Aero-engine blade damage assessment method based on elastic metamaterial structure

Abstract

The invention provides an aero-engine blade damage assessment method based on an elastic metamaterial structure, and belongs to the technical field of nondestructive testing, and the method comprises the steps: S1, determining the size of a detection region according to an actual detection demand; s2, determining the size of the metamaterial array; s3, determining the structure of the metamaterial unit; s4, calculating a meta-material unit energy band diagram through a finite element method, and determining an excitation signal frequency; s5, arranging a metamaterial array and a sensor array; and S6, calculating pixel values of all the detection areas by adopting a DAS algorithm, carrying out positioning evaluation on the damage according to the pixel value distribution condition of the detection areas, and generating an image. According to the method, the wave field of the Lamb wave in the variable-thickness blade is controlled by using the elastic metamaterial structure with a special size, so that efficient and accurate positioning and damage identification of various types of damages are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing, and in particular relates to a damage assessment method for an aero-engine blade based on an elastic metamaterial structure. Background Art

[0002] At present, variable thickness structures have been widely used in transportation, construction and other fields: wings, fuselage skins, engine blades, etc. in aerospace equipment use variable thickness designs to meet different load requirements and reduce resistance to improve fuel efficiency; rail transit train bodies and track structures use variable thickness materials to improve the strength and fatigue resistance of the structure while reducing the overall weight; the main beams and steel cables of bridges use variable thickness structural designs to enhance wind resistance; key components such as floor slabs and walls of high-rise buildings use variable thickness structures to effectively improve local bearing capacity and reduce the impact of seismic loads. This type of configuration is more prone to fatigue, creep, wear and other damages than general uniform structures in harsh working conditions such as high-frequency vibration and alternating loads, external shocks and vibrations, and corrosive environments (such as rain, salt spray, etc.), affecting the safe operation of the structure. At present, the use of variable thickness structures is still expanding, and the importance of damage detection is increasing. However, traditional detection methods have been unable to meet the health monitoring requirements of complex structures. Ultrasonic testing, as a commonly used non-destructive testing technology, has the advantages of high precision, wide application range, large detection depth, and strong real-time performance. It can transmit structural damage information through reflection, transmission, and mode conversion. However, the ultrasonic waves in the existing methods have a dispersion effect during the propagation process. Coupled with the complexity of the variable thickness structure itself, the ultrasonic waves will produce extremely complex changes during the propagation process, which will cause signal energy loss. Therefore, the accuracy of the ultrasonic detection results is reduced. Therefore, it is necessary to propose a method that can be applied to variable thickness structure damage assessment in order to solve the problems existing in the existing technology. Summary of the invention

[0003] In view of the defects in the above-mentioned prior art, the present invention introduces bandgap elastic metamaterials into damage detection of variable thickness structures, utilizes the principle of local resonance, that is, the characteristic of prohibiting the propagation of a certain wave within a specific frequency range, filters out other clutter except direct waves and damage reflected waves, and achieves the purpose of manipulating the sound field. Therefore, under the condition of any single-frequency excitation wave, a reflected wave signal with a high signal-to-noise ratio can be obtained, thereby retaining the propagation characteristics of the reflected wave in the blade to the greatest extent and improving the efficiency of damage detection.

[0004] To achieve the above-mentioned purpose, the present invention proposes a method for assessing damage of an aero-engine blade based on an elastic metamaterial structure, which includes: given the basic unit form of the metamaterial, calculating the relationship between the metamaterial structure parameters and the band gap under different excitation frequencies; determining the excitation frequency to be used, thereby determining the metamaterial structure parameters, and designing the overall structure of the metamaterial; given the detection area, emitting an excitation signal after the sensor array and the overall structure of the metamaterial are pasted, and using an imaging algorithm to calculate the pixel value to represent the probability of damage, thereby identifying the damage location. The present invention realizes the use of an elastic metamaterial structure to manipulate the wave field of Lamb waves in a variable thickness blade, thereby achieving efficient and accurate positioning of various types of damage.

[0005] Specifically, the present invention provides an aerospace engine blade damage assessment method based on an elastic metamaterial structure, which comprises the following steps:

[0006] S1. Determine the size of the detection area according to actual detection requirements. The long side of the detection area is a and the short side is b;

[0007] S2. Determine the size of the metamaterial array: the width of the metamaterial array is 1 / 6*a-1 / 2*a, and the length of the metamaterial array is the same as the side length of the corresponding detection area;

[0008] S3. Determine the structure of the metamaterial unit: The metamaterial unit is placed on the blade. The metamaterial unit includes an upper non-metallic cylinder and a middle non-metallic base. The height of the upper cylinder is 5-15 mm, the cylinder interval is 1-3 mm, and the thickness of the middle non-metallic base is 1-2 mm.

[0009] S4. Calculate the band diagram of the metamaterial unit by the finite element method to determine the excitation signal frequency; and construct the relationship between the excitation signal frequency and the cylinder height. When the height of the upper cylinder is modified, the excitation signal frequency is calculated by the relationship between the excitation signal frequency and the cylinder height. The relationship between the excitation signal frequency and the cylinder height is:

[0010] f=-m*h+n

[0011] Where f is the band gap center frequency in kHz, h is the cylinder height in mm, and m and n are fitting parameters;

[0012] S5, forming an array of the upper non-metallic cylinder and the middle non-metallic base of the metamaterial unit based on the size determined in step S2 and 3D printing, pasting them to the outside of the detection area boundary and surrounding the detection area, evenly arranging sensors on the inside of the detection area boundary to form an array, respectively emitting excitation signals and obtaining corresponding damage reflection signals;

[0013] S6. Use the DAS algorithm to calculate the pixel values ​​of all detection areas, locate and evaluate the damage according to the distribution of pixel values ​​in the detection areas, and generate images.

[0014] Preferably, the value of a is 7.63 and the value of b is 112.58.

[0015] Preferably, in step S3, the density of the upper and middle layers of non-metallic material is less than or equal to half of the density of the lower blade metal material.

[0016] Preferably, step S6 specifically includes the following sub-steps:

[0017] S61, re-dividing the detection area into grids, and calculating the theoretical time for each group of signals to reach the i-th grid:

[0018]

[0019] Among them, (x n1 ,y n1 ) and (x n2 ,y n2 ) are the position coordinates of the excitation and response sensors in the nth excitation-response sensor group, respectively, (x i ,y i ) is the position coordinate of the center point of the i-th grid, c g is the propagation speed of the reflected wave in the blade;

[0020] S62, calculate the amplitude corresponding to each group of signals when they arrive at the i-th grid at the above time and combine them into a vector:

[0021]

[0022] Among them, r n (T ni ) represents the reflection signal of the nth stimulus-response sensor group at time T ni The amplitude when passing through the i-th grid;

[0023] S63, adding the above signal amplitudes to obtain the pixel value of the i-th grid:

[0024]

[0025] S64. Display all pixel values ​​in the detection area to obtain the damage status of the area.

[0026] Preferably, arranging the sensors in step S5 specifically includes the following steps:

[0027] S51. Design an array consisting of S sensors and arrange them evenly inside the boundary of the detection area;

[0028] S52, when the product is in an undamaged state, stimulate sensors 1 to S in sequence, and each time all other sensors collect response signals at the same time, and obtain response signals r corresponding to N excitation-response sensor groups in the undamaged state. a1 (t), r a2 (t)...r an (t)...r aN (t);

[0029] S53, when the product is damaged, sensors 1 to S are stimulated again in sequence, and each time all other sensors collect response signals at the same time, and obtain response signals r corresponding to N excitation-response sensor groups in the damaged state. b1 (t), r b2 (t)...r bn (t)...r bN (t);

[0030] S54, subtract the signal obtained in S32 from the signal obtained in S33 to obtain the reflected signals r1(t), r2(t)...r n (t)...r N (t).

[0031] Compared with the prior art, the technical effects of the present invention are:

[0032] (1) The invention discloses an aero-engine blade damage assessment method based on an elastic metamaterial structure, which can obtain reflected wave amplitude information from multiple sets of excitation-receiving sensor signals, thereby extracting damage location information and realizing the positioning and assessment of variable thickness structure damage using Lamb waves.

[0033] (2) The present invention designs an aero-engine blade damage assessment method based on an elastic metamaterial structure. Through the design of an elastic bandgap metamaterial structure, other clutter except direct waves and damage reflected waves is filtered out by the principle of local resonance to achieve the purpose of manipulating the sound field, thereby achieving the purpose of obtaining a reflected wave signal with a high signal-to-noise ratio under the condition of any single-frequency excitation wave, and retaining the propagation characteristics of the reflected wave in the blade to the greatest extent.

[0034] (3) The method of the present invention designs the array size and unit structure of the metamaterial, and designs the width of the metamaterial array according to the long side length of the measurement area. The design principle is that the metamaterial array width is between 1 / 6 and 1 / 2 of the long side length of the measurement area, and the metamaterial array length is equal to the side length of the measurement area, so as to ensure that the metamaterial structure can completely surround the measurement area, thereby ensuring the filtering performance of the metamaterial and the positioning accuracy of the damage position. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings.

[0036] Figure 1 It is a flow chart of the damage assessment method of an aero-engine blade based on an elastic metamaterial structure of the present invention;

[0037] Figure 2 is a schematic diagram of an elastic metamaterial structure unit and its lower blade structure in an embodiment of the present invention;

[0038] Figure 3 is an energy band diagram of an elastic metamaterial structural unit in an embodiment of the present invention;

[0039] Figure 4 is a schematic diagram of an elastic metamaterial array in an embodiment of the present invention;

[0040] Figure 5 is a schematic diagram of sensor positions in an embodiment of the present invention;

[0041] Figure 6 is a schematic diagram of simulated point damage in an embodiment of the present invention;

[0042] Figure 7 is a schematic diagram of the location of a physical crack damage in an embodiment of the present invention;

[0043] Figure 8 are several typical reflection signal diagrams in the embodiments of the present invention;

[0044] Fig. 9 is a comparison diagram of the position of the damage point D1 and the positioning result of the algorithm in the embodiment of the present invention;

[0045] Fig.10 is a comparison diagram of the position of the damage point D2 and the positioning result of the algorithm in the embodiment of the present invention;

[0046] Fig.11 is a comparison diagram of the position of the damage point D3 and the positioning result of the algorithm in the embodiment of the present invention;

[0047] Fig.12 is a comparison diagram of the position of the damage point D4 and the positioning result of the algorithm in the embodiment of the present invention;

[0048] Fig.13 It is a comparison diagram of the location of crack damage and the algorithm positioning result in the embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should also be noted that, for ease of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0050] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0051] Figure 1 The invention shows an aero-engine blade damage assessment method based on an elastic metamaterial structure, which comprises the following steps:

[0052] S1. Determine the size of the detection area according to actual detection requirements, and set the long side of the detection area to a and the short side to b.

[0053] S2. Determine the size of the metamaterial array: the width of the metamaterial array is 1 / 6*a-1 / 2*a, and the length of the metamaterial array is the same as the side length of the corresponding detection area, so as to ensure that the detection area is completely covered.

[0054] S3. Determine the structure of the metamaterial unit: The metamaterial unit includes an upper non-metallic cylinder and a middle non-metallic base, the upper cylinder height is 5-15 mm, the cylinder interval is 1-3 mm, and the middle non-metallic base thickness is 1-2 mm. Then, arrange the metamaterial unit on the bottom blade, and the density of the upper and middle non-metallic materials is less than or equal to half of the density of the metal material of the lower blade.

[0055] S4. Calculate the band diagram of the metamaterial unit by the finite element method to determine the excitation signal frequency. And construct the relationship between the excitation signal frequency and the cylinder height. When the height of the upper cylinder is modified, the excitation signal frequency is calculated by the relationship between the excitation signal frequency and the cylinder height. The relationship between the excitation signal frequency and the cylinder height is:

[0056] f=-m*h+m

[0057] Wherein, f is the band gap center frequency, in kHz, h is the cylinder height, in mm, and m and n are fitting parameters. In a specific embodiment, the value of m is 7.63, and the value of n is 112.58.

[0058] In a specific embodiment, Figure 2As shown in the figure, the basic shape of the metamaterial unit includes a rubber cylindrical structure on the upper layer and a rubber rectangular base structure, and the metamaterial unit is placed on the blade at the bottom. The cylinder diameter d = 5mm, the blade thickness h2 varies between 1.5mm and 2.7mm, the rubber base thickness h1 = 1mm, and the cylinder structure height h = 6.8mm. In this case, the frequency band diagram of the metamaterial unit is as follows Figure 3 As shown, it can be seen that the band gap is between 58.63-61.94kHz, and the center frequency of the band gap is 60.70kHz according to the fitting relationship, which is consistent with the result of the frequency band diagram, so the excitation signal frequency is determined to be 60kHz. In actual work, the excitation signal frequency can also be quickly obtained based on the determined cylinder height directly through the relationship between the excitation signal frequency and the cylinder height.

[0059] S5. The upper non-metallic cylinder and the middle non-metallic base of the metamaterial unit are formed into an array based on the size determined in step S2 and 3D printed. After printing, they are pasted to the outer side of the detection area boundary of the blade and surround the detection area. At the same time, sensors are evenly arranged on the inner side of the detection area boundary to form an array, and excitation signals are respectively emitted and corresponding damage reflection signals are obtained.

[0060] In this embodiment, a 150 mm × 150 mm square detection area is arranged on the upper side of an aircraft engine blade, and the metamaterial unit is expanded into an array with a size of 25 * 12 and pasted around the detection area. Figure 4 shown.

[0061] The specific steps for arranging sensors are as follows:

[0062] S51. Design an array consisting of S sensors and arrange them evenly inside the boundary of the detection area.

[0063] S52, when the product is in an undamaged state, stimulate sensors 1 to S in sequence, and each time all other sensors collect response signals at the same time, and obtain response signals r corresponding to N excitation-response sensor groups in the undamaged state. a1 (t), r a2 (t)...r an (t)...r aN (t).

[0064] S53, when the product is damaged, sensors 1 to S are stimulated again in sequence, and each time all other sensors collect response signals at the same time, and the response signals r corresponding to the N excitation-response sensor groups in the damaged state are obtained. b1 (t), r b2 (t)...r bn (t)...r bN (t).

[0065] S54, subtract the signal obtained in S32 from the signal obtained in S33 to obtain the reflected signals r1(t), r2(t)...r n (t)...r N (t).

[0066] In a specific embodiment, Figure 5 , Figure 6 and Figure 7 As shown, S = 8 sensors are arranged in the detection area, evenly arranged at the inner boundary of the detection area to form a square array. At the same time, four circular damages with a diameter of 20 mm and a crack-like damage with a length of 32 mm and a depth of 3 mm are set at different positions. Sensors 1-8 are stimulated in turn, and the other 7 sensors collect response signals at the same time each time they are stimulated. For the same path, such as 1-2 and 2-1, only the former is selected. First, the response signal in the healthy state is collected, and then the damage is applied to collect the signal in the damaged state. In each case, N = 28 groups of reflection signals r1(t), r2(t)...r 28 (t). The entire test system is approximately a linear system, and only the A0 mode is considered. Typical reflected wave signals are as follows: Figure 8 shown.

[0067] S6. Calculate the pixel values ​​of all detection areas using the DAS algorithm, perform damage location assessment and generate images based on the pixel value distribution of the detection area. This step specifically includes the following sub-steps:

[0068] S61, re-dividing the detection area into grids, and calculating the theoretical time for each group of signals to reach the i-th grid:

[0069]

[0070] Among them, (x n1 ,y n1 ) and (x n2 ,y n2 ) are the position coordinates of the excitation and response sensors in the nth excitation-response sensor group, respectively, (x i ,y i ) is the position coordinate of the center point of the i-th grid, c g is the propagation speed of the reflected wave in the blade.

[0071] S62, calculate the amplitude corresponding to each group of signals when they arrive at the i-th grid at the above time and combine them into a vector:

[0072]

[0073] Among them, r n (T ni) represents the reflection signal of the nth stimulus-response sensor group at time T ni The amplitude when passing through the i-th grid.

[0074] S63, adding the above signal amplitudes to obtain the pixel value of the i-th grid:

[0075]

[0076] S64. Display all pixel values ​​in the detection area to obtain the damage status of the area.

[0077] In a specific embodiment, the detection area is divided into grids with a step length of 2 mm, and a total of 75×75=5625 grids are divided. The imaging algorithm is used to calculate the theoretical time for each group of signals to reach each grid, and then the amplitude corresponding to each group of signals when they reach each grid at the above time is calculated and summed to obtain the pixel value of each grid. Finally, all pixel values ​​are imaged to obtain the damage identification result.

[0078] Figure 9-12 The imaging results corresponding to the circular damage at four locations are displayed. It can be seen that the damage location identification results basically coincide with the actual prefabricated damage. Fig.13 The imaging results corresponding to the crack-like damage are displayed. It can be seen that in addition to identifying the location of the damage, this method also roughly depicts the outline of the crack, which proves the effectiveness of the method and the accuracy and robustness of its damage location assessment.

[0079] The invention designs an aero-engine blade damage assessment method based on an elastic metamaterial structure, which can obtain reflected wave amplitude information from multiple groups of excitation-receiving sensor signals, thereby extracting damage location information, and realizing the positioning and assessment of variable thickness structure damage using Lamb waves. The principle of local resonance is utilized, and the purpose of manipulating the sound field is achieved through the design of an elastic bandgap metamaterial structure, thereby achieving the purpose of obtaining a reflected wave signal with a high signal-to-noise ratio under any single-frequency excitation wave condition, retaining the propagation characteristics of the reflected wave in the blade to the greatest extent, and more accurately locating and assessing the damage.

[0080] Finally, it should be noted that the embodiments described above are only for illustration and not for limiting the technical solutions of the present invention. Although the present invention has been described in detail with reference to the embodiments described above, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A damage assessment method for an aero-engine blade based on an elastic metamaterial structure, characterized in that: It includes the following steps: S1. Determine the size of the detection area according to actual detection requirements. The long side of the detection area is a and the short side is b; S2. Determine the size of the metamaterial array: the width of the metamaterial array is 1 / 6*a-1 / 2*a, and the length of the metamaterial array is the same as the side length of the corresponding detection area; S3. Determine the structure of the metamaterial unit: The metamaterial unit is placed on the blade. The metamaterial unit includes an upper non-metallic cylinder and a middle non-metallic base. The height of the upper cylinder is 5-15 mm, the cylinder interval is 1-3 mm, and the thickness of the middle non-metallic base is 1-2 mm. S4. Calculate the band diagram of the metamaterial unit by the finite element method to determine the excitation signal frequency; and construct the relationship between the excitation signal frequency and the cylinder height. When the height of the upper cylinder is modified, the excitation signal frequency is calculated by the relationship between the excitation signal frequency and the cylinder height. The relationship between the excitation signal frequency and the cylinder height is: f=-m*h+n Where f is the band gap center frequency in kHz, h is the cylinder height in mm, and m and n are fitting parameters; S5, forming an array of the upper non-metallic cylinder and the middle non-metallic base of the metamaterial unit based on the size determined in step S2 and 3D printing, pasting them to the outside of the detection area boundary and surrounding the detection area, and at the same time, evenly arranging sensors on the inside of the detection area boundary to form an array, respectively emitting excitation signals and obtaining corresponding damage reflection signals; S6. Use the DAS algorithm to calculate the pixel values ​​of all detection areas, locate and evaluate the damage according to the distribution of pixel values ​​in the detection areas, and generate images.

2. The damage assessment method for aerospace engine blades based on elastic metamaterial structure according to claim 1 is characterized in that: The value of m is 7.63 and the value of n is 112.

58.

3. The damage assessment method for aero-engine blades based on elastic metamaterial structure according to claim 1 is characterized in that: In step S3, the density of the upper and middle layers of non-metallic material is less than or equal to half of the density of the lower blade metal material.

4. The damage assessment method for aerospace engine blades based on elastic metamaterial structure according to claim 1 is characterized in that: Step S6 specifically includes the following sub-steps: S61, re-dividing the detection area into grids, and calculating the theoretical time for each group of signals to reach the i-th grid: Among them, (x n1 ,y n1 ) and (x n2 ,y n2 ) are the position coordinates of the excitation and response sensors in the nth excitation-response sensor group, respectively, (x i ,y i ) is the position coordinate of the center point of the i-th grid, c g is the propagation speed of the reflected wave in the blade; S62, calculate the amplitude corresponding to each group of signals when they arrive at the i-th grid at the above time and combine them into a vector: Among them, r n (T ni ) represents the reflection signal of the nth stimulus-response sensor group at time T ni The amplitude when passing through the i-th grid; S63, adding the above signal amplitudes to obtain the pixel value of the i-th grid: S64. Display all pixel values ​​in the detection area to obtain the damage status of the area.

5. The damage assessment method for aerospace engine blades based on elastic metamaterial structure according to claim 1 is characterized in that: Arranging the sensors in step S5 specifically includes the following steps: S51. Design an array consisting of S sensors and arrange them evenly inside the boundary of the detection area; S52, when the product is in an undamaged state, stimulate sensors 1 to S in sequence, and each time all other sensors collect response signals at the same time, and obtain response signals r corresponding to N excitation-response sensor groups in the undamaged state. at (t), r a2 (t)...r an (t)...r aN (t); S53, when the product is damaged, sensors 1 to S are stimulated again in sequence, and each time all other sensors collect response signals at the same time, and the response signals r corresponding to the N excitation-response sensor groups in the damaged state are obtained. bt (t), r b2 (t)...r bn (t)...r bN (t); S54, subtract the signal obtained in S32 from the signal obtained in S33 to obtain the reflected signal r caused by the damage t (t), r2(t)...r n (t)...r N (t).

Images