Digital image correlation for test bench

Abstract

The present invention relates to a burst test bench (0) for a turbomachine component (1), comprising: - a cylindrical tank (3) in which a shaft (2) is mounted for rotation, configured to drive the component (1) in rotation when the component (1) is fixed to the shaft (2); - an image acquisition device (4) configured to acquire images of the component (1); - a lighting device (6) disposed in the tank (3), the lighting device (6) being configured to illuminate the component (1); - a processing unit (8) configured to control the simultaneous acquisition of images of the component (1) and the illumination of the component (1) and to perform correlation processing of the acquired images with a reference image of the component (1) showing the component before a test, in order to measure deformations of the component (1) during the test. Figure for the abstract: Fig. 1

Description

Title of the invention: Digital image correlation for test bench Technical field

[0001] The present application relates to the control of the conformity of rotating mechanical parts, in particular rotating parts constituting a turbomachine. It relates more specifically to a test bench for such control. STATE OF THE ART

[0002] Checking the conformity of mechanical components to specifications requires the use of test benches allowing the parts to be subjected to mechanical and physical stresses generally much higher than those of normal operating conditions.

[0003] For example, in the aeronautical field, the design of turbomachines requires increasingly precise prediction of the service life of the parts that compose them. The overspeed resistance of rotating parts of turbines, such as disks, is an important step in the design of new engines. Furthermore, the regulations require the demonstration during tests on a test bench that the parts in question do not burst under the effect of centrifugal loading, and this for speeds generally at least 20% higher than the maximum operating conditions. These tests aim to evaluate a burst speed and temperature of the rotating disks, by subjecting them to an increasing rotation speed and high temperatures, similar to those of real operating conditions, until the disk bursts.

[0004] Such test benches comprise a cylindrical tank in which displacement sensors are placed and an image acquisition device whose role is to monitor the behavior of the disc during the test, in order to improve the understanding of the phenomena which precede the bursting of the disc. In particular, the image acquisition device makes it possible to locate the primary rupture zone, that is to say the zone where the bursting begins.

[0005] The image acquisition devices used for this purpose are coupled to recording devices and lighting devices, generally LED light projectors.

[0006] The displacement sensors are generally non-contact sensors, for example laser sensors. One part of the displacement sensors has the function of measuring the displacement or swelling of the periphery of the disc, while another part measures the displacement of the bore in the center of the disc. A To this end, the displacement sensors are carried by a frame fixed to the top of the inside of the test bench tank and surrounding the disc. To limit vibrations, the frame is made of large-section steel plates and rods. The frame comprises an annular assembly, which surrounds the disc and carries the displacement sensors of the disc periphery and a crossbar passing under the disc, vertical to the disc bore, which carries the displacement sensors measuring the displacement of the disc bore.

[0007] However, these test benches suffer from numerous problems. In particular, the displacement sensors are point sensors positioned perpendicular to their measurement point. Consequently, the measurement of the displacement sensors is a measurement of displacement along the axis of the normal of the disk. Since the disk is rotating, the measurement is also carried out on the entire circumference of the disk. However, particularly in the case of the periphery of the disk, this surface is not always axisymmetrical, in particular when the disk is equipped with dummy blades to increase the realism of the test. In this case, the measurements of such displacement sensors are unusable, because of the significant differences in axial length caused by the dummy blades. In other cases, the measurement of the displacement sensors is still limited to a single direction and therefore does not allow local deformations on the disk to be measured.

[0008] Furthermore, the frame carrying the displacement sensors can distort the results of the macroscopic and microscopic expertises which are carried out on the rupture surfaces of the disc after bursting. Indeed, the plates and rods constituting it are potential obstacles to the projected fragments of the disc. An impact between a fragment and the frame would deteriorate the rupture surface and distort the analysis of the metallurgical structure of the fragment. To avoid this, the frame must be dismantled before carrying out the burst test, during which the disc reaches the theoretical burst speed. Consequently, since the displacement sensors are fixed to the frame, the swelling of the disc is not monitored until bursting. Conversely, bursting may occur before the theoretical burst speed is reached.In this case, the frame also constitutes a visual obstacle to the image acquisition device because of the crossbar carrying the disk bore displacement sensors.

[0009] Furthermore, the displacement sensors do not withstand the temperatures necessary to reproduce the actual operating conditions of the disc, which are of the order of several hundred degrees. These temperatures are reached by the action of an inductive or radiative furnace arranged circumferentially around the rim of the disc, that is to say in the space occupied by the frame during the first test, which consequently only concerns the speed resistance of the disc.

[0010] These problems are the causes of many additional manipulations on the test bench, which lengthen and complicate the tests while increasing the risk of damaging the disk under test. The need to carry out at least two tests, during which the metrics acquired and the stresses undergone by the disk are different, constitutes a major obstacle to obtaining reliable results representative of the behavior of the component in real conditions. Statement of the invention

[0011] An aim of the present application is to remedy the aforementioned drawbacks.

[0012] For this purpose, according to a first aspect of the invention, a test bench is proposed bursting of a turbomachine component comprising:

[0013] - a cylindrical tank in which is mounted in rotation a shaft extending according to an axis, the shaft being configured to rotate the component when the component is secured to the shaft;

[0014] - an image acquisition device arranged in the tank, the acquisition device of images being configured to acquire images of the component at a rate greater than 5,000 images per second;

[0015] - a lighting device arranged in the tank, the lighting device being configured to illuminate the component;

[0016] - a processing unit configured to, during rotation of the component, to control the acquisition of images of the component and the illumination of the component simultaneously and to implement a correlation processing of the acquired images with a reference image of the component showing the component before a test to measure deformations of the component during the test.

[0017] The test bench according to the invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations: - the image acquisition device is configured to acquire images of the component at a rate greater than 1,000,000 images per second; - the external surface of the component comprises random patterns, the processing unit being configured to follow the evolution of the shape of the random patterns during the test to measure the deformations of the component; - the image acquisition device is configured to acquire a first image according to a first viewing angle and a second image according to a second viewing angle different from the first viewing angle, the first and second viewing angles partially overlapping and the processing unit being configured to implement before the correlation processing a step of obtaining a plurality of 3D images from the images acquired according to the first and second viewing angles, the correlation processing being implemented between the obtained 3D images and a reference 3D image; - the image acquisition device comprises a first image acquisition unit configured to acquire images according to the first viewing angle and a second image acquisition unit configured to acquire images according to the second viewing angle; - the image acquisition device comprises a first image acquisition unit, the test bench comprising an optical device configured to capture light beams from the illuminated component at two different viewing angles and direct them towards the acquisition unit, the processing unit being configured to obtain, from the acquired beams, a first image at the first viewing angle and a second image at the second viewing angle; - the optical device comprises a first mirror arranged to capture, according to the first viewing angle, light beams coming from the component, a second mirror arranged to capture, according to the second viewing angle, light beams coming from the component, the optical device further comprising an optical recombination device; - the tank comprises an openwork bottom and an openwork ceiling, the first image acquisition unit being placed beyond one of the bottom and the ceiling, the image acquisition device preferably comprising another image acquisition unit placed beyond the other of the bottom or the ceiling beyond which the first image acquisition unit is placed; - the tank comprises an openwork bottom and an openwork ceiling, at least one image acquisition unit being placed beyond one of the bottom and the ceiling, the other comprising at least one mirror positioned so as to reflect, in a viewing angle of the image acquisition unit, the image of a surface of the component;

[0018] The invention also relates to a method for testing a component in a test bench according to the invention, comprising the following steps:

[0019] - marking the component with random patterns;

[0020] - securing the rotating component to the shaft;

[0021] - acquisition, by the image acquisition device, of a reference image of the component ;

[0022] - rotating the component by the shaft;

[0023] - illumination by the lighting device of the rotating component;

[0024] - acquisition of images of the rotating component by the acquisition device of images;

[0025] - correlation processing of the images of the rotating component acquired with the reference image of the component to follow an evolution of the shape of the random patterns;

[0026] - analysis of the deformations of the component during the test.

[0027] The method of testing a component is advantageously completed by the following steps, taken alone or in any of their technically possible combinations:

[0028] - obtaining three-dimensional images of the component from acquired images from two different shooting angles;

[0029] - obtaining a first image according to the first shooting angle and a second image according to the second shooting angle from an image captured by the image acquisition device through the optical device.

[0030] Finally, the turbomachine component may be a turbomachine disk. DESCRIPTION OF FIGURES

[0031] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0032] [Fig.l] is a schematic view in vertical section of a test bench according to one embodiment of the invention;

[0033] [Fig.2] is a diagram showing the digital correlation of two images of a component according to one embodiment of the invention;

[0034] [Fig. 3] is a schematic view in vertical section of a test bench according to another embodiment of the invention;

[0035] [Fig.4] is a schematic horizontal sectional view of a test bench according to one embodiment of the invention;

[0036] [Fig.5] is a diagram showing the digital correlation of two images of a component according to one embodiment of the invention;

[0037] [Fig.6] is a schematic view in vertical section of a test bench according to another embodiment of the invention;

[0038] [Fig.7] is a schematic view in vertical section of a test bench according to another embodiment of the invention;

[0039] [Fig.8] is a schematic horizontal sectional view of a test bench according to another embodiment of the invention;

[0040] [Fig.9] is a diagram showing the steps of a method for implementing an embodiment of the invention.

[0041] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0042] In what follows, as illustrated in [Fig.l], we are more particularly in the context of a test bench 0 for bursting a component 1 in which the component 1 is a turbomachine disk, but any other component 1 is conceivable. A shaft 2 configured to rotate the component 1 is placed in the center of the test bench 0 and the component 1 is attached thereto by means adapted so that its center is aligned with the axis of rotation A of the shaft 2. A cylindrical tank 3 isolating the test bench 0 from its environment contains the shaft 2 and the component 1, the shaft 2 extending from one of the bases of the tank 3. The tank 3 also comprises a bottom 31, corresponding to a base of the cylinder opposite the ceiling 32, which is the base of the tank 3 comprising the shaft 2. The component 1 is marked prior to the test in a random and permanent manner, that is to say that the surface of the component 1 comprises irregular patterns 11, each pattern 11 being unique.The patterns 11 are visible and preferably of a color different from the color of the component 1.

[0043] The axial direction corresponds to the direction of the axis A and a radial direction is a direction perpendicular to this axis and passing through it. Furthermore, the circumferential (or lateral) direction corresponds to a direction perpendicular to the axis A and not passing through it. Unless otherwise specified, internal (respectively, inside) and external (respectively, outside), respectively, are used with reference to a radial direction such that the internal part or face of an element is closer to the axis A than the external part or face of the same element.

[0044] Outside the tank 3 is arranged an image acquisition device 4 configured to acquire images of the component 1. The component 1 being rotated at high speeds, the image acquisition device 4 consequently has a high acquisition frequency, greater than 5,000 images per second. For example, the image acquisition device 4 comprises a so-called “high speed” or “fast” camera, that is to say that the image acquisition device 4 has an acquisition frequency preferably of at least 10,000 images per second, even more preferably of several hundred thousand images per second, for example 500,000 images per second or ideally more than 1,000,000 images per second. To be protected from fragments projected by the bursting of the component 1, the image acquisition device 4 is advantageously placed behind a transparent and shatter-resistant porthole 5a.The image acquisition device 4 is preferably placed beyond the bottom 31 of the tank 3, so that the viewing angle of the image acquisition device 4 on the component 1 is as wide as possible and includes at least one critical zone of the component 1, which in the case of a turbomachine disk can be the central bore, the web, the cell or other parts depending on the . type of turbomachine disk. Preferably, the viewing angle of the image acquisition device 4 on the component 1 comprises several critical zones of the component 1. The bottom 31 is then perforated. By perforated, it is meant that the bottom 31 comprises orifices adapted so as not to obstruct the view of the acquisition device 4. By viewing angle, we mean the angle formed in an axial plane by the optical axis of the image acquisition device 4 and the axis A. Optionally, the image acquisition device 4 comprises one or more image acquisition units 41, 42 placed so as to acquire images of the entirety of an area of ​​interest of the component 1, for example the entirety of the bore of a turbomachine disk.

[0045] Optionally, as illustrated [Fig.6], the ceiling 32 can also be perforated and the image acquisition device 4 then comprises one or more image acquisition units 43, 44 placed beyond the ceiling 32 of the tank 3, so as to acquire images of the surface of the component 1 located outside the viewing angle of the image acquisition units 41, 42.

[0046] Alternatively, with reference to Figures 7 and 8, the image acquisition device 4 additionally comprises, in addition to the image acquisition units 41, 42, one or more image acquisition units 45, 46, all placed beyond the perforated bottom 31 of the tank 3, the ceiling 32 then comprising a set of mirrors 73 positioned so as to reflect, for the image acquisition units 45, 46, the image of the surface of the component 1 located outside the viewing angle of the image acquisition units 41, 42. In other words, the viewing angle of the image acquisition units 45, 46 gives onto the surface of the component 1 facing the ceiling 32 of the tank via the mirrors 73. Such an arrangement allows the observation of deformation over the entire surface of the component 1 without modification of the ceiling of the tank 3.

[0047] The tank 3 constituting a confined space, the test bench 0 comprises a lighting device 6 configured to illuminate the component 1. To be protected from the fragments projected by the bursting of the component 1, the lighting device 6 is preferably placed beyond the bottom 31 of the tank 3 and optionally placed behind a transparent porthole 5b resistant to the fragments of the component 1 projected by its bursting.

[0048] The illumination by the illumination device 6 and the acquisition by the image acquisition device 4 are controlled simultaneously by a processing unit 8. The illumination device 6 illuminates simultaneously with the image acquisition device 4, that is to say that the light is emitted at the time of capturing an image, at the same frequency as the image acquisition frequency. Thus, the illumination device 6 comprises for example a stroboscope illuminating at a lighting frequency respecting an exposure time of the order of 200 nanoseconds, which is the exposure time necessary for an image acquisition device 4, the lighting frequency being synchronized with an acquisition frequency of the image acquisition device 4. The lighting device 6 is preferably placed in a similar manner to the image acquisition device 4 so as to illuminate in the shooting angle.

[0049] With reference to [Fig. 2], the processing unit 8 also implements a correlation processing of the acquired images 101 with a reference image 100 of the component 1 showing the component 1 in a previous state to follow an evolution over time of the shape of the random patterns 11. By following an evolution, it is meant to compare the patterns 11 of an image 101 with the respective patterns 11 of the reference image 100 and to obtain for each pattern 11 displacement distances, rotation angles and relative deformation surfaces. This information makes it possible to measure deformations undergone by the component 1 during the time interval separating the acquisition of the reference image 100 and the acquisition of the image 101 and consequently to measure the deformations undergone by the component 1 during the test.

[0050] Advantageously, as illustrated in Figures 1, 3 and 4, the tank 3 comprises an image acquisition device 4 composed of at least two image acquisition units 41 and 42, configured to acquire images of the component 1 from at least two different shooting angles, that is to say that the acquired images represent at least partially the same area of ​​the component 1 but from a different angle. The image acquisition units 41, 42 then operate simultaneously, the processing unit 8 controlling the capture of an image at the same time. Preferably, there are as many lighting devices 6 as there are image acquisition units 41, 42 placed in the tank 3 to illuminate the component 1, each lighting device 6 also being controlled by the processing unit 8 to expose the component 1 to light so as to allow efficient acquisition of images by the image acquisition devices 4.

[0051] With reference to [Fig. 5], the processing unit 8 is then configured to implement a correlation processing of the images acquired from at least two reference images 200, 300 acquired according to the first and second viewing angles of the component 1 and two other images 201, 301 showing the component 1 according to the first and second viewing angles during the test, after the acquisition of the reference images 200, 300. Prior to the correlation processing, the processing unit 8 obtains a 3D reference image 400 of the component 1 from the reference images 200, 300 acquired according to the first and second viewing angles and a 3D image 401 of the component 1 obtained from the images 201, 301. Finally, the processing unit 8 performs the correlation processing of the images 400, 401 to follow an evolution of the shape of the random patterns 11. The use of more than one image allows a reconstruction of the component 1 observed in three dimensions in the images 400 and 401, which makes it possible to follow the deformations of the component 1 in all directions of space.

[0052] Alternatively, as illustrated [Fig. 3], an optical device 7 is placed between an image acquisition device 4 and the component 1, so as to capture, at two different viewing angles, light beams emitted by the lighting device 6 and reflected on the component 1 to direct them towards the image acquisition unit 41, the beams coming from each viewing angle being distinguishable. The optical device 7 comprises for this purpose a set of planar mirrors, a diffraction grating or a prism and / or any other suitable device to allow the image acquisition device 4 to acquire images of the component 1 at two different viewing angles from the light beams directed by the optical device 7. For example, two planar mirrors 71 direct the light from a lighting device 6 reflected on the component 1 towards a prism 72.The prism 72 then directs the two beams, polarizing them differently, toward the image acquisition device 4. The processing unit 8 is then configured to separate the two images 201, 301 acquired by the image acquisition device 4 by separating them according to their respective polarity. As previously, the processing unit 8 implements a three-dimensional image correlation processing 400, 401 obtained from the reference images 200, 300 and the images 201, 301 to quantify the deformations of the component 1 during the test. The use of a single image acquisition unit 41, in addition to being more economical, considerably simplifies the acquisition of images since it is no longer necessary to synchronize several image acquisition units 41, 42 with each other and possibly with several lighting devices 6.

[0053] With reference to [Fig. 9], the method for testing a component 1 in a test bench 0 according to the invention begins with the marking of the component 1 with random patterns 11, then the component 1 is secured in rotation (step E1) with the shaft 2. Next, the image acquisition device 4 acquires reference images 100, 200, 300 of the component 1 (step E2). The component 1 is then rotated (step E3) by the shaft 2 and illuminated throughout the duration of its rotation by the lighting device 6 (step E4), while simultaneously the image acquisition device 4 acquires images 101, 201, 301 of the component 1 (step E5). The processing unit 8 then implements a correlation processing of the images of the rotating component 1 acquired with a reference image of the component 1 to follow an evolution of the shape of the random patterns 11 (step E8) arranged on the surface of the component 1. It is then possible to analyze the deformations undergone by component 1 during the test (step E9). The test method makes it possible to precisely locate the primary fracture site of component 1. Of course, the steps described can be carried out in any other technically possible order.

[0054] When an optical device 7 is present, the processing unit 8, prior to the correlation processing (step E8), separates the different viewing angles from an image captured by the image acquisition device 4 to obtain two distinct images 201, 301 (step E6). The two images 201, 301 thus obtained are used to obtain a three-dimensional image 401 of the component 1 (step E7). Alternatively, the step of reconstructing a three-dimensional profile can be carried out directly from viewing angles originating from several image acquisition units 41, 42.

[0055] The test bench 0 according to the invention makes it possible to do without displacement sensors and the frame carrying these displacement sensors. The use of image correlation makes it possible to monitor deformations in space, as well as other information on the component 1, throughout the duration of the test and for all fields of vision of the image acquisition devices 4. Finally, an existing test bench requires few structural modifications to be converted into a test bench 1 according to the invention.

Claims

Claims

1. Test bench (0) for bursting a turbomachine component (1) comprising: - a cylindrical tank (3) in which a shaft (2) extending along an axis A is rotatably mounted, the shaft (2) being configured to rotate the component (1) when the component (1) is secured to the shaft (2); - an image acquisition device (4) arranged in the tank (3), the image acquisition device (4) being configured to acquire images of the component (1) at a frequency greater than 5,000 images per second; - a lighting device (6) arranged in the tank (3), the lighting device (6) being configured to illuminate the component (1);- a processing unit (8) configured to, during the rotation of the component (1), control the acquisition of images of the component (1) and the lighting of the component (1) simultaneously and to implement a correlation processing of the acquired images with a reference image of the component (1) showing the component before a test to measure deformations of the component (1) during the test.;

2. A test bench (0) for bursting a component (1) according to claim 1, wherein the image acquisition device (4) is configured to acquire images of the component (1) at a rate greater than 1,000,000 images per second.

3. Test bench (0) for bursting a component (1) according to one of claims 1 or 2, in which the external surface of the component (1) comprises random patterns, the processing unit (8) being configured to follow the evolution of the shape of the random patterns (11) during the test to measure the deformations of the component (1).

4. Test bench (0) for bursting a component (1) according to one of claims 1 to 3, in which the image acquisition device (4) is configured to acquire a first image according to a first viewing angle and a second image according to a second viewing angle different from the first viewing angle, the first and second viewing angles partially overlapping and the processing unit (8) being configured to implement before the correlation processing (step E8) a step of obtaining (step E7) a plurality of 3D images from the images acquired according to the first and second shooting angles, the correlation processing (step E8) being implemented between the 3D images obtained and a reference 3D image.

5. Test bench (0) for bursting a component (1) according to claim 4, wherein the image acquisition device (4) comprises a first image acquisition unit (41) configured to acquire images according to the first viewing angle and a second image acquisition unit (42) configured to acquire images according to the second viewing angle.

6. Test bench (0) for bursting a component (1) according to claim 4, in which the image acquisition device (4) comprises a first image acquisition unit (41), the test bench comprising an optical device (7) configured to capture, according to two different viewing angles, light beams coming from the illuminated component (1) and direct them towards the acquisition unit (4), the processing unit (8) being configured to obtain, from the acquired beams, a first image according to the first viewing angle and a second image according to the second viewing angle.

7. Test bench (0) for bursting a component (1) according to claim 6, in which the optical device (7) comprises a first mirror (71) arranged to capture, according to the first viewing angle, light beams coming from the component (1), a second mirror (71) arranged to capture, according to the second viewing angle, light beams coming from the component (1), the optical device (7) further comprising an optical recombination device (72).

8. Test bench (0) for bursting a component (1) according to one of claims 5 to 7, in which the tank (3) comprises a perforated bottom (31) and a perforated ceiling (32), the first image acquisition unit (41) being placed beyond one of the bottom (31) and the ceiling (32), the image acquisition device (4) preferably comprising another image acquisition unit (43) placed beyond the other of the bottom (31) or the ceiling (32) beyond which the first image acquisition unit (41) is placed.

9. Test bench (0) for bursting a component (1) according to one of claims 5 to 7, in which the tank (3) comprises a perforated bottom (31) and a perforated ceiling (32), at least one image acquisition unit (45) being placed beyond one of the bottom (31) and the ceiling (32), the other comprising at least one mirror (73) positioned so as to reflect, in a viewing angle of the image acquisition unit (45), the image of a surface of the component (1).

10. Method for testing a component (1) in a test bench (0) according to any one of claims 1 to 9, comprising the following steps: - E0 marking the component (1) with random patterns (11); - E1 securing the component (1) in rotation with respect to the shaft (2); - E2 acquisition, by the image acquisition device (4), of a reference image of the component (1); - E3 rotation of the component (1) by the shaft (2); - E4 illumination by the lighting device (6) of the rotating component (1); - E5 acquisition of images of the rotating component (1) by the image acquisition device (4); - E8 correlation processing of the images of the rotating component (1) acquired with the reference image of the component (1) to follow an evolution of the shape of the random patterns (11); - E9 analysis of the deformations of the component (1) during the test.

11. Method for testing a component (1) according to claim 10, comprising between steps E5 and E8, the following step: - E7 obtaining three-dimensional images of the component (1) from images acquired from two different shooting angles.

12. Method for testing a component (1) according to one of claims 10 or 11, comprising between steps E5 and E8, the following step: - E6 obtaining a first image according to the first viewing angle and a second image according to the second viewing angle from an image captured by the image acquisition device (4) through the optical device (7).

13. A method according to any one of claims 10 to 12, wherein the turbomachine component (1) is a turbomachine disk.