping the lead ends of several copper wires exposed to the surface of the concrete member to be tested;

[0070] S8. First, the actual stress magnitude of the entire concrete component to be inspected in the three directions of X, Y, and Z is calculated using the initial parameters and sensitivity values ​​of the smart concrete linear strip. The specific method is as follows:

[0071] According to the relationship between resistance and stress:

[0072] S = aR + b;

[0073] Wherein, R is the resistance value of the concrete component to be tested (known and measurable), a and b are the initial parameter values ​​obtained in S6 (known);

[0074] Combined with the sensitivity value obtained in S6, the specific value of the actual stress S exerted on the concrete component to be inspected along the three directions of X, Y, and Z can be converted and calculated.

[0075] Secondly, the press machine applies external forces of different directions and magnitudes to the concrete component to be inspected in S7, and measures the resistance values ​​between the pairs of copper wires in number D corresponding to different external forces, and obtains the variation law of the resistivity of the smart concrete point electrode with the change of external force;

[0076] It is concluded that the overall damage state of the concrete component to be inspected can be divided into the following three situations:

[0077] Case 1: If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 is within ±0.1%, it indicates that the smart concrete substrate is not damaged, that is, the concrete component to be inspected is in a non-damaged stage;

[0078] Case 2: If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 varies from greater than 0.1% to less than or equal to 5%, it indicates that there is slight damage on the smart concrete substrate, that is, the concrete component to be inspected is in the damage stage;

[0079] Case 3: If the resistivity between the two copper wires on the smart concrete point electrode varies by more than 5% from the initial value of the resistivity of the smart concrete point electrode obtained in S6, it indicates that the smart concrete substrate is seriously damaged or even cracked, that is, the concrete component to be inspected is in the destruction stage.

[0080] Finally, the press machine applies external forces of different directions and magnitudes to the concrete component to be inspected in S7, and measures the resistance values ​​between the pairs of copper wires numbered E corresponding to different external forces, and obtains the variation law of the resistivity of the smart concrete ring strip with the change of external force;

[0081] It is concluded that the overall volume deformation state of the concrete component to be inspected can be divided into the following three situations:

[0082] Case 1: If the resistivity between the two copper wires on the smart concrete ring strip gradually decreases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip shrinks, and further indicates that the volume of the concrete component to be inspected shrinks;

[0083] Case 2: If the resistivity between the two copper wires on the smart concrete ring strip gradually increases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip has expanded, and further indicates that the volume of the concrete component to be inspected has expanded;

[0084] Case 3: If the resistivity between the two copper wires on the smart concrete annular strip varies by more than 5% from the initial resistivity value of the smart concrete annular strip obtained in S6, it indicates that cracks appear in the inner area of ​​the smart concrete annular strip, which further indicates that the volume of the concrete component to be inspected has further expanded compared to the state in Case 2.

[0085] S9. Collect measurement parameters and data based on the measurement results obtained in S8, and issue early warnings and take structural maintenance measures in a timely manner.

[0086] Embodiment 1:

[0087] The high resistivity smart concrete ratio used in this embodiment is cement: sand: water: graphene: superplasticizer = 1: 3: 0.5: 0.005: 0.005; the low resistivity smart concrete ratio is cement: sand: water: graphene: superplasticizer = 1: 3: 0.5: 0.04: 0.04;

[0088] According to the above steps S1-S7, a concrete component to be inspected containing an intelligent concrete detection device is prepared, and the initial parameter value of the relationship between the resistance of the intelligent concrete straight strip and the external force, the initial value of the resistivity of the intelligent concrete point electrode and the intelligent concrete annular strip, and the sensitivity value of the intelligent concrete detection device are obtained;

[0089] Then, external forces in the vertical direction were applied to the concrete components to be inspected, and the following conclusions were obtained in combination with the temperature compensation principle:

[0090] like Figure 3 As shown in the figure, the resistivity between the copper wires of the smart concrete point electrodes changes significantly with the increase of external force, but there is no linear feature between the two:

[0091] (1) When the resistivity fluctuates in a non-obvious pattern with the change of external force, that is, the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode is within ±0.1%, it indicates that the smart concrete substrate is in the undamaged stage;

[0092] (2) When the resistivity tends to increase with the change of external force, that is, the change range between the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode is greater than 0.1% and less than or equal to 5%, it indicates that the smart concrete substrate is in the damage stage;

[0093] (3) When the resistivity suddenly increases significantly, that is, the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode varies by more than 5%, it indicates that the smart concrete substrate is seriously damaged or even cracked, and is in the destruction stage.

[0094] like Figure 4-6 As shown, the resistivity change between the straight copper conductors of the smart concrete is roughly linearly related to the magnitude of the external force, and the two are inversely proportional. Based on the initial parameters obtained in S6, the actual stress values ​​of the concrete component to be inspected along the three directions of X, Y, and Z can be calculated;

[0095] like Figure 7 As shown in the figure, the resistivity change between the copper conductors in the smart concrete straight strips and the magnitude of the external force can be roughly divided into three stages:

[0096] Stage I is a linear change stage, in which the concrete is in an elastic state, and the resistivity decreases with the increase of external force, that is, the volume of the concrete component to be tested shrinks in the initial stage of compression;

[0097] Stage II is the stage of fine damage development. In this stage, the concrete is in a plastic state, and the resistivity shows a nonlinear relationship with the change of external force. In this stage, the concrete component to be inspected begins to expand.

[0098] Stage III is the stage of rapid damage development, and the resistivity will increase sharply. In this stage, the concrete components to be inspected will expand further compared to stage II.

[0099] That is, when the resistivity between the two copper wires on the smart concrete annular strip gradually decreases with the change of external force, it indicates that the volume of the area inside the smart concrete annular strip shrinks; when the concrete component to be inspected is in a slow stress state or a complex stress state, the resistivity between the two copper wires on the smart concrete annular strip will also show a trend of slowly increasing with the change of external force, indicating that the volume of the area inside the smart concrete annular strip begins to expand; when the resistivity between the two copper wires on the smart concrete annular strip increases significantly, it indicates that cracks have appeared in the area inside the smart concrete annular strip and the volume of the structure has further expanded.

[0100] In actual engineering applications, it is only necessary to prepare the intelligent concrete detection device in the laboratory and measure the initial parameters of the relationship between the resistance of the intelligent concrete straight strip and the external force, the initial resistivity values ​​of the intelligent concrete point electrode and the intelligent concrete annular strip, and the sensitivity value of the intelligent concrete detection device; then place the intelligent concrete detection device in the detection area of ​​the concrete building to be tested, and by referring to the initial resistivity value and observing the change of resistivity over time, the structural damage, strain stress and volume deformation of the detection point of the concrete building to be tested can be accurately judged, and then accurate early warning can be made and structural maintenance measures can be taken in time to avoid irreparable major losses and reduce safety hazards.

[0101] The invention has a simple structure, is easy to operate and has a low cost. It can detect health parameters such as internal damage evolution, multi-dimensional strain distribution, and volume deformation of concrete structures. The research results can be used in structural test research and in structural health monitoring. It is of great significance to improve the safety of civil engineering facilities, reasonably guide structural health maintenance, and extend their service life.

[0102] In the present invention, the orientation or position relationship indicated by terms such as "upper", "lower", "bottom", "top", etc. is based on the orientation or position relationship shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationship of the various parts or elements of the present invention. They do not specifically refer to any part or element in the present invention and cannot be understood as limitations on the present invention. Terms such as "connected" and "connected" should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances, and they cannot be understood as limitations on the present invention.

[0103] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for detecting stress damage of intelligent concrete using 3D printing technology, characterized in that: Specifically include the following steps: S1. Cast two high-resistivity smart concrete substrates; S2. Use a 3D printer to print low-resistivity smart concrete linear strips along the X, Y, and Z directions on the top of one of the smart concrete substrates; and print two low-resistivity smart concrete point electrodes and a smart concrete annular strip on the top and bottom of another smart concrete substrate; S3. Insert copper wires into the smart concrete straight strip, smart concrete point electrode, and smart concrete ring strip in S2 before solidification and mark them; S4. The two smart concrete bases in S3 are stacked, and one side of the smart concrete straight strip is set back to the other side of the smart concrete annular strip; S5. Pour ordinary concrete encapsulation layer on one side of the smart concrete straight strip and one side of the smart concrete ring strip, and obtain the smart concrete detection device after solidification, keeping the lead ends of several copper wires exposed on the surface of the smart concrete detection device; S6. Apply external force to the smart concrete detection device, measure the resistivity change law between the copper wires on the three smart concrete straight strips under different external forces, and calibrate the initial parameters of the relationship between the resistance of the smart concrete straight strip and the external force; calculate the initial resistivity values ​​of the smart concrete point electrode and the smart concrete ring strip, and obtain the sensitivity value of the smart concrete detection device; S7. Casting the concrete member to be inspected, and placing the intelligent concrete detection device obtained in S5 in the concrete member to be inspected, keeping the lead ends of several copper wires exposed to the surface of the concrete member to be inspected; S8. Calculate the actual stress magnitude of the entire concrete component to be inspected in the three directions of X, Y, and Z through the initial parameters and sensitivity values ​​of the smart concrete straight strip; By applying external forces of different directions and magnitudes to the concrete components to be inspected, measuring the resistivity change law of the smart concrete point electrode under different external forces, analyzing the damage state of the smart concrete base, and then obtaining the overall damage state of the concrete components to be inspected; By applying external forces of different directions and magnitudes to the concrete component to be inspected, measuring the resistivity variation of the smart concrete annular strip under different external forces, analyzing the volume deformation of the area inside the smart concrete annular strip, and then obtaining the overall volume deformation of the concrete component to be inspected; S9. Collect measurement parameters and data based on the measurement results obtained in S8, and issue early warnings and take structural maintenance measures in a timely manner.

2. The intelligent concrete stress damage detection method using 3D printing technology according to claim 1 is characterized in that: The value range of the high resistivity is >10000Ω·m; the value range of the low resistivity is ≤10000Ω·m.

3. The intelligent concrete stress damage detection method using 3D printing technology according to claim 1 is characterized in that: The material ratio of the smart concrete base in S1 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.0025-0.01: 0.0025-0.01; The material ratio of the smart concrete straight strip, smart concrete point electrode and smart concrete annular strip described in S2 is cement: sand: water: graphene: superplasticizer = 1-1.5: 2.5-3: 0.4-0.6: 0.03-0.08: 0.03-0.

08.

4. The intelligent concrete stress damage detection method using 3D printing technology according to claim 1 is characterized in that: The specific insertion position of the copper wire in S3 is as follows: Take six copper wires, insert one copper wire at each end of each smart concrete straight strip, and lead out the other end of the copper wire; regard the two copper wires on each smart concrete straight strip as a group, and number the three groups of copper wires A, B, and C respectively; Take two copper wires, insert one copper wire into each smart concrete point electrode, and lead out the other end of the copper wire; regard the copper wires on the two smart concrete point electrodes as a group, numbered D; Take two more copper wires, select two points at the intersection of any diameter and the arc on the smart concrete ring strip, insert a copper wire at each point, and lead out the other end of the copper wire; regard the two copper wires on the smart concrete ring strip as a group, numbered E.

5. The intelligent concrete stress damage detection method using 3D printing technology according to claim 4 is characterized in that: The method for measuring the resistivity variation law between the copper wires on the smart concrete straight strip in S6 is as follows: External forces of different directions and magnitudes are applied to the smart concrete detection device through a press, and the resistance values ​​between the pairs of copper wires in groups A, B, and C corresponding to different external forces are measured respectively. The variation law of the resistivity of the smart concrete straight strips in three directions with the change of external forces is obtained, and then the initial parameter value of the relationship between the resistance of each smart concrete straight strip and the external force it is subjected to is calculated.

6. The intelligent concrete stress damage detection method using 3D printing technology according to claim 5 is characterized in that: The specific conversion method of the actual stress magnitude of the entire concrete component to be inspected in S8 in the three directions of X, Y, and Z is as follows: According to the relationship between resistance and stress: S = aR + b; Where R is the resistance value of the concrete component to be tested, a and b are the initial parameter values ​​obtained in S6, and S is the stress; Combined with the sensitivity value obtained in S6, the specific values ​​of the actual stresses on the concrete component to be inspected along the three directions of X, Y, and Z can be calculated.

7. The intelligent concrete stress damage detection method using 3D printing technology according to claim 4 is characterized in that: The method for measuring the resistivity variation between the copper wires of the intelligent concrete point electrodes in S8 is as follows: The press machine applies external forces of different directions and magnitudes to the concrete component to be inspected in S7, and measures the resistance values ​​between the paired copper wires in D corresponding to different external forces, thereby obtaining the variation law of the resistivity of the smart concrete point electrode with the change of external force.

8. The intelligent concrete stress damage detection method using 3D printing technology according to claim 7 is characterized in that: The overall damage state of the concrete component to be inspected described in S8 is divided into the following three cases: If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 is within ±0.1%, it indicates that the smart concrete substrate is not damaged, that is, the concrete component to be inspected is in a non-damaged stage; If the resistivity between the two copper wires on the smart concrete point electrode and the initial value of the resistivity of the smart concrete point electrode obtained in S6 varies by more than 0.1% and less than or equal to 5%, it indicates that the smart concrete substrate has slight damage, that is, the concrete component to be inspected is in the damage stage; If the resistivity between the two copper wires on the smart concrete point electrode varies by more than 5% from the initial value of the resistivity of the smart concrete point electrode obtained in S6, it indicates that the smart concrete substrate is seriously damaged or even cracked, that is, the concrete component to be inspected is in the destruction stage.

9. The intelligent concrete stress damage detection method using 3D printing technology according to claim 4 is characterized in that: The method for measuring the resistivity variation law between the copper wires on the smart concrete ring strip in S8 is as follows: External forces of different directions and magnitudes are applied to the concrete component to be inspected in S7 by a press, and the resistance values ​​between the paired copper wires numbered E corresponding to different external forces are measured, thereby obtaining the variation law of the resistivity of the smart concrete annular strip with the change of external force.

10. The intelligent concrete stress damage detection method using 3D printing technology according to claim 9 is characterized in that: The volume deformation state of the entire concrete component to be inspected in S8 is divided into the following three situations: Case 1: If the resistivity between the two copper wires on the smart concrete ring strip gradually decreases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip shrinks, and further indicates that the volume of the concrete component to be inspected shrinks; Case 2: If the resistivity between the two copper wires on the smart concrete ring strip gradually increases with the change of external force, it indicates that the volume of the area inside the smart concrete ring strip has expanded, and further indicates that the volume of the concrete component to be inspected has expanded; Case 3: If the resistivity between the two copper wires on the smart concrete annular strip varies by more than 5% from the initial resistivity value of the smart concrete annular strip obtained in S6, it indicates that cracks appear in the inner area of ​​the smart concrete annular strip, which further indicates that the volume of the concrete component to be inspected has further expanded compared to the state in Case 2.

Images