An ultrasonic measurement method for winding angle and layer thickness of a carbon fiber full-winding gas cylinder

Abstract

The application discloses an ultrasonic measurement method for winding angle and layer thickness of a carbon fiber full-winding gas cylinder, and comprises the following steps: collecting full-matrix data of ultrasonic waves; calculating anisotropic sound velocity matrices corresponding to different winding angles; performing focus delay calculation on each A-scan signal to complete full-focus imaging; identifying and extracting structure signals closest to the surface of the carbon fiber full-winding gas cylinder in the full-focus image; evaluating the focus effect to obtain a full-focus image with the highest matching degree; determining the current layer thickness; determining the anisotropic sound velocity and winding angle of the current layer according to the used focus delay; changing the full-focus imaging range and correcting the focus delay, repeating steps three to six to obtain the winding angle and thickness of each layer in the multi-layer structure of the carbon fiber full-winding gas cylinder. The application realizes ultrasonic detection of the winding angle and layer thickness of the type IV carbon fiber full-winding gas cylinder, has the advantages of non-destructive and high detection efficiency, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to an ultrasonic measurement method, in particular to an ultrasonic measurement method for a winding angle and a layer thickness of a carbon fiber full-winding gas cylinder. BACKGROUND

[0002] As an important development direction of mobile composite pressure equipment, a composite gas cylinder with a fiber-wound plastic liner has the advantages of light weight, long service life and good medium compatibility, and is applied on a large scale in vehicle-mounted hydrogen storage gas cylinders, long-pipe trailer pipe bundles and other storage and transportation equipment. Hydrogen is the most easily leaked 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 civil use of the existing composite pressure container is in the initial stage, in particular, the IV type gas cylinder with a plastic liner, which mainly comprises a carbon fiber winding layer, a glass fiber reinforced layer and an inner liner layer. The carbon fiber composite material has high strength and excellent corrosion resistance and fatigue resistance, so the gas cylinder often bears the main structural load through the composite material winding layer. Since the winding angle and the layer thickness are two main process parameters of the composite material winding layer, which directly affect the strength and stress distribution of the gas cylinder, accurately obtaining the parameters is a necessary condition for accurately characterizing defects and evaluating the mechanical properties of the gas cylinder, and is of great significance to ensure 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, an urgent need exists for a non-destructive measurement method that can accurately obtain the winding angle and the layer thickness, which has great research value and practical significance. SUMMARY

[0005] The purpose of the application is to overcome the deficiencies in the prior art, and to provide an ultrasonic measurement method for the winding angle and the layer thickness of a carbon fiber full-winding gas cylinder, which has high detection efficiency and is non-destructive.

[0006] Technical scheme: The ultrasonic measurement method for the winding angle and the layer thickness of a carbon fiber full-winding gas cylinder comprises the following steps:

[0007] Step one, place an array ultrasonic sensor axially along the surface of the gas cylinder body, use each wafer array element of the array ultrasonic sensor as an excitation source in turn, and collect full matrix data of ultrasonic waves in a manner that all wafer array elements simultaneously act as receiving sources;

[0008] Step two, calculate an anisotropic sound velocity matrix corresponding to different winding angles in the winding layer of the gas cylinder body according to the mechanical constitutive relation of the winding composite material and the Christoffel equation;

[0009] Step three, based on the anisotropic sound velocity matrix and the sound propagation path at different focusing positions, the calculation of the focusing delay of each A-scan signal in the full matrix data is completed, and the full focusing imaging is completed;

[0010] Step four, through the automatic clustering algorithm and the edge-based active contour evolution model, the structural signals closest to the surface of the carbon fiber full-winding gas cylinder in the full focusing imaging image are identified and extracted;

[0011] Step five, according to the integrity and morphological characteristics of the structural signals, the focusing effect is evaluated, and the full focusing image with the highest matching degree is obtained;

[0012] Step six, according to the depth of the layered structure signal in the full focusing image, the current layer thickness is determined; according to the used focusing delay, the anisotropic sound velocity and the winding angle of the current layer are determined;

[0013] Step seven, according to the determined current layer thickness and winding angle, the full focusing imaging range is changed and the focusing delay is corrected, steps three to six are repeated, and the winding angle and thickness of all carbon fiber layers in the multi-layer structure of the carbon fiber full-winding gas cylinder are obtained.

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

[0015] Further, in step two, the mechanical constitutive relationship of the winding 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: the initial stiffness matrix of the material is converted into the stiffness matrix corresponding to different winding angles through 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] Further, in step three, the formula used for calculating the focusing delay is:

[0017]

[0018] In the formula, t represents the focusing delay, n represents the number of layers where the current focusing point is located, l1 represents the distance from the excitation element to the focusing point, l2 represents the distance from the receiving element to the focusing point, D n represents the distance from the focusing point to the sample surface, h i represents the thickness of the i-th layer, v i1 represents the sound velocity of the excitation element to the focusing point on the sound propagation path in the i-th layer, and v i2represents the sound velocity on the sound propagation path from the i-th layer and the receiving element to the focus point, v n1 represents the sound velocity on the sound propagation path from the n-th layer and the receiving element to the focus point, v n2 represents the sound velocity on the sound propagation path from the n-th layer and the receiving element to the focus point, v

[0019] Further, in step four, the automatic clustering algorithm is the K-means clustering algorithm. After the foreground useful signal and the background noise signal in the full-focus image are classified by using the K-means clustering algorithm, the signal edge is recognized and extracted by using the edge-based active contour evolution model.

[0020] Further, 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] Further, in step seven, the imaging range of the full-focus image is dynamically adjusted according to the completed detection layer thickness, and the part that has been completed detection is removed from the imaging area.

[0022] Beneficial effects: compared with the prior art, the present application has the following remarkable features:

[0023] 1. The present application realizes the ultrasonic detection of the winding angle and the layer thickness of the type IV carbon fiber full-winding gas cylinder, has the advantages of non-destructive and high detection efficiency, and can be popularized to the non-destructive detection of other composite structures, and has a wide application prospect.

[0024] 2. The present application first collects the ultrasonic full-matrix data of the gas cylinder, then performs full-focus imaging by using the anisotropic sound velocity matrix of the carbon fiber composite material, accurately extracts the structural signal based on the automatic clustering algorithm and the active contour model, evaluates the imaging quality by taking the signal morphology and integrity as the target parameters, obtains the image with the best imaging effect, obtains the corresponding layer thickness and winding angle according to the depth of the structural signal in the image and the focus delay used for imaging, and dynamically adjusts the imaging range and repeats the step to realize the measurement of the multi-layer structure. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a flowchart of the present application;

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

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

[0028] Figure 4 is a schematic diagram of signal feature analysis of the present application, wherein (a) is the structural signal profile extraction result, (b) is the profile line shape analysis diagram, and (c) is the profile line integrity analysis diagram;

[0029] Figure 5 is a schematic diagram of layered focusing imaging of the present application, 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 is the measurement result of the present application and the visual method for the thickness and winding angle of the winding layer, wherein (a) is the layered thickness measurement result, (b) is the layered winding angle measurement result, (c) is the overhead view of the carbon fiber full-winding cylinder body sample, and (d) is the cross-sectional view of the carbon fiber full-winding cylinder body sample. DETAILED DESCRIPTION

[0031] The layered thickness and winding angle of the carbon fiber winding layer are detected by ultrasonic detection, and the specific steps are as follows, as shown in Figure 1 .

[0032] S1. The array ultrasonic sensor is placed on the sample surface along the axis of the carbon fiber full-winding cylinder body at uniform intervals, the probe and the cylinder body are well coupled through the coupling agent. When the thickness of the carbon fiber winding layer is greater than 20 mm, the array ultrasonic sensor is preferably 0.5L64-96×22 type, and when the thickness of the carbon fiber winding layer is less than or equal to 20 mm, the array sensor is preferably 1.0L64-64×20 type. The frequency of the array ultrasonic sensor is 0.5 MHz, the number of wafer array elements is 64, the wafer spacing is 1.5 mm, and the wafer width is 22 mm. The full matrix data of ultrasonic waves is collected in the manner that each wafer array element is used as an excitation source and all wafer array elements are used as receiving sources.

[0033] S2. According to the mechanical constitutive relation of the winding composite material and the Christoffel equation, the anisotropic sound velocity matrix corresponding to different winding angles is calculated. The mechanical constitutive relation is the stiffness matrix of the carbon fiber winding composite material or the mechanical parameters including the elastic modulus, shear modulus, and Poisson's ratio. The calculation method of the anisotropic sound velocity matrix corresponding to different winding angles is to convert the initial stiffness matrix of the material into the stiffness matrix corresponding to different winding angles through coordinate transformation, and then solve the corresponding Christoffel equation with this as the coefficient to obtain the anisotropic sound velocity corresponding to different winding angles, as shown in Figure 2 . Figure 2 The left is the polar coordinate diagram of the anisotropic sound velocity distribution under a specific winding angle (0°), and the polar axis direction represents the sound propagation direction, and the length represents the sound velocity, Figure 2Right is the anisotropic sound speed corresponding to different winding angles (0°-90°), different curves in the figure correspond to different winding angles, the horizontal axis represents the sound propagation direction, and the vertical axis represents the sound speed.

[0034] S3, according to the obtained anisotropic sound speed matrix and the sound propagation path at different focusing positions, the calculation of the focusing delay of each A-scan signal in the full matrix data is carried out, and the full focusing imaging is completed.

[0035] The formula used for the calculation of the focusing delay is:

[0036]

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

[0038] S4, through the automatic clustering algorithm and the edge-based active contour evolution model, the structure signal closest to the surface in the full focusing image is identified and extracted. For example Figure 3 , first, the K-means clustering algorithm is used to distinguish the foreground useful signal and the background noise signal in the image, and then the edge-based contour evolution model is used to identify and extract the boundary of the signal.

[0039] S5, according to the integrity and morphological characteristics of the structure signal, the focusing effect is evaluated, and the full focusing image with the highest matching degree is obtained. For example Figure 4 , the signal features used are calculated through the center line of the extracted signal region, including the ratio of the signal width to the imaging region width and the deviation value between the signal center line and the actual contour line.

[0040] S6, according to the depth of the layered structure signal in the full focusing image, the current layer thickness is determined; according to the focusing delay used, the anisotropic sound speed and the winding angle of the current layer are determined.

[0041] S7, after the measurement of the thickness and winding angle of a certain layer of carbon fiber structure layer is completed, the region is removed from the full-focus imaging range, the focus delay is corrected, and steps S3 to S6 are repeated to obtain the winding angle and thickness of each layer in the multi-layer structure of the full-winding carbon fiber type IV gas cylinder, see Figure 5 The obtained layered focus imaging schematic diagram.

[0042] S8, the gas cylinder sample is cut along the thickness direction, and the thickness of each layer in the winding layer is calibrated by visual method, see Figure 6 The measurement results of the thickness and winding angle of the winding layer by the visual method, compared with the visual method, the measurement error of the thickness of the present application is not more than 2.4mm, and the measurement error of the winding angle is not more than 5°.

Claims

1. A method for ultrasonic measurement of winding angle and ply thickness of a carbon fiber full-wrapped gas cylinder, characterized by, The method comprises the following steps: Step one, place the array ultrasonic sensor along the surface of the cylinder body in the axial direction, take each wafer array element of the array ultrasonic sensor as an excitation source in turn, and take all wafer array elements as a receiving source at the same time to collect full matrix data of ultrasonic waves; Step two, calculate the anisotropic sound velocity matrix corresponding to different winding angles in the winding layer of the cylinder body according to the mechanical constitutive relation of the winding composite material and the Christoffel equation; Step three, calculate the focusing delay of each A-scan signal in the full matrix data based on the anisotropic sound velocity matrix and the sound propagation path at different focusing positions to complete full focusing imaging; Step four, identify and extract the structural signal closest to the surface of the carbon fiber full-winding cylinder in the full focusing image through an automatic clustering algorithm and an edge-based active contour evolution model; Step five, evaluate the focusing effect according to the integrity and morphological characteristics of the structural signal to obtain the full focusing image with the highest matching degree; Step six, determine the current layer thickness according to the depth of the layered structural signal in the full focusing image, and determine the anisotropic sound velocity and winding angle of the current layer according to the focusing delay used; Step seven, change the full focusing imaging range and correct the focusing delay according to the determined current layer thickness and winding angle, repeat steps three to six until the winding angle and thickness of all carbon fiber layers in the multi-layer structure of the carbon fiber full-winding cylinder are obtained; In step two, 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 through 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; In step three, the formula used for calculating the focusing delay is: In the formula, t represents a focusing delay, n represents a layer number where a current focus point is located, li represents a distance from an excitation element to the focus point, l2 represents a distance from a receiving element to the focus point, D n represents a distance from the focus point to a sample surface, h i represents a thickness of an i-th layer, vi i1 represents a sound speed on a sound propagation path from the excitation element to the focus point in the i-th layer, vi i2 represents a sound speed on a sound propagation path from the receiving element to the focus point in the i-th layer, vi n1 represents a sound speed on a sound propagation path from the excitation element to the focus point in the n-th layer, vn n2 represents a sound speed on a sound propagation path from the receiving element to the focus point in the n-th layer.

2. The method of claim 1, wherein the method is characterized by: In step one, the frequency of the array ultrasonic sensor is 0.5-1 MHz, and the number of wafer array elements is greater than or equal to 64.

3. The method of claim 1, wherein the method is characterized by: In step one, the wafer spacing in the array ultrasonic sensor is 1-2 mm, the wafer width is 20-25 mm, and the arrangement direction of the wafers in the array ultrasonic sensor is parallel to the axial direction of the cylinder body surface.

4. The method of claim 1, wherein the method is characterized by: In step two, the mechanical constitutive relation of the winding composite material includes the stiffness matrix, the elastic modulus, the shear modulus, and the Poisson's ratio.

5. The method of claim 1, wherein the method is characterized by: In step four, the automatic clustering algorithm is the K-means clustering algorithm.

6. The method of claim 5, wherein the method is characterized by: In step four, the signal recognition and extraction is the classification of the foreground useful signal and the background noise signal in the full focusing image by using the K-means clustering algorithm, and the recognition and extraction of the signal edge by using the edge-based active contour evolution model.

7. The method of claim 1, wherein the method is characterized by: 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 characteristics are quantitatively described by the difference between the center line and the contour line of the signal image.

8. The method of claim 1, wherein the method is characterized by: In step seven, the imaging range of the full focusing image is dynamically adjusted according to the layer thickness that has been detected, and the part that has been detected is removed from the imaging area.

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