Aero-engine blade full-field dynamic stress measurement system and method

Abstract

The application discloses an aero-engine blade full-field dynamic stress measurement system and method, and belongs to the technical field of testing, which comprises a high-temperature-resistant photoelastic transparent coating, a photoelastic image acquisition device and a visualization device.The measurement method comprises the following steps: firstly, the high-temperature-resistant photoelastic transparent coating is sintered on the aero-engine blade; when the blade rotates or vibrates, the blade surface generates strain and transmits to the photoelastic coating.Polarized light is used to irradiate the coating on the blade, four phase shift images are obtained by one-time exposure of a polarization camera, and the full-field dynamic stress (strain) distribution of the blade can be obtained by program processing.Because the high-temperature-resistant photoelastic transparent coating and the photoelastic device based on the polarization camera are adopted, the measurement system and method can be used for non-contact measurement of the full-field dynamic stress of the blade under high temperature and high speed.

Description

Technical Field

[0001] This invention relates to the field of digital photoelasticity measurement, and in particular to a system and method for measuring the full-field dynamic stress of aero-engine blades. Background Technology

[0002] The aero-engine is the heart of an aircraft and a critical power component. Its performance and safety are directly related to the aircraft's overall performance and safety. Engines operate under extremely harsh conditions. During operation, the blades rotate at high speeds and are subjected to a complex combination of loads, including aerodynamic excitation forces, centrifugal forces, thermal stresses, and mechanical bending moments. Turbine blades, in particular, bear even greater loads. Blade fractures are a frequent occurrence during the research, development, production, and use of aero-engines, and these fractures can cause serious damage to both the engine and the aircraft. According to incomplete statistics, 70%-80% of engine failures are caused by blades, and these failures have repeatedly led to aircraft accidents, highlighting a significant problem.

[0003] Studying the blade fracture mechanism and eliminating blade fracture faults to improve blade design is a crucial task in engine development. When measuring stress on aero-engine blades, electrical strain gauges, based on the resistance effect of resistance strain gauges, offer advantages such as high sensitivity and small error. However, they cannot reflect the continuous distribution of the stress field on the component surface and cannot detect defects such as stress concentration. Photoelastic patch methods utilize the optical effects of photoelastic materials to measure surface strain, continuously displaying the stress distribution on the component surface; however, the patching process is complex. Photoelastic coatings overcome these shortcomings, enabling full-field stress field measurement on the component surface. They offer intuitive visualization, a large amount of information, and direct observation of stress concentration areas. Unlike resistance strain gauge measurements, photoelastic coatings do not suffer from zero-point drift, and the aging of photoelastic materials is very slow, making them suitable for long-term monitoring. However, current photoelastic materials are all organic, suitable only for low-temperature measurements and unable to perform stress measurements on aero-engine blades under high-temperature conditions. Furthermore, current photoelastic coating methods cannot simultaneously acquire multiple phase-shift maps for calculating full-field stress, thus preventing transient measurements of rotating or high-frequency vibrating blades. These are the main reasons why the photoelastic stress measurement method is currently not applicable to the study of high-temperature and high-speed fatigue characteristics of blades. Summary of the Invention

[0004] This invention provides a system and method for measuring the full-field dynamic stress of aero-engine blades, in order to solve the technical problem of accurately measuring the full-field dynamic stress, stress concentration areas, and analyzing fatigue failure sites of blades under high-temperature and high-speed operating conditions.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A full-field dynamic stress measurement system for aero-engine blades includes: a high-temperature resistant photoelastic transparent coating, a photoelastic image acquisition device, and a visualization device;

[0007] The high-temperature resistant photoelastic transparent coating is applied to the aero-engine blades;

[0008] The photoelastic image acquisition device includes: a laser source; a convex lens, a polarizer, a first quarter-wave plate, and a depolarizing beam splitter are sequentially arranged on the light line of the laser source; the aero-engine blade is arranged on one side of the depolarizing beam splitter, and a second quarter-wave plate, a narrowband filter, an imaging lens, and a polarizing camera are sequentially arranged on the other side.

[0009] The visualization device is embedded with a stress calculation program and is connected to a polarization camera.

[0010] As a further improvement of the present invention, the high-temperature resistant photoelastic transparent coating is sintered on the aero-engine blade.

[0011] As a further improvement of the present invention, facing the laser source, the polarization axis of the polarizer is located in the vertical direction, the fast axis of the first quarter wave plate is at 45° with the horizontal direction, the fast axis of the second quarter wave plate is at 135° with the horizontal direction, and the first polarization direction of the polarization camera is parallel to the polarization axis of the polarizer.

[0012] As a further improvement of the present invention, the visualization device includes a computer host and a monitor, an image transmission data cable, an image processing and stress calculation program and software;

[0013] The computer host and the monitor are electrically connected. The computer host is electrically connected to the polarization camera via an image transmission data cable. The stress calculation program and software are embedded in the computer host.

[0014] As a further improvement of the present invention, the stress calculation program and software include: an equal inclination angle calculation program, a phase difference calculation program, an equal inclination angle unwrapping program, a phase difference unwrapping program, a shear stress calculation program, and a principal stress calculation program.

[0015] A measurement method for a full-field dynamic stress measurement system for aero-engine blades, comprising:

[0016] A high-temperature resistant photoelastic transparent coating is sintered onto aero-engine blades;

[0017] The photoelastic image acquisition device uses polarized light to irradiate the high-temperature resistant photoelastic transparent coating on the blade, and uses a polarized camera to obtain multiple phase-shift images in a single exposure. The full-field dynamic stress-strain distribution of the blade can then be obtained through program processing.

[0018] As a further improvement of the present invention, the steps of using the photoelastic image acquisition device include:

[0019] Turn on the light source so that the light field completely covers the area of ​​the blade coating that needs to be measured;

[0020] To make the sintered coated blades rotate or vibrate;

[0021] Control the polarization camera to perform one exposure and acquire four phase-shifted images.

[0022] As a further improvement of the present invention, the polarization camera obtains four phase shift images in a single exposure. These four phase shift images correspond to polarization directions of 0°, 45°, 90° and 135°, respectively. The phase difference and the inclination angle are calculated from these four phase shift images, and then the magnitude and direction of the overall stress are calculated.

[0023] As a further improvement to the present invention, it includes:

[0024] The process of sintering a high-temperature resistant photoelastic transparent coating onto an aero-engine blade includes:

[0025] 1) The blade surface is polished smooth to serve as the substrate for preparing phosphate glass powder and deionized water slurry;

[0026] 2) Apply the slurry evenly to the surface of the blades and let it dry;

[0027] 3) The dried blades and their coatings are subjected to the following processes in sequence: heat preservation, air quenching and cooling, so that they are cooled below the glass transition temperature, and finally stress-relief annealing is performed.

[0028] The present invention has the following beneficial effects:

[0029] This invention applies a high-temperature resistant photoelastic transparent coating to the blade surface, and the polarization camera of this invention can instantly acquire four phase-shift maps capable of calculating the full-field stress-strain distribution. Therefore, this invention can perform full-field dynamic stress measurement on blades under high-temperature conditions, high-speed rotation, or vibration. The measurement results are entirely derived from real experimental environments and operating conditions, reliably reflecting the stress distribution of the blade under working conditions. Because it is a non-contact measurement, it can perform rapid and effective full-field stress measurement regardless of the load on the blade. Furthermore, it can also identify and measure the yield region after unloading of the component. Through computer-aided technology, it is possible to accurately measure the full-field dynamic stress of the blade, stress concentration areas, and analyze the technical problems of fatigue failure sites.

[0030] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a full-field dynamic stress measurement system for aero-engine blades based on a high-temperature resistant transparent photoelastic coating.

[0032] Figure 2 A schematic diagram of the photoelastic image acquisition device;

[0033] Figure 3 Here is a flowchart of the stress calculation program;

[0034] The attached figures are labeled as follows: 1. Laser; 2. Convex lens; 3. Polarizer; 4. 1 / 4 wave plate; 5. Blade; 6. Coating; 7. Depolarizing beam splitter; 8. 1 / 4 wave plate; 9. Narrowband filter; 10. Imaging lens; 11. Polarizing camera; 12. Image transmission data cable; 13. Computer host; 14. Monitor. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. When referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present invention as detailed in the appended claims. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0036] To address the two problems and shortcomings of the existing technology, this invention proposes a non-contact measurement system and method for the full-field dynamic stress of aero-engine blades based on a high-temperature resistant photoelastic transparent coating, which can solve the problem of measuring the transient full-field stress of aero-engine blades under high-temperature and high-speed operating conditions.

[0037] A preferred embodiment of the present invention provides a non-contact measurement system for full-field stress of a blade, used to measure the full-field dynamic stress distribution of an aero-engine blade as the test piece under high temperature and high speed conditions.

[0038] The full-field dynamic stress measurement system for aero-engine blades includes: a high-temperature resistant photoelastic transparent coating, a photoelastic image acquisition device, and a visualization device.

[0039] The general steps involved in sintering a high-temperature resistant photoelastic transparent coating onto the blades include:

[0040] 1) The blade surface is polished smooth to serve as the substrate, and then phosphate glass powder and deionized water slurry are prepared in a ratio of 8:2.

[0041] 2) Apply the slurry evenly to the surface of the blade and dry it at around 50°C;

[0042] 3) The dried blades and their coatings are subjected to the following processes in sequence: heat preservation, air quenching and cooling, so that they are cooled below the glass transition temperature, and finally stress-relief annealing is performed.

[0043] The photoelastic image acquisition device includes: a laser source 1, a convex lens 2, a polarizer 3, a first quarter-wave plate 4, a depolarizing beam splitter 7, a second quarter-wave plate 8, an imaging lens 10, a narrowband filter 9, and a polarizing camera 11.

[0044] A convex lens 2 is placed behind the laser source 1 to increase the divergence angle of the light source, ensuring that the light field completely covers the measurement area of ​​the blade coating. A polarizer is placed behind the convex lens. A first quarter-wave plate 4 is placed behind the polarizer 3. A depolarizing beam splitter 7 is placed behind the first quarter-wave plate 4 to ensure that the light is incident perpendicularly onto the surface of the blade coating, reducing errors caused by oblique incidence. A second quarter-wave plate 8 is placed on the side of the line connecting the depolarizing beam splitter 7 and the polarizer 3. A polarizing camera 11 is placed behind the second quarter-wave plate 8, with its imaging lens 10 facing the depolarizing beam splitter 7. A narrow-band filter 9 is placed in front of the imaging lens 10 to filter out stray light and improve system accuracy. The positions of these components determine the calculation formulas for the phase difference and constant tilt angle related to the full-field stress in this invention.

[0045] Facing the laser source 1, the polarization axis of polarizer 3 is vertical. The fast axis of the first quarter-wave plate 4 forms a 45° angle with the horizontal direction, and the fast axis of the second quarter-wave plate 8 forms a 135° angle with the horizontal direction. The first polarization direction of polarization camera 11 is parallel to the polarization axis of polarizer 3. The angle settings of these components determine the calculation formulas for the phase difference and equitability angle related to the full-field stress in this invention.

[0046] The polarization camera 11 can obtain four phase shift images in a single exposure. These four phase shift images correspond to polarization directions of 0°, 45°, 90° and 135°, respectively. The phase difference and the inclination angle can be calculated from these four phase shift images. Furthermore, the magnitude and direction of the stress in the entire field can be calculated.

[0047] Therefore, through the above description, the present invention provides a full-field dynamic stress measurement system for aero-engine blades, including: a high-temperature resistant photoelastic transparent coating, a photoelastic image acquisition device, and a stress calculation and visualization device;

[0048] The high-temperature resistant photoelastic transparent coating is prepared on the blade surface by sintering.

[0049] The photoelastic image acquisition device includes: a laser source, a convex lens, a polarizer, a first quarter-wave plate, a depolarizing beam splitter, a second quarter-wave plate, and a polarizing camera; a convex lens 2, a polarizer 3, a first quarter-wave plate 4, and a depolarizing beam splitter 7 are sequentially arranged on the light path of the laser source 1; the aero-engine blade 5 is arranged on one side of the depolarizing beam splitter 7, and a second quarter-wave plate 8, a narrowband filter 9, an imaging lens 10, and a polarizing camera 11 are sequentially arranged on the other side.

[0050] The functions of each component are as follows: The convex lens is placed behind the light source to increase the divergence angle of the light source, ensuring that the light field completely covers the measurement area of ​​the blade coating. The polarizer is placed behind the convex lens. The first quarter-wave plate is placed behind the polarizer. The depolarizing beam splitter is placed behind the first quarter-wave plate to ensure that the light is incident perpendicularly onto the surface of the blade coating, reducing errors caused by oblique incidence. The second quarter-wave plate is placed on the side of the line connecting the depolarizing beam splitter and the polarizer. The narrowband filter is placed behind the second quarter-wave plate to filter out stray light and improve system accuracy. The imaging lens is placed behind the narrowband filter. The polarizing camera is placed behind the imaging lens to acquire photoelastic images of the high-temperature resistant coating on the blade surface. The positions of these components determine the calculation formulas for the phase difference and equal tilt angle related to the full-field stress in this invention.

[0051] Facing the light source, the polarization axis of the polarizer is vertical. The fast axis of the first quarter-wave plate forms a 45° angle with the horizontal, and the fast axis of the second quarter-wave plate forms a 135° angle with the horizontal. The first polarization direction of the polarizing camera is parallel to the polarization axis of the polarizer. The angle settings of these components determine the calculation formulas for the phase difference and equal tilt angle related to the full-field stress in this invention.

[0052]

[0053]

[0054]

[0055] Where θ represents the isoclimax angle, δ represents the phase difference, and the subscript c indicates that the result is calculated using inverse trigonometric functions. i This represents the phase shift diagram corresponding to the i-th optical path setting.

[0056] The steps for using the photoelastic image acquisition device include:

[0057] Step 1: Turn on the light source so that the light field completely covers the area of ​​the blade coating that needs to be measured;

[0058] Step 2: Rotate or vibrate the blade with a high-temperature resistant photoelastic transparent coating.

[0059] Step 3: Control the polarization camera to perform an exposure once to collect four phase-shifted images.

[0060] The visualization device includes a computer host and a display, as well as image processing and stress calculation software. The four phase-shifted images are transmitted to the computer through the polarization camera. Through program processing, the全场应力 (full-field stress) and its direction are calculated, and the results are displayed on the software interface.

[0061] The visualization device includes a computer host 13, a display 14, an image transmission data cable 12, image processing and stress calculation programs and software. The four phase-shifted images are transmitted to the computer through the polarization camera, and the images are acquired by the software supporting the polarization camera. Through program processing, the full-field stress and its direction of the blade are calculated, and the results are displayed on the software interface. Among them, the stress calculation program includes: an equal-inclination calculation program, a phase difference calculation program, an equal-inclination unwrapping program, a phase difference unwrapping program, a shear stress calculation program, and a principal stress calculation program.

[0062] Through the visualization software of the present invention, the full-field stress gradient and the overall stress distribution can be quickly and intuitively identified, and the areas with excessive stress, stress concentration, and insufficient stress can be quickly identified;

[0063] Based on the urgent needs in the research and manufacturing fields of aeroengine blades, the present invention provides a convenient and reliable new system device and method for the research on the fatigue characteristics of blades, improving the blade life and reliability, and provides technical support for the further development of aeroengine blades.

[0064] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications should be regarded as the protection scope of the present invention.

Claims

1. A full-field dynamic stress measurement system for aero-engine blades, characterized in that, include: High-temperature resistant photoelastic transparent coating (6), photoelastic image acquisition device, visualization device; The high-temperature resistant photoelastic transparent coating (6) is applied to the aero-engine blade (5); The photoelastic image acquisition device includes: a laser source (1); a convex lens (2), a polarizer (3), a first quarter-wave plate (4), and a depolarizing beam splitter (7) are arranged sequentially on the light line of the laser source (1); the aero-engine blade (5) is arranged on one side of the depolarizing beam splitter (7), and a second quarter-wave plate (8), a narrowband filter (9), an imaging lens (10), and a polarizing camera (11) are arranged sequentially on the other side. The visualization device is embedded with a stress calculation program and is connected to a polarization camera (11); The high-temperature resistant photoelastic transparent coating (6) is sintered on the aero-engine blade (5); Facing the laser source (1), the polarization axis of the polarizer (3) is in the vertical direction, the fast axis of the first quarter wave plate (4) is at 45° with the horizontal direction, the fast axis of the second quarter wave plate (8) is at 135° with the horizontal direction, and the first polarization direction of the polarization camera (11) is parallel to the polarization axis of the polarizer (3). The high-temperature resistant photoelastic transparent coating (6) is sintered onto the aero-engine blade (5), specifically including: 1) The blade surface was polished smooth to serve as the substrate, and phosphate glass powder and deionized water slurry were prepared in a ratio of 8:

2. 2) Apply the slurry evenly to the blade surface and let it dry; 3) The dried blades and their coatings are subjected to the following processes in sequence: heat preservation, air quenching and cooling, so that they are cooled below the glass transition temperature, and finally stress-relief annealing is performed.

2. The full-field dynamic stress measurement system for aero-engine blades according to claim 1, characterized in that, The visualization device includes a computer host (13) and a monitor (14), an image transmission data cable (12), and image processing and stress calculation programs and software; The computer host (13) and the monitor (14) are electrically connected. The computer host (13) is electrically connected to the polarization camera (11) through the image transmission data line (12). The stress calculation program and software are embedded in the computer host (13).

3. The full-field dynamic stress measurement system for aero-engine blades according to claim 1, characterized in that, The stress calculation program and software include: an equal inclination angle calculation program, a phase difference calculation program, an equal inclination angle unwrapping program, a phase difference unwrapping program, a shear stress calculation program, and a principal stress calculation program.

4. A measurement method for a full-field dynamic stress measurement system for aero-engine blades according to any one of claims 1 to 3, characterized in that, include: A high-temperature resistant photoelastic transparent coating (6) is sintered onto the aero-engine blade (5); The photoelastic image acquisition device uses polarized light to irradiate the high-temperature resistant photoelastic transparent coating (6) on the blade, and uses a polarized camera to obtain multiple phase-shift images in one exposure. The full-field dynamic stress-strain distribution of the blade can then be obtained through program processing.

5. The measurement method according to claim 4, characterized in that, The steps for using the photoelastic image acquisition device include: Turn on the light source so that the light field completely covers the area of ​​the blade coating that needs to be measured; To make the sintered coated blades rotate or vibrate; Control the polarization camera to perform one exposure and acquire four phase-shifted images.

6. The measurement method according to claim 4, characterized in that, include: The polarization camera (11) obtains four phase shift images in one exposure. These four phase shift images correspond to polarization directions of 0°, 45°, 90° and 135° respectively. The phase difference and the inclination angle are calculated from these four phase shift images, and then the magnitude and direction of the stress in the whole field are calculated.

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