# US 2021/0239652 A1 · Method and system for the non-destructive testing of a mechanical part

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- Number: US 2021/0239652 A1
- Document ID: US20210239652A1
- Status: Published application
- Kind: A1
- Application number: 17/049,944
- Filed: 2019-04-19
- Published: 2021-08-05
- Earliest claimed: 2018-04-23
- Assignees: Safran; Centre National De La Recherche Scientifique
- Applicants: Safran; Centre National De La Recherche Scientifique
- Inventors: Aurélien BAELDE; Claire PRADA; Frédéric JENSON
- Web page: https://patentgrep.com/patent/US20210239652A1

## CPC

- G01N 29/043: {in the interior, e.g. by shear waves}
- G01N 29/262: {by electronic orientation or focusing, e.g. with phased arrays (phased arrays per se G10K11/34)}
- G01N 29/4463: {Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering}
- G01N 29/46: by spectral analysis, e.g. Fourier analysis {or wavelet analysis (spectral signal processing per se G06F17/14)}
- G01N 2291/0258: Structural degradation, e.g. fatigue of composites, ageing of oils
- G01N 2291/0289: Internal structure, e.g. defects, grain size, texture
- G01N 2291/106: one or more transducer arrays
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

The invention relates to a method for the non-destructive testing of a mechanical part (2) by propagation of ultrasonic waves accomplished by means of a multi-element transducer (3) placed opposite the mechanical part and comprising a plurality of piezoelectric elements e(1), e(2), . . . , e(N), N>1. It comprises: for each element e(i) of the transducer, the emission of an ultrasonic wave at a given frequency and measurement, by each element e(j) distinct from the element e(i), of a time-varying signal kij(t) representing the back-scattered ultrasonic wave received by the element e(j); the determination of a first matrix of time-varying components based on the measured signals kij(t), i,j=1, . . . , N; the determination of a second matrix of frequency components corresponding to a determined frequency based on the frequency of the ultrasonic wave by applying a Fourier transform to said first matrix; the filtering of said second matrix comprising a projection of it onto a single scattering sub-space determined by means of a numerical calculation using a ray tracing algorithm; and the verification of the integrity of the mechanical part by using said filtered second matrix.

## Claims

### Claim 1

A method for the non-destructive testing of a mechanical part by propagation of ultrasonic waves accomplished by means of a multi-element transducer placed opposite the mechanical part and comprising a plurality of piezoelectric elements e(1), e(2), . . . , e(N), N designating an integer greater than 1, said testing method comprising:
a measuring step comprising, for each element e(i) of the transducer, the emission of an ultrasonic wave at a given frequency and the measurement, by each element e(j) of the transducer distinct from the element e(i), of a time-varying signal denoted kij(t) representing the back-scattered ultrasound wave received by the element e(j);
a step of determining at least one first matrix of time-varying components based on the measured signals kij(t), i,j=1, . . . , N, taken over a predetermined duration around a time reference denoted T;
a step of determining at least one second matrix of frequency components corresponding to a predetermined frequency based on the frequency of the sound wave by applying a Fourier transformation to the time-varying components of said at least one first matrix;
a step of filtering said at least one second matrix comprising a projection of said at least one second matrix of frequency components onto a single scattering sub-space; and
a step of verifying the integrity of the mechanical part by using said at least one filtered second matrix;
the testing method being characterized in that the single scattering sub-space used during the filtering step is determined by means of a numerical calculation using a ray tracing algorithm.

### Claim 2 (depends on 1)

The testing method according to claim 1, wherein the step of filtering said at least one second matrix comprises:
a step of determining the single scattering sub-space, said single scattering sub-space being defined based on a base of 2N−1 matrices denoted Em, m=1, . . . , 2N−1, said determining step comprising:
for each couple of distinct elements e(i) and e(j) of the transducer, i, j=1, . . . , N, a numerical calculation step using a ray-tracing algorithm, for a plurality D of scatterers denoted Pd, d=1 . . . , D distributed in various points of the mechanical part and situated at a depth determined from the time reference T, of a propagation time tijd of an ultrasonic wave emitted by the element e(i), diffracted by the scatterer Pd and received by the element e(j), the propagation time tijd being calculated taking into account the shape of the mechanical part, the placement of the transducer and the media in which the ultrasonic wave is propagated between the elements e(i) and e(j) of the transducer and the scatterer Pd;
a step of estimating a contribution of single scattering in the frequency components of the second matrix, based on the propagation times calculated for each couple of distinct elements e(i) and e(j) of the transducer, said estimating step supplying a third matrix;
a step of extracting the frequency components from a central anti-diagonal of the third matrix to construct the matrix base Em, m=1, . . . , 2N−1 defining the single scattering sub-space;
a step of projecting said at least one second matrix onto each of the matrices Em, m=1, . . . , 2N−1 of the base of 2N−1 matrices; and
a step of evaluating said at least one filtered second matrix by summing the matrices Em of the base weighted by the projections obtained during the projection step.

### Claim 3 (depends on 2)

The testing method according to claim 2, wherein each propagation time tijd is calculated according to:
tijd=minPetid(Pe)+minPstdj(Ps)
where Pe designates an entry point with coordinates (xe, ze) of the ultrasonic wave into the mechanical part and Ps an exit point with coordinates (xs, zs) of the ultrasonic wave diffracted by the point Xd with coordinates (xd, zd), with:
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and
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where c1 designates the propagation speed of the ultrasonic wave in the medium separating the transducer from the mechanical part and c2 designates the propagation speed of the ultrasonic wave in the mechanical part.

### Claim 4 (depends on 1)

The testing method according to claim 1, wherein the mechanical part is a billet or a fan disk or a one-piece impeller of an aircraft engine.

### Claim 5 (depends on 1)

The testing method according to claim 1, wherein several first matrices corresponding to different time references and/or to different predetermined durations are determined.

### Claim 6 (depends on 1)

The testing method according to claim 1, wherein said at least one second matrix is determined at the frequency of the ultrasonic wave.

### Claim 7 (depends on 6)

The testing method according to claim 6, wherein several second matrices are determined at a plurality of frequencies contained in a predetermined interval around the frequency of the ultrasonic wave.

### Claim 8 (depends on 1)

The testing method according to claim 1, in which the step of verifying the integrity of the mechanical part uses a DORT technique of diagonalization of the time reversal operator or a total focusing method.

### Claim 9

A system for non-destructively testing a mechanical part comprising:
a multi-element transducer placed opposite the mechanical part and capable of emitting ultrasonic waves, said transducer comprising a plurality of piezoelectric elements e(1), e(2), . . . , e(N), N designating an integer greater than 1, said transducer being configured to emit, via each element e(i) of the transducer, an ultrasonic wave at a given frequency, and to measure, via each element e(j) of the transducer distinct from the element e(i), a time-varying signal denoted kij(t) representing the back-scattered ultrasonic wave received by the element e(j);
a validation device comprising:
a first determination module, configured to determine at least one first matrix of time-varying components based on the measured signals kij(t), i,j=1, . . . , N, taken for a predetermined duration around a time reference denoted T;
a second determination module, configured to determine at least one second matrix of frequency components corresponding to a frequency determined based on the frequency of the sound wave by applying a Fourier transformation to the time-varying components of said at least one first matrix;
a filtering module, configured to filter said at least one second matrix by projecting said at least one second matrix of frequency components onto a single scattering sub-space; and
an analysis module, configured to verify the integrity of the mechanical part by using said at least one filtered second matrix;
the testing system being characterized in that said filtering module is configured to determine the single scattering sub-space by means of a numerical calculation using a ray tracing algorithm.

### Claim 10 (depends on 9)

The testing system according to claim 9, wherein said filtering module comprises:
a third determination module configured to determine the single scattering sub-space based on a base of 2N−1 matrices denoted Em, m=1, . . . , 2N−1, said third determination module being configured to:
for each couple of distinct elements e(i) and e(j) of the transducer, i, j=1, . . . , N, calculate numerically, but using a ray-tracing algorithm, for a plurality D of scatterers denoted Pd, d=1 . . . , D distributed in various points of the mechanical part and situated at a depth determined from the time reference T, a propagation time tijd of an ultrasonic wave emitted by the element e(i), diffracted by the scatterer Pd and back-scattered by the element e(j), said propagation time being calculated taking into account the shape of the mechanical part, the placement of the transducer and the media in which the ultrasonic wave is propagated between the elements e(i) and e(j) of the transducer and the scatterer Pd;
estimate a contribution of single scattering in the frequency components of the second matrix, based on the propagation times calculated for each couple of distinct elements e(i) and e(j) of the transducer, and obtaining a third matrix based on the estimated contributions;
extract frequency components from a central anti-diagonal of the third matrix to construct the matrix base Em, m=1, . . . , 2N−1 defining the single scattering sub-space;
a projection module, configured to project said at least one second matrix onto each of the matrices Em, m=1, . . . , 2N−1 of the base of 2N−1 matrices; and
an evaluation module configured to evaluate said at least one filtered second matrix by summing the matrices Em of the base weighted by the projections obtained during the projection step.

### Claim 11 (depends on 9)

The testing system according to claim 9, also comprising a robotic arm on which is placed the multi-element transducer, said robotic arm being configured to allow displacement of the multi-element transducer around the mechanical part.

### Claim 12 (depends on 9)

The testing system according to claim 9, wherein the transducer is linear.