Engineering test piece internal fracture occurrence visualization method based on piezoelectric ceramics

Abstract

The invention discloses an engineering test piece internal crack occurrence visualization method based on piezoelectric ceramics. The method comprises the following steps: uniformly arranging three groups of piezoelectric ceramic signal monitoring points on six surfaces of an engineering test piece; calculating the difference value of the peak values of the piezoelectric ceramic signals monitored at each position point before and after the blasting test, if the difference values of the three pairs of piezoelectric ceramic signals corresponding to one position point exceed a threshold value, determining that the position point has a crack and recording the position point as a crack point, and traversing all the position points to obtain all the crack points; fracture points are divided into different clusters by adopting a clustering analysis method, and then plane fitting is performed to obtain different fracture planes. According to the method, the cracks in the engineering test piece after the engineering blasting model test can be accurately identified, the occurrence of the cracks can be visualized, destructive operation does not need to be carried out on the engineering test piece of the engineering blasting model test, and therefore the method can be used for damage monitoring under the action of the cyclic blasting load.

Description

Technical Field

[0001] The invention belongs to the field of engineering blasting, and in particular relates to a method for visualizing the occurrence of internal cracks in an engineering specimen based on piezoelectric ceramics. Background Art

[0002] Blasting is a common engineering technology, which is often used in tunneling, earthwork excavation, building demolition and other fields. However, since the calculation of the hole network parameters of blasting engineering often adopts empirical formulas, the calculation results are often accompanied by great uncertainty in practical application. Therefore, it is usually necessary to conduct a small model test before blasting construction to determine whether the blasting parameter values ​​are accurate. When conducting small model tests, concrete with similar geological rock properties to the blasting engineering is often used as a model specimen. When the amount of explosives used in the model test is small, the model often does not show obvious damage on the outside, but cracks have appeared inside under the dynamic action of the explosion stress wave generated by the explosion of the explosives and the quasi-static action of the detonation gas. Accurately identifying the occurrence of cracks inside the engineering specimen and visualizing them can provide a more reliable basis for adjusting the explosion parameters, and provide a possibility for further understanding the damage mechanism of rock materials under blasting. At the same time, the emergence of piezoelectric ceramic monitoring equipment makes it possible to visualize the cracks inside the engineering specimen. The transmitting end of the piezoelectric ceramic monitoring equipment emits an acoustic signal of a specified waveform, amplitude, and width. After passing through the monitored object, the receiving end converts the acoustic signal into an electrical signal and records it in the computer system. When an obvious crack appears in the object being measured, the peak value of the piezoelectric ceramic signal will be significantly reduced. If there is no crack in the object being measured, the peak value of the piezoelectric signal will not change significantly. Therefore, the attenuation degree of the piezoelectric ceramic signal can be used to determine whether there is a crack in the object being measured. Summary of the invention

[0003] To solve the above problems, we proposed a method for visualizing the internal crack occurrence of engineering specimens based on piezoelectric ceramics. The purpose is to obtain the internal damage of the specimens under the action of explosive loads without performing destructive testing on the model test specimens, thereby providing the possibility for adjusting the blasting parameters of engineering blasting and studying the rock damage mechanism.

[0004] The technical solution of the present invention is as follows:

[0005] A method for visualizing crack occurrence inside an engineering specimen based on piezoelectric ceramics comprises the following steps:

[0006] Step 1, evenly setting three groups of piezoelectric ceramic signal monitoring points on six surfaces of the engineering specimen, wherein one group of piezoelectric ceramic signal monitoring points includes a plurality of pairs of piezoelectric ceramic signal monitoring points correspondingly set on two opposite surfaces of the engineering specimen;

[0007] Step 2: Before and after the blasting test of the engineering specimen, three groups of piezoelectric ceramic signal monitoring points are used to collect signals to obtain three groups of piezoelectric ceramic signals monitored before and after the blasting test;

[0008] Step 3, establish a spatial grid three-dimensional model of the engineering specimen, and determine the three pairs of piezoelectric ceramic signal monitoring points closest to each position point in the engineering specimen on the six surfaces as the piezoelectric ceramic signal monitoring points corresponding to this position point;

[0009] Step 4, calculate the difference between the peak values ​​of the piezoelectric ceramic signals monitored before and after the blasting test for each pair of piezoelectric ceramic signal monitoring points corresponding to each position point, and determine whether the difference exceeds a preset threshold value. If so, it is determined that the pair of piezoelectric ceramic signal monitoring points are offset after the blasting. If the three pairs of piezoelectric ceramic signals corresponding to a position point are offset after the blasting, it is considered that there is a crack at this position point and it is recorded as a crack point. After traversing all the position points, all the crack points are obtained;

[0010] Step 4: Use the DBSCAN cluster analysis method to divide the crack points into different clusters, perform plane fitting on the crack points in each cluster, and obtain different crack planes;

[0011] Step 5: Use triangulation to generate a three-dimensional mesh of the crack plane, and obtain a visualized three-dimensional crack plane whose plane shape is close to that of a real crack.

[0012] Furthermore, in step 4, a convex hull algorithm is used to determine the boundary of the crack in the process of generating the crack plane.

[0013] Furthermore, in step 1, the distance between adjacent piezoelectric ceramic signal monitoring points is 0.1 cm-1 cm.

[0014] The present invention has the following beneficial technical effects:

[0015] 1. The present invention can accurately identify the cracks inside the engineering specimen after the engineering blasting model test and visualize the cracks.

[0016] 2. The method of the present invention is simple to operate, uses a single device, and does not require destructive operations on engineering specimens in engineering blasting model tests. Therefore, it can be used for damage monitoring under cyclic blasting loads.

[0017] Therefore, the present invention can meet the actual needs in the engineering blasting model test process, identify the internal cracks of the engineering specimen without destroying it, and visualize its occurrence, providing a basis for adjusting blasting parameters and studying the damage mechanism of rock under the action of explosive load. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Flow chart of the method of the present invention

[0019] Figure 2 Schematic diagram of engineering test pieces and measurement point layout

[0020] Figure 3 Schematic diagram of piezoelectric ceramic monitoring equipment

[0021] Figure 4 Schematic diagram of the visualization results of the internal crack occurrence of the engineering specimen

[0022] The parts represented by the part numbers in the figure are as follows:

[0023] 1. Engineering specimens for engineering blasting model tests; 2. Piezoelectric ceramic signal monitoring measurement points; 3. Computer system; 4. Piezoelectric ceramic signal monitoring equipment host; 5. Piezoelectric ceramic signal monitoring equipment sensor; 6. Data transmission line; 7. Signal amplifier DETAILED DESCRIPTION

[0024] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0025] like Figure 1 As shown, the present invention mainly uses piezoelectric ceramic monitoring equipment to monitor the piezoelectric ceramic signals of the engineering specimens of the engineering blasting model test before and after the blasting test, and obtains the difference between the peak values ​​of the piezoelectric ceramic signals before and after the blasting test after processing the signals, and uses the MATLAB program to process to obtain the occurrence of the internal cracks of the specimen and visualize it. The specific implementation of this method includes the following specific steps:

[0026] like Figure 2 As shown, the engineering specimen in this embodiment adopts a concrete specimen, and the six surfaces of the concrete specimen of the engineering blasting model test are evenly marked with measuring points for piezoelectric ceramic monitoring, wherein the measuring points of the opposite surfaces should correspond one to one, forming a set of piezoelectric ceramic signal data, and one specimen has three sets of data in three directions of XYZ;

[0027] The piezoelectric ceramic signal monitoring is carried out on the concrete specimens of the engineering blasting model test before and after the blasting test. The monitoring process is as follows: Figure 3 As shown, the piezoelectric ceramic signal monitoring device sensor 5 is placed parallel and directly opposite to the position of the piezoelectric ceramic signal monitoring measuring point 2, the transmitting end is connected to the pulse signal interface, the receiving end is connected to the channel 1 interface, and the piezoelectric ceramic signal is collected and stored by the computer system 3;

[0028] The wavelet threshold denoising method is used to denoise the piezoelectric ceramic signal and obtain the peak value of the processed piezoelectric ceramic signal;

[0029] Calculate the differences Z1, Z2, and Z3 of the three groups of piezoelectric ceramic signal peaks before and after the blasting experiment;

[0030] The locations of the cracks inside the concrete specimens are determined using the differences of the three groups of piezoelectric ceramic signal peaks, Z1, Z2, and Z3 (expressed as scattered points).

[0031] The method of using MATLAB program to calculate the three-dimensional scatter plot of the crack position inside the concrete is to traverse the spatial grid of the specimen, and for each position point (i, j, k), determine whether the monitoring data exceeds the set threshold. If all three sets of signals meet the conditions, it is considered that there is a crack at this point and it is recorded as a crack point.

[0032] As an implementation mode, in the process of fitting the crack plane using the MATLAB program, the DBSCAN clustering analysis method can be used to identify different crack planes. The principle is to divide the crack points into different clusters by examining the density of the points in the point cloud.

[0033] As an implementation mode, the method of fitting the crack plane using the MATLAB program is to perform plane fitting on the crack points in each cluster, thereby obtaining different crack planes.

[0034] As an implementation method, a triangulation method can be used to generate a three-dimensional mesh of the fracture plane to ensure that the plane shape is close to the real fracture. The boundary of the fracture surface is determined and the fracture occurrence is visualized, such as Figure 4 shown.

[0035] As an implementation method, during the collection of piezoelectric ceramic signals, a coupling agent may be applied between the piezoelectric ceramic signal monitoring device sensor 5 and the concrete specimen 1 of the engineering blasting model test, thereby reducing unnecessary losses of the piezoelectric ceramic signal during transmission.

[0036] As an implementation method, a larger pulse signal source width can be set during the acquisition of piezoelectric ceramic signals, thereby ensuring that effective piezoelectric ceramic signal data can still be monitored when there are many cracks inside the specimen.

[0037] As an implementation mode, when processing the piezoelectric ceramic signal, multiple signal processing methods may be tried and optimized.

[0038] The above is an example of the best implementation of the present invention, and the parts not described in detail are common knowledge of ordinary technicians in the field. The protection scope of the present invention shall be based on the content of the claims, and any equivalent transformation based on the technical enlightenment of the present invention is also within the protection scope of the present invention.

Claims

1. A method for visualizing the internal crack occurrence of an engineering specimen based on piezoelectric ceramics, characterized in that: The following steps are involved: Step 1, evenly setting three groups of piezoelectric ceramic signal monitoring points on six surfaces of the engineering specimen, wherein one group of piezoelectric ceramic signal monitoring points includes a plurality of pairs of piezoelectric ceramic signal monitoring points correspondingly set on two opposite surfaces of the engineering specimen; Step 2: Before and after the blasting test of the engineering specimen, three groups of piezoelectric ceramic signal monitoring points are used to collect signals to obtain three groups of piezoelectric ceramic signals monitored before and after the blasting test; Step 3, establish a spatial grid three-dimensional model of the engineering specimen, and determine the three pairs of piezoelectric ceramic signal monitoring points closest to each position point in the engineering specimen on the six surfaces as the piezoelectric ceramic signal monitoring points corresponding to this position point; Step 4, calculate the difference between the peak values ​​of the piezoelectric ceramic signals monitored before and after the blasting test for each pair of piezoelectric ceramic signal monitoring points corresponding to each position point, and determine whether the difference exceeds a preset threshold value. If so, it is determined that the pair of piezoelectric ceramic signal monitoring points are offset after the blasting. If the three pairs of piezoelectric ceramic signals corresponding to a position point are offset after the blasting, it is considered that there is a crack at this position point and it is recorded as a crack point. After traversing all the position points, all the crack points are obtained; Step 4: Use the DBSCAN cluster analysis method to divide the crack points into different clusters, perform plane fitting on the crack points in each cluster, and obtain different crack planes; Step 5: Use triangulation to generate a three-dimensional mesh of the crack plane, and obtain a visualized three-dimensional crack plane whose plane shape is close to that of a real crack.

2. The method for visualizing the internal crack occurrence of an engineering specimen based on piezoelectric ceramics according to claim 1, characterized in that: In step 4, a convex hull algorithm is used to determine the boundary of the crack in the process of generating the crack plane.

3. The method for visualizing the internal crack occurrence of an engineering specimen based on piezoelectric ceramics according to claim 1, characterized in that: In the step 1, the distance between adjacent piezoelectric ceramic signal monitoring points is 0.1 cm-1 cm.

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