METHOD FOR JOINING TWO AIRCRAFT COMPONENTS AND FOR ANALYSING A JOINING BETWEEN TWO AIRCRAFT COMPONENTS

Description

Technical field of the invention

[0001] The present invention relates to a bonding method and a method for analyzing the bond between two aeronautical parts. Technical background

[0002] The prior art includes in particular documents FR-A1-2 956 057, FR-A1-3 029 134 and FR-A1-3 051 386. US 2010 / 015455 A1 relates to processes and devices for validating bonding lines.

[0003] The use of composite materials is advantageous in the aeronautical industry in particular because these materials have interesting mechanical performance for relatively low masses.

[0004] A manufacturing process for composite parts in the aerospace industry, well known to those skilled in the art, is the RTM molding process, whose initials refer to the Anglo-Saxon acronym for Resin Transfer Molding.

[0005] This is a process for manufacturing a part from a composite material based on resin-impregnated fibers. Such a process is used, for example, to manufacture a turbomachine fan blade. A preform is created and then heated so that the resin polymerizes and forms the final part, such as a blade. This blade has an upper and lower surface extending from a leading edge to a trailing edge.

[0006] The composite material of the blade is relatively fragile, and particularly sensitive to impacts, and it is known to protect it by means of a metal shield which is attached and fixed to the leading edge of the blade.

[0007] After the resin on the blade has cured, the shield can be attached to the blade, for example, with an epoxy adhesive. The complex geometry of the parts can lead to difficulties in matching them and impact the quality of the bonded assembly.

[0008] Bonding can indeed present numerous defects, such as porosity or excessive adhesive thickness. To verify the quality of a bonded assembly, there are two different methods: The destructive testing method, particularly optical microscopy on sections, requires cutting out the area of ​​the adhesive film to be analyzed. This method has the disadvantage that the analysis is limited to the cut area and, more importantly, that the part is destroyed to perform the analysis. The conventional non-destructive testing method, particularly ultrasonic testing, also has limitations in characterizing adhesive films. For example, when parts have highly variable geometries or significant material heterogeneities, as is the case with blades, it is impossible to distinguish the effect induced by the bonding process parameters from that induced by the geometry of the parts.

[0009] The two methods described above, being costly and time-consuming, make it impossible to perform large-scale testing during the development or industrialization of a new bonding process. Furthermore, the quality of this bonding analysis remains limited. Consequently, the bonds still contain numerous anomalies.

[0010] The invention aims to improve at least one of the aforementioned problems. Résumé de l'invention

[0011] The invention proposes a method for analyzing the bond between two aeronautical parts, characterized in that it comprises the steps of: (i) apply a first pore-sealing agent to a first surface to be bonded of a first part, and a second pore-sealing agent to a second surface to be bonded of a first part, (a) apply a first release agent to the first pore-sealing agent, and a second release agent to the second pore-sealing agent, (b) apply an adhesive to at least one of the first and second release agents and position the first and second parts on top of each other so that the adhesive is located between the first and second release agents, the adhesive forming an adhesive film after polymerization, (c) separate the parts from each other and remove the adhesive film in one piece, (d) analyze the adhesive film in order to inspect the quality of the adhesive film over the entire effective bonding surface.

[0012] The invention thus makes it possible to remove the adhesive film in one piece, enabling analysis of the entire effective bonding area under real-world conditions. Furthermore, it allows both parts to remain intact after separation, thus allowing the test to be repeated several times within a short period.

[0013] The parameters related to the geometry of the part are then identical for all tests carried out on the same pair of parts.

[0014] Since the geometry parameters of the parts are fixed, it is possible to isolate the effect of the bonding process parameters during repeated analyses, thus eliminating the root cause of bonding anomalies. This allows for optimal adjustment of the bonding process parameters to improve performance.

[0015] This analysis method is notably more economical than destructive techniques and more precise than current non-destructive techniques.

[0016] The method of the invention is therefore non-destructive, allows the glue film to be analyzed without the creation of artifacts and is insensitive to the geometric variations of the parts studied.

[0017] The method according to the invention may include one or more of the following features, taken individually or in combination with each other: Step d) is performed by analyzing at least one image obtained by holding the adhesive film up to a light source. The image analysis includes comparing and interpreting differences in color or contrast. The image analysis includes evaluating the thickness of the adhesive film in one or more areas of the image. The image analysis includes evaluating the porosity of the adhesive film. The first part is metallic. The second part is made of a composite material and comprises, for example, carbon fibers embedded in a polymer matrix. The second part is a blade or rotor blade, and the first part is a reinforcing shield for the leading edge of this blade or rotor blade.

[0018] The present invention also relates to a method of bonding two aeronautical parts, characterized in that it comprises the steps of the method as described above, followed by the steps of: e) applying an adhesive to at least one of the first and second surfaces and positioning these surfaces one on top of the other, the adhesive forming an adhesive film after polymerization.

[0019] The bonding process further includes, between steps d) and e), a cleaning step of the first surface of the first part and the second surface of the second part. Brève description des figures

[0020] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which: [ Fig.1 ] there figure 1 is a schematic perspective view of a composite turbine blade for an aircraft turbomachine; Fig.2 ] there figure 2 is a schematic diagram of a bonding method according to the invention; [ Fig.3 ] there figure 3 is a schematic perspective view of a film of glue after it has been separated from the dawn and a shield; [ Fig.4a-4c ] THE figures 4a, 4b et 4c are schematic views of a process for analyzing adhesive by digitizing an image obtained by holding the adhesive film up to a light; Fig.5a-5b ] THE figures 5a et 5b are schematic views of digitized images of two glue films; [ Fig.6 ] there figure 6 is a correlation graph between the grey levels present in the image and the thickness of the glue film; and [ Fig.7 ] there figure 7 is a schematic view of an image of a glue film allowing identification of porosities. Description détaillée de l'invention

[0021] We first refer to the figure 1 which illustrates a blade 10 made of composite material for a turbomachine, this blade 10 being for example a blower blade.

[0022] The blade 10 includes a blade 12 connected by a strut 14 to a foot 16 which has for example a dovetail shape and is shaped to be engaged in a cavity of complementary shape of a rotor disk, in order to retain the blade on this disk.

[0023] The blade 12 comprises a leading edge 12a and a trailing edge 12b of the gases flowing into the turbomachine. The blade 12 has a curved or even twisted aerodynamic profile and comprises an intrados 20 and an extrados 18 extending between the leading edge 12a and trailing edge 12b.

[0024] Blade 12 is made from a fibrous preform obtained by weaving fibers in three dimensions, for example carbon fiber.

[0025] The leading edge 12a of the blade is reinforced and protected by a shield 22, which is metallic and fixed to the leading edge 12a. The shield 22 is, for example, made of a titanium-based alloy.

[0026] This fixing is achieved in particular by gluing, forming a film of glue after polymerization, between the blade 12 and the shield 22.

[0027] As seen on the figure 2 The invention relates to a method for analyzing the bond between a first part 30, for example the metal shield 22, and a second part 32, for example the blade 10 or the rotor blade 12, made of composite material and comprising, in particular, carbon fibers embedded in a polymer matrix. To enable the analysis of this adhesive film 24, the invention proposes obtaining the adhesive film 24 in one continuous piece by following the steps a), b), and c).

[0028] Step a) consists of applying a first release agent 26A to a first surface 31 to be bonded of the first part 30, and a second release agent 26B to a second surface 33 to be bonded of the second part 32. Step a) is preceded by a step of applying a pore-sealing agent to the first and second surfaces 31, 33.

[0029] Step b) then consists of applying an adhesive to at least the first or second release agent 26A, 26B, and positioning the first and second parts 30, 32 one on top of the other so that the adhesive is located between the first and second release agents 26A, 26B, the adhesive forming a film or adhesive joint 24 after polymerization. This bonding step of the analysis process, including the presence of the first and second release agents 26A, 26B, is carried out under conditions almost identical to the conventional bonding process during blade production. During this bonding step, certain parameters, such as the pressure or the flow rate of the adhesive, are known and can be adjusted.

[0030] In the next step c), it is possible to separate the first and second parts 30, 32 from each other and remove the adhesive film 24 in one piece, as shown in the figure 3 , thanks to the first and second release agents 26A, 26B.

[0031] It is then possible to proceed to the next step d) of the process which consists of analyzing the glue film 24, in particular to inspect the quality of the glue film 24 over the entire useful surface of the bonding.

[0032] For the analysis of the glue film 24 and as illustrated on the figures 4a, 4b et 4c The invention provides for the placement of the adhesive film 24 on a light screen 42. The light is thus transmitted transparently through the adhesive film 24, giving variations in contrast, grey level and / or colour which are linked to variations in thickness of the adhesive film 24 and therefore variations in light transmission.

[0033] The method involves acquiring a digital image of the illuminated adhesive film 24, notably using a digital camera 44, positioned at a specific location, particularly on a fixed frame 45. The light screen 42 can also be located on the frame 45. Thus, the assembly formed by the light screen 42, the digital camera 44, and the frame 45 creates a fixed unit, particularly for the purpose of improving image quality and analysis. Alternatively, the digital camera 44 is positioned at a specific location marked on the ground by a fixed reference point relative to the light screen 42.

[0034] The frame 45 can, for example, be mounted on casters 61. The frame 45 includes, in particular, a cover 49 covering the digital camera 44 and the light screen 42, especially with the aim of improving the quality of the images and the analysis.

[0035] This digitalization is illustrated schematically on the figures 5a et 5b , on which the images 40 of two adhesive films 24, extrados side 15A and intrados side 15B, were obtained by two different methods. The first method, shown on the figure 5a , consists of assembling a vane with a shield. The second method, shown on the figure 5b , consists of assembling the same alb but with a different shield.

[0036] A computer analysis of the image can then be carried out in particular to compare and interpret differences in colours or contrasts to evaluate the thickness over the whole of the glue film 24. Thus a specific application has been developed to allow a correlation between the grey level recorded on the image 40 of glue film and the thickness of the glue film.

[0037] This correlation or reference chart between grey level and thickness was found empirically by following these steps: Marking of different areas on the adhesive film 24, specifically seven areas. The marking is done with a circle using a black marker and ensures precise identification of the areas on the adhesive film 24, visible in the digital image 40. The seven selected areas will be approximately identical on all samples of adhesive film 24. Physical measurements of the thickness of the adhesive film 24 at the seven areas previously marked with the marker. The measuring instrument allows measurements with micrometer precision or any other means capable of measurement. Filtering of the gray values ​​on the digital image to obtain a colored tint, for example, a fire-colored tint, called fire grayscale filtering In Anglo-Saxon terms. More precisely, between a black pixel, with a value of 0, and a white pixel with a value of 255, the intermediate values ​​will tint the pixels blue, red, orange, and yellow. This involves measuring the grayscale levels, that is, the hue values ​​of the pixels in the digital image within the seven areas previously marked with a marker, visible in the image. The size of the area to be measured can be, for example, 25 to 50 pixels. A graph is then created, showing the grayscale values ​​and the physically measured thickness for the seven areas, in order to obtain a correlation curve between the grayscale values ​​and the thickness of the adhesive film.

[0038] This experiment is applied to both sides of the glue film 24, that is, the upper surface 15A and the lower surface 15B, and to each method, in particular the method figure 5a and the method figure 5b .

[0039] As illustrated on the figure 6 The graph displays the gray values, from 0 to 255, on the x-axis and the thicknesses in millimeters of the adhesive film 24 on the y-axis. A different curve is plotted for each method used and for each side (intrados and extrados) of the adhesive film. The curve is drawn from points whose x-coordinate corresponds to the average gray value of the pixels in an area of ​​the adhesive film 24, and whose y-coordinate corresponds to the thickness in millimeters of that same area of ​​the adhesive film 24.

[0040] On the graph, curve 51 represents the values ​​obtained on the intrados side with the method figure 5a Curve 52 represents the values ​​obtained on the extrados side using the method figure 5a Curve 53 represents the values ​​obtained on the extrados side using the method figure 5b and curve 54 represents the values ​​obtained on the intrados side with the method figure 5b .

[0041] Thanks to these four curves, it is possible to evaluate the thickness at any point of the glue film 24 using the grey level of the pixels of the digital image 40.

[0042] The thickness of the adhesive film 24 must be between 30 and 400 µm, and in particular less than 350 microns. The grey level must therefore be within the area of ​​the graph referenced 55, that is to say, between 170 and 190.

[0043] Returning to the examples illustrated in figures 5a et 5b A light-colored area, referenced as 46, corresponds to a thin layer of adhesive film 24. A dark-colored area, referenced as 47, notably illustrated by dotted lines, corresponds to a thick layer of adhesive film 24. For clarity, the figures 5a et 5b represent only two distinct areas, light 46 and dark 47, but the images 40 actually include a gradient of grey level and / or colour as explained previously.

[0044] Image analysis also allows for the evaluation of the porosity rate of the adhesive film 24 on the intrados and extrados, as shown in the figure 7To obtain this image, the 40 digital images of the 24 adhesive films are processed, notably by following these steps: assembly, conversion to 8-bit grayscale, background uniformity, bandwidth filtering, grayscale inversion, clipping of the area of ​​interest, black and white thresholding, and binarization. The porosities are thus represented by areas of black pixels on a white background. These 48 porosity areas can be counted, their calculated surface area allowing comparisons between different 24 adhesive films whose bonding parameters, such as the pressure applied to the film or the adhesive flow rate, vary in order to reduce the porosity rate. Comparing the porosity rate also allows for improvements to the bonding process.

[0045] The analysis method of the invention can be repeated several times consecutively between the same first and second parts 30, 32, but by varying the bonding parameters, such as the pressure applied to the film or the adhesive flow rate, in order to study the effect of these parameters on the bond quality and, in particular, on the thickness and porosity of the adhesive film. The interpretation and comparison of the different thicknesses and porosity levels will allow for the optimization of the bonding parameter settings to achieve an improved bonding process between two aeronautical parts, such as a shield and a blade.

[0046] The invention further relates to such a bonding process comprising the preceding steps of the analysis process, followed by the steps of: e) applying an adhesive to at least one of the first and second surfaces 31, 33, and positioning these surfaces one on top of the other, the adhesive forming an adhesive film 24 after polymerization.

[0047] Thus, thanks to the invention and in particular to the prior analysis of the glue film, the parameters of the gluing process are optimized, so that the gluing is optimized in particular with regard to the thickness of the glue film and its porosity.

[0048] The bonding process of the invention further includes, between steps d) and e), a cleaning step, for example of release agent residues, of the first and second surfaces 31, 33, mentioned above.

Claims

1. A method for analysing a bonding between two aeronautical parts (30, 32), characterised in that it comprises the steps of: i) applying a first pore-sealing agent to a first surface (31) to be bonded of a first part (30) and a second pore-sealing agent to a second surface (33) to be bonded of a second part (32), a) applying a first release agent (26A) to the first pore-sealing agent, and a second release agent (26B) to the second pore-sealing agent, b) applying an adhesive to at least one of the first (26A) and second (26B) agents and positioning the first (30) and second (32) parts on top of each other so that the adhesive is located between the first (26A) and the second (26B) release agents, the adhesive forming an adhesive film (24) after polymerisation, c) separating the parts (30, 32) from each other and removing the adhesive film (24) in one piece, d) analysing the adhesive film (24) to monitor the adhesive film (24) quality on the overall surface bonding.

2. The method according to any of the preceding claims, wherein the step d) is carried out by analysing at least one image (40) obtained by transparency of the adhesive film (24) to light (42).

3. The method according to the preceding claim, wherein the analysis of the image (40) comprises the comparison and the interpretation of the differences in colour or contrast.

4. The method according to the preceding claim, wherein the analysis of the image (40) comprises the evaluation of the thickness of the adhesive film (24) in one or more areas of the image.

5. The method according to claim 4 or 5, wherein the analysis of the image (40) comprises the evaluation of the porosity rate of the adhesive film (24).

6. The method according to any of the preceding claims, wherein the first part (30) is metallic.

7. The method according to any of the preceding claims, wherein the second part (32) is made of composite material and comprises, for example, carbon fibres embedded in a polymeric matrix.

8. The method according to one of the preceding claims, wherein the second part (32) is a vane (10) or a blade (12) and the first part (30) is a shield (22) for reinforcing a leading edge (12a) of this vane (10) or blade (12).

9. A method for bonding two aeronautical parts, characterised in that it comprises the steps of the method according to one of the preceding claims, followed by the steps of: e) applying an adhesive to at least one of the first (31) and second (33) surfaces and positioning these surfaces on top of each other, the adhesive forming an adhesive film (24) after polymerisation.

10. The method according to any of the preceding claims, wherein it comprises, between the steps d) and e), a step of cleaning said first (31) and second (33) surfaces.