Measuring and testing – Vibration – By mechanical waves
Patent
1986-03-12
1988-02-23
Levy, Stewart J.
Measuring and testing
Vibration
By mechanical waves
73632, G01N 2900
Patent
active
047262311
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an arrangement for the ultrasonic examination of objects in local immersion.
PRIOR ART
It is known that the investigation of internal defects in objects by means of a beam of ultrasonic waves is only possible with a high degree of efficiency if the ultrasonic waves are transmitted directly to the object from a layer of liquid which is in contact with the object and in which they are propagated. This result is generally obtained by immersing the object to be examined in a cell, which is generally filled with water and in which the ultrasonic transducer is likewise immersed. This method has the disadvantage of giving rise to a certain oxidation of metallic objects and to instances of water retention in objects constructed of composite materials.
In order to remedy the abovementioned disadvantages, recourse has already been had to the process referred to as "local immersion", which makes use of an arrangement comprising a hydraulic circuit with a pump, in order to produce at least one jet of liquid, more especially of water, and to direct the jet onto the object to be examined, as well as at least one ultrasonic transducer disposed in such a manner that the jet of water guides the ultrasonic waves between the transducer and the said object, a relative movement being produced between the latter and the jet of water in such a manner as to scan the various superficial zones of the object to be examined.
This process may make use either of the transmission of the ultrasonic waves through the object to be examined or of reflection thereof by its internal defects. In the first case, two jets of liquid must be directed onto opposite surfaces of the object, and ultrasonic emitter and receiver, which are distinct from one another, must be coupled with the two jets respectively. In the second case, a single ultrasonic emitter-receiver may be coupled with a single jet.
By reducing the time of contact of each superficial zone of the object to be examined with the water, the local immersion process reduces the risks of oxidation of metallic objects and of water retention in objects constructed of composite materials. Moreover, it permits examination of objects exhibiting strong absorption or having a large thickness. Finally, as the investigation of defects is based on a process of scanning the surface of the object, it requires less accurate relative positioning of the object and of the jet of water, and thus also of the ultrasonic transducer.
However, the local immersion process has not permitted detection of defects in objects with the same precision and the same certainty as the process of total immersion of a cell. This is principally due to the difficulty in obtaining a jet of water, the pressure of which is entirely stable with the passage of time. The instability of the pressure causes interference with the beam of ultrasonic waves and, consequently, fluctuations of the signal of the latter on entry thereof into the object to be examined or on exit thereof from the latter.
On the other hand, it is very difficult to avoid entirely eddies, sources of loss of ultrasonic energy, and, in consequence, of impairment of the signal-to-noise ratio, which corresponds to poor coupling between the beam of ultrasonic waves and the jet of water which guides it.
For the purpose of remedying these disadvantages, there was proposed, for example, in the U.S. Pat. No. 3,908,445 of Sept. 30, 1975 an arrangement for the ultrasonic examination of an object by a local immersion technique, comprising: towards the object to be examined a jet of said liquid and a beam of ultrasonic waves which is contained in said jet and is coaxial with this jet, diffracted by said object when it is struck by the said jet and the said beam of ultrasonic waves, the said coupling head comprising: chamber by at least one channel for the passage of the liquid, by means of an active surface, which is directed towards the object, said active surface being situated within the second chamber, centered on
REFERENCES:
patent: 3255626 (1966-06-01), Van der Veer
patent: 3908445 (1975-09-01), Verdon et al.
patent: 4507969 (1985-04-01), Djordjevic et al.
Pepin Philippe
Tretout Herve
Arana L. M.
Levy Stewart J.
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