Method for testing the condition of a drive shaft of a rotary machine
A method for non-destructive testing of a drive shaft that is accessible by only one of its ends in longitudinal waves, using a multi-element annular ultrasonic transducer. Such a transducer consists of independent elements that can be excited by electrical pulses of the same frequency, but for which different electronic phase shifts will be applied, in the invention, to the pulses transmitted to the elements. Such an electronic phase shift allows the focussing or deflection of a final beam synthesized by all the elements constituting the transducer, the said final beam being concentrated to adopt a generally cylindrical shape with a cross-section that is far smaller than the cross-section of the shaft to be tested and is highly energetic over a long distance due to the waveguide effect created by the cylindrical geometry of the shaft.
1. A method for testing a drive shaft of a rotary machine, the drive shaft being solid, of a generally cylindrical shape, the method comprising the steps of:
providing, at one end of the shaft to be tested, an annular transducer including a plurality of independent elements, each element being capable of at least transmitting an ultrasonic elementary beam in longitudinal waves in the drive shaft; and
applying a first predetermined law of focussing to at least some of the independent elements, the first law of focussing including a number of transmission delays to be respected between the different elements of the transducer, in order to generate a first final beam having a generally cylindrical shape and deflected at a predetermined angle in order to target a first particular sector of the drive shaft to be tested.
2. The method according to claim 1 , further comprising modifying the first law of focussing in order to obtain a second law of focussing generating a second final beam in order to target a second particular sector of the drive shaft to be tested.
3. The method according to claim 1 , further comprising rotating the annular transducer using a motor and about a central axis of the drive shaft.
4. The method according to claim 1 , further comprising applying the first law of focussing on several occasions by shifting, on each occasion, by at least the same number of the individual elements, each delay.
5. The method according to claim 1 , wherein the annular transducer includes eight of the independent elements distributed in a single ring.
6. The method according to claim 5 , further comprising:
applying a first delay to a first element of the independent elements and a second delay to a second element, the second delay being longer than or equal to the first delay;
applying a third delay to a third element, a fourth delay to a fourth element, a fifth delay to a fifth element, a sixth delay to a sixth element, the sixth delay being equal to the fifth delay, itself longer than the fourth delay, itself equal to the third delay, itself longer than the second delay;
applying a seventh delay to a seventh element, and an eighth delay to an eighth element, the eighth delay being equal to the seventh delay, itself longer than the sixth delay, in order to generate a seventh elementary beam and an eighth elementary beam, concentrated on a circular focal point, thereby creating, downstream from the focal point, the first final beam.
7. The method according to claim 6 , wherein the first element, the third element, the seventh element and the fifth element are located consecutively on a first half of the annular transducer, these elements being symmetrical, in relation to a plane perpendicular to a transmission surface of the circular annular transducer and centered on the transducer, to the second element, the fourth element, the eighth element and the sixth element respectively.
8. The method according to claim 1 , wherein the annular transducer includes a first outer ring, arranged on a periphery of the transducer, and a second inner ring, arranged closer to the center of the transducer, the first and second rings being concentric.
9. The method according to claim 8 , wherein the annular transducer includes thirty two of the independent elements, the first and second rings each comprising sixteen of the independent elements.
10. The method according to claim 1 , wherein the delays applied to generate two consecutive elementary beams are of the order of one hundred of a nanoseconds.
11. The method according to claim 1 , wherein a sum of the delays constituting all the delays of the first law of focussing is shorter than a transmission time of the elementary beam transmitted by each independent element of the annular transducer.
12. The method according to claim 1 , wherein the drive shaft is a wheel shaft of a primary pump of a nuclear reactor.