CN111189914B - Method for determining gradient thickness coefficient for ultrasonic detection of composite material - Google Patents
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Abstract
The invention discloses a method for determining a gradient thickness coefficient for ultrasonic detection of a composite material, which aims at the characteristics of the shape, the structure and the process of the composite material with the gradient thickness and the distinguishing influence of the change of ultrasonic detection signals on the defects of different gradient thickness areas, and provides the gradient thickness coefficient for the ultrasonic detection of the composite material, which is used for compensating the ultrasonic detection signals of the structure of the composite material with the gradient thickness, preventing missing detection and improving the defect detection rate and the accuracy and the reliability of the ultrasonic detection.
Description
Technical Field
The invention discloses a method for determining a gradient thickness coefficient for ultrasonic detection of a composite material, belongs to the technical field of nondestructive detection, and is used for ultrasonic detection of a gradient thickness composite material structure.
Background
The composite material is widely applied to many engineering fields such as aviation, building, traffic and the like, in engineering, various engineering parts and products thereof with gradually changed thickness are designed according to application objects, structural stress and the like through the design of composite material layering, and a gradually changed thickness composite material structure is formed, so that parts with different thicknesses have enough bearing capacity, the using amount of the composite material can be reduced, the weight of the composite material structure is lightened, and the cost of the composite material parts is reduced. Most of the composite material structures adopted in the prior engineering have the geometric characteristics of gradually changing thickness, which are called gradually-changing thickness composite material structures for short, and in order to ensure the quality and the safe service of the gradually-changing thickness composite material structures, the full-coverage nondestructive testing is generally required to be carried out on the gradually-changing thickness composite material structures. The ultrasonic detection method mainly comprises the step of judging defects according to ultrasonic signals from the surface and the bottom surface of the detected composite material and changes of the ultrasonic signals.
In the ultrasonic detection process of the composite material structure with the gradually-changing thickness, the size in the thickness direction, namely the thickness, of different composite material structure parts can be gradually changed, so that an ultrasonic propagation interface which is geometrically unparallel is formed between the surface and the bottom surface of the detected composite material structure, the gradually-changing thickness interface is referred to as the gradually-changing thickness interface, the propagation behavior of incident sound waves in the composite material structure can be obviously influenced by the gradually-changing thickness interface, the receiving and the indication of ultrasonic detection signals are influenced, the extra loss of the ultrasonic signals is caused, the judgment of defects is influenced, the omission is easily caused, and the correctness and the detection reliability of detection results are influenced. An improved method is to make a given amplitude compensation to the detection signal from the composite material with gradually changed thickness by referring to the thickness change of the composite material structure with gradually changed thickness, but because of the structure of the composite material with gradually changed thickness and its internal complexity, the diversity and hard predictability of the geometric characteristic change caused by the thickness change, the thickness gradually changes at different positions of the structure of the composite material with gradually changed thickness, thereby possibly generating different degrees of influence, and the different areas with gradually changed thickness have different degrees of influence on the ultrasonic signal caused by the change of the gradually changed thickness. If the structure of the composite material with gradually changed thickness is abstracted into ultrasonic big data, each detection position point corresponds to an ultrasonic data point, the ultrasonic data is printed on the surface of the composite material structure in different gradually changed thickness areas, the thickness change of each detection position point is inevitably related to the gradual change of the thickness of the position point, ultrasonic data from each given position in the gradually changed thickness areas are measured and recorded, an ultrasonic data matrix is built in a reasonable method, ultrasonic signals such as surface reflection signals, bottom reflection signals or penetrating signals, which reflect the propagation of ultrasonic waves in the gradually changed thickness areas, are separated from the ultrasonic data matrix, corresponding ultrasonic characteristic signal parameter matrixes are obtained, then, an ultrasonic detection parameter matrix of the gradually changed thickness areas is built on the basis of the acoustic principle of ultrasonic detection and defect criteria, ultrasonic characteristic parameters reflecting the thickness change of the composite material structure are obtained through active mean values, ultrasonic functions reflecting the thickness are obtained from the ultrasonic characteristic parameters, and limited gradually changed thickness composite material test blocks are utilized according to the detected gradually changed thickness composite material structure to obtain more representative ultrasonic gradually changed thickness coefficients for compensating the ultrasonic detection signals of the composite material structure and carrying out ultrasonic detection of the gradually changed thickness composite material. The ultrasonic gradient thickness coefficient reflects the change of ultrasonic signals caused by the geometric change of the thickness in the whole composite material structure, and simultaneously fully considers various possible conditions of different thickness areas. Therefore, the ultrasonic detection device has representativeness and accuracy, can reflect the change of ultrasonic signals caused by the geometric and physical characteristics of the composite material structure in the gradual-change thickness area, is further favorable for ultrasonic detection and defect detection of the composite material structure in the gradual-change thickness area, reduces the defect omission ratio, and improves the accuracy and reliability of the ultrasonic detection result of the composite material structure in the gradual-change thickness area.
The prior art has the following defects:
in the ultrasonic detection method of the composite material structure adopted at present, defect judgment is mainly carried out according to an ultrasonic echo signal or projection size between the surface and the bottom surface of a detected composite material and the size of bottom waves, and the method has the main defects that: (1) Due to the gradual change process of the thickness of the composite material and the change of the geometric structure of the thickness gradual change area in the thickness direction, the reflection or transmission of incident sound waves on the surface and the bottom surface of the detected composite material is changed, so that the loss of ultrasonic receiving signals is caused, the judgment of defects is influenced, the detection omission is easily generated, the correctness of a detection result is interfered, and the reliability of the detection result is influenced; (2) When a certain thickness compensation is adopted, due to the fact that the structure of the composite material with the gradually-changed thickness, the complexity of the interior of the composite material with the gradually-changed thickness, the variety of the geometric characteristic changes caused by the thickness changes, the unpredictability and the like are difficult, the incident sound waves are different at different positions of the structure of the composite material with the gradually-changed thickness, the thickness changes are different, influences of different degrees can be generated, the influence degrees of the thickness changes on ultrasonic signals are different in different gradually-changed thickness areas, and the influence caused by the geometric characteristic changes of the structure of the composite material with the gradually-changed thickness in the thickness direction is difficult to consider by adopting a single and simple amplitude compensation method.
Disclosure of Invention
The invention provides a method for determining a gradient thickness coefficient for ultrasonic detection of a composite material, aiming at the defects of the composite material with the gradient thickness, such as shape, structure and process characteristics and the discrimination influence of the change of ultrasonic detection signals on the defects of different gradient thickness areas, and the invention provides the gradient thickness coefficient for ultrasonic detection of the composite material, which is used for compensating the ultrasonic detection signals of the composite material with the gradient thickness, preventing missing detection and improving the defect detection rate and the accuracy and reliability of ultrasonic detection.
The purpose of the invention is realized by the following technical scheme:
the method for determining the gradient thickness coefficient for ultrasonic detection of the composite material is characterized by comprising the following steps of: the method for determining the gradient thickness coefficient comprises the following steps:
step one, preparing test blocks 1 with different thicknesses, wherein the thickness of each test block is H i I =1,2,. ·, m; minimum thickness H of test block 1 min And a maximum thickness H max Respectively the same as the minimum and maximum thickness of the part to be detected, and measuring the ultrasonic signal of each test block 1 according to the same measurement track and measurement parameters, wherein the ultrasonic measurement signal is u ij Denotes that j is the number of ultrasound measurement signals, j =1, 2.., n; the ultrasonic measurement signal u for each test block 1 is then calculated ij An arithmetic mean of
Show and drawThickness H i And
the relationship curve of (1);
step two, preparing one or more test blocks 2 with continuous gradual thickness, wherein the minimum thickness h in the continuous gradual thickness formed by the test blocks 2 with the gradual thickness is min And a maximum thickness h max Respectively same as the minimum and maximum thicknesses of the part to be detected, and measuring ultrasonic signals of each test block 2 with gradually changed thickness according to the same measurement track and measurement parameters as the step I, wherein the ultrasonic measurement signals are k x [ v ] v a ，h a ] b Group, wherein v a Ultrasonic signal representing the a-th measuring point, h a The thickness of the test block 2 with the gradually-changed thickness corresponding to the a-th measuring point is represented, a =1,2, a, b and b are the total number of the measuring points of the test block 2 with the gradually-changed thickness, k is a constant, and the value range of k is 1-10;
then according to the principle of taking the same thickness, determining kX [ v ] a ，h a ] b According to different thickness values h c Corresponding mean value
Wherein h is min ≤c≤h max ；
Step three, aiming at different thickness values h c According to the plotted thickness H i And
relation curve, calculation
And
to obtain the ultrasonic gradual change thickness coefficient delta corresponding to different gradual change thicknesses c And drawing the thickness and ultrasonic gradient thickness coefficient delta c The relationship of (1).
In one implementation, the material of the test block 1 is the same as the composite material of the part to be inspected.
In one implementation, the number of test blocks 1 is no less than 5.
In one implementation, the ultrasonic measurement trajectory and measurement parameters are the same as the inspection requirements of the part to be inspected.
In one implementation, the ultrasonic measurement trajectory and measurement parameters include measurement trajectory path and measurement point calibration.
In one implementation, the material of the graduated thickness block 2 is the same as the composite material of the part to be inspected.
In one implementation, the thickness gradient between test blocks 1 of different thicknesses is 2mm.
In one implementation, in the ultrasonic measurement track and the measurement parameter, the measurement track is in a scanning mode, the scanning speed is 100mm/s, and the measurement parameter is that the distance between adjacent measurement points is 2mm.
The invention provides a method for determining a gradient thickness coefficient for ultrasonic detection of a composite material structure based on the characteristics of ultrasonic wave propagation and the geometric characteristics of the composite material structure with the gradient thickness, and the determination of the gradient thickness coefficient takes the interference of ultrasonic signal change generated between the surface and the bottom surface of the composite material structure with the detected gradient thickness on defect judgment into consideration; the influence of the change of incident sound waves in various geometric reflection behaviors caused by different thickness regions of the composite material on defect judgment during ultrasonic detection of the structure of the composite material with the gradually-changed thickness is considered; the influence of the gradual change thickness of the composite material structure on the change of the propagation behavior of the incident sound wave in the composite material and the defect judgment of the gradual change thickness area is considered. Based on the gradient thickness coefficient, the defect judgment is carried out, and the method is more suitable for ultrasonic detection and quality evaluation of the gradient thickness composite material structure, thereby being more beneficial to improving the accuracy of ultrasonic detection of the gradient thickness composite material structure and improving the accuracy and reliability of a detection result of the gradient thickness composite material structure.
Drawings
FIG. 1 is a schematic view of the shape of a test block 1 according to the present invention
FIG. 2 is a schematic view of the shape of a test block 2 with gradually changing thickness according to the present invention
FIG. 3 is a schematic view of another shape of a test block 2 with gradually changing thickness according to the present invention
Detailed Description
The technical scheme of the invention is further detailed in the following by combining the drawings and the embodiment:
the method for determining the gradient thickness coefficient for the ultrasonic detection of the composite material comprises the following steps:
step one, preparing test blocks 1 with different thicknesses, wherein the thickness of each test block is H i I =1,2,. ·, m; minimum thickness H of test block 1 min And a maximum thickness H max The minimum thickness and the maximum thickness of the part to be detected are the same, and referring to fig. 1, in the embodiment, the size of the carbon-fiber composite material wall plate with the gradual change characteristic is 1500 × 2500mm, the minimum thickness is 2mm, the maximum thickness is 8mm, m =5 i And (5) carrying out ultrasonic signal measurement on each test block 1 according to the same measurement track and measurement parameters for 5 groups of test blocks made of the composite material, wherein in the embodiment, an ultrasonic reflection detection mode is adopted, the scanning speed is 100mm/s, the data acquisition density is 2 x 2mm, and the ultrasonic measurement signals are u/s ij Let j be the number of ultrasonic measurement signals, j =1, 2., n, in this embodiment, i =1,2,3,5, j =1, 2., 100 is taken, and then the ultrasonic measurement signal u for each test block 1 is calculated ij An arithmetic mean of
Express, and plot thickness H i And with
The relationship curve of (1);
step two, preparing one or more test blocks 2 with continuous gradient thickness, wherein the minimum thickness h in the continuous gradient thickness formed by the test blocks 2 with continuous gradient thickness min And a maximum thickness h max Respectively the same as the minimum and maximum thickness of the part to be detectedIn the embodiment, k =3 groups of gradient thickness test blocks of composite material are taken to form a gradient thickness difference consistent with the gradient thickness range of 6mm of the detected composite material wallboard, namely, the gradient thickness difference delta h =2mm, and h of the 1 st group of gradient thickness test blocks min ＝2mm，h max H of group 2 test block with gradually changed thickness =4mm min ＝4mm，h max H of group 3 tapered thickness test block =6mm min ＝6mm，h max =8mm, and the ultrasonic signal measurement is carried out on each gradient thickness test block 2 according to the same measurement track and measurement parameters as the step one, and the total k x [ v ] is total a ，h a ] b Group, wherein v a Ultrasonic signal, h, representing the a-th measurement point a The thickness of the gradient thickness test block 2 corresponding to the a-th measurement point is shown, referring to fig. 2 and fig. 3, a =1,2, a, b, b is the total number of measurement points of the gradient thickness test block 2, k is a constant, k ranges from 1 to 10, and k x [ v ] is determined according to the principle of taking the same thickness a ，h a ] b According to different thickness values h c Corresponding mean value
Wherein h is min ≤c≤h max In this embodiment, k =3 is taken, and ultrasonic signal measurement and composite material block thickness measurement corresponding to the ultrasonic signal position are performed on 3 sets of gradient thickness composite material test blocks to obtain 3 × [ v ] v a ，h a ] 100 Set ultrasound signals and corresponding thicknesses, take a =1,2 a ，h a ] 100 Calculating to obtain each thickness h of the test block made of the composite material with the gradually changed thickness c Corresponding mean value
Here, c =1,2,. -, 64;
step three, aiming at different thickness values h c According to the drawn thickness H i And
relation curve, calculation
And
to obtain the ultrasonic gradual change thickness coefficient delta corresponding to different gradual change thicknesses c And drawing the thickness coefficient delta and the ultrasonic gradient thickness coefficient delta c The relationship between the thickness and the ultrasonic gradient thickness coefficient delta c The relation curve is led into a CUJ-6000 ultrasonic detection system, so that the ultrasonic detection and evaluation of 3 carbon fiber composite material wall plates with the characteristic of gradual change of thickness are completed, the layering defect between the gradual change of thickness and the difference of 1 layer of the surface of the composite material wall plate can be effectively detected, the layering defect is difficult to detect clearly by adopting the conventional ultrasonic method without leading in the ultrasonic gradual change of thickness coefficient, and the ultrasonic detection result is clearer after the ultrasonic gradual change of thickness coefficient is led in, so that the evaluation and defect judgment of the detection result are facilitated.
Claims (8)
1. A method for determining a gradient thickness coefficient for ultrasonic detection of a composite material is characterized by comprising the following steps: the method for determining the gradient thickness coefficient comprises the following steps:
step one, preparing test blocks (1) with different thicknesses, wherein the thickness of each test block is H i I =1,2,. ·, m; minimum thickness H of test block (1) min And a maximum thickness H max The ultrasonic signals are measured on each test block (1) according to the same measurement track and measurement parameters, and the ultrasonic measurement signals are u ij Denotes that j is the number of ultrasound measurement signals, j =1, 2.., n; then, an ultrasonic measurement signal u for each test block (1) is calculated ij An arithmetic mean of
Express, and plot thickness H i And
the relationship curve of (1);
step two, preparing one or more test blocks (2) with continuous gradual thickness, wherein the minimum thickness h in the continuous gradual thickness formed by the test blocks (2) with the gradual thickness is min And a maximum thickness h max Respectively same as the minimum and maximum thickness of the part to be detected, and measuring ultrasonic signals of each test block (2) with gradually changed thickness according to the same measuring track and measuring parameters as the step I, wherein the ultrasonic measuring signals are kx [ v ] v a ，h a ] b Group (v) of a Ultrasonic signal, h, representing the a-th measurement point a The thickness of the test block (2) with the gradual change thickness corresponding to the a-th measuring point is represented, a =1,2, a, b, b is the total number of the measuring points of the test block (2) with the gradual change thickness, k is a constant, and the value range of k is 1-10;
then according to the principle of taking the same thickness, determining kX [ v ] a ，h a ] b According to different thickness values h c Corresponding mean value
Wherein h is min ≤c≤h max ；
Step three, aiming at different thickness values h c According to the plotted thickness H i And
relation curve, calculation
And with
To obtain the ultrasonic gradual change thickness coefficient delta corresponding to different gradual change thicknesses c And drawing the thickness and ultrasonic gradient thickness coefficient delta c The relationship of (1).
2. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1, wherein: the material of the test block (1) is the same as the composite material of the part to be detected.
3. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1, wherein: the number of the test blocks (1) is not less than 5.
4. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1, wherein: the measurement track and the measurement parameters are the same as the detection requirements of the part to be detected.
5. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1 or 4, wherein: the measurement track and the measurement parameters comprise a measurement track path and measurement point calibration.
6. The method for determining a progressive thickness coefficient for ultrasonic testing of composite materials according to claim 1, wherein: the material of the test block (2) with the gradually-changed thickness is the same as the composite material of the part to be detected.
7. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1, wherein: the thickness gradient between test blocks (1) of different thicknesses is 2mm.
8. The method for determining a progressive thickness coefficient for ultrasonic inspection of composite materials according to claim 1 or 4, wherein: in the measurement track and the measurement parameters, the measurement track is in a scanning mode, the scanning speed is 100mm/s, and the measurement parameters are that the distance between adjacent measurement points is 2mm.
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