Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-04-30
2001-03-20
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S641000, C073S622000
Reexamination Certificate
active
06202489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ultrasonic testing method, particularly of an immersed, cylindrical part. More specifically, the invention relates to such a method for detecting internal defects within billets such as titanium billets used in aeronautics.
2. Description of the Related Art
Many part testing systems which operate in the ultrasonic transmission or reflection mode are known.
Ultrasonic part testing may be implemented using a plurality of acoustic transducers elements of fixed focus to detect defects at different depths in the part being tested. Each transducer emits an ultrasonic beam focused at a predetermined depth in the part. The transducers are fitted with focal planes at increasing depths to allow testing the entire volume of the part from the surface to the center.
Ultrasonic part testing also may be carried out using an acoustic probe comprising several electronically focused transducer elements, in which the focusing is implemented by applying different time delays to the signals emitted by each transducer. When obtaining a part's image and using a grid of transducers as the source/receiver, a major difficulty is encountered in that echoes from the reflection at the microstructure of the material are high relative to echoes from any defects such that the former echoes mask the latter. This problem is compounded when the shape of the part is complex and/or the part has a heterogeneous structure, for instance in the case of titanium billets.
It is known to overcome this problem using an appropriate ultrasonic amplification technique with conjugate phase, also called time reversal. According to this technique, following transmission of an unfocused or barely focused ultrasonic beam and reception of the echo returned by the defect to be detected, the returned echo is re-emitted after its time and shape distribution have been reversed in time. An application of this procedure to ultrasonic, cylindrical part testing is described in U.S. Pat. No. 5,513,532. This technique allows optimal focusing on any defect in heterogeneously structured parts such as titanium parts; however, it suffers the major drawback of being time-consuming in the focusing of the ultrasonic beam, thereby substantially increasing the time required to inspect the part as compared to the conventional procedures using electronic focusing.
SUMMARY OF THE INVENTION
The objective of the invention is to mitigate the drawbacks of the known ultrasonic tests for parts of complex geometry and heterogeneous structure such as titanium billets, such that the testing of the part's volume is accomplished in a minimum of time and with a constant and highest possible detection sensitivity level.
To that end, the testing method according to the invention uses a multi-element transducer transmitting focused ultrasonic waves into the part, with the focusing being carried out in two different modes by multichannel electronics. The two focusing modes are an electronic focusing mode and a time reversal focusing mode, which are selected as a function of the depth of the zone being tested.
The time reversal focusing mode is selected to inspect central zones located at the largest depths around the longitudinal axis of the part.
The electronic focusing mode is selected to inspect intermediate zones located at depths between the central zones and a peripheral zone of the part.
According to the invention, ultrasonic immersion testing of a geometrically complex part having a longitudinal axis is carried out such that during rotation of the part, ultrasonic waves are transmitted into test zones located at different billet depths, with the focusing being carried out by one transducer, comprising a plurality of transducing elements, in two different focusing modes, which are selected as a function of the depth of the particular zone being tested.
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Beffy Lionel
Fink Mathias Alexandre
Mangenet Yves Gérard
Miette Véronique
Wu Jean François
Bacon & Thomas PLLC
Kwok Helen
Societe Nationale d'Etude et de Construction de Moteurs d&a
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