ULTRASONIC MEASUREMENT METHOD FOR TRANSMISSION OF A MECHANICAL PART OF AN AIRCRAFT TURBOMACHINE
Patent Information
- Application Number
- FR2021010516
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-10-05
- Publication Date
- 2025-03-14
- Estimated Expiration
- 2041-10-05
Smart Images
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Abstract
Description
Title of the invention: METHOD FOR MEASURING BY ULTRASOUND IN TRANSMISSION A MECHANICAL PART OF AN AIRCRAFT TURBO-MACHINE Technical field of the invention
[0001] The invention relates to the field of non-destructive testing of mechanical parts of aircraft turbomachines and in particular to a method of measuring by ultrasound in transmission of such a mechanical part. Technical background
[0002] It is now well known to use three-dimensionally woven composite materials for the manufacture of certain mechanical parts of an aircraft turbomachine. For example, certain turbomachine fan blades are manufactured from a central part, made of three-dimensionally woven composite materials, onto which titanium reinforcements are bonded on either side by means of a resin.
[0003] To guarantee the quality of a mechanical part manufactured in this way, it is necessary to control the bonding of the elements that compose it. Indeed, once manufactured, the mechanical part may contain defects such as the presence of areas of detachment or areas of porosity for example.
[0004] The ultrasonic testing method is a widespread method for carrying out this type of testing as it allows these defects to be identified while being non-destructive. Furthermore, for this type of mechanical part, a transmission measurement is more suitable than a reflection measurement. Indeed, for example, three-dimensional weaving tends to disperse the ultrasonic signal and the resin tends to absorb it.
[0005] The result of a transmission ultrasound measurement is presented in the form of an amplitude map, also called C-scan, which links the amplitude of the ultrasonic signal transmitted through the measured mechanical part to a given measurement position. Typically, the mechanical part to be measured is immersed in a basin or sprayed with water jets (to promote the circulation of ultrasound) and sensors (also called translators) move around the part to measure the transmitted ultrasonic signal in different areas of the part.
[0006] In the known state of the art, the calibration of the measurement can be carried out via a method based on the use of a mechanical calibration part.
[0007] On the one hand, the measurement of an amplitude map of the ultrasonic signal transmitted through a reference mechanical part is carried out so as to subtract this amplitude map from all the amplitude maps of the mechanical parts. mechanical parts measured subsequently (i.e. production mechanical parts). The reference mechanical part is a part identical (in terms of structure) to the mechanical parts measured subsequently but which is free from defects. This step makes it possible to avoid the impact on the measurement of a complex geometry of the measured mechanical part as well as a significant variation in its thickness over the area to be measured.
[0008] On the other hand, the calibration itself consists of measuring an amplitude map of the ultrasonic signal transmitted through a mechanical part which comprises a plurality of intentional defects, for example tetrafluoroethylene inserts (known as Teflon®) of known size and position, and determining, from this amplitude map, a single threshold then used for measuring the production mechanical parts, as a criterion for detecting the presence of a defect and for sizing said defects.
[0009] This calibration is based on the link between a given attenuation of the amplitude of the transmitted ultrasonic signal and the surface area of a given tetrafluoroethylene insert located on the path of said transmitted ultrasonic signal. More precisely, the association of different attenuations with different known insert sizes makes it possible to set an attenuation threshold below which it is considered that a defect is identified. It is from this attenuation threshold that defects are detected in the mechanical parts subsequently measured. In addition, defect identification combines the use of this attenuation threshold with the use of a dimensional threshold to confirm or not the presence of a defect.
[0010] A limitation of this latter type of calibration comes from the fact that the use of a single threshold results in the over-dimensioning or under-dimensioning of certain inserts of the mechanical calibration part and, consequently, an imprecise dimensioning of the defects in the mechanical parts to be measured.
[0011] [Fig. 1] illustrates an example of a measurement of a mechanical calibration part, in this case a turbomachine fan blade. In the example shown, the calibration blade comprises twelve tetrafluoroethylene inserts. Said tetrafluoroethylene inserts are arranged in a film of glue and have dimensions consistent with the defects sought. They are placed so as to guarantee the correct detection of the defects sought.
[0012] [Fig.l] represents (in the middle) the amplitude map 100 of the ultrasonic signal transmitted through the calibration blade. In the amplitude map 100 represented, each pixel has a shade (more or less dark) which corresponds to an attenuation value of the transmitted ultrasonic signal.
[0013] [Fig.l] also represents (at the top), the attenuation curve 102 (in decibels) of the amplitude measured for each insert from the amplitude mapping 100. The attenuation curve 102 illustrates the fact that the attenuation varies significantly from one insert to another, including in proportions which may exceed the strict variation in the surface area of the different inserts. Furthermore, in the example shown, inserts 12 to 7 have a surface area of 36 mm2 and inserts 6 to 1 have a surface area of 72 mm2.
[0014] Finally, [Fig.l] represents (at the bottom) the gap 104 (in mm2) between the surface determined (by the ultrasound measurement in transmission) and the known surface for each insert. Once a single attenuation threshold (i.e. a detection threshold) has been set, the different attenuation values measured lead to a surface value for each insert. In addition, the gap 104 between the determined surface and the known surface which is obtained is also very variable. Thus, when the curve of the gap 104 has negative values, the insert is undersized and, conversely, when the curve has positive values, the insert is oversized. This over or under sizing can therefore be found, ultimately, in the measurements subsequently carried out (not shown) on production blades.
[0015] One approach considered to address this problem is partitioning the measured mechanical part into different zones to which a different threshold is applied to account for the measured gap between the different inserts on the reference mechanical part.
[0016] However, the application of a different threshold for different zones must be carried out "by hand", that is to say that a different threshold must be implemented by an operator, for each determined zone, during the measurement. Summary of the invention
[0017] The present invention proposes a solution making it possible to remedy at least in part the aforementioned drawbacks.
[0018] To this end, the invention relates to a method for measuring a mechanical part by ultrasound transmission, comprising:
[0019] - the measurement of a first amplitude map of a transmitted ultrasonic signal through the mechanical part,
[0020] and being characterized in that it further comprises:
[0021] - the measurement of a second amplitude map of a transmitted ultrasonic signal through a reference mechanical part comprising a plurality of voluntary defects, of known surface, distributed in a plane substantially perpendicular to the direction of the measurement;
[0022] - the determination of the surface of each voluntary defect from the second car amplitude tography;
[0023] - the comparison, for each voluntary defect, of its determined surface with its known surface,
[0024] and, if the difference between the determined surface and the known surface is greater than a first determined threshold value,
[0025] - the determination of a corrective gain, adapted so that, after application of said gain corrective to the second amplitude mapping, the difference between the determined surface and the known surface, obtained from the second corrected amplitude mapping, is less than or equal to the first determined threshold value; and,
[0026] - applying the corrective gain to the first amplitude mapping so as to obtain a first corrected amplitude map.
[0027] The method according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:
[0028] - the corrective gain determined for each voluntary defect is applied to the first amplitude mapping in a determined zone of influence, located around the position of the voluntary defect, and of an area greater than or equal to the known area of the voluntary defect.
[0029] - the corrective gain applied to the first amplitude mapping, between the zones of influences of voluntary defects, is determined by interpolation of the values of the corrective gain obtained for each zone of influence.
[0030] - the mechanical part and the reference mechanical part are fan blades.
[0031] - the fan blades comprise a core made of composite material, preferably obtained by three-dimensional weaving, and, on either side of said core, thicknesses of resin and titanium reinforcements.
[0032] - for each voluntary defect, the threshold value determined is equal to thirty percent of its known surface.
[0033] - the intentional defects are round, square or rectangular in shape, preferably obtained from a cut tetrafluoroethylene ribbon.
[0034] - the known surface of the voluntary defects is previously determined by a reference method.
[0035] - the method further comprises:
[0036] - the measurement of a third amplitude map of an ultrasonic signal transmitted through a mechanical calibration part; and,
[0037] - subtracting the third amplitude map from the first map of amplitude.
[0038] - the method further comprises:
[0039] - identification of defects in the mechanical part from the first mapping corrected amplitude. Brief description of the figures
[0040] The present invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description of a non-limiting example which follows, with reference to the appended drawings in which:
[0041] [Fig.l] is an example of ultrasonic transmission measurement of a calibration blade comprising tetrafluoroethylene inserts;
[0042] [Fig.2] is a C-scan mapping of an example of a fan blade and a schematic representation of an example of a reference fan blade to which the transmission ultrasound measurement method according to the invention is applied;
[0043] [Fig. 3] is a step diagram of an embodiment of a method for measuring by ultrasound in transmission of a mechanical part of an aircraft turbomachine according to the invention;
[0044] [Fig.4] is an example of determining the surface area of an insert from the measured amplitude; and,
[0045] [Fig.5] is an example of determining a corrective gain from the comparison of a determined surface and a known surface of inserts. Detailed description of the invention
[0046] [Fig.2] shows a C-scan type mapping of an example of a mechanical part 200 and a schematic representation of a reference mechanical part 202 to which the transmission ultrasound measurement method according to the invention can be applied.
[0047] In the examples shown, the mechanical part 200 and the reference mechanical part 202 are aircraft turbomachine fan blades. In particular, the fan blades 200 and 202 shown comprise a core made of composite material, obtained by three-dimensional weaving, and, on either side of said core, thicknesses of resin and titanium reinforcements (for example in “TA6V” alloy).
[0048] Beyond the example described, those skilled in the art will appreciate that the invention applies to any mechanical part of an aircraft turbomachine for which transmission ultrasound measurement can be used for control. This is the case, for example, of a fan casing.
[0049] The reference blade 202 comprises a plurality of inserts 204 made of tetrafluoroethylene, of known dimensions, positioning and surface, distributed in a plane substantially perpendicular to the direction of measurement.
[0050] Those skilled in the art will appreciate that the example described relates to a reference blade comprising tetrafluoroethylene inserts; however, the invention applies to a reference blade which generally comprises so-called intentional defects. that is to say defects introduced voluntarily into the blade and therefore the dimensions, surface and positioning are known.
[0051] Furthermore, generally speaking, intentional defects are introduced at the location that needs to be checked. For example, inserts may be distributed in a glue joint.
[0052] Similarly, the invention is not limited to round shaped defects such as those shown but applies to any shape of defects such as, for example, square or rectangular inserts. Furthermore, these can be obtained, for example, by cutting tetrafluoroethylene ribbons adapted to obtain the desired shape.
[0053] In all cases, in order to be able to implement the measuring method described below, the surface of the inserts of the reference mechanical part must be known beforehand. For example, it may have been determined beforehand by tomography, by thermography or by any other known method making it possible to determine said surface, conventionally called the reference method.
[0054] In addition, the number, size and arrangement of the inserts present in the reference part can be adjusted to optimize the result of the measuring method described below to a particular profile of mechanical part to be measured. For example, such an adjustment can be made according to the geometry of a mechanical part or the type of defect expected in different areas or another of the mechanical part.
[0055] With reference to [Fig.3], [Fig.4] and [Fig.5], we will now describe an embodiment of a transmission ultrasound measurement method according to the invention.
[0056] The method 300 applies to a mechanical part of an aircraft turbomachine such as the fan blade 200 described with reference to [Fig. 2] and further involves the measurement of a reference mechanical part such as the reference blade 202 also described with reference to [Fig. 2].
[0057] In the non-limiting example described, the method 300 comprises the measurement 302 of an amplitude map of an ultrasonic signal transmitted through a mechanical calibration part. The mechanical calibration part is a healthy mechanical part, that is to say a mechanical part whose geometry and structure are identical to those of the mechanical part to be measured and which does not suffer from any defects such as those which one seeks to measure via the method.
[0058] Step 304 consists of measuring an amplitude map of an ultrasonic signal transmitted through the mechanical part to be measured.
[0059] Step 306 consists of subtracting the amplitude mapping of the ultrasonic signal transmitted through the mechanical calibration part from the amplitude mapping of the ultrasonic signal transmitted through the mechanical part to be measured. As stated above, this subtraction makes it possible to overcome the effects linked to a complex geometry of the mechanical part to be measured and / or local thickness variations of this mechanical part.
[0060] Step 308 consists of measuring an amplitude map of an ultrasonic signal transmitted through a reference mechanical part. As a reminder, as described for the case of the reference blade 202, the reference mechanical part comprises a plurality of tetrafluoroethylene inserts, the surface area of which is known and which are distributed in the part. For example, in a plane substantially perpendicular to the direction of the measurement or, in another example, in a glue joint.
[0061] Step 310 consists of determining the surface area of each insert from the second amplitude mapping of the ultrasonic signal transmitted through the reference mechanical part.
[0062] [Fig.4] illustrates an example of determining the surface area of a round insert from the amplitude of the ultrasonic signal transmitted through the part which contains this insert.
[0063] Curve 400 represents the amplitude of the transmitted ultrasonic signal (from the amplitude mapping) for a single insert. More precisely, it is the ultrasonic signal transmitted on a line running through the insert over its entire diameter.
[0064] As described above, the surface area determined for the insert in question depends on an attenuation threshold value chosen to extract the relevant information. In other words, it is a threshold beyond which the attenuation of the amplitude is taken into consideration.
[0065] In the example shown, the thresholds 402a, 402b and 402c respectively lead to determining a surface 404a of 9 mm2, a surface 404b of 18 mm2 and a surface 404c of 36 mm2 for the same measured insert. This therefore illustrates the role of the threshold value chosen on the value of the surface ultimately determined.
[0066] Step 312 consists of comparing, for each insert, its determined surface area with its known surface area. A corrective gain is then determined from the result of this comparison. More precisely, a non-zero corrective gain is determined if the difference between the determined surface area of the insert and the known surface area is greater than a determined threshold value. For example, the determined threshold value may be equal to thirty percent of the known surface area of the insert. In this case, a corrective gain is determined for each insert for which the determined surface area of the insert is beyond a margin of thirty percent error relative to its actual surface area.
[0067] Step 314 therefore consists of determining a corrective gain, adapted so that, after applying this corrective gain to the amplitude mapping of the ultrasonic signal transmitted through the reference mechanical part, the difference between the determined surface and the known surface of each insert, obtained from this corrected amplitude mapping, is less than or equal to the determined threshold value. In the example described above, the application of the corrective gain results in the difference obtained between the determined surface and the known surface being less than thirty percent of the known surface. Generally speaking, the person skilled in the art will be able to set a margin of error depending on the type of defect targeted by the measurement or the precision desired for a given area, for example.
[0068] For each insert, the “good” corrective gain value, i.e. the one that makes it possible to reduce the difference between the determined surface and the known surface below a chosen threshold value, can be obtained, for example, by iteration. In particular, the corrective gain value for each insert can be modified iteratively until the one that sufficiently reduces the difference between the determined surface and the known surface is obtained.
[0069] [Fig. 5] illustrates an example of determining a corrective gain from the comparison of the determined surface and the known surface of inserts. In particular, the surfaces of 5 inserts are represented for which the determined surface 502 varies according to the inserts while the known surface 504 is the same for all the inserts. More precisely, the determined surface 502a and the known surface 504a are equal, the determined surfaces 502b and 502c are less than the known surfaces 504b and 504c and the determined surface 502d is greater than the known surface 504d.
[0070] In the example shown, the determined surfaces 502 were obtained by extracting the amplitude of the transmitted ultrasonic signal below a determined single attenuation threshold.
[0071] Since the determined surfaces 502b, 502c and 502d and the known surfaces 504b, 504c and 504d are different, a corrective gain must be applied to the amplitude of the transmitted ultrasonic signal. The value of this corrective gain is determined, for example, by modifying the threshold (used to determine the surface of the inserts) for each insert until the difference between the determined surface and the known surface is sufficiently small.
[0072] For example, the threshold in question can be modified iteratively, in steps of 0.5 decibels, until equality is obtained (within the margin of error) between the determined surface and the known surface for each insert. Finally, the difference between the different threshold values that made it possible to obtain the correct surface determined for each insert corresponds to the corrective gain value that is determined for a given insert.
[0073] In the example shown, the determined value of the corrective gain 508 is 0 decibels for the determined surface 502a, 1 decibel for the determined surface 502b, 1.5 decibels for the determined surfaces 502c and -0.5 decibels for the determined surface 502d. This corrective gain makes it possible to finally obtain, for each insert, a determined surface 506 equal to the known surface.
[0074] For reasons of simplicity, the example given in [Fig.5] is restricted to a one-dimensional case; however, in practice, non-zero values of corrective gain are determined for all positions of the inserts in an amplitude map which is two-dimensional.
[0075] Step 316 then consists of applying the determined corrective gain to the amplitude map of the ultrasonic signal transmitted through the mechanical part to be measured so as to obtain a corrected amplitude map.
[0076] Advantageously, the application of the corrective gain is a simple digital processing carried out on the entire amplitude mapping and which therefore does not require differentiated processing by an operator depending on the different zones of the measured mechanical part.
[0077] Furthermore, the corrective gain determined for each insert can be applied to the amplitude mapping in a determined zone of influence located around the position of the insert (i.e. its equivalent in the amplitude mapping of the mechanical part to be measured) and a surface greater than or equal to the known surface of the insert. In other words, the value of the corrective gain that has been determined for an insert can be applied to a larger area than the surface of the insert in which it is considered that the same correction value can be applied. Typically, the size of a zone of influence is determined upstream by a succession of acquisitions and observations aimed at determining whether the inserts are sized uniformly or not.
[0078] Furthermore, in a particular embodiment, the value of the corrective gain between the zones of influence may be determined by interpolation of the values of the corrective gain obtained for each zone of influence. Such interpolation may be carried out, for example, in a polynomial manner.
[0079] Finally, step 318 consists of identifying defects in the measured mechanical part from the corrected amplitude map.
[0080] Thus, advantageously, the corrected amplitude mapping makes it possible to optimize the precision of the detection and dimensioning of defects in all the desired areas of the mechanical part to be measured.
Claims
Claims
1. Method (300) for ultrasonic transmission measurement of a mechanical part (200), comprising: - the measurement (304) of a first amplitude map of an ultrasonic signal transmitted through the mechanical part, and being characterized in that it further comprises: - the measurement (308) of a second amplitude map of an ultrasonic signal transmitted through a reference mechanical part (202) comprising a plurality of voluntary defects (204), of known surface, distributed in a plane substantially perpendicular to the direction of the measurement; - determining (310) the surface area (502) of each voluntary defect (204) from the second amplitude mapping; - the comparison (312), for each voluntary defect (204), of its determined surface (502) with its known surface (504), and, if the difference between the determined surface (502) and the known surface (504) is greater than a first determined threshold value, - determining (314) a corrective gain (508), adapted so that, after applying said corrective gain (508) to the second amplitude mapping, the difference between the determined surface (502) and the known surface (504), obtained from the second corrected amplitude mapping, is less than or equal to the first determined threshold value; and, - applying (316) the corrective gain (508) to the first amplitude mapping so as to obtain a first corrected amplitude mapping.
2. Method (300) according to claim 1, in which the corrective gain (508) determined for each voluntary defect (204) is applied to the first amplitude mapping in a determined zone of influence, located around the position of the voluntary defect (204), and of a surface greater than or equal to the known surface of the voluntary defect. land.
3. Method (300) according to claim 2, in which the corrective gain (508) applied to the first amplitude mapping, between the zones of influence of the inserts (204), is determined by interpolation of the values of the corrective gain (508) obtained for each zone of influence.
4. A method (300) according to any preceding claim, wherein the mechanical part (200) and the reference mechanical part (202) are fan blades.
5. Method (300) according to claim 4, in which the fan blades (200, 202) comprise a core of composite material, preferably obtained by three-dimensional weaving, and, on either side of said core, thicknesses of resin and titanium reinforcements.
6. Method (300) according to any one of the preceding claims, wherein, for each intentional defect (204), the determined threshold value is equal to thirty percent of its known surface area (504).
7. A method (300) according to any preceding claim, wherein the intentional defects (204) are round, square or rectangular in shape, preferably obtained from a cut tetrafluoroethylene ribbon.
8. Method (300) according to any one of the preceding claims, in which the known surface area (504) of the intentional defects (204) is previously determined by a reference method.
9. A method according to any preceding claim further comprising: - measuring (302) a third amplitude map of an ultrasonic signal transmitted through a mechanical calibration part; and, - subtracting (306) the third amplitude map from the first amplitude map.
10. Method according to any one of the preceding claims further comprising: - identifying (318) defects of the mechanical part (200) from the first corrected amplitude map.