FR3042277A1 - MOUNTING FOR TRACTION TESTING ON A COATING - Google Patents

Abstract

An assembly for testing the pull-out resistance of a coating (2) attached to a substrate (4) on a test specimen (6) is concerned. The assembly comprises a support frame (8), the test specimen (6), a connecting structure (20) fixed on one side to a face (18) of the coating, and, on the contrary, to a traction means (28) for pulling the coating (2) in a direction (100) of bias with respect to said face (18) for fixing the coating. In addition, there is provided a holding means (30) fixed to the support frame (8) and having a bearing surface (34) perpendicular to the traction direction (100), and at least one shim (32) having: a first flat surface (72) parallel to the bearing surface (34) and a second surface (70) opposite to the first surface (72) and conforming to the shape of said fixing face (18) for, then that the traction operates, press said first surface (72) against the bearing surface (34) of the holding means (30).

Description

MOUNTING FOR TRACTION TESTING ON A COATING

The present invention relates to an assembly for testing the pull-out resistance of a coating attached to a substrate, on the surface, on a test specimen.

This set is particularly suitable for testing specimens from fan blades.

The present invention also relates to a method of implementing such an assembly for determining the corresponding tearing force.

The ISO 4624 standard defines characteristics for measuring the force required to tear a coating from a substrate, following the application, in a direction perpendicular to the surface to which the film adheres, of a sufficient tensile force to cause tearing.

The test according to ISO 4624 requires the use of tensile test pieces with flat and standardized surfaces. The geometry of the surface imposed by ISO 4624 does not necessarily correspond to the final geometry of the parts. In some cases, this even requires re-machining the specimens. The manufacture of such specimens is therefore often expensive. However, some tests must still be conducted on specimens whose surface to be tested is, for example, not flat. This may be the case when it comes to controlling the quality of the bonding of an anti-erosion film on the intrados or extrados of a fan blade of an aircraft reactor. Indeed, the fan blades have externally variable curvatures, varying thicknesses, etc.

Thus, although the pull-out test device according to ISO 4624 is well suited to specimens made specifically or simple geometries, it is not suitable for specimens of more complex shapes, such as those having faces of varying curvatures, varying thicknesses, and / or non-parallel opposed surfaces.

On the basis of this observation, the invention provides a simple, effective and economical solution, making it possible to carry out, in accordance with the standard, a characterization of the fixing of a coating with a substrate, on specimens each provided with a coated face. which can be flat. For this purpose, it proposes an assembly adapted to test the tear resistance of a coating attached to a substrate, on a test specimen, this assembly comprising: - a support frame, - the test specimen, - a bonding structure fastened: - from one side to one side of the coating and which matches said face of the coating, - and, in contrast, to a traction means for pulling on the coating in a direction of bias relative to said fixing face of the coating, - a holding means fixed to the support frame and having a bearing surface perpendicular to the traction direction, - and at least one wedge having: - a first flat surface, parallel to the surface of d support, and - a second surface opposite to the first surface and conforming to the shape of said fixing face (which is confused with that of coating the substrate) for, while the traction operates, to press said first surface against the surfacesupport of the holding means.

The possibility offered by the invention of adapting the surfaces of the shim (s) and the bonding structure to the surface of the coating makes it possible to obtain a test device suitable for surfaces having variable curvatures, thicknesses variables and nonparallel faces, without having to modify the geometry of the specimen.

It is advisable that, in the aforementioned assembly, the holding means is arranged around the connecting structure and the traction means.

Such an arrangement will indeed promote a balanced distribution of the support force that is formed in response to the pulling force. This will prevent the creation of spurious forces that could disrupt the test.

As understood, the substrate is the rigid structure to which the coating is attached, such as an adhesively bonded film. At least in the case of a film, it will be sufficiently thin and flexible not to change the shape of the surface to which it adheres. Membership will typically be by collage.

According to yet another feature the holding means and the connecting structure will favorably, between them, a first difference greater than a second difference established between the connecting structure and the / shims, in a direction transverse to the direction of traction.

This will ensure a guiding of the connecting structure during the installation thereof on the film, while avoiding interaction with the holding means during the traction phase.

In a particular embodiment, the shims and the holding means will be monoblock.

This may facilitate the implementation of the assembly concerned by overcoming any problems related to the relative displacement of the shim / wedges relative to the holding means during the traction phase.

This also simplifies the implementation of the various elements of the device especially when the preform is directed downwards (Figure 9 below). The invention is therefore particularly suitable for specimens from parts having a non-planar outer surface and vis-à-vis which the holding of a suitable coating is to be tested.

This is the case in the aeronautical field, where some equipment has substrates with complex (volume) external surfaces which are coated with protective films such as, for example, fan blades.

In particular in this field, therefore, adhesions of films or anti-erosion coatings may be tested, such as polyurethane films of a few tenths to a few millimeters in thickness.

Indeed, the films in question are subjected to critical conditions known to cause erosion phenomena, such as the contact of the blades with the air masses which, which may contain various waste (stones ..), erode them in licking them.

Tensile strength tests of films are therefore necessary, to prevent operating conditions that would lead to expose the outer surface of an initially protected substrate.

And this will be all the more useful if the substrate is composite material, a material very frequently used in the aeronautical field.

An additional advantage of this device is that it makes it possible to characterize the tearing of the coating on different zones of the test piece that may have different characteristics, said different zones of the test piece corresponding to characteristic parts of a turbomachine blade.

With reference to the same problem as that stated above, the subject of the present invention is also a method for characterizing a pull-out force of a coating with respect to a substrate.

In this process: a) there is provided: - a support frame, and - a test specimen comprising said substrate, one face of which is fixed with said coating, b) the specimen is held opposite the support frame by the intermediate of at least one shim bearing with the substrate and a first flat surface is adapted to bear against a bearing surface of a holding means attached to the support frame, c) via a bonding structure attached to the coating, following a surface not parallel to said first planar surface, the coating is pulled with a pulling force (Fm) in a first direction: - at an angle to the orientation of the surface fixing between the connecting structure and the coating, - and substantially perpendicular to said first flat surface then bearing against said bearing surface of the holding means, d) measuring the tear force (Fm). Other details, features and advantages of the present invention will appear if necessary more clearly on reading the description which follows, given by way of nonlimiting example and with reference to the appended drawings, in which: FIGS. 1 and 9 are diagrams in vertical section of an assembly intended to test the resistance to tearing of a film adhering to a substrate, on a test specimen, according to the invention, with respectively upward and low; FIG. 2 is a view on a larger scale of the area I of FIG. 1; - Figure 3 shows a connecting structure; FIG. 4 is a view on a larger scale of zone II of FIG. 1; - Figure 5 is a variant of the section of Figure 1; - Figure 6 is a dive view of a specimen from a blade; - Figure 7 is a side view of the assembly being mounted; - Figure 8 is a view from below of a wedge positioner.

Although other coatings than an adhesively bonded film can be tested, reference is hereinafter made to a case, as in FIG. 1, where a device 1 is proposed to test the tearing resistance of a film 2, a few tenths to a few mm thick, adhering to a substrate 4, on the surface, on a test specimen 6, according to a preferred embodiment.

Moreover, the connections considered here between the substrate 4 and its coating 2 and this coating and at least the connecting structure 20 through which the tensile test pulling will take place are collages.

In the figures, the thicknesses of the different layers (in particular layers of glue) are not to scale.

In the solution of Figure 1, the device 1 comprises a support frame 8 having a first face 10 flat support. The support frame 8 can be a table, which can be fixed to the ground, and is sized to withstand the expected traction. The table here presents a horizontal top plate.

Disposed in the device 1, the substrate 4 has a flat face 12, here bearing against the face 10 of the frame, parallel to it. In contrast, the substrate 4 has a face 14 not parallel to the face 12. At this face 14, adheres, by marrying the shape, the film 2. The adhesion of the film 2 to the surface 14 of the substrate is done here by means of a uniform layer 202 of glue. A second uniform layer 204 of adhesive fixed in the same way to the second face 18 of the film the connecting structure 20 (face 22), as shown in Figure 2 which details the area I of Figure 1, showing the different layers since the substrate to the connecting structure.

The fastener 204 will be sufficiently strong so that the result of the tearing test does not correspond here to a cohesive failure facies in the glue. The fracture facies are described in ISO 10365-1992. The chosen glue should not produce any visible change in the layer under test. For example, EA 9394 glue can be used after polymerization for 3 to 5 days at 25 ° C.

To better see the coated specimen 6, reference can be made to FIG. 6 which shows it as part of a fan blade made of a composite material 60 covered with the film 2. It is clearly seen that the non-planar shape, here concave , that can have the outer face 18 of the coated dawn.

The connecting structure 20 may have a cylindrical shape and be aluminum, as shown in Figure 3. And it is therefore by its machined surface 22 that it matches the face 18 of the coating.

For the tear test, a thread 24 provides the connection between the connecting structure 20 and a means 28 of traction. This traction means 28 will make it possible to fire with a force Fm on the film in a direction 100.

A holding means 30 removably attached to the support frame 8 by fastening means 36 enables the specimen to be held by means of at least one shim 32 when the traction force Fm is exerted.

Figure 7 shows in particular the shim 32 engaged via a passage 300 around the connecting structure 20. The face 18 of the coating is in contact with a surface 70 of the wedge which comes to marry. Opposite the surface 70 parallel to the axis 100, the wedge 32 has a flat surface 72.

For, when the traction will take place, ensure that it operates in the direction 100, the holding means 30 has a transverse wall 340 provided with a flat support surface 34 parallel to the surface 72.

During the pulling, the surface 72 will be pressed against the surface 34 of the holding means 30.

Preferably, the film will cover the entire substrate. However, it is possible that this coating is not present in front of the wedge.

Wedge 32 will in any case preferably not attached to the coating 2, but just in support against.

Figure 4, which details the zone II of Figure 1, also shows the different faces in contact, from the substrate to the wedge.

The shim 32 will therefore make it possible to restore the flatness of the test piece as required by the ISO 4624 standard and to make the surfaces 34 and 72 parallel to each other. By its bearing surface 34, the holding means 30 will thus bear on the top of the shim 32, which will then be arranged around the connecting structure 20 so as to distribute the traction force around it.

In one embodiment, the hold could be sectored, in several parts. Figure 1, the shim 32 and the holding means 30 form two separate parts.

Figure 5, the shim 32 and the holding means form a single piece. This could facilitate the implementation of the assembly by overcoming any problems related to the relative displacement of the shim relative to the holding means, during the traction phase.

In the example chosen, the holding means is a bell 33 which is thus fixed firmly to the support frame 8 by the fastening means 36, such as screws.

Here, the surfaces 12 and 72 are parallel, which promotes a clamping along the axis 100 of the test piece 6 and the wedge in this bell, between it and the frame 8.

To allow traction by the traction means 28, the transverse wall 340 of the holding means 30 is traversed by the connecting structure 20, at 300, along the axis 100 (see reference Figure 5).

As represented in FIG. 1, the holding means 30 and the connecting structure 20 will have a first gap e1 greater than a second distance e2 established between the structure 20 and the shim 32 according to each other at the location of said passage. a direction transverse to the direction 100 of traction.

The surfaces 70 of the shim and 22 of the part 20 being oriented parallel to those 14 and 18 of the test piece and the surfaces 34 and 72 generally at an angle to them, it will be possible to draw without any disadvantage for the quality of the test, along the axis 100, perpendicular to said surfaces 34 and 72. In this regard, Figure 3 shows the non-zero angle α that exists between the surface 18 of the film 2 (which can typically have a double concavity as shown schematically in FIG. ) and the plane 106 perpendicular to the traction direction 100, and therefore parallel to the planes of the surfaces 34 and 72.

This angle α is therefore formed locally between the direction 100 of said force Fm and the direction 110 perpendicular to the face 18 of the film passing through the point 40 of contact between this face 18 and the connecting structure 20, where the axes intersect. 100 and 110. This contact point 40 will typically correspond to the center of the face 22 of the connecting means 20, where the traction along the axis 100 takes place.

The value of this angle a is used at least for the preliminary machining of the contact surface 22 of the connecting means 20, so that it matches the complementary face 18, at the corresponding places.

To measure this angle α and more generally to have the orientation in the space of the face 18 of the test piece, it may have been possible to use a device 112, such as an inclinometer or a feeler, for locating in the space of the faces for which this data is needed.

For example if it is a probe, it has been placed in contact with the face 18 of the film 2, in particular at point 40 to determine the angle a, and then has been moved around the point 40, in its environment. The machining of the surface 70 of the shim could have been performed on the same bases, so that the surfaces 70 and 18 (or 14) also marry each other.

Once these shapings have been made, the positioning of the connecting structure 20 can be carried out using a positioner 76, such as that of FIG. 8. This positioner comprises an internal recess 80 adapted to receive the specimen 6 and an orifice 302. allowing passage of the connecting structure 20. A groove 82 in the positioner at the orifice 302 can accommodate a removable key 82 fixed to the connecting structure 20 to properly position the surface of this structure on the surface of the test piece. Typically, the polarizer 84 may be a screw inserted into a tapping 86 of the connecting structure 20, as shown in FIG.

Thus, the positioner will be able to center the connecting structure 20 on the test piece 6 during their fixing together and to ensure a constant thickness of glue, if gluing as preferred.

Once this fixation is completed, it is advisable to carry out on the specimen, through the coating and up to the substrate 4, a trimming, or a cutout, 200, around the connecting structure 20, as represented in FIG. This will prevent the tensile force Fm from spreading in the adhesive between the bonding structure 20 and the face 18, in the film 2 or in the adhesive thickness 202.

All this achieved, we can then conduct the test. First, it will block the holding means 30 vis-à-vis the support frame 8, so with the specimen 6, the wedge 32 and the connecting structure 20 inside. Then, once this connecting structure 20 also fixed to the pulling means 28, it will therefore draw in the direction 100 on the film 2, with said force Fm, until tearing of the film.

Measuring means 102, such as a dynamometer, connected to the traction means 28 makes it possible to measure and record the value of this tearing force (Fm) along the axis 100.

A computer 114, containing programmed software, is connected to the measuring device 102 and to the tracking device 112. A display 116 will display the results.

The preferred embodiment described above in connection with Figure 1 is suitable for upward pulls.

For pulls down, still in the direction 100 but enjoying the gravity, it is possible to overturn the device 1 which implies that the device is tilted 180 ° about a horizontal axis.

This embodiment is shown in FIG. 9. It does not even imply that the faces 10 and 12 are in contact during the test, because the action of the force of gravity will naturally plumb the surfaces 72 and 34 against each other. 'other. The support frame 8 can then be a ceiling or for example a system of beams fixed to walls and under which the device 1 is suspended in the illustrated position.

Claims (7)

1. Assembly (1) for testing the peel strength of a coating (2) fixed to a substrate (4) on a test specimen (6), characterized in that the assembly comprises: - a frame support (8), - the test specimen (6), - a connecting structure (20) fixed: - from one side to one face (18) of the coating (2) and which matches said face of the coating, - and, in contrast, a traction means (28) for pulling on the coating (2) in a direction (100) of bias relative to said face (18) for fixing the coating, - a means of retainer (30) fixed to the support frame (8) and having a bearing surface (34) perpendicular to the traction direction (100), and at least one shim (32) having: - a first planar surface (72) parallel to the bearing surface (34), and - a second surface (70) opposite the first surface (72) and conforming to the shape of said attachment face (18) for, while the traction is operating, to press said p first surface (72) against the bearing surface (34) of the holding means (30). 2. The assembly of claim 1 characterized in that the holding means (30) is disposed around the connecting structure (20) and the traction means (28). 3. The assembly of claim 1 or 2 characterized in that the holding means (30) and the connecting structure (20) have between them a first difference (e1), greater than a second difference (e2) established between the structure link (20) and the shim (32) in a direction transverse to the traction direction (100). 4. The assembly of claims 1 to 3, characterized in that the substrate (4) of the test piece (6) is a composite material suitable for use in a turbomachine blade. 5. The assembly of claim 4, characterized in that the specimen (6) is a part of a turbomachine blade having an outer face coated with said film (2). 6. The assembly of claim 5, characterized in that said coating (2) is an anti-erosion film. 7. Assembly according to one of the preceding claims, characterized in that the wedge (32) and the holding means (20) are monobloc.