Non-destructive testing of mechanical parts made of polycrystalline materials

Abstract

The invention relates to a device for non-destructive testing of mechanical parts made of polycrystalline material, said device comprising: - an ultrasonic probe (1) comprising a two-dimensional array of transducers capable of transmitting and receiving signals at different excitation angles, and - a processing module (2) adapted to control the transmission and reception of the transducers, to process the signals received by the transducers so as to express the signals received by the ultrasonic probe in two plane wave planes constituted by the transmission and reception wave vectors of the probe, and to derive therefrom information representative of the three-dimensional orientation of the fibrous structure of the mechanical part.

Description

TECHNICAL FIELD

[0001] The present application relates generally to the non-destructive testing of mechanical parts. It is particularly applicable to mechanical parts made of polycrystalline material. BACKGROUND

[0002] A large number of critical parts of aircraft engines are made of titanium alloys. These parts are forged from cylinders called "billet". Optionally, they are pre-machined or machined.

[0003] Titanium, like certain alloys, is a polycrystalline material, that is to say, it is composed of grains which are liable to deform during the various forging steps undergone. The shaping of the part causes a deformation of its macrostructure and can lead to the presence of defects in the part.

[0004] The fibrous structure plane corresponds to a map of the deformations undergone by the part during shaping. The deformation of the grains at any point of the part can be numerically predicted by software, but the results are not completely reliable. For example, due to errors in the manufacturing of the billet or drifts during the forging of the part, the actual fibrous structure of the part is sometimes not in agreement with the theoretical fibrous structure.

[0005] In order to ensure the integrity of these parts before assembly in the reactor and to test that they are free of any defects (such as cracks, porosities or inclusions), the parts are tested non-destructively by ultrasound in order to detect any possible signs of defects. These tests are carried out on the billet, as well as on the part formed after forging. They are carried out using one or more piezoelectric transducers. It is known to use a single-element piezoelectric probe or a multi-element probe (annular or linear).

[0006] The ultrasound testing of the part is designed with the fibrous structure plane of the part envisaged as being known.

[0007] It is known that, when the incident ultrasound propagates in a direction perpendicular to the fibrous structure, that is to say, perpendicular to the preferred direction of elongation of the grains of the polycrystalline material constituting the part, it is optimal for defect detection. The direction of the acoustic beam is therefore determined by the fibrous structure plane envisaged: this is an important factor to take into account when designing the testing plane. The determination of the fibrous structure of the part is therefore essential to ensure optimal reliability and safety.

[0008] However, as has been discovered, it is possible that the actual fibrous structure of the part is not in agreement with the theoretical fibrous structure used for the design of the test. This is a problem because the test carried out is not adapted to the part and, in the most extreme cases, this can have a detrimental effect on the detection of defects.

[0009] Furthermore, knowledge of the fibre structure also provides information about the mechanical strength of the component.

[0010] WO 2018 / 138430 proposes an ultrasonic testing of a component to determine the elongation direction of elongated microstructures located in the component. For this purpose, a linear transducer is moved translationally and rotationally by a motion device comprising for example a robot arm or a movable support. The measurement results are mathematically processed in real space.

[0011] US 6 387 197 relates to a method of processing titanium to form a titanium article that reduces the ultrasonic noise generated during ultrasonic inspection.

[0012] Coarse granular materials are generally difficult to evaluate ultrasonically. The difficulty arises because the acoustic waves used for ultrasonic inspection can be partially reflected from the granules and exhibit "structure noise", or granule noise. The resulting structure noise can hide defects in the material and is therefore undesirable.

[0013] US 5 471 878 relates to a method for suppressing granule noise during ultrasonic inspection of an object, thereby achieving a high defect detection rate and a low defect false indication rate.

[0014] WO 2010 / 142927 discloses an ultrasonic method and apparatus for characterizing a medium. In particular, it relates to non-destructive testing of the state of a mechanical component, such as a human or animal bone. The apparatus uses a one-dimensional probe whose transducers are not able to emit and receive signals at different excitation angles. "Trajectories" are determined, which are defined as lines of high energy, each reflecting a vibration mode and forming a component characteristic of the propagation medium. They correspond to energy maxima in a frequency-velocity-of-propagation reference frame. These trajectories are therefore independent of the three-dimensional orientation of the fibre structure of the mechanical component.

[0015] There is currently no efficient industrial non-destructive method to determine the fibre structure orientation of a component made of polycrystalline material. SUMMARY

[0016] The present invention aims to solve the problems existing in the prior art by providing a non-destructive testing apparatus for a mechanical component made of polycrystalline material, said non-destructive testing apparatus comprising:

[0017] - an ultrasonic probe comprising a two-dimensional array of transducers, said transducers being able to emit and receive signals at different excitation angles, and

[0018] - a processing module adapted to control the transducers in emission and reception, and to process the signals received by the transducers so as to express the signals received by the transducers in two planes of plane waves constituted by the emission and reception wave vectors of the probe, and to derive therefrom information representative of the three-dimensional orientation of the fibrous structure of the mechanical part.

[0019] Thanks to the application, it is possible to emit ultrasound beams having different angles without rotating the probe. Thus, in a single acquisition and without user intervention, it is possible to acquire a set of ultrasound signals sufficient to carry out a suitable processing. This processing then makes it possible to construct virtual wave vectors, thus making it possible to derive information on the local and three-dimensional orientation of the fibrous structure.

[0020] The application makes it possible to obtain greater robustness of the measurements while being compatible with industrial systems.

[0021] According to a preferred feature, the processing module is adapted to construct a three-dimensional reflection matrix.

[0022] According to a preferred feature, the processing module is adapted to express the signals received by the transducers in a basis of plane waves.

[0023] According to a preferred feature, the processing module is adapted to construct the two planes of plane waves by the sum and the difference, respectively, of the wave vectors associated with the plane waves emitted and received by the probe.

[0024] According to a preferred feature, the processing module is adapted to derive information representative of the three-dimensional orientation of the fibrous structure of the mechanical part by determining the direction associated with the intensity maxima of the received signals expressed in the two planes of plane waves constituted by the emission and reception wave vectors of the probe.

[0025] The application also relates to a method for non-destructive testing of a mechanical part made of polycrystalline material, implemented in the device described above, characterized in that it comprises a step of controlling the transducers in emission and reception, a step of processing the signals received by the transducers, a step of expressing the signals received by the transducers in two planes of plane waves constituted by the emission and reception wave vectors of the probe, and a step of deriving information representative of the three-dimensional orientation of the fibrous structure of the mechanical part.

[0026] This method has similar advantages to those set out previously.

[0027] In a particular embodiment, the steps of the method according to the application are implemented by computer program instructions.

[0028] The application therefore also relates to a computer program on an information medium, which program is capable of being implemented in a computer, the program comprising instructions adapted to implement the steps of the method described above.

[0029] The program can be in any programming language and can be in the form of source code, object code, or intermediate code such as partially compiled form, or any other desired form for including use of a computer program.

[0030] The application also relates to a computer-readable information medium comprising computer program instructions adapted to implement the steps of the method described above.

[0031] The information medium can be any entity or device capable of storing the program. For example, the medium can comprise a storage medium such as a ROM, for example a CD ROM or microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a hard disk.

[0032] On the other hand, the information medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed by cable or optical cable, by radio or by other means. The program according to the application can be especially downloaded from a network of the Internet type.

[0033] Alternatively, the information medium can be an integrated circuit in which the program is incorporated, the circuit being adapted to execute the method according to the application or to use in the execution of the method according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0034] Other features and advantages will become apparent on reading the following description, given as a non-restrictive example, of preferred embodiments, with reference to the attached drawings in which:

[0035] [ Figure 1 ] shows a non-destructive testing device according to one embodiment of the application, in the detection of a mechanical part,

[0036] [ Figure 2 ] shows a top view of an ultrasonic probe applied in the device according to one embodiment of the application, Figure 1

[0037] [ Figure 3 ] shows a method for non-destructive testing of a mechanical part according to one embodiment of the application,

[0038] [ Figure 4 ] is a schematic view of wave vectors associated with plane waves emitted and received by an ultrasonic probe according to one embodiment of the application.

[0039] Identical, similar or equivalent parts of different drawings are provided with the same reference numerals so as to facilitate the transition from one drawing to another.

[0040] The different parts shown in the drawings are not necessarily shown to the same scale in order to make the drawings more readable. ​

[0041] The various possibilities (variants and embodiments) must be understood as not mutually exclusive and capable of being combined with one another. DETAILED DESCRIPTION

[0042] Figure 1 A mechanical part P made of polycrystalline material, for example titanium, is shown. The part P is forged and, optionally, pre-machined and / or machined. The part P comprises an internal fibrous structure, which is schematically shown as a cylinder.

[0043] The part P must be detected in a non-destructive manner, in order to verify that it is free of any defects, such as cracks, porosities or inclusions. Such detection can be carried out using ultrasonic technology. For this purpose, the user needs to know the direction of the fibrous structure of the part, i.e. the preferred local direction of elongation of the material grains. In fact, it is known that when the incident ultrasonic waves propagate in a direction perpendicular to the fibrous structure, it is optimal for defect detection.

[0044] The non-destructive detection device that will be described is able to determine the direction of the fibrous structure of the part P.

[0045] According to Figure 1 The preferred embodiment shown, the device for non-destructive detection of a mechanical part made of polycrystalline material comprises an ultrasonic probe 1 comprising a two-dimensional network of transducers capable of emitting and receiving signals at different propagation angles.

[0046] Figure 2 A bottom view of the ultrasonic probe 1 is shown. The transducers are rectangular, with two dimensions a x and a y distributed along the axes X and Y. The transducers are independent of one another and capable of performing emission and reception tests. It should be noted that other transducer geometries are possible and the arrangement of these transducers can be regular or arbitrary.

[0047] The non-destructive detection device also comprises a processing module 2 connected to the ultrasonic probe 1. The processing module 2 is adapted to test the transducers when emitting and receiving and to process the signals received by the transducers, as described below.

[0048] The processing module 2 is implemented as a computer.

[0049] In particular, the computer 5 comprises a processor 100, a memory 101, an input interface 102 and an output interface 103.

[0050] These different elements are generally connected by a bus 105.

[0051] The processor 100 executes a computer program implementing the method according to the application. These processing operations are performed in the form of computer program code instructions, stored by the memory 101 before being executed by the processor 100.

[0052] The output interface 103 is connected to the probe 1 and transmits data representative of control instructions for the transducers of the probe 1.

[0053] The input interface 102 is connected to the probe 1 and is used to receive data representative of the signals received by the transducers.

[0054] Two configurations for detecting the component are possible, as described below:

[0055] - in a first configuration, the probe is positioned directly on the component to be detected (configuration called "contacted"), the transmission of ultrasound then being ensured by a coupling gel or water;

[0056] - in a second configuration, the component to be detected and the probe are immersed in water, the probe being positioned facing the component to be detected, the correct transmission of ultrasound then being ensured by the water.

[0057] Figure 3 The non-destructive testing method of Figure 1 shows an embodiment of the operation of the non-destructive testing device of

[0058] It is assumed that the component P has been arranged in this way to be tested.

[0059] Step El is the emission of ultrasound signals, controlled by the probe 1. For this, all or part of the probe is used to emit a series of signals in the real space related to the plane of the probe. The emission is for example made by the transducers. Each elementary shot of the transducers emits a circular wave. Obtaining a matrix called "real space" matrix requires all elementary shots (that is one elementary shot per transducer).

[0060] If the signal to noise ratio is insufficient, the emission of ultrasound signals can also be made in other spaces, for example a series of plane waves with defined wave vectors k 发射 for detecting different angles. In this case, all the transducers are used, so the total radiated energy is higher.

[0061] The plane wave beam uses all the transducers and sends plane waves at precise and defined angles. The angles of the reflection matrix are obtained directly in the plane wave space, requiring a sequence of beams corresponding to each angle of the reflection matrix.

[0062] The next step E2 is the reception of ultrasound signals by the probe 1.

[0063] For the emission, there are different possibilities in terms of reception. The first possibility is to apply a delay law to the received ultrasound signals in order to express them in a plane-wave base. In this case, the reception of the ultrasound signals is performed in a plane-wave base.

[0064] Another possibility is to perform the reception in real space. In this case, as explained below, a double spatial Fourier transform will be applied to the received ultrasound signals in order to perform a base change to return to the plane-wave base.

[0065] In a next step E3, all the signals received by the probe 1 are rearranged into a reflection matrix K in order to be able to perform advanced signal processing on these signals.

[0066] Step E3 is to construct a reflection matrix K comprising the signals received by the probe 1 expressed in one of the following bases:

[0067] a. Canonical base or elementary base: the elements of the probe emit or receive backscattered signals independently one by one.

[0068] b. Plane-wave base: the elements of the probe emit or receive backscattered signals with certain delays to produce plane waves of a selected propagation direction k 发射 .

[0069] c. Combination of the two bases above in emission and reception.

[0070] The reflection matrix K is composed of 3 dimensions: the selected base in emission, the selected base in reception, and the time.

[0071] The selected base in emission is the canonical base u 发射 or the plane-wave base k 发射 . The selected base in reception is the canonical base u 接收 or the plane-wave base k 接收 .

[0072] The probe 1 is a matrix (2D), each dimension u 发射 , u 接收 , k 发射 , k 接收 is a vector with two components labeled x and y.

[0073] Figure 4 The wave vectors k 发射 and k 接收 associated respectively with the plane waves emitted and received by the probe 1 are illustrated.

[0074] The next step E4 is to apply a time Fourier transform to each of the acquired elementary signals in order to represent these signals in the frequency space according to the last dimension of the reflection matrix K. It is worth recalling that the reflection matrix K comprises two spatial dimensions and one time dimension.

[0075] The result of step E4 is a reflection matrix Kf whose third dimension is the frequency.

[0076] It is possible to consider a single frequency, for example the nominal frequency of the transducer. This limits the computation time.

[0077] It is also possible to consider a bandwidth, for example the bandwidth of the transducer, in which case the signals are averaged over the considered bandwidth in order to improve the signal-to-noise ratio.

[0078] In all cases, the computation is done frequency by frequency.

[0079] The next step E5 is to determine whether the emission or the reception of the ultrasound signals has been done in the regular basis or whether the emission and the reception of the ultrasound signals have been done in the regular basis. When this is the case, the received signals are spatially Fourier transformed over the relevant dimension of the reflection matrix in order to express the received signals in the plane wave basis.

[0080] The transfer matrix from the regular basis to the plane wave basis is as follows: P(u, k) = exp(±i k.u), this sign depending on the convention chosen for the Fourier transform, u denoting the regular basis, k denoting the plane wave basis, and "." denoting the scalar product.

[0081] If the emission and the reception are done in the plane wave basis, the reflection matrix is not changed at this step.

[0082] The reflection matrix has 3 dimensions: the plane wave basis k 发射 = (k x，发射 , k y，发射 ) in emission, the plane wave basis k 接收 = (k x，接收 , k y，接收 ) in reception and the considered frequency or frequencies f.

[0083] In the next step E6, two virtual matrices are constructed from the sum and the difference of the wave vectors k 接收 and k 发射 of the probe:

[0084] K1(k x，发射 +k x，接收 ; k y，发射 +k y，接收 ; k x，发射 ; k y，发射 ; f), and

[0085] K2(kx，接收 -k x，发射 ; k y，接收 -k y，发射 ; k x，发射 ; k y，发射 ; f).

[0086] From a physical point of view, these two matrices contain information on the local fiber structure direction.

[0087] In a next step E7, the matrices K1 and K2 are averaged over the third, fourth and fifth dimension k x，发射 , k y，发射 and the frequency. This operation consists in computing the average of the elements of the matrices by changing the indices of the third, fourth and fifth dimension of the elements of the matrices (while the indices of the other dimensions remain unchanged).

[0088] It should be noted that for the frequency dimension, the average computation is only performed if the bandwidth is taken into account. In this case, the information is averaged over the bandwidth. If only one frequency is considered, there is no average computed over the frequency dimension.

[0089] This step results in the following two two-dimensional matrices: K1 m (k x，发射 +k x，接收 ; k y，发射 +k y，接收 ) and K2 m (k x，接收 -k x，发射 ; k y，接收 -k y，发射 ).

[0090] The signal backscattered by the piece P is expressed in terms of plane waves "k 发射 +k 接收 " and "k 接收 -k 发射 " whose planes are constituted by the wave vectors k 接收 and k 发射 of the probe. These planes of plane waves "k 接收 +k 发射 " and "k 接收 -k 发射 " carry the available information to determine the direction of the fiber structure.

[0091] In a next step E8, the matrices K1 m and K2 m are analyzed to deduce the three-dimensional (3D) structure direction of the fibers.

[0092] Step E8 is based on the analysis of the matrices K1 m and K2m The orientation of the fibre structure at each point under consideration is determined from the direction associated with the maximum of the intensity of the signal in K1

[0093] The point of maximum intensity is the point of the matrix K1 m and K2 m which is the point of maximum of the maximum. When the part has an anisotropic fibre structure, the point of maximum intensity follows a preferred direction which provides information on the direction of the fibre structure.

Claims

1. Apparatus for non-destructive testing of mechanical parts made of polycrystalline material, comprising: - an ultrasonic probe (1) comprising a two-dimensional array of transducers capable of transmitting and receiving signals at different excitation angles, and - a processing module (2) adapted to test the transducers in transmission and reception, and to process the signals received by the transducers so as to express the signals received by the transducers in terms of two planes of plane waves constructed with the sum and the difference of the wave vectors respectively associated with the plane waves transmitted and received by the probe, and to derive therefrom information representative of the three-dimensional orientation of the fibre structure of the mechanical part. The processing module (2) is adapted to construct a three-dimensional reflection matrix (K). The processing module (2) is adapted to express the signals received by the transducers in terms of a plane wave basis.

2. The device for non-destructive testing of mechanical parts made of polycrystalline material according to claim 1, wherein, The processing module (2) is adapted to derive information representative of the three-dimensional orientation of the fibre structure of the mechanical part by determining the directions associated with the intensity maxima of the received signals expressed in terms of the two planes of plane waves constructed with the transmission and reception wave vectors of the probe.

3. Apparatus for non-destructive testing of mechanical parts made of polycrystalline material according to claim 1 or 2, wherein, The method comprises the steps of controlling the transducers in transmission and reception (El, E2), processing the signals received by the transducers, expressing the signals received by the transducers in terms of the two planes of plane waves constructed with the transmission and reception wave vectors of the probe (E7), and deriving information representative of the three-dimensional orientation of the fibre structure of the mechanical part (E8).

4. Apparatus for non-destructive testing of mechanical parts made of polycrystalline material according to claim 1 or 2, wherein, 6. A computer program product comprising instructions for performing the steps of the method according to claim 5 when executed by a computer.

5. A method for non-destructive testing of mechanical parts made of polycrystalline material, said method being implemented in a device according to any one of claims 1 to 4, characterized in that, 7. A computer-readable recording medium having recorded thereon a computer program comprising instructions for performing the steps of the method according to claim 5. ​ ​

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