Small structures are checked by monitoring samples for acoustical signal count. Flaws are located by observing relatively high acoustical activity within given area. Acoustical monitoring has been extended to large structures by dividing large samples into small areas and then monitoring each area separately

Moskal, F. J.

Sugg, F. E.

English

NASA Technical Reports Server

June 1973	 B73-10212 
n NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Real Time Statistical Analysis of Acoustic 
Emission Signals for Flaw Monitoring Systems 
The problem: 
Acoustical signals are a useful means for detection 
of flaws in physical structures. Small structures are 
checked this way by monitoring the samples for 
acoustical signal count or count rate. Any flaws in the 
structure are located by observing the relatively high 
acoustical activity within a given area of the sample. 
Large structures, however, are more difficult to analyze 
this way because of the greater areas that must be 
monitored. 
The solution: 
Based on the technique used in small structures, 
acoustical monitoring has been extended to large struc- 
tures by dividing the large samples into small areas and 
then by monitoring each individual area separately. 
How it's done: 
The sample used in this development is a 105-in. 
(263-cm) diameter tank which consists of 3480 areas 
each approximately 10 in. 2 (63 cm 2 ). The tank surface 
is proportioned to allow the layout of 20 equilateral 
triangles in the form of a slightly distorted icosahedron. 
Twelve transducers are equally positioned on the tank 
surface at the vertex of each of these triangles. The 
equilateral triangles are slightly elongated to account for 
the small cylindrical section of the tank, but are other-
wise identical in size and shape. The system is divided 
into two distinct data handling segments, an analog 
and a digital.
The first segment operates in the analog mode and 
continuously monitors input signals from each trans-
ducer. Approximate location of the acoustic event is 
obtained by processing signal detection sequences and 
delay. This data is packed in the binary form and 
passed to the digital computer for further processing. 
The second segment operates in the digital mode. 
Delay information from the analog unit is processed to 
provide an exact location of the acoustic event. The 
surface of the tank is divided into 3480 areas. A digital 
computer contains separate storage locations corre-
sponding to each of these areas. A running sum of all 
acoustic activity is maintained in these storage locations 
by the digital computer. System operation is controlled 
through a standard teletypewriter. The data received 
and stored in the computer can be requested by the 
operator at any time and in any form that he desires. 
Although noise rejection is used throughout the 
system, i.e., dual element transducers and bandpass 
filters, a constant background or random noises uni-
formly raise the totals of a large number of signal 
counts from all the storage areas. In this technique, a 
growing flaw area is localized and easily identified using 
the statistical capabilities of the on-line computer. For 
example, mean averages can be obtained of desired 
specific sub-areas of the entire tank at any time. The 
rate of emission signals for any given time can also be 
obtained. Statistical calculations are obtained from all 
input data in less than one second. 
.
(continued overleaf) 
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Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000212 2020-03-17T07:13:06+00:00Z
Note: 
Requests for further information may be directed to 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10212
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS.PAT 
Marshall Space Flight Center, Alabama 35812 
Source: F. E. Sugg and F. J. Moskal of

Rockwell International Corp. 
under contract to

Marshall Space Flight Center 
(MFS.24402)
. 
B73 . 10212	 Category 03, 06


Real time statistical analysis of acoustic emission signals for flaw monitoring systems

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