CN110988002A - Rapid imaging method for microcracks of damaged section of foreign object based on image recognition - Google Patents
Rapid imaging method for microcracks of damaged section of foreign object based on image recognition Download PDFInfo
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- CN110988002A CN110988002A CN201911179182.2A CN201911179182A CN110988002A CN 110988002 A CN110988002 A CN 110988002A CN 201911179182 A CN201911179182 A CN 201911179182A CN 110988002 A CN110988002 A CN 110988002A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/2202—Preparing specimens therefor
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V10/00—Arrangements for image or video recognition or understanding
- G06V10/40—Extraction of image or video features
- G06V10/46—Descriptors for shape, contour or point-related descriptors, e.g. scale invariant feature transform [SIFT] or bags of words [BoW]; Salient regional features
- G06V10/462—Salient features, e.g. scale invariant feature transforms [SIFT]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V20/00—Scenes; Scene-specific elements
- G06V20/20—Scenes; Scene-specific elements in augmented reality scenes
Abstract
The invention relates to a method for quickly imaging microcracks on a damaged section of a foreign object based on image recognition. The FOD damage is prefabricated by an air shot method, the FOD position of a damaged blade is longitudinally cut to obtain a microcrack observation sample piece at the FOD position, a scanning electron microscope is used for observing the sample piece, and a microscopic image with microcracks is shot. And obtaining coordinate values of pixel points corresponding to the microcrack features by using an image recognition technology, drawing a spline curve in the shape of the microcrack according to the coordinate values by using a Matlab compiler, and providing a technical means for obtaining microcracks in different states and establishing an FOD gap model containing the microcracks.
Description
Technical Field
The invention belongs to the technical field of damage analysis of blades of an aircraft engine.
Background
The aircraft engine has extremely high rotating speed, the front end of the engine in operation is like a huge air extractor, and the airplane often sucks 'hard objects' such as stones, gravels, bolts, metal fragments and the like in the taking-off and landing process of a runway or an aircraft carrier deck, and the foreign objects enter the engine and impact the front stages of compressor blades, particularly the front edges of the blades, to cause damage. The standard of US military standard MIL-E-5007D, US military standard GJB242-87 and JGS-87231A and the like refers to Damage caused by hard objects such as metal, sand and stone impacting an engine as Foreign Object Damage (FOD for short, Foreign Object Damage), the relative speed of the typical millimeter-sized Foreign objects such as stones, sand and the like and the blades of the engine compressor can reach 100m/s-350m/s, if the damaged blades are not found and treated in time, fatigue fracture failure can occur under high-frequency vibration, and the broken blades can penetrate through a casing and even Damage the blades of the compressor of later stages, so that serious flight accidents are caused.
Compared with a smooth blade, impact damage of the type of forming a notch, tearing and the like on a damaged position of the blade with the FOD macroscopically can have stress concentration phenomena of different degrees, so that the damaged position can bear larger centrifugal force and vibration stress load under a service condition, and the FOD position is more prone to fatigue failure. In order to research the influence of damage on the fatigue performance of the blade, the scholars in China prefabricate semicircular notches with the same depth on the front edges of the same blades by using two methods of machining and steel ball impact of air cannons, and perform a high-cycle fatigue strength test, and the result shows that the fatigue strength of the impact notches of the air cannons has higher dispersity, and the fatigue strength of the machining notches is higher than that of the notches obtained by the impact of the air cannons. The harm of FOD to blade fatigue strength is not solely dependent on stress concentration from macroscopic damage.
The external hard object impacts the front edge of the blade at a high speed, so that the loss, accumulation and layering of materials at the damaged position can be caused, and micro damage such as microcracks, shearing dimples, heat insulation shearing bands and the like can also be caused. Of these micro-damage, microcracks are a very specific phenomenon, and microcracks generated by impact can directly propagate to become the source of fatigue cracks, and the damage to the fatigue performance of the blade is the greatest. However, no means for identifying and studying microcracks is given in the prior art.
Therefore, a new technical solution is needed to solve the above problems.
Disclosure of Invention
In order to solve the problems, the invention discloses a method for quickly imaging microcracks on a damaged section of a foreign object based on image recognition, which solves the problem how to quickly image microcracks caused by FOD damage in an aircraft engine blade FOD test.
In order to achieve the purpose, the invention adopts the following technical scheme:
a fast imaging method for microcracks of damage sections of foreign objects based on image recognition is characterized by comprising the following steps:
(1) the FOD damage is prefabricated on the front edge of the blade of the aero-engine by using an air cannon method, namely, the FOD damage is caused by the fact that shot is shot by the air cannon to impact the front edge of a test piece of the blade of the aero-engine; the FOD damage area of the aeroengine blade test piece is an FOD area;
(2) acquiring a microcrack observation sample piece at the FOD position by adopting a method of longitudinally sectioning the FOD area; the cutting starting point of the longitudinal cutting FOD is the bottom of the recess in the FOD area, and the FOD is longitudinally cut from the cutting starting point to the entity position of the test piece;
(3) observing the microcrack observation sample prepared in the step (2) and shooting a microscopic image with microcracks;
(4) and identifying the image to obtain a microcrack coordinate point set, which comprises the following steps:
(4.1) pretreatment: denoising and smoothing the read-in image to strengthen important characteristics of the image;
(4.2) obtaining and converting information: reading in the preprocessed micro-crack microscopic image, and acquiring the gray value of a pixel point in the image;
(4.3) feature extraction and classification decision: extracting all pixel points corresponding to the microcrack characteristic according to the difference of the gray values of the pixel points corresponding to the microcracks;
and (4.4) establishing a plane coordinate system by taking the pixel points of the sectioning starting point as the origin of coordinates, and extracting coordinates of all the pixel points corresponding to the microcrack characteristic.
And (4.5) picking up the coordinate point set extracted in the step (4.4) and drawing a microcrack graph.
Compared with the prior art, the invention has the following beneficial effects:
the FOD damage is prefabricated by an air shot method, the FOD position of a damaged blade is longitudinally cut, a microcrack observation sample piece at the FOD position is obtained, and a microscopic image with microcracks is photographed. The image recognition technology is utilized to obtain the coordinate value of the pixel point corresponding to the microcrack feature, the software compiling program is utilized to draw the spline curve in the microcrack shape according to the coordinate value, and a technical means is provided for obtaining microcracks in different states and establishing an FOD gap model containing microcracks.
Drawings
FIG. 1 is a flow chart of a method for rapidly imaging microcracks on a damaged section of a foreign object based on image recognition.
FIG. 2 is a schematic view of a cutting direction in a method of cutting FOD region longitudinally.
Detailed Description
Referring to fig. 1, the present invention discloses a method for rapidly imaging a microcrack on a damaged section of a foreign object based on image recognition, which includes the following steps:
(1) and damaging the FOD prefabricated at the front edge of the blade of the aircraft engine by using an air cannon method. Typical microscopic damage characteristics of damage of an aircraft engine foreign object during microcracking, an air cannon method is a method which is closest to damage caused by a real foreign object impacting a blade under a laboratory condition, the basic structure of the air cannon can refer to the Chinese patent application with the publication number of 110160728A or the Chinese patent with the publication number of 103512423B, and the air cannon comprises a speed measuring device, an air cylinder, a cannon barrel connected with the air cylinder and a bullet holder positioned in the cannon barrel, wherein a bullet is positioned in the bullet holder; the tested aeroengine blade test piece is opposite to the gun barrel. Also, a guard may be employed around the aero-engine blade test pieces. In the air cannon, steel balls are generally used for simulating foreign objects sucked by the aircraft engine, and in the launching process, a valve is opened to release gas in a cylinder to push the loaded foreign objects to move in a cannon barrel in an accelerating manner, so that the front edge of a blade test piece of the aircraft engine is impacted, and FOD damage is caused. The area of the test piece of the aircraft engine blade having FOD damage is the FOD area.
(2) In combination with fig. 2, due to the material defect at the damage position caused by the impact, the microcracks are mostly generated at the bottom of the impact gap, and in order to observe the complete appearance of the microcracks, in this embodiment, a method of longitudinally sectioning the FOD region is adopted to obtain a microcrack observation sample at the FOD position; the cutting starting point of the longitudinal cutting FOD is the bottom of the recess in the FOD area, and the FOD is longitudinally cut from the cutting starting point to the entity position of the test piece.
(3) And observing the microcrack observation sample prepared in the step (2) and shooting a microscopic image with the microcrack. The Scanning Electron Microscope (SEM) is a scientific research instrument widely used in current scientific research, has the advantages of high magnification, large depth of field, simple sample preparation and the like, and is a main means of microscopic imaging of materials at present, so in this embodiment, a microscopic image with microcracks is photographed by using the SEM.
(4) And identifying the image to obtain a microcrack coordinate point set, which comprises the following steps:
(4.1) pretreatment: denoising and smoothing the read-in image to strengthen important characteristics of the image;
(4.2) obtaining and converting information: reading in the preprocessed micro-crack microscopic image, and acquiring the gray value of a pixel point in the image;
(4.3) feature extraction and classification decision: extracting all pixel points corresponding to the microcrack characteristic according to the difference of the gray values of the pixel points corresponding to the microcracks;
and (4.4) establishing a plane coordinate system by taking the pixel points of the sectioning starting point as the origin of coordinates, and extracting coordinates of all the pixel points corresponding to the microcrack characteristic.
And (4.5) picking up the coordinate point set extracted in the step (4.4), importing the coordinate point set into a compiler in Matlab software, drawing a microcrack graph, and establishing an FOD notch model containing microcracks.
Through the steps, a microcrack pattern in the FOD area of the aircraft engine blade test piece is finally obtained.
In addition, the present invention has many specific implementations and ways, and the above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.
Claims (5)
1. A fast imaging method for microcracks of damage sections of foreign objects based on image recognition is characterized by comprising the following steps:
(1) the FOD damage is prefabricated on the front edge of the blade of the aero-engine by using an air cannon method, namely, the FOD damage is caused by the fact that shot is shot by the air cannon to impact the front edge of a test piece of the blade of the aero-engine; the FOD damage area of the aeroengine blade test piece is an FOD area;
(2) acquiring a microcrack observation sample piece at the FOD position by adopting a method of longitudinally sectioning the FOD area; the cutting starting point of the longitudinal cutting FOD is the bottom of the recess in the FOD area, and the FOD is longitudinally cut from the cutting starting point to the entity position of the test piece;
(3) observing the microcrack observation sample prepared in the step (2) and shooting a microscopic image with microcracks;
(4) and identifying the image to obtain a microcrack coordinate point set, which comprises the following steps:
(4.1) pretreatment: denoising and smoothing the read-in image to strengthen important characteristics of the image;
(4.2) obtaining and converting information: reading in the preprocessed micro-crack microscopic image, and acquiring the gray value of a pixel point in the image;
(4.3) feature extraction and classification decision: extracting all pixel points corresponding to the microcrack characteristic according to the difference of the gray values of the pixel points corresponding to the microcracks;
(4.4) establishing a plane coordinate system by taking the pixel points of the sectioning starting point as the origin of coordinates, and extracting coordinates of all the pixel points corresponding to the microcrack characteristic;
and (4.5) picking up the coordinate point set extracted in the step (4.4) and drawing a microcrack graph.
2. The method for rapidly imaging the microcracks on the damaged section of the foreign object according to claim 1, wherein in the step (1), the adopted air cannon comprises a speed measuring device, an air cylinder, a cannon barrel connected with the air cylinder and a bullet support positioned in the cannon barrel, wherein the bullet is positioned in the bullet support; the tested aeroengine blade test piece is opposite to the gun barrel.
3. The method for rapidly imaging the microcracks on the damaged section of the foreign object according to claim 2, wherein in the step (1), a protective device is adopted to surround the aircraft engine blade test piece.
4. The method for rapidly imaging the microcracks on the damaged sections of the foreign objects according to the claim 1, the claim 2 or the claim 3, wherein in the step (3), a microscopic image with the microcracks is shot by using a scanning electron microscope.
5. The fast imaging method for microcracks on the damage section of a foreign object according to claim 1, 2 or 3, wherein in the step (4.5), the set of coordinate points is imported into a compiler in Matlab software and a microcrack map is drawn.
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| CN201911179182.2A CN110988002A (en) | 2019-11-27 | 2019-11-27 | Rapid imaging method for microcracks of damaged section of foreign object based on image recognition |
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Cited By (1)
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| CN115077832A (en) * | 2022-07-28 | 2022-09-20 | 西安交通大学 | Method for measuring vibration fatigue damage of three-dimensional surface of high-temperature-resistant component of airplane |
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