Ultrasonic measurement method for winding angle and layering thickness of carbon fiber fully-wound gas cylinder

Abstract

The invention discloses an ultrasonic measurement method for the winding angle and the layering thickness of a carbon fiber fully-wound gas cylinder. The ultrasonic measurement method comprises the following steps: acquiring ultrasonic full-matrix data; calculating anisotropic sound velocity matrixes corresponding to different winding angles; performing focusing delay calculation on each A scanning signal to complete full-focusing imaging; identifying and extracting a structure signal closest to the surface of the carbon fiber fully-wound gas cylinder in a fully-focused imaging image; the focusing effect is evaluated, and a full-focusing image with the highest matching degree is obtained; determining the thickness of the current layer; determining an anisotropic sound velocity and a winding angle of the current layer according to the used focusing delay; and changing the full-focusing imaging range and correcting the focusing delay, and repeating the steps 3-6 to obtain the winding angle and thickness of each layer in the multi-layer structure of the carbon fiber fully-wound gas cylinder. According to the invention, ultrasonic detection of the winding angle and the layering thickness of the IV-type carbon fiber fully-wound gas cylinder is realized, and the method has the advantages of no damage and high detection efficiency, and has wide application prospects.

Description

Technical Field

[0001] The invention relates to an ultrasonic measurement method, in particular to an ultrasonic measurement method for a winding angle and layer thickness of a carbon fiber fully-wound gas cylinder. Background Art

[0002] As an important development direction for mobile composite pressure-bearing equipment, composite gas cylinders with fiber-wound plastic liner have the advantages of light weight, long life, and good medium compatibility. They are used on a large scale in storage and transportation equipment such as vehicle-mounted hydrogen storage cylinders and long-tube trailer bundles. Hydrogen is the gas that is most prone to leakage and has the widest explosion range (4.0%-75.6%), and its transportation and storage safety has become the focus of social attention.

[0003] The civilian use of existing composite pressure vessels is in its infancy, especially Type IV gas cylinders with plastic liners, whose main structure consists of a carbon fiber winding layer, a glass fiber reinforcement layer, and a liner layer. Carbon fiber composites have high strength and excellent corrosion and fatigue resistance, so gas cylinders often bear the main structural load through the composite winding layer. Since the winding angle and layer thickness are the two main process parameters of the composite winding layer, they directly affect the strength and stress distribution of the gas cylinder. Accurately obtaining these parameters is a necessary condition for accurate defect characterization and evaluation of the mechanical properties of the gas cylinder, which is of great significance for ensuring the quality and service life of the gas cylinder.

[0004] Traditional measurement methods often rely on destructive testing, which is difficult to meet the detection needs in actual engineering. Therefore, there is an urgent need for a non-destructive measurement method that can accurately obtain the winding angle and layer thickness, which has great research value and practical significance. Summary of the invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide an ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder with high detection efficiency and non-destructive testing.

[0006] Technical solution: The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder of the present invention comprises the following steps:

[0007] Step 1: Place the array ultrasonic sensor axially along the surface of the gas cylinder body, use each chip array element of the array ultrasonic sensor as an excitation source in turn, and all chip array elements as receiving sources at the same time to collect full matrix data of ultrasound;

[0008] Step 2: Calculate the anisotropic sound velocity matrix corresponding to different winding angles in the winding layer of the gas cylinder body according to the mechanical constitutive relationship of the wound composite material and the Christofel equation;

[0009] Step 3: Based on the anisotropic sound velocity matrix and the sound propagation paths at different focusing positions, the focusing delay of each A-scan signal in the full matrix data is calculated to complete the full focusing imaging;

[0010] Step 4: Identify and extract the structural signal closest to the surface of the carbon fiber fully wrapped gas cylinder in the fully focused imaging image through an automatic clustering algorithm and an edge-based active contour evolution model;

[0011] Step 5: evaluate the focusing effect based on the integrity and morphological characteristics of the structural signal to obtain the most matched fully focused image;

[0012] Step 6: Determine the thickness of the current layer according to the depth of the layered structure signal in the full focus image; determine the anisotropic sound velocity and winding angle of the current layer according to the focus delay used;

[0013] Step seven, according to the determined current layer thickness and winding angle, change the full focus imaging range and correct the focus delay, repeat steps three to six, and obtain the winding angle and thickness of all carbon fiber layers in the multilayer structure of the carbon fiber fully wrapped gas cylinder.

[0014] Furthermore, in step 1, the frequency of the array ultrasonic sensor is 0.5-1 MHz, and the number of chip array elements is ≥ 64. Preferably, the chip spacing of the array ultrasonic sensor is 1-2 mm, and the chip width is 20-25 mm. The arrangement direction of the chips in the array ultrasonic sensor is parallel to the axial direction of the bottle body surface.

[0015] Furthermore, in step 2, the mechanical constitutive relation of the wound composite material includes stiffness matrix, elastic modulus, shear modulus, and Poisson's ratio. The calculation method of the anisotropic sound velocity matrix corresponding to different winding angles is as follows: the initial stiffness matrix of the material is converted into the stiffness matrix corresponding to different winding angles by coordinate transformation, and then the corresponding Christoffel equation is solved with this as the coefficient to obtain the anisotropic sound velocity corresponding to different winding angles.

[0016] Furthermore, in step 3, the formula used to calculate the focus delay is:

[0017]

[0018] In the formula, t represents the focusing delay, n represents the layer number of the current focusing point, l1 represents the distance from the excitation array element to the focusing point, l2 represents the distance from the receiving array element to the focusing point, and D n Indicates the distance from the focus point to the sample surface, h i represents the thickness of the i-th layer, v i1 represents the speed of sound on the path from the excitation element to the focal point in the i-th layer, v i2represents the speed of sound in the i-th layer and on the sound propagation path from the receiving array element to the focal point, v n1 represents the speed of sound on the path from the excitation array element to the focal point in the nth layer, v n2 It represents the speed of sound in the nth layer and on the sound propagation path from the receiving array element to the focal point.

[0019] Furthermore, in step 4, the automatic clustering algorithm is a K-means clustering algorithm. Signal recognition and extraction is to classify the foreground useful signal and the background noise signal in the full-focus image using the K-means clustering algorithm, and then recognize and extract the signal edge through an edge-based active contour evolution model.

[0020] Furthermore, in step five, the integrity of the structural signal is calculated by the ratio of the width of the extracted structural signal boundary to the width of the imaging area, and the morphological feature is quantitatively described by the difference between the center line and the contour line of the signal image.

[0021] Furthermore, in step seven, the imaging range of the all-focus image is dynamically adjusted according to the thickness of the layer that has been inspected, and the portion that has been inspected is removed from the imaging area.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0023] 1. The ultrasonic detection of the winding angle and layer thickness of the type IV carbon fiber fully wrapped gas cylinder has been realized, which has the advantages of non-destructive and high detection efficiency. It can also be extended to the non-destructive detection of other composite materials and has broad application prospects.

[0024] 2. First, collect the full ultrasonic matrix data of the gas cylinder, and then perform full-focus imaging through the anisotropic sound velocity matrix of the carbon fiber composite material; accurately extract the structural signal based on the automatic clustering algorithm and active contour model, and use the signal morphology and integrity as the target parameters to evaluate the imaging quality and obtain the image with the best imaging effect; according to the depth of the structural signal in the image and the focusing delay used for imaging, the corresponding layer thickness and winding angle can be obtained; dynamically adjust the imaging range and repeat this step to achieve the measurement of multi-layer structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 Schematic diagram of anisotropic sound velocity of carbon fiber composite material of the present invention, wherein (a) is a specific winding angle, and (b) is a different winding angle;

[0027] Figure 3 It is a schematic diagram of signal recognition and extraction of the present invention;

[0028] Figure 4 Schematic diagram of signal feature analysis of the present invention, wherein (a) is the structural signal contour extraction result, (b) is the contour line morphology analysis diagram, and (c) is the contour line integrity analysis diagram;

[0029] Figure 5 Schematic diagram of layered focusing imaging of the present invention, wherein (a) is layer 1, (b) is layer 2, (c) is layer 3, (d) is layer 4, (e) is layer 5, and (f) is layer 6;

[0030] Figure 6 The figures are the measurement results of the winding layer thickness and winding angle by the present invention and the visual method, wherein (a) is the layer thickness measurement result, (b) is the layer winding angle measurement result, (c) is the top view of the carbon fiber fully wrapped gas cylinder body sample, and (d) is the cross-sectional view of the carbon fiber fully wrapped gas cylinder body sample. DETAILED DESCRIPTION

[0031] The body of the Type IV carbon fiber fully wrapped gas cylinder is taken as the test object, and the layer thickness and winding angle of the carbon fiber winding layer are ultrasonically tested. The specific steps are as follows: Figure 1 As shown:

[0032] S1. Take the body of the gas cylinder fully wrapped with type IV carbon fiber as the sample, place the array ultrasonic sensor on the surface of the sample at uniform intervals along the axis of the gas cylinder body, and the probe and the gas cylinder body are well coupled through the coupling agent. When the thickness of the carbon fiber winding layer is greater than 20mm, the array ultrasonic sensor is preferably a 0.5L64-96×22 model, and when the thickness of the carbon fiber winding layer is less than or equal to 20mm, the array sensor is preferably a 1.0L64-64×20 model. The frequency of the array ultrasonic sensor is 0.5MHz, the number of chip array elements is 64, the chip spacing is 1.5mm, and the chip width is 22mm. With each chip array element as an excitation source in turn, and all chip array elements as receiving sources at the same time, the full matrix data of ultrasound is collected.

[0033] S2. According to the mechanical constitutive relationship of the wound composite material and the Christofel equation, the anisotropic sound velocity matrix corresponding to different winding angles is calculated. The mechanical constitutive relationship is the stiffness matrix of the carbon fiber wound composite material or the mechanical parameters including elastic modulus, shear modulus, and Poisson's ratio. The calculation method of the anisotropic sound velocity matrix corresponding to different winding angles is to transform the initial stiffness matrix of the material into the stiffness matrix corresponding to different winding angles through coordinate transformation, and then use this as the coefficient to solve the corresponding Christofel equation to obtain the anisotropic sound velocity corresponding to different winding angles, such as Figure 2 As shown, Figure 2 The left is a polar coordinate diagram of the anisotropic sound velocity distribution at a specific winding angle (0°). The polar axis direction represents the direction of sound propagation, and the length represents the magnitude of the sound velocity. Figure 2On the right is the anisotropic sound velocity corresponding to different winding angles (0°~90°). Different curves in the figure correspond to different winding angles. The horizontal axis represents the direction of sound propagation and the vertical axis represents the sound velocity.

[0034] S3. Based on the obtained anisotropic sound velocity matrix and the sound propagation paths at different focusing positions, the focusing delay of each A-scan signal in the full matrix data is calculated to complete the full focusing imaging.

[0035] The formula used to calculate the focus delay is:

[0036]

[0037] In the formula, t represents the focusing delay, n represents the layer number of the current focusing point, l1 represents the distance from the excitation array element to the focusing point, l2 represents the distance from the receiving array element to the focusing point, and D n Indicates the distance from the focus point to the sample surface, h i represents the thickness of the i-th layer, v i1 represents the speed of sound on the path from the excitation element to the focal point in the i-th layer, v i2 represents the speed of sound in the i-th layer and on the sound propagation path from the receiving array element to the focal point, v n1 represents the speed of sound on the path from the excitation array element to the focal point in the nth layer, v n2 It represents the speed of sound in the nth layer and on the sound propagation path from the receiving array element to the focal point.

[0038] S4. The structure signal closest to the surface in the full-focus image is identified and extracted through the automatic clustering algorithm and the edge-based active contour evolution model. Figure 3 ,Firstly, the foreground useful signal and background noise signal in the image are distinguished by the K-means clustering algorithm, and then the signal boundary is identified and extracted by the edge-based contour evolution model.

[0039] S5. Evaluate the focusing effect based on the integrity and morphological characteristics of the structural signal to obtain the most matched fully focused image. Figure 4 ,The signal features used are calculated by the center line of the extracted signal area, including the ratio of the signal width to the imaging area width and the deviation value between the signal center line and the actual contour line.

[0040] S6. Determine the thickness of the current layer according to the depth of the layered structure signal in the fully focused image; determine the anisotropic sound velocity and winding angle of the current layer according to the focusing delay used.

[0041] S7. After completing the measurement of the thickness and winding angle of a certain layer of carbon fiber structure, remove the area from the full focus imaging range, correct the focus delay, repeat steps S3 to S6, and obtain the winding angle and thickness of each layer in the multilayer structure of the type IV carbon fiber fully wrapped gas cylinder, see Figure 5 Schematic diagram of the obtained layered focusing imaging.

[0042] S8. Cut the cylinder sample in the thickness direction and calibrate the thickness of each layer in the wrapping layer by visual inspection. Figure 6 The present invention and the visual method are the measurement results of the winding layer thickness and the winding angle. Compared with the visual method, the measurement error of the present invention for the thickness does not exceed 2.4 mm, and the measurement error for the winding angle does not exceed 5°.

Claims

1. An ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder, characterized in that: The following steps are involved: Step 1: Place the array ultrasonic sensor axially along the surface of the gas cylinder body, use each chip array element of the array ultrasonic sensor as an excitation source in turn, and all chip array elements as receiving sources at the same time to collect full matrix data of ultrasound; Step 2: Calculate the anisotropic sound velocity matrix corresponding to different winding angles in the winding layer of the gas cylinder body according to the mechanical constitutive relationship of the wound composite material and the Christofel equation; Step 3: Based on the anisotropic sound velocity matrix and the sound propagation paths at different focusing positions, the focusing delay of each A-scan signal in the full matrix data is calculated to complete the full focusing imaging; Step 4: Identify and extract the structural signal closest to the surface of the carbon fiber fully wrapped gas cylinder in the fully focused imaging image through an automatic clustering algorithm and an edge-based active contour evolution model; Step 5: evaluate the focusing effect based on the integrity and morphological characteristics of the structural signal to obtain the most matched fully focused image; Step 6: Determine the thickness of the current layer according to the depth of the layered structure signal in the full focus image; determine the anisotropic sound velocity and winding angle of the current layer according to the focus delay used; Step seven, according to the determined current layer thickness and winding angle, change the full focus imaging range and correct the focus delay, repeat steps three to six until the winding angles and thicknesses of all carbon fiber layers in the multilayer structure of the carbon fiber fully wrapped gas cylinder are obtained.

2. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1, characterized in that: In the step 1, the frequency of the array ultrasonic sensor is 0.5-1 MHz, and the number of chip array elements is ≥64.

3. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1 is characterized in that: In the step 1, the chip pitch of the array ultrasonic sensor is 1-2 mm, the chip width is 20-25 mm, and the arrangement direction of the chips in the array ultrasonic sensor is parallel to the axial direction of the bottle body surface.

4. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1 is characterized in that: In the step 2, the mechanical constitutive relation of the winding composite material includes a stiffness matrix, an elastic modulus, a shear modulus, and a Poisson's ratio.

5. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1, characterized in that: In the step 2, the calculation method of the anisotropic sound velocity matrix corresponding to different winding angles is: the initial stiffness matrix of the material is converted into the stiffness matrix corresponding to different winding angles by coordinate transformation, and then the corresponding Christofel equation is solved using this as the coefficient to obtain the anisotropic sound velocity corresponding to different winding angles.

6. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1 is characterized in that: In step 3, the formula used to calculate the focus delay is: In the formula, t represents the focusing delay, n represents the layer number of the current focusing point, l1 represents the distance from the excitation array element to the focusing point, l2 represents the distance from the receiving array element to the focusing point, and D n Indicates the distance from the focus point to the sample surface, h i represents the thickness of the i-th layer, v i1 represents the speed of sound on the path from the excitation element to the focal point in the i-th layer, v i2 represents the speed of sound in the i-th layer and on the sound propagation path from the receiving array element to the focal point, v n1 represents the speed of sound on the path from the excitation array element to the focal point in the nth layer, v n2 It represents the speed of sound in the nth layer and on the sound propagation path from the receiving array element to the focal point.

7. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1 is characterized in that: In the step 4, the automatic clustering algorithm is a K-means clustering algorithm.

8. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 7, characterized in that: In the step 4, the signal is identified and extracted by using a K-means clustering algorithm to classify the foreground useful signal and the background noise signal in the fully focused image, and then identifying and extracting the signal edge through an edge-based active contour evolution model.

9. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1, characterized in that: In the step 5, the integrity of the structural signal is calculated by the ratio of the width of the extracted structural signal boundary to the width of the imaging area, and the morphological feature is quantitatively described by the difference between the center line and the contour line of the signal image.

10. The ultrasonic measurement method for the winding angle and layer thickness of a carbon fiber fully wrapped gas cylinder according to claim 1, characterized in that: In the step seven, the imaging range of the all-focus image is dynamically adjusted according to the thickness of the layer that has been inspected, and the portion that has been inspected is removed from the imaging area.

Images