Measuring and testing – Vibration – By mechanical waves
Patent
1982-05-07
1984-07-17
Ciarlante, Anthony V.
Measuring and testing
Vibration
By mechanical waves
G01N 2904
Patent
active
044598513
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for localizing and analyzing sound emissions, wherein the position of the sound-emitting source is determined by incoming sound pulses at various measuring locations. Further, the invention relates to a device operating in accordance with this method for localizing and analyzing sound emissions, which is particularly intended for testing for points of damage in apparatus and structural components, and for monitoring apparatus and structural components.
The object of the invention shall be explained below with reference to the principal field of application of the invention. However, the invention cannot only be used in this field, but in any other field in which a localization of the source of sound emissions by incoming sound pulses is to be effected.
In the operation of machines and apparatus, noises may occur which are produced in the interior of the materials and are related to an impending failure. For example, cracks in the microrange which are in the process of formation emit such sound waves, sometimes a long time prior to the failure. These sound waves are utilized for an early recognition of damage, so that the degree of damage and the continuance of the failure can be detected. In addition to the analysis of the processes, i.e. definition of the type of sound sources, particularly the localization of the sound source is of substantial importance for finding remedy measures.
As is well known, sound sources are localized by measuring the differences in propagation time which occur in the travel of the sound from the sound source to various receivers which are arranged individually and in large spacings around the source, and by computing the position of the sound source from these differences in propagation time with the aid of the position coordinates of the receivers. When this method is used for points of damage which are already existing or in the process of formation, several receivers are fastened to the surface of the sample in spacings of 1 to 5 m. When a sound pulse reaches the receivers, the signals emitted by these receivers start a counting of the propagation time. The propagation times of the adjacent probes are compared and the position of the sound source is determined from the differences in propagation time and from the coodinates of the receivers. (H. Bretfeld, A. Moller und H. -A. Crostack: Anwendung der Schallemissionanalyse bei der Belastung eines Druckbehalters mit pulsierendem Innendruck; Materialprufung [Utilization of the Sound Emission Analysis in Stressing a Pressure Container with Pulsating Internal Pressure; Material Testing] 19 (1977) 11, Pages 467/70).
The following essential prerequisites must be met in order to obtain correct results in this known determination of the position:
1. The velocity developed by the sound wave on its travel from the sound source to the receiver must be known, because otherwise it would not be possible to compute from the propagation time values the distance travelled by the sound wave and, thus, the distance of the sound source from the receiver.
2. The sound pulses may not occur in a dense time sequence, but must have distinct spacings. An erroneous localization results when a new pulse occurs at a different point before the wave of the first pulse has reached all the receivers required for the localization. (H.-D. Steffens und H.-A. Crostack: Einflussgrossen bei der Analyse von Schallemissionen; Zeitschrift fur Werkstofftechnik [Influence Variables in the Analysis of Sound Emissions; Magazine for Material Engineering] (1973), 8, Pages 442/7).
3. The sound pulses must be very similar to one another because a change in the type of waves or in the pulse shape (for example, the amplitude or the rise time) causes the electronic recording instruments (triggers) to respond at different times (H. D. Steffens, D. Krempel, D. Stegemann und H.-A. Crostack: Analyse von Signalen der Schallemission; Zeitschrift fur Werkstofftechnik [Analysis of Signals of Sound Emissions; Magazine for Material Engineering] 6 (1975)
REFERENCES:
patent: 3875381 (1975-04-01), Wingfield et al.
patent: 4004463 (1977-02-01), Vercellotti et al.
patent: 4033179 (1977-07-01), Romrell
patent: 4354388 (1982-10-01), Diepers et al.
The Soviet Journal of Non-Destructive Testing, vol. 16, Aug. 1980, No. 8, New York, U.S.A.
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