Note: Descriptions are shown in the official language in which they were submitted.
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D-6689
1 BACKGROUND OF THE INVENTION
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The present invention relates/flaw and defect discrimina-
4 tion pursuant to nondestructive ultrasonic testing of structural
5 material, particularly metals.
Ultrasonic testing involves primarily the detection of
8 the location of a defect on the basis of the transit time of an
¦ echo; i.e., the defect constitutes a discontinuity in the propa~
gation characteristics of an ultrasonic test signal, causing a
11 portion of that signal to be reflected; e.g., back towards the ,
12 launching transducer which has been switched from the transmit
13 mode to the receive mode follo~ing the launch. The travel path
1~ of the launched signal and the retul~n path of an echo are geomet-
ricàlly predeterminable on the basis of the geometry of the part
16 tested. The location of the transducer on the ob~ect and the ~;
17 orientation of transducers (direction of launching) to the test
18¦ object and its curface are supplem~ontal parameters. There,ore,
19 the time of occurance of any echo in reiation to the launch tlme
is indicative generally and directly usable for finding the
21 location of the discontinuity causing that echo. In order to
22 exclude echos from "natural" boundaries in the error detection
23 process proper, one usually chooses certàin expectancy ranges
24 (loo~ing windows) and determines whether an echo does or does not
occur in such a w.indow. On that basis, one distinguishes, for
26 exampler whether a defect is located near or in the ~surface of~
27 the test object, or in the interior thereof. That,distinction
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can already be used as a criterion with regard to the type of
2 defect involved because certain types of defects are more preve-
3 lant near the surface, other types are more likely to occur in
4 ¦ the interior. Instrumental here is, further, the conduction of
51 tests in different test planes and from different directions,
61 primarily to localize the defect and to gain some information on
7 its extension and orientation. However, this type of evaluation
is not discriminating enough for many purposes. It should be
g observed that there is a need for identifying ~ny defect as to
its type because some defects are relatively harmless, others
11 are extremely critical. Thus~ even a fairly large nonmetallic
lZ inclusion may bë tolerable while a fine crack is not.
13
E~Taluàtion of a flaw or dPfect on the ~asis of a r~c~ived
15 ~ echo has been limited in the past to the determination of whether
16 ¦ or not a particular amplitude (test level) has been e~ceeded.
17 ¦ Of course, this approach requires extensive calibration because
18 ¦ the return signal amplitude depends on many other factors,
19 ¦ including the construction and operation of the transducer
20 I as transmitter; the characteristic of the transduber when
21¦ operated as receiver; the mode and manner of coupling the trans-
22¦ ducer to the test ob~ect; the band uidth of the system, including
231 particularly the recelver circuit; the angle of incidence of
241 the launched test beam; etc. Another factor which influences
25¦ the amplitude of the echo is the condition under which the reflec-
26¦ tion occurs at the boundary of the test object material and the
271 defect. >
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l Automated test equipment as it has been used is not capable
2 of providing an ade~uate indication and representation of the
3 specific type of defect involved. The amplitude, per se, just is
4 not an adequate indication. Thus, in practice, one has used
e~perienced test personne] for inspecting the wave form of a
6 returned signal to arrive at a highly subjective conclusion as
7 to the cause of this return signal. The automated equipment
8 was, thus, used only for detection of (a) mere presence of a
9 defect,-and (b) its location; and, e.g., a loo~ at the envelope
of the received signal did reveal, hopefullyj whether the
ll defect is a crack, a slag inclusion, a void, etc.; and whether
12 it was harmless or not.
13
1~ It sho~ld be noted that in ar.othe~ type of testing (na~ely,
testing by means of induced electrical eddy currents), one could
16 determine àny phase shift between the energizing (input) si~nal
17 and a resulting output signal. This phase shift does give some
18 indication as to the physical characteristics of the defect.
'19 . . ' ' .
This approach is not possible in ultrasonic testing, since
; 21 one cannot determine any phase between an electrical signal
22 which triggers launching of the ultrasonic test signal, and a
23 received ultrasonic signal and its electric replica.
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D-6689
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l DESCRIPTION OF T~IE INVENTION
3 It is an object of the present invention to provide a ne~
4 method for discriminating among various types of defects in
structural materials, particularly in metals, on the basis of
6- ultrasonic test signals.
81 It is a particular object of the present invention to
9 analyze ultrasonic return signals without requiring any reference
to the phase of the launching signal.
11 ' _ .
12 It is, thus, a specific object of the present invention
13 to analyze an ultrasonic signal which results from interaction
i~ of a launched test signal with a structural materia].
15 I
16 ¦ In accoxdance with the preferred embodiment of the present
17¦ invention, it is suggested to process the returned ultrasonic
l8¦ signal after its interaction with, e.g., reflection on a defect
l9 in structural material, by interpreting the signal as the real
component of a complex s1gnal and generating the companion
21 imaginary component. The resulting function in the complex planè~
22 is processed to determine the value and location of the maximum
23 amplitude,~the location being defined by the angle in relation
24 to the real or imaginary function axis. That angle represents
the displacement of the complex function peak from the read
26 signal peak. Particùlarly that peak displacement angle is an
27 indi tion of signal distortion a~ the re1e^ting interface
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1 and that, in turn, is a criterion for classifying defects.
2 In addition, one provides a companion pair of amplitude and
3 angle data, using the same, or the same type of,
4 test equipment, but a ~nown type of interaction, e.g.,
a known reflecting surface known in the sense of producing
6 a definite response, i.e., return, to thereby eliminate equip-
7 menl parameters from the result. The information now used
8 for clarifying defects is the difference between these two
9 angles as taken from the complex plane. The resulting normal-
ized peak displacement angle is used as defect-classifying
11 criterion. It was found empirically that harmless defects
12 and harmfull dè~ects can be distinguished by determining
13¦ whether or not the normalized angle fà]ls into one or the
1~L other of a plurality of empi ically dètermined angles. This
15 ¦ lends itself directly to objectively operating automation.
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1 DESCRIPTION OF THE DRAWINGS .
2 _
3 While the speciflcation concludes with claims, particu-
4 larly pointing out and distinctly claiming the subject matter
which is regarded as the invention, it is believed that the
6 inven~ion, the objects and features of the invention and
7 further objects, featuxes, and advantages thereof will be better
8 understood from the following description taken in connection
with the accompanying dra~7ings in which
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11 Figure 1 is a composite representation of three rëlated
12 diagràms a), b), and c), illustrating a flrst phase of the
13 procedure and process involved in practicing the present
14 invention,
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16 Figure 2 is a perspective view of a three-dimensional
17 signal plot; and
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19 Figure 3 is a graph, showiny the envelopc of the signal
as shown in Figure 2. -
21 :
22 Proceeding now to the detailed description of the drawings
and of the in~-entive process in accordance Wit}l the preferred
2~ embodimen~, the portion a) o~ Figure 1 illustrates an example
of an echo as r~ceived by an ultrasonic transdùcer, operated
26 in the recei~e mode. This part a) of Figure 1 could.be inter- ~ ~ .
27 preted as a display on the screen o an oscilloscope. Such ;~
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1 a display is not, per se, part of the inventive process; a
2 received signal, if displayed, may look like the plot in
3 Figure 1, diagram a).
This particular signal may have been produced as an echo
6 of an ultrasonic test pulse which was launched by the ultra-
7 sonic transducer then being operated in the transmit mode.
8 The transducer, its energizing and driving ¢ircuit for the
9 transmit mode, its operational mode controlj and the amplifier
connected to the~transducer in the receive-mode are all . .
11 conventional; Moreover, it is also known, for example, to
12 digitize this analo~ signal and to store the resulting digital
13 signal for further processing.
14 . ,
The fu~ther processing is based on the principle that..
16 the function, as deli.niated by the signal (Figure 1, a)),.can
17 be interpreted as the real component RE of a complex function
18 RE ~ l. The (or, an) imaginary component IM of that func-
19 tion is generated as quadrature by means of, for example, a ~
Fourier transformation, or a Hilbert Kern~l transformation, etc. :
21 Part b) of Figure 1 depicts the resulting imaginary component IM
22 generated via such a function transformation, being correspond-
23 ingly associated with the real component as per Figure 1,
24 part a). :
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1 The function IM, as per part b) of Figure 1, iS7 of course,
2 also a function in time. Accordingly, for eaeh instant on the
3 abseissa axis, one will now find a real component amplitude
4 (Figure 1, part a)) being associated with an imaginary component
amplitude (Figure 1, part b)). By associating these values in
a common, complex ~unction plane, one obtains a graphie repre-
7 sentation as per part e) of Figure 1. The actual generation
8 of such a plot is not necessary for practiclng the invention;
9 the plot is shown here for the p~rpose of demonstration.
10 . .
11 Diagram e) of Figure 1 shows the location of the maximum
12 amplitude Am in the eomplex function plane and diagram. That
13 amplitude loeation can be represented by a vector which has
1~ a particular angle ~, e.g., rel~tive to the imaginary function
axis. The angle-~ signifies that the absolu-te maximum, or pea~,
16 of the complex signal function does not coincide with the
17 maximum, or peak, of the signal as received. It is, therefore,
18 eonvenient to cail this angle ~ the peak displacement angle.
1~
These ~alues (Am,~) are used as a eriterion for identi-
21 fying the deect which has caused the particular (real~~siynal.
22 For partieular purposes, the ultrasonic signal, as received,
23 amplified and digitized, is processed in a programmed computer
which provides the function transform and generates there~rom
the imaginary component for the complex function (Figure 2).
26 The program then determines the absolute maximum Am and, for
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D-6689
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1 example, the peak displacement angle ~ relative to the imaginary
2 axis. T~ese values are suitably stored for further processing,
3 to be described hereaf~er.
Figure 2 shows real and imaginary components of the complex
6 signal as generated (in parts) and plotted as a function of time.
Figure 3 sho~^7s the envelope of the comple~ signal also as a function
8 of time. It was discovered that the complex signal and function
9 generated out of the r~ceived signal by interpreting it as a real
10 ¦ component of such a complex function is better suited for identify-
11 ¦ ing the defect. As stated earlier, the real signal contour depends
12 ¦ on the acoustic impedance of the defect, but also on other factors,
13¦ and the complex function permits more readily the extraction of
1~¦ defec~-identiIyillg criteria, which are the maximum amplitude and~
primarily, its phase in the complex function plane. Particularly,
16 the displacement of the maximum amplitude in the complex plane is
17 indicatit~e of the signal distortion at the reflecting boun~ary due to
18 its acoustic properties. That angular displacement ~8, for
19 example, for reflection of an acoustic wave at a crack or at a non-
metallic inclusion.
21 - ~
22 ` In order to eliminate from this processed measurlng result
interfering components which relate to particular, even unique,
24 features of the test equipment itself, par-ticularly in conjunc-
tion with the controlling transmitter circuit, one provides,
26 broadly, a reference standard by using the same (or the same -
27 type of) electr:ic circuit and equipment. The reference standard
;20 is a~ echo signal generated under known condtions. ~or example,~ :~
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one uses here the echo generated by a true surface of the part, or
of a similar part (front-wall echo or rear-wall echo). Or one can
use a calibration wire placed across the transducer, or a calibra-
tion standard, to which the transducer is coupled. Examples of this
type of referen oe elements are shown in Canadian Patent applications
Serial No. 284,167, filed August 5, 1977, or Serial No. 305,016,
filed June 8, 1978. See also printed German Patent applications
2,635,982 and 2,726,400.
In either case of generating a reference, a signal contour
'O similar to the type shown in Figure l, part a), will be produced.
m at signal is (a) digitized, (b) processed as to the Fourier or
Hilbert Kernel transformation, (c) further processed to generate the
companion imaginary function component to obtain (d) the complex
function. The maximum, or peak, amplitude and the corresponding
peak displaoement angles in that ccmplex function plane are deter-
mined.
These referenoe values are suitably stored also and pro-
vide, in effect, equipment constants and parameters. It should be
noted that in those cases, in which a rear-wall echo and/or a front-
wall echo is available on a running basis, such an echo is then
directly available during the same test cycle in which the echo
occurs; these referen oe echos just occur at times different from de-
fect echos. me referen oe signal in accordance with the Canadian
application mentioned above (Serial No. 305,016) is also generated
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1 during each test cycle. Thus, the signal representing such
2 a rear-wall echo can be computer-processed whenever the need
3 arises to generate on the 5pO~ the pair reference data (Am,~)ref .
This way, one eliminates, for example, varying coupliny con-
ditions as bet~Jeen transducer and test ob~ect, signal drift
6 in the electronics, etc.
7 . i
81 The reference signal pair (Aml ~)ref.
9 ' the processing circuit to normalize the measuxin~ values.
10 ' The difference between the peak displacement angle ~, resulting
11 from the processing of the flaw echo signal as described
12 (Figure 1, part c)) and the reference angle generated analo-
13 gously, is the nor~alized'pea~ displacement angle which represents
1 the signal distortion resulting from the specific acoustic
conditions at the defect. Analogously, one may form a
16 normalized amplitùde.
17 '
18 The differènce in the maximum amplitudes of the two
19 'complex functions ~measuring and reference) can be used directly
'for determining the relevant signal level for determining the
~i severeness of the defect (reject level). More important,
22 qualitatively, is the nor~alized peak dlspiacement angle.
23 This difference is usable as a criterion for identifying the
24 cause of the echo. The difference in the acoustic impedancès
across the interface between the defect and the material pro-
26 duces the reflection. But -this difference itself is'different
27 for different types of defects, such as laminations, crac~s,~` ~ ;
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1 inclusions, pockets, etc. Th,us, the incident ultrasonic signal
2 is differently distorted upon reflection by these different
3 types of interfaces and discontinuities in acoustic impedance.
4 This di~ference in distortion is reflected in different normalized
peak dlsplacement angles in the complex functlon plane. Thus,
6 one will generate in advance a variety of normalized peak
7 aisplacement angles for co~parison purposes. These several
8 no~mali2ed alphas are generated on the basis of kno~rn defect
9 types. More particularly, various pieces of structural material
with different particular types o~ defects'can be prepared,
11 such as lamination~, cracks, seams, ~oids, nonmetallic inclusions,
12 etc.; preferably~ these defects have a large variety o~ shapes,
13 orlentation materials, etc. For each SUC}l type of defect, the
a ¦ normalized pea~. displacement angle is generated, an~ the varloùs
-151 ' angles are grouped into ranges. These ranges will ~e appropri-
16 àtely defined as stored signals in the processing and computiny ,
" I7 facility. As the facility now generates a normali~ed peak '
1 18 displacement angie from a true defect echo, a determinatlon is
; 19 made into which range that angle falls. The defect is now
classified on that basis.
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22 It should ~e noted that classifying the detected defects
23 in the msnner described above is primari~y of interest for the
purpose of separating harmless imperfections from harmful defects
and flaws. `
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1 It was found that there is a direct correspondence between
2 peak displacement angle ranges for normalized angles and the
3 severity of the type of defect involved. Cracks, l~mination.s,
4 seams, and the like, are deemed severe and lead more readily
to product rejection. Their normalized peak dispiacement angles
6 are rather closely placed on the comparison scale, while less
7 severe defects, such as nonrnetallic inclusions, voids, or the like,
8 are readily distinguishable by a different, normalized peak dis-
9 ¦ placement angle range. The boundary is, for example,
with smaller angles constitutiny harmless defects.
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12 Thus, the procedure lends itself to automation in that it is
~- 13 determined whether the normalized alpha angle is, or is not,
14 in a dal-ger range, i.e., a ran~e signifying critical defects.
15- This determination can be made pursuant to the same program
16 which generates the normalized peak displacement ~ngIes out of
- 17 a flaw echo signal.
18 '
19 The information concerning peak displacement angles as a
criterion for distinguishing harmfull defects from harmless ones ;~
21 should be supPlemented by the normalized amplitude as that
22~ am~litude is indicative of the siæe of the defects. ;
23
24 The peak disp].acement angle,as deflned, can broadly
be interpreted as phase information. It is significant, however,
~;~ 2~ that one does not~determine dlrectly any phase in relation to
27 the launch cont:rol signal. The launch signal as such is not
2~ used in the determination of the peak displacement angle.
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1 The phase relation is an indirect or relative one, based upon
2 different conditions for reflecting an ultrasonic vibration.
3 .............................................. . .
.4 The invention is not limited to the embodiments described
~ above, but all changes and modifirations thereof not constituting
.6 departures from the spirit znd scope of the invention are intended
8 to be included. .
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