FR3133925A1 - Test bench and processes using this test bench - Google Patents

Abstract

Test bench for observing the dynamic behavior in compression of a granular or pasty material, comprising a receptacle (36), having a bottom (54), for receiving the granular or pasty material, a mobile support member (16) in the receptacle (36) and defining, facing the bottom (54), a surface (76) of contact with the granular or pasty material, a stressing device capable of exerting on the support member (16) a support force oriented towards the bottom (54), and a measuring system capable of dynamically measuring the distance from the contact surface (76) to the bottom (54). Figure for abstract: Fig. 3

Description

Test bench and processes using this test bench FIELD OF INVENTION

The present invention relates to a test bench for observing the dynamic compression behavior of a granular or pasty material. It also relates to a method for determining the mechanical characteristics of the particles constituting a granular material by means of such a test bench, and to a method for predicting the wear of an assembly of parts, implementing such a method of determination.

The present invention applies more particularly to the determination of the mechanical characteristics of a third body, in particular with a view to predicting the wear of an assembly between a blade and a turbine or compressor disk, for example within a turbomachine.

BACKGROUND

In many mechanical systems, parts contact each other through non-lubricated contact. This is particularly the case for assemblies of parts, such as turbomachine rotors, in which parts are fitted into one another and held together by the friction forces occurring at their interface. The study of these non-lubricated contacts is essential to be able to predict the wear and therefore the lifespan of these assemblies.

A difficulty in this study arises from the formation, at the level of non-lubricated contacts, of a body, comparable to a granular material, resulting from the degradation of the surfaces in contact. This body is commonly called the “third body”. To be able to predict the wear of an unlubricated contact, it is necessary to know precisely the behavior of this third body, in particular the way in which it interacts with the surfaces in contact, and, for this purpose, to model it. However, this modeling requires knowing certain particular mechanical characteristics of the third body, including the stiffness and cohesion of the particles composing it.

Analysis methods making it possible to determine the mechanical characteristics of the third body are known. They include:

• micro-indentation, which is described in particular in the articles: Kermouche, G., Loubet, JL, Bergheau, JM: “ Extraction of stress–strain curves of elastic–viscoplastic solids using conical/pyramidal indentation testing with application to polymers ”, Mech. Mater. 40, 271–283 (2008); Tumbajoy-Spinel, D., Descartes, S., Bergheau, J.-M., Lacaille, V., Guillonneau, G., Michler, J., Kermouche, G.: “ Assessment of mechanical property gradients after impact-based surface treatment: application to pure α-iron ”, Mater. Sci. Eng. A. 667, 189–198 (2016); Colas, G., Serles, P., Saulot, A., Filleter, T.: “ Strength measurement and rupture mechanisms of a micron thick nanocrystalline MoS 2 coating using AFM based micro-bending tests ”, J. Mech. Phys. Solids. 128, 151–161 (2019);
• scratch tests (better known by their English name “scratch tests”), described in particular in the article Benayoun, S., Hantzpergue, J., Bouteville, A.: “ Micro-scratch test study of TiN films grown on silicon by chemical vapor deposition ”, Thin Solid Films. 389, 187–193 (2001);
• the compression of micropillars (better known by its English name “micropillar compression”), described in particular in the article Schreijäg, S., Kaufmann, D., Wenk, M., Kraft, O., Mönig, R.: “ Size and microstructural effects in the mechanical response of α-Fe and low alloyed steel ”, Acta Mater. 97, 94–104 (2015);
• peeling tests (better known by their English name “peeling tests”), described in particular in the article Peng, T., Yan, Q., Li, G., Zhang, X.: “ The Influence of Cu/Fe Ratio on the Tribological Behavior of Brake Friction ”, Materials. Tribol. Lett. 66, 18 (2018)

However, these analysis methods do not make it possible to determine the stiffness and cohesion of the particles composing the third body.

Thus, today we do not know any method of analysis of the third body making it possible to determine the stiffness and cohesion of the particles composing it. It is therefore today very difficult, if not impossible, to predict the wear of an unlubricated contact.

An objective of the invention is to facilitate the determination of certain mechanical characteristics of the particles composing a third body, for example their stiffness and their cohesion. Another objective is to allow the prediction of the wear of an assembly of parts held together by the friction forces occurring at their interface.

To this end, the subject of the invention is, according to a first aspect, a test bench for observing the dynamic behavior in compression of a granular or pasty material, comprising:

• a receptacle, having a bottom, for receiving the granular or pasty material,
• a movable support member in the receptacle and defining, facing the bottom, a contact surface with the granular or pasty material,
• a stressing device capable of exerting on the support member a support force oriented towards the bottom, and
• a measuring system capable of dynamically measuring the distance from the contact surface to the bottom.

According to particular embodiments of the invention, the test bench also has one or more of the following characteristics, taken in isolation or in any technically possible combination(s):

• the measuring system is also capable of dynamically determining the upper profile of the granular or pasty material received in the receptacle;
• the measuring system comprises at least one camera capable of capturing a dynamic image of the granular or pasty material received in the receptacle and an image processing system capable of processing the dynamic image captured by the camera to determine the distance from the surface contact at the bottom and the upper profile of the granular or pasty material received in the receptacle;
• the receptacle is delimited at least in part by a transparent wall forming an angle with the bottom, the camera being able to capture the dynamic image of the granular or pasty material through said transparent wall;
• the contact surface is rounded, for example in the shape of a portion of a cylinder of revolution or a sphere;
• the support member is movable in translation relative to the receptacle along a first axis substantially orthogonal to the bottom and along a second axis substantially parallel to the bottom;
• the receptacle is constituted by a groove delimited by two side walls, the contact surface having a width substantially equal to that of the groove;
• the groove has a width of less than two millimeters, preferably less than 1.1 millimeters;
• the support member is movable in translation relative to the receptacle along two axes included in a plane parallel to the side walls of the groove; And
• each side wall has a face, oriented towards the groove, substantially devoid of roughness.

The invention also relates, according to a second aspect, to a method for determining the mechanical characteristics of the particles constituting a granular material tested, comprising the following steps:

• inserting a sample of the granular material tested into the receptacle of a test bench according to the first aspect, so as to form in the receptacle a pile of granular material tested,
• positioning the support member so that it is flush with a top of the pile of granular material tested,
• increase in the support force exerted on the support member by the stressing device with observation of the dynamic behavior of the pile of granular material tested by means of the measuring system,
• use of modeling software to model the dynamic behavior of a pile of fictitious granular material subjected to uniaxial compression, the mechanical characteristics of the particles constituting the fictitious granular material being modified until the modeled dynamic behavior is at most close to the observed dynamic behavior,
• definition of the mechanical characteristics of the particles constituting the granular material tested as being equal to the mechanical characteristics of the particles constituting the fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the observed dynamic behavior.

According to particular embodiments of the invention, the determination method also has one or more of the following characteristics, taken in isolation or according to any technically possible combination(s):

• the observation of the dynamic behavior includes a dynamic measurement of the distance from the contact surface to the bottom and the dynamic determination of the upper profile of the pile of granular material tested;
• the granular material tested has a particle size of between 0.1 µm and 100 µm;
• the granular material tested consists of a third body;

- the method includes a preliminary step of taking the sample of the granular material tested at the interface between two first bodies in contact with each other;

• the method comprises the following additional step:
  • application of a shear force between the support member and the receptacle simultaneously with the observation of the dynamic behavior of the pile of granular material tested by means of the measuring system,

the modeling software also being used to model the two-dimensional behavior of the pile of fictitious granular material when subjected to a shear force substantially orthogonal to the direction of the compressive force, the mechanical characteristics of the particles constituting the fictitious granular material being modified until the modeled dynamic behavior is as close as possible to the observed dynamic behavior,

the mechanical characteristics of the particles constituting the granular material tested being defined as equal to the mechanical characteristics of the particles constituting the fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the dynamic behavior observed both for the behavior in compression and for the shear behavior; And

• the mechanical characteristics determined include the stiffness and/or cohesion of the particles.

The invention also relates, according to a third aspect, to a method for predicting the wear of an assembly of parts, comprising the following steps:

• production of a prototype of the assembly of parts,
• aging of the prototype,
• taking a sample of the third body at the interface between parts of the prototype,
• determination of mechanical characteristics of the particles composing this third body by means of a determination method according to the second aspect, and
• modeling the behavior of the assembly of parts using the mechanical characteristics of the particles of the third body determined in the previous step.

According to a particular embodiment of the invention, the prediction method also has the following characteristic:

• the assembly of parts comprises a blade with a blade and a root and a turbomachine rotor disk defining a cell in which the foot is received.

Brief description of FIGURES

Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

• there is a front view of a test bench according to the invention;
• there is a side view of the test bench of the ;
• there is a cross-sectional view of a detail marked III of the ;
• there is a longitudinal sectional view of a support member of the test bench of the ;
• there is a side view of a detail marked V of the , a third body sample being received in a sample holder of the test bench;
• there is a diagram illustrating a method for determining the mechanical characteristics of the particles constituting a third body using the test bench of the ;
• there is a diagram illustrating a method for predicting the wear of an assembly of parts implementing the method for determining the ; And
• there is an exploded perspective view of an assembly of parts subject to the method of predicting the .

DETAILED DESCRIPTION OF THE INVENTION

The test bench 10 shown in Figures 1 and 2 is configured to observe the dynamic behavior in compression of a granular or pasty material.

It comprises a frame 12, a sample holder 14 intended to receive a sample 15 ( ) of the granular or pasty material, a support member 16 intended to press on the sample 15 of granular or pasty material, a stressing device 18 capable of exerting a support force on the support member 16 , and a measurement system 20.

In the following, the orientation terms are understood with reference to an orthogonal marker represented in the Figures, comprising:

• a longitudinal direction X extending from the rear to the front,
• a transverse direction Y extending from right to left and defining with the longitudinal direction X a horizontal plane, and
• a vertical direction Z extending from bottom to top.

In reference to the , the frame 12 comprises a foot 22, substantially horizontal, and an upright 24 substantially vertical.

In the example shown, the foot 22 is constituted by a substantially flat plate.

The upright 24 extends vertically upwards from the foot 22. It is here eccentric longitudinally towards the rear relative to the foot 22. It is also centered laterally relative to the foot 22.

In the example shown, the frame 12 also includes two protuberances 26 each projecting forward from a front face 28 of the upright 24. These protuberances 26 are at a distance from the foot 22 and spaced laterally from one another. Each protuberance 26 is here formed by a bar 30 of a bracket 32 fixed to the front face 28 of the upright 24.

In reference to the , the sample holder 14 is mounted on the foot 22. In particular, the sample holder 14 is mounted on a platform 33 arranged on an upper face 34 of the foot 22.

The sample holder 14 includes a receptacle 36 for receiving the sample 15 of granular or pasty material.

In the example shown, the receptacle 36 is constituted by a groove 42 delimited by two opposite side walls 40 of the sample holder 14. Here, these walls 40 are each substantially longitudinal and spaced laterally from one another, the groove 42 being substantially longitudinal.

Each wall 40 has a flat face 44 oriented towards the groove 42. This flat face 44 is preferably substantially devoid of roughness, that is to say that it has a roughness characterized by a lower arithmetic mean deviation (Ra). at 0.5 µm, ideally less than 0.05 µm.

The flat face 44 of each wall 40 is substantially parallel to the flat face 44 of the other wall 40. Thus, the groove 42 is substantially flat. It has a width, constituted by the distance between the walls 40, less than two millimeters, preferably less than 1.1 millimeters.

Preferably, at least one of the walls 40 is constituted by a transparent wall 45. Advantageously, each of the walls 40 is constituted by a transparent wall 45.

In the example shown, each wall 40 is made up of a flat blade 46. For at least one of the walls 40, this blade 46 is preferably made of sapphire. This makes it possible to have, at a lower cost, a strictly flat blade, the surface of which is noticeably devoid of roughness, and which is also transparent.

Each blade 46 is received in a cavity 48 of a support 50 of the sample holder 14, said blade 46 partly projecting out of the cavity 48.

The receptacle 36 includes a flat bottom 54. Here, this bottom 54 is delimited by a wedge 52 of the sample holder 14 interposed between the blades 46, in the cavity 48. This wedge 52 is for example made of steel.

The support 50 comprises a body 51 defining the cavity 48 and a clamping member for pressing the blades 46 against the wedge 52. This clamping member is here constituted by a vice comprising a first jaw 56 and a second jaw 58 movable one relative to the other. In the example shown, the first jaw 56 is constituted by a wall 60 of the cavity 48 and the second jaw 58 is constituted by a plate 62 movable in the cavity 48. The vice also includes screws 64 each bearing against the movable plate 62. Each screw 64 is engaged in a respective through-tapped hole (not shown) provided in the body 51 and opening into the cavity 48 and into an external face 66 of the body 51.

As a variant (not shown), the clamping member does not have a movable plate 62, the screws 64 then pressing directly against one of the blades 46. The movable plate 62 is nevertheless preferred when the blade 46 located on the side of the screws 64 is made of sapphire, in order to prevent the blade 46 from splitting under the effect of the pressure of the screws 64.

The elements delimiting the receptacle 36, that is to say, in the example shown, the side walls 40 and the wedge 52, are rigid, that is to say that each of these elements has a module of Young, measured using the ISO standard applicable to the type of material composing it, greater than 220 GPa. These elements are also hard, that is to say that each has a Rockwell hardness, measured using the ISO 6508-1 standard, greater than 50 HRC.

In reference to the , the support member 16 here comprises a flat blade 70. This blade 70 includes two large flat faces 72 ( ), substantially parallel to each other, and a slice 74 connecting said flat faces 72. It is at least partly engaged in the groove 42. The portion of the slice 74 facing the bottom 54 has a surface 76 of contact with granular or pasty material.

The blade 70 is rigid, that is to say it has a Young's modulus, measured using the ISO standard applicable to the type of material it is composed of, greater than 220 GPa. It is also hard, that is to say it has a Rockwell hardness, measured using the ISO 6508-1 standard, greater than 50 HRC.

The blade 70 is oriented in the longitudinal direction X.

The blade 70 has a thickness substantially equal to, although less than, the width of the groove 42. Typically, the ratio between the thickness of the blade 70 and the width of the groove 42 is between 98% and 99.99% . The width of the contact surface 76 is equal to this thickness. Thus, the contact surface 76 has a width substantially equal to, although less than, the width of the groove 42.

The contact surface 76 is preferably rounded. In the example shown, it is in the shape of a portion of a cylinder of revolution. This makes it easy to control the relative positioning of the contact surface 76 and the bottom 54 and gives great reproducibility to the tests carried out on the test bench 10. Alternatively, the contact surface 76 is flat or formed from a juxtaposition flat and curved surfaces.

The blade 70 is typically made of sapphire.

In reference to the , the support member 16 also comprises a support 80 connecting the blade 70 to the stressing device 18. This support 80 comprises a body 82 and a wedge 84.

As visible on the , the body 82 defines a housing 85 in which the blade 70 is received. This housing 85 opens into a lower face 86 of the body 82 through an opening 88. It has a bottom 90 opposite the opening 88 and is closed on the one of its lateral sides by a wall 91. The wall 91 is preferably substantially flat and vertical.

In the example shown, the housing 85 is open on its side opposite the wall 91, so that it opens entirely, that is to say from the opening 88 to the bottom 90, into a side face 92 ( ) of body 82.

The blade 70 rests against the bottom 90 and projects out of the housing 85 through the opening 88.

In the example shown, the bottom 90 is V-shaped flaring towards the opening 88. This makes it easier to position the blade 70 in the housing 85 when it is, as here, cylindrical, the blade 70 then coming to rest against the bottom 90 at two support points, which allows good transmission of vertical forces between the support 80 and the blade 70.

The housing 85 has a width, taken in the transverse direction Y, less than the thickness of the blade 70. Preferably, the width of the housing 85 is slightly less than the thickness of the blade 70, that is to say say that the ratio of the width of the housing 85 to the thickness of the blade 70 is greater than 90%. Thus, when one of the large faces 72 of the blade 70 rests against the wall 91, a part of the blade 70 projects out of the housing 85 relative to the side face 92.

The body 82 is rigid, that is to say it has a Young's modulus, measured using the ISO standard applicable to the type of material composing it, greater than 220 GPa. It is also hard, that is to say it has a Rockwell hardness, measured using the ISO 6508-1 standard, greater than 50 HRC. It is typically made of steel.

Back to the , the wedge 84 rests against a large face 72 of the blade 70, on the side of the lateral face 92 of the body 82. In other words, the wedge 84 rests against the large face 72 of the opposite blade 70 to that which rests against the wall 91. At least one screw 94, in the example shown several screws 94, engaged through the wedge 84 and screwed into a threaded hole (not shown) in the body 82, maintains (maintains) the wedge 84 tight against the blade 70. Thus, the blade 70 is held in a vice between the wedge 84 and the body 82, which ensures good retention of the blade 70 in the support 80.

The support 80 is integral with the stressing device 18. In the example shown, it is embedded in a plate 95 of the stressing device 18. For this purpose, the support 80 here comprises a ring 96 surmounting the body 82 This crown 96 defines a radial shoulder 98, oriented downwards, at its junction with the body 82. This radial shoulder 98 bears against an annular stop 100 defined by the plate 95, this annular stop 100 surrounding a through orifice 102 through which the body 82 extends.

In the example shown, the crown 96 came from one piece with the body 82.

Returning to Figures 1 and 2, the stressing device 18 comprises, in addition to the plate 95, a force generator 110 capable of producing the support force.

In the example shown, this force generator 110 is constituted by a gravity loading device 112, arranged above the movable member 16. This gravity loading device 112 comprises a receiving member 114 capable of receiving at least a mass 116, and a transfer member 118 capable of transferring at least part of the weight of the mass(es) 116 onto the support member 16. The force generator 110 is thus simple and inexpensive.

The receiving member 114 is preferably, as shown, located vertically to the movable member 16.

In the example shown, the receiving member 114 is suitable for receiving masses 116 made up of cast iron bodybuilding discs. For this purpose, the receiving member 114 is formed of a stop 120 surmounted by a substantially vertical axis 122. The cast iron bodybuilding discs are thus mounted on the axis 122 and lowered along the axis 122 until they come into contact with the stop 120.

The transfer member 118 comprises a rigid arm 124 extending from the receiving member 114 to the support member 16. By "rigid", we understand that the arm 124 has a Young's modulus, measured using the ISO standard applicable to the type of material composing it, greater than 220 GPa. In the example shown, this rigid arm 124 is substantially vertical.

As visible in Figures 3 and 4, a lower end 126 of the rigid arm 124 is in direct contact with an upper surface 128 of the support 80 of the movable member 16.

The plate 95 is integral with this lower end 126. For this purpose, it is typically screwed to said lower end 126.

The receiving member 114, the arm 124, the plate 95 and the support member 16 together form a one-piece assembly 129 whose elements are fixed relative to each other in the vertical direction Z.

Returning to Figures 1 and 2, in the example shown, the one-piece assembly 129 is guided relative to the frame 12 by a slide 130 of the test bench 10. This slide 130 is in particular intended to maintain the orientation of the monobloc assembly 129 relative to the frame 12. It is indeed easy to see that, without such a slide 130, the balance of the assembly 129 would be precarious and that it would risk tipping forward, backward, left or right.

The slide 130 is capable of guiding the one-piece assembly 129 relative to the frame 12 in translation in the vertical direction Z. It is capable of opposing any movement of the one-piece assembly 129 relative to the frame 12 in the longitudinal directions transverse Y. It is also capable of opposing any rotation of the one-piece assembly 129 relative to the frame 12 around the longitudinal X and transverse Y directions.

It is thus understood that the support member 16, more particularly the blade 70 composing it, is movable in translation in the vertical direction Z relative to the receptacle 36 of the sample holder 14.

The slide 130 is advantageously adapted to minimize friction with the one-piece assembly 129. For this purpose, the slide 130 typically consists of an air stop.

Alternatively, the slide 130 is made up of a slide in direct contact, in a dovetail shape, by a splined shaft, by ball bearings or bushings, or by the use of rollers, the slide 130 being lubricated or not lubricated.

The stressing device 18 is thus adapted so that the support force it exerts on the support member is oriented towards the bottom 54 of the receptacle 36 of the sample holder 14.

The force generator 110 also comprises, in the example shown, a device 132 for initializing the support force. This initialization device 132 is capable of canceling the support force produced by the force generator 110 when the support member 16 is in a reference position. Typically, the initialization device 132 is capable of compensating the own weights of the force generator 110 and of the support member 16 when the support member 16 is in the reference position, so that the support member 16 remains in said reference position.

Here, the initialization device 132 is formed by a member 134 for returning the support member 16 to its reference position.

The return member 134 typically comprises, as shown, at least one spring 140 connected, by a first end 142, to the frame 12 and, by a second opposite end 144, to the one-piece assembly 129. The or each spring 140 is for example, as shown, a vertically oriented extension spring. Alternatively (not shown), the or each spring 140 is a vertically oriented compression spring.

Here, there are two springs 140. They frame the one-piece assembly 129 transversely, that is to say that one of the springs 140 is on a left side of the one-piece assembly 129, the other spring 140 being on the right side of said assembly 129 The first end 142 of each spring 140 is attached to a respective protuberance 26. The second end 144 of each spring 140 is connected to the one-piece assembly 129 by a transverse bar 146 secured to the one-piece assembly 129.

Advantageously, the test bench 10 also comprises, as shown, a device 150 for adjusting the reference position of the support member 16. This adjustment device 150 is capable of modifying the reference position of the support member 16 relative to frame 12.

The adjustment device 150 is for example, as shown, formed by a member 152 for adjusting the position of the first end 142 of the or each spring 140 relative to the frame 12.

In the example shown, the adjustment member 152 comprises, for each spring 140, a threaded socket 154 and a nut 156 screwed to the socket 154. The socket 154 is engaged through a through hole (not shown), here vertical, formed in one of the protuberances 26. It has, on one side of said protuberance 26, a hooking end 158 to which the first end 142 of the spring 140 is hooked. The nut 156 bears against the opposite side of the protrusion 26. It is easily understood that, by modifying the position of the nut 156 along the threaded socket 154, the first end 142 of the spring 140 is brought closer or further away from the protrusion 26, and therefore that the position of said first end 142 is modified relative to the frame 12.

As a variant (not shown), the force generator 110 is formed of a pneumatic, oil-pneumatic or hydraulic cylinder, a connecting rod-crank, pinion-rack or cam system powered by any motor, a screw-nut system, a electric linear actuator, or a piezoelectric actuator.

The measuring system 20 is capable of dynamically measuring the distance from the contact surface 76 of the support member 16 to the bottom 54 of the receptacle 36 of the sample holder 14. Advantageously, the measuring system 20 is also capable of determining dynamically the upper profile 160 ( ) of the sample 15 of granular or pasty material received in the receptacle 36. By “dynamically”, we understand here and in the following that several measurements/determinations are carried out on the basis of data collected successively at regular time intervals, so as to follow the evolution over time of the measured/determined quantity.

For this purpose, the measurement system 20 includes here, as visible on the , at least one camera 162, here a single camera 162, capable of capturing a dynamic image of the contents of the receptacle 36 of the sample holder 14. By “dynamic image”, we understand here and in the following a succession of captured still images at regular time intervals, for example less than 10 ms. In the example shown, the camera 162 is able to capture this image through a transparent wall 45 of the groove 42.

The measuring system 20 also includes an image processing system 164 capable of processing the dynamic image captured by the camera 162 to dynamically determine the distance from the contact surface 76 of the support member 16 to the bottom 54 of the receptacle 36 of the sample holder 14 and the upper profile 160 of the sample 15 of granular or pasty material received in the receptacle 36. Typically, the image processing system 164 is able to determine the distance from the contact surface 76 at the bottom 54 and the upper profile of the pile of granular material tested for each of the still images composing said dynamic image.

Camera 162 is for example a high-speed camera. Alternatively or optionally, the camera 162 is coupled to a microscope.

Preferably, the platform 33 on which the sample holder 14 is mounted is movable in translation in the longitudinal direction to the frame 12. Advantageously, an actuator (not shown) is capable of driving the platform 33 along said slide. The support member 16, more particularly the blade 70, is then also movable in translation relative to the receptacle 36 of the sample holder 14 in the longitudinal direction X. Thus, the support member 16 is movable in translation relative to the receptacle 36 along a first axis substantially orthogonal to the bottom 54 and along a second axis substantially parallel to the bottom 54, the two axes being included in a plane parallel to the side walls 40. This makes it possible to observe the behavior of the sample 15 of granular material or pasty not only in compression, but also in shear.

A method 200 for determining the mechanical characteristics of the particles constituting a granular material tested, using the test bench 10, will now be described, with reference to the .

The granular material tested has, for example, a particle size of between 0.1 µm and 100 µm.

This process 200 begins with a preliminary step 210 of taking a sample of the granular material tested.

Preferably, the granular material tested consists of a third body. During step 210, the sample is then taken at the interface between two first bodies in contact with each other. For example, the first bodies include a blade root and an imprint of a turbomachine rotor disk.

Step 210 is followed by a step 220 of inserting the sample of granular material tested into the receptacle 36 of the test bench 10, so as to form in this receptacle 36 a pile of granular material tested.

Step 220 is followed by a step 230 of positioning the support member 16 so as to place it in a reference position in which the contact surface 76 is flush with the top of the pile of granular material tested, typically by manipulating the adjustment device 150. For example, the nut 156 of each adjustment member 152 is moved along the threaded socket 154 of said adjustment member 152 so as to raise or lower the first ends 142 of the springs 140 relative to the frame 12.

The support member 16 is then immobile in its reference position, the restoring force exerted by the initialization device 132 on the support member 16 compensating for the other forces to which the support member 16 is subjected , namely the own weights of the force generator 110 and the support member 16.

Then, during a step 240 of increasing the support force, the support force exerted on the support member 16 by the stressing device 18 is increased. Typically, masses 116 are loaded into the receiving member 114 of the force generator 110. These masses 116 weigh down the force generator 110, the weight of which is transmitted to the support member 16 via the arm 124. This weight urges the support member 16 towards the bottom 54 of the receptacle 36. The contact surface 76 therefore tends to approach said bottom 54. However, it encounters resistance due to the presence of the pile of granular material tested, which thus finds itself compressed between the support member 16 and the bottom 54 of the receptacle 36.

Optionally, step 240 is followed by a step 250 of applying a shear force. During this step 250, a shearing force is applied between the support member 16 on the one hand and the receptacle 36 on the other hand. This shear force is here applied parallel to the axis of elongation of the groove 42 of the sample holder 14, that is to say, in the present case, in the longitudinal direction X. For this purpose, the sample holder 14 is urged forwards or backwards by application to the platform 33 of a force oriented in the longitudinal direction the support member 16 and the bottom 54 of the receptacle 36.

Parallel to step 240 and, where appropriate, to step 250, the dynamic behavior of the pile of granular material tested is observed during an observation step 260.

This observation step 260 includes a first sub-step 262 of capturing a dynamic image of the pile of tested granular material received in the receptacle 36. This capture is carried out by the camera 162, through the transparent wall 45.

The observation step 260 also includes a sub-step 264 for dynamically measuring the distance from the contact surface 76 to the bottom 54 of the receptacle 36, and a sub-step 266 for dynamically determining the upper profile of the pile of granular material tested. These sub-steps 264, 266 are implemented by the image processing system 164 from the dynamic image captured by the camera 162 in sub-step 252. In particular, during these sub-steps 264, 266, the image processing system 164 measures the distance from the contact surface 76 to the bottom 54 and determines the upper profile of the pile of granular material tested for each of the still images composing the dynamic image captured during the sub-step 262.

Only sub-step 262 is necessarily implemented at the same time as step 240 of increasing the support force and, where appropriate, as step 250 of applying a shear force. Sub-steps 264, 266 are implemented simultaneously or subsequently in step 240, respectively step 250.

Step 260 is followed by a step 270 of using modeling software. During this step 270, modeling software (not shown) is used to model the dynamic behavior in two dimensions of a pile of fictitious granular material subjected to uniaxial compression. This modeling software is typically discrete element analysis software, for example the MELODY_2D software published by Dr. Guilhem Mollon, Lecturer at INSA Lyon.

The pile of fictitious granular material is first parameterized with a particle number, particle density, average size, and particle size standard deviation corresponding to the particle population of the granular material being tested. These characteristics are easily determined by conventional methods well known to those skilled in the art.

Then the stiffness and cohesion of the particles constituting the fictitious granular material, as well as the viscosity of the fictitious granular material, are parameterized with arbitrary values.

Then, the modeling software is configured to simulate the dynamic behavior in two dimensions of the pile of fictitious granular material when subjected to uniaxial compression with a first intensity equal to a first value of the support force exerted by the placing device. constraint 18.

The stiffness and cohesion of the particles constituting the fictitious granular material, as well as the viscosity of the fictitious granular material, are then modified, and the modeling software parameterized to produce a new simulation of the two-dimensional dynamic behavior of the pile of fictitious granular material when subjected to uniaxial compression with the first intensity.

These steps are repeated iteratively until the modeled dynamic behavior is as close as possible to the dynamic behavior observed when the support force exerted by the stressing device 18 has the first value.

The modeling software is then configured to simulate the dynamic behavior in two dimensions of the pile of fictitious granular material when subjected to uniaxial compression with a second intensity equal to a second value of the support force exerted by the stressing device 18.

The stiffness and cohesion of the particles constituting the fictitious granular material, as well as the viscosity of the fictitious granular material, are then modified, and the modeling software parameterized to produce a new simulation of the two-dimensional dynamic behavior of the pile of fictitious granular material when subjected to uniaxial compression with the second intensity.

These steps are repeated iteratively until the modeled dynamic behavior is as close as possible to the dynamic behavior observed when the support force exerted by the stressing device 18 has the second value.

These steps are repeated for all the support force values tested.

When step 250 exists, the modeling software is also used to model the behavior in two dimensions of the pile of fictitious granular material when subjected to a shear force substantially orthogonal to the direction of the compressive force.

For this purpose, the pile of fictitious granular material is parameterized as detailed above, then the modeling software is configured to simulate the dynamic behavior in two dimensions of the pile of fictitious granular material when subjected:

• to a uniaxial compression with an intensity equal to the value of the support force exerted by the stressing device 18 during the application of the shear force, and
• to a shear force of intensity equal to the value of the shear force applied during step 250.

The stiffness and cohesion of the particles constituting the fictitious granular material, as well as the viscosity of the fictitious granular material, are then modified, and the modeling software parameterized to produce a new simulation of the two-dimensional dynamic behavior of the pile of fictitious granular material when subject to the same constraints as those detailed above.

These steps are repeated iteratively until the modeled dynamic behavior is as close as possible to the dynamic behavior observed during step 250.

Step 270 is followed by a step 280 of defining the stiffness and cohesion of the particles constituting the granular material tested, as well as the viscosity of said granular material tested.

During this step 280, said stiffness, cohesion and viscosity are defined as being equal respectively to the stiffness and cohesion of the particles constituting the fictitious granular material and viscosity of the fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the dynamic behavior observed for each of the different support force values tested.

When step 250 exists, the stiffness and cohesion of the particles constituting the granular material tested, as well as the viscosity of said granular material tested, are defined as being equal respectively to the stiffness and cohesion of the particles constituting the fictitious granular material and viscosity of the granular material tested. fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the dynamic behavior observed both for the behavior in compression and for the behavior in shear.

A method 300 for predicting the wear of an assembly of parts implementing the method 200 will now be described, with reference to the .

This method 300 is for example used to predict the wear of the assembly of parts 400 represented on the .

The assembly of parts 400 here is a turbomachine rotor, for example a fan, a compressor rotor, or a turbine rotor. It includes, as visible on the , a blade 402 and a disk 404. The disk 404, with axis of rotation A, has at its periphery a plurality of cells 406 open towards the outside of the disk 404 and regularly distributed around the axis of rotation A. The blade 402 comprises a blade 410 and a foot 412. The foot 412 is received in a respective cell 406 of the disc 404, thus forming a blade-disc connection.

Back to the , the method 300 comprises a first step 310 of producing a prototype of the assembly of parts.

This step 310 is followed by a step 320 of aging the prototype.

Step 320 is followed by a step 330 of taking a sample of the third body at the interface between parts of the prototype. In the case of a prototype of the assembly 400, the third body sample is typically taken at the interface between the root 412 of the blade 402 and the cell 406 of the disk 404 in which it is received.

Then, during a step 340, the stiffness and cohesion of the particles constituting this third body, as well as the viscosity of said third body, are determined by means of method 200.

The process 300 ends with a step 350 of modeling the behavior of the assembly of parts using the stiffness, cohesion and viscosity characteristics determined in the previous step 340.

Thanks to this modeling 350, the wear of the assembly of parts can be predicted.

Thus, thanks to the example embodiment of the invention described above, it is possible to determine the stiffness and cohesion of the particles constituting a third body, as well as the viscosity of said third body.

In addition, this exemplary embodiment allows the prediction of the wear of an assembly of parts held together by the friction forces occurring at their interface, which is very advantageous with a view to the development of new innovative assemblies.

Although the description above focuses on an exemplary embodiment in which the dynamic behavior in compression which is observed is a dynamic behavior in two dimensions, it is understood that the invention is not limited to such a case. The invention also extends to cases in which the dynamic behavior observed is dynamic behavior in three dimensions.

Thus, in a variant (not shown) of the invention, the receptacle 36 is adapted to receive a pile of granular or pasty material of height greater than or equal to 100 µm, preferably greater than or equal to 150 µm, without said pile of granular or pasty material reaches an edge of the receptacle 36. For this purpose, the receptacle 36 is for example formed by a platform each of whose dimensions in width and length is greater than 5 mm, preferably greater than 10 mm, this platform delimiting the bottom 54. The support member 16 then comprises, replacing the blade 70, a punch whose lower face, which defines the contact surface 76, is flat or, preferably, spherical. In addition, the measurement system 20 comprises at least two cameras 162 oriented towards the receptacle 36 in two different directions so that the dynamic image of the contents of the receptacle 36 captured by the cameras 162 is a stereoscopic image. During step 270, the dynamic behavior modeled by the modeling software is then a three-dimensional dynamic behavior of a pile of fictitious granular material subjected to uniaxial compression.

Claims (15)

Test bench (10) for observing the dynamic behavior in compression of a granular or pasty material, comprising:

• a receptacle (36), having a bottom (54), for receiving the granular or pasty material,
• a support member (16) movable in the receptacle (36) and defining, facing the bottom (54), a surface (76) of contact with the granular or pasty material,
• a stressing device (18) capable of exerting on the support member (16) a support force oriented towards the bottom (54), and
• a measuring system (20) capable of dynamically measuring the distance from the contact surface (76) to the bottom (54).

Test bench (10) according to claim 1, in which the measuring system (20) is also capable of dynamically determining the upper profile of the granular or pasty material received in the receptacle (36). Test bench (10) according to claim 2, in which the measuring system (20) comprises at least one camera (162) capable of capturing a dynamic image of the granular or pasty material received in the receptacle (36) and a system image processing device (164) capable of processing the dynamic image captured by the camera (162) to determine the distance from the contact surface (76) to the bottom (54) and the upper profile of the granular or pasty material received in the receptacle (36). Test bench (10) according to claim 3, in which the receptacle (36) is delimited at least in part by a transparent wall (45) forming an angle with the bottom (54), the camera (162) being able to capturing the dynamic image of the granular or pasty material through said transparent wall (45). Test bench (10) according to any one of the preceding claims, in which the contact surface (76) is rounded, for example in the shape of a portion of a cylinder of revolution or a sphere. Test bench (10) according to any one of the preceding claims, in which the support member (16) is movable in translation relative to the receptacle (36) along a first axis substantially orthogonal to the bottom (54) and according to a second axis substantially parallel to the bottom (54). Test bench (10) according to any one of the preceding claims, in which the receptacle (36) is constituted by a groove (42) delimited by two side walls (40), the contact surface (76) having a width substantially equal to that of the groove (42). Method (200) for determining the mechanical characteristics of the particles constituting a tested granular material, comprising the following steps:

• insertion (220) of a sample of the granular material tested into the receptacle (36) of a test bench (10) according to any one of the preceding claims, so as to form in the receptacle (36) a pile of granular material tested,
• positioning (230) of the support member (16) so that it is flush with a top of the pile of granular material tested,
• increase (240) of the support force exerted on the support member (16) by the stressing device (18) with observation (260) of the dynamic behavior of the pile of granular material tested by means of the system of measurement (20),
• use (270) of modeling software to model the dynamic behavior of a pile of fictitious granular material subjected to uniaxial compression, the mechanical characteristics of the particles constituting the fictitious granular material being modified until the modeled dynamic behavior either as close as possible to the observed dynamic behavior,
• definition (280) of the mechanical characteristics of the particles constituting the granular material tested as being equal to the mechanical characteristics of the particles constituting the fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the observed dynamic behavior.

Determination method (200) according to claim 8, wherein the observation of the dynamic behavior (260) comprises a dynamic measurement (264) of the distance from the contact surface (76) to the bottom (54) and the dynamic determination ( 266) of the upper profile of the pile of granular material tested. Determination method (200) according to claim 8 or 9, in which the granular material tested has a particle size of between 0.1 µm and 100 µm. Determination method (200) according to any one of claims 8 to 10, in which the granular material tested consists of a third body. Determination method (200) according to any one of claims 7 to 11, comprising the following additional step:

• application (250) of a shear force between the support member (16) and the receptacle (36) simultaneously with the observation (260) of the dynamic behavior of the pile of granular material tested by means of the measuring system ( 20),

the modeling software also being used to model the two-dimensional behavior of the pile of fictitious granular material when subjected to a shear force substantially orthogonal to the direction of the compressive force, the mechanical characteristics of the particles constituting the fictitious granular material being modified until the modeled dynamic behavior is as close as possible to the observed dynamic behavior,
the mechanical characteristics of the particles constituting the granular material tested being defined as equal to the mechanical characteristics of the particles constituting the fictitious granular material for which the modeling software produces a dynamic behavior modeled as close as possible to the dynamic behavior observed both for the behavior in compression and for the shear behavior. Determination method (200) according to any one of claims 8 to 12, in which the mechanical characteristics determined include the stiffness and/or cohesion of the particles. Method (300) for predicting the wear of an assembly of parts (400), comprising the following steps:

• production (310) of a prototype of the assembly of parts (400),
• aging of the prototype (320),
• taking (330) a sample of the third body at the interface between parts of the prototype,
• determination (340) of mechanical characteristics of the particles composing this third body by means of a determination method (200) according to any one of claims 8 to 13, and
• modeling (350) of the behavior of the assembly of parts (400) using the mechanical characteristics of the particles of the third body determined in the previous step.

Prediction method (300) according to claim 14, wherein the assembly of parts (400) comprises a blade (402) with a blade (410) and a root (412) and a turbomachine rotor disk (404) defining a cell (406) in which the foot (412) is received.