Note: Descriptions are shown in the official language in which they were submitted.
~,~d /f~ ~6~9
¦~NON-DESTR~CTIVE EVAL~ATION OF ROPES BY ~SING
TRANSVERSE IMPULSE VIBRATIONAL WAVE' METHOD
~ ~1~
3 1 l. ~ield o~_the Invention. The pre~ent invention relate~ to
4 ¦ non-~es~ruc~.ive testing ~f ropes, cables, and ~tal strands ~or
6 ! ~l~ws and tcnsion.
~ I
7 1 2. ~es~ription o~ the Prior Art. No~-de~truc~i~e e~luation
, (ND~) of r~pes is known in the ar~. sume NDE methods are ln
9 1 prac~ice, whi~e other m~thod~ have heen proposed, but are not
ye~ perfected. As will b~ shown hereinafter, no NDE method
¦ co~bine~ the advantageous features o~ the tran~ver~e impulse
¦ vihra~ onal wave me~hod disclosed i~ this application.
¦ In an article ~ James H. Williams, Jr, John Hainswo~h,
¦ and Samson S. Lee en~itled /'Acous~ic-Ultr~fionic ~ondestr~c~ive
l 1¦ EYalu~tlon o~ Double Braid~d Nylon Ropes Using ~he Stre~s WaYe
F~ctor" which appeared in ~ibre Sciç~çe and ~echnol~y, 21
), pp l6g-l80, experiment~ion perform~d on synthe~ic
ropes with the obj~ct of ~ons~ructi~g an a~alytical model
¦ wherein ul~ra~onic wave conductivity ~stress Wave Factor) of a
¦ r~pe is A fuhction of the condi~ion of th~ rbpe and the ~ension
!i on the rope. It i~ proposed that ~uch a model would enable
a~urate ~esting of rope~ for flaws by mea~ring S-~ess ~a~e
I P~ctors. To date, n~ Stress W~ve Factor model has be~n
2~
p~oposed ha~inq reliable utili~y for ~op~ test~ng. The
~' variation in the relationship b~tween St~e3s Wav~ ~actor,
,I tension, and rope ~ondltio~ among di~erent ~ope compo~itions
and structures is no~ yet ~ully unders~ood.
~8 .I Even if an adequate model for int~rpretin~ Str~s~ Wave
: ! ~a&tor ~st resuIts ware found, th~ utility of Stress Wave
¦ Fa~to~ testing would ~ot compare favorably with th~ ~ransverse
I impulse vibrational mekhod. Whi.le th~ -transverse impulse
.
3~ ' 2
.
I ~ 69g
l vi~rational wave method permits testing t~e entlrè length of ~.
rop~ from a sinqle test site near one o~ it5 e~d~, stress Wa~e
~actor me~hod tests only ~ short le~gth of a synt~etic rope
~ecause synthetic ropes quiokly disslpate the energy ~ the
vih~ations Use~ i~ Stress ~ave Factor te~ting,
~leotromag~etic NDE are presen~ly ~he only type of non-
visual method which ls in current, widespread pr~ct1ce.
8 Electromagneti~ NDE ~ethods are discussed in an article by9 ~ Herbert R. Weische~el ehtitled ~The Inspecti~n of Wire Ropes i~
0 1 Service. A Critical Revie~" appearing in ~aterials Evalua~lon,
43, Decem~er 138~, pp 15~Z~1~05.
12 1 ~lectromagnetic N~E methods are used for: 1) locali~ed
¦ ~ault detection (L.~.) and 2) loss of ~etallic ~ross-sectional
14 1 area testing ~L.M.A.)
16 ~lectromaqnetic NDE meth~ds ~re limited to use ~n
1~ ferromagnetic matexials~ ~nlike t~ansve~rse. i~p~lse vibrational
17 ¦ wave method which may be per~ormed on ferromagnetic or non-
8 1 ferromagne~ic materials as well as synthe~ic materials.
I L.F. testing is based on the princlpal th~t broken Wires20 , in a wire rope made o~ ferromagnetic steels distort a maqnetic
¦¦ flux passin~ tha point of breakage caUsing ~agnetic flux
¦¦ leaXage whlch is detectable in the area surrounding the rope.
! L.~. testing is conduct~d by posit~oning a s~rong permanent or
¦¦ electromag~et in close proximity to a wi~e rope to be tested.
I! As th~ rope passes the m~net or ~he magnet is movQd along the
~; ,
2~ length of the rope, a magnetic flux is initi~ted in the length
a7:: of rope ad~acent to the pole inte~spaGe ~f the maqnet.
2~ Differential sensing eoil~ are positioned around the rope to
2~ ¦ detect magnetic flux leaka~e.
only maior ~laws, such ~s broken wires a~d severe
so l
Sl ', corrosion pittlhg, are detec~ed b~ L.F~ ~estin~, because only
li
3~ ~ 3
1 substantial ch~nges in the m~gnetic flux l.eakage are det~cted
2 by the differ~ntial sensors. Small flaws, or widely dispersed
3 flaws, do not produce substan-tial and r~pid magneti~ rlur
4 l~akage ¢han~es and ~re ofte~ missed using L.F~ testing.
L.M.A. t~s~ involves direct measurement of ~gnetic
~ ¦ fluX through a length of ~ wire rope. Variation in the
: ~ m~gne~ic flUX through dif~'erent p~rtions of a singl~ rope
i~dicate a change in the ~r~ss-sectional area of the rDpe,
whi~h, in turn, indicates possible deterioration of the rope at
'I areas of decre~sed oross-sectional area.
lQ I
11 1 The ele~tromagnetic ~ne~hods require passin~ the entire
12 leng~h of a metallic rope to be tested through the testing
13 1 appara~us or the testing apparatus be moved ~long th~ entire
14 1 len~th of the rope. As wi~h Stress Wave Facto~ testing, the
15 1 necessity ~or access to the entire length o~ a rope reduces tha
¦¦ utility of electromagne~i~ NDE ~ethods.
: 17 ~ Methods base~ on measuring vibra~onal frequencies o~
rn~ n~ c~b~ es far determinin~ te~sion are a].s~ knQwt- ~n the
ar~. U.S. Patent No. 45~,099 issuad to Ar~old, U.S. Patent No.
i! ~,376,3~3 issued to Wils~n, and U.S. Patent No. 4,15~,~62
; !1 issued ~o Conoval each rel~ed ~o ~alculating the tension sn a
rope or cable as a ~unction of i~s f~ndam~n~al fxe~uency of
Z :
vibration. The squipment and methods shown in these p~ten~s
¦ and otherwise known in the art ar~ no~, howevet, sul~able ~r
¦ practicing t~ non-tension relate~ aspect~ o~ the transverse
l¦ impulse vib~ational wave me~ho~ a~ de~cribed ~erein.
27 1 I~ would, therefore, be advanta~eous to develop an ~DE
28 1 ~ethod havin~ utility for testing ferro~agnetic and non-
29 ' ferroma~ne~ic ropes alike, which would require ac~ss to only a
llmit~d portion of the rope to be teSted, which would dotect
~1 1
3~ :j 4
.i
:~Z~4~
1 minor as well as major rope flaws, and ~Ath~ch would permit
calculating tensi.on on ropes ~ithout additional equipment.
4 ~M~Y OF THE INV~NTI~N
5 ¦ It is an ohjeot o~ the prese~t lnvention to provlde an
8 app~r~tu~ and non-destrllc1:~ve ~v~ ;.~n m~tho~ ~h~c~h apprises
7 a user ~ flaws in, ~nd tension o~, ~ ¢able, rope, or metal
8 strand.
~ It is ano~her objec~ of the present invention to pro~.ide
lO I an apparatus and non-destructive evaluation metho~ which
ll ¦ appri~es ~ user of the relative ampli~ude~ and ~rrival ti~e of
~2 1 pulsed, ~ransverse, vibrational waves passin~ through cable,
13 , rope, and metal strand,
t is another ob~ect of the present invention to provide
16 ~n apparatus and non-destructive evaluation method hy which the
18 location of a fl~w in ~ cable, rope, or metal s~r~nd is
de~ermined .
~7
18 It is ano~her object o~ the present i.nvention to provide
l9 an apparatus and non~d~structive evaluatiorl method by which the
20 I overall flaw population of a tes~ed cable, ropa, or me~al
21 1 strand may ~e determined.
2~ ~I It is another oh~ect of t~e present invention to pro~ide
I
23 an apparatus and non-destru~tive evalu~tion method b~ which th~
tension on cable, rope, or metal strand may be ~easured.
:8~ Accordin~lyj the present invention provides ~n appara~3s
and method u~ilizing pulsed, ~ransverse, vibrational waves ~or
~ non-destructive ~valuation o~ cables, rop~, and metal stran~s
28 for flaws and for tension, The method is re~crred to as
~ransverse i~pul~e vibrational wave me~hod.
. ~ The apparatus ~or transverse impulse vibrational wav~
50 1
I¦ me~hod is de~igned for initiating a transverse vi~rational wave
32 S
Il
~ 3g
1 motion in a xope, and for measuring the amplitude of and time
2 intervals between the resulting waves as they travel though the
3 rope. The apparatus comprises an exciting mechanism which
4 applies a transverse impulsive force to the ~ested rope, a
6 sensor which detects individual waves as they pass a particular
~ point on the rope, a signal amplifier which raises the
7 amplitude of the electrical signals form the sensor, a signal
8 conditioner which filters unwanted signals ~rom the sensor/ and
9 an oscilloscope which displays the measurements of the sensor
in time versus amplitude units.
11 The apparatus optionally includes a computer and recorder
12 or graphics printer. The computer is for automating the
13 measurements and calculations involved in detecting and
14 locating flaws in a tested rope, as well as in determining the
16 tension on a tested rope. The recorder and graphics printer
1~ are for recording and producing a permanent record of the
17 time/amplitude relationships of the vibrational waves as
18 detected by the sensor.
}9 The transverse impulse vibrational method for NDE of ropes
is based on the fact that flaws in a rope partially reflect
~0
21 vibrational wave energy because of the acoustic impedance
mismatches at the flaw locations. The wave is also reflected
22
as at the ends (or terminations) of the rope. The sensor of the
24 above-described testing apparatus producas corresponding
electrical signals.
Calculations based on measurements of the time betwaen the
2~
27 flaw signals and the end-reflected signals and on measurements
28 o~ the relative amplitudes of the signals detected by the
testing apparatus allow the user to locate rope flaws, to
29
determine tension on the tested rope, and to measure the
51
52 1 6
11
11
i :L294699
1 1 relative population of flaws in the ~ested rope as compare~ to
a ~on~rol ~ope sample.
4 BRIE~_DESRIPTIO~ ~F_THE DRAWINGS
5 1 ~ig. 1 is a sche~atic depiction o~ the tes~in~ apparatus
l for transverse ~mpulse vlbr~tlon~ ave method along with a
r 1I roPe ~r te~ting,
'i Fig. 2 shows ~ magnet/coil combination sensor.
g !¦ Fig. 3 shows the transverse impul~e vibrational wave
'I ~e~hod testing ~pparatus set ~p for field testing a large guy
I wire.
11 '~
12 Flg. ~ shows an exa~ple of an oscilloscope display
¦ obtained by using th~ tran~v~r6s impul~e vibrat~onal m~od,
appearing with Fig. 1.
14 ,I DE~AILED DE5CRIPTION O~ ~HE_PR~F~RRED EMBODIMENT
16 The present invention comprises a method and apparatus fo~
non-destructive evaluation (ND~) of cables, synthetic rope~,
,¦ and wire ropes ~or tension and flaws. ThP method will be
: ¦¦ referred ~o as ~transverse impulse vibrational wave metho~
¦ herein. Por the purpos~s of this discussion, cable, syn~h~tic
rope, or wixe rope w~ll be ~eerred to ~ollectively a~ r'rope"
~0 ',
in m~st instances.
. 21 '!
Referrin~ to Fiqure 1, the testlny appara~us i~ d~picted
~2
schematically, and is ref~red to ~enerally by the reference
'! numeral 10. ~or reasons to be discussed hereinafter, the
~4
test1~g apparatus 10 is for detecting individual vibrational
wava~ in ~ rop~ 12 ~nd apprigin~ a u~er of th~ pre~ence, ~he
¦I relntive amplitudes, and the sequential arrangement o~ the
ves.
2~ 1
~ A ~ope 12 i~ shown in Figures 1, 2 and 3 to show the
29
I relati~nsh~p of the testing apparatus' 10 co~ponents to a rop~
I lZ which is to be tested.
31 ~
~2 ~, 7
~I
;'
l ~2~ 9
l Transverse Impulse Vibra~ional (TIV) wave method invol~es
2 ¦ strlking a rope 12 to propa~ate vibra~ional wa~es through the
3 ¦ rope 12~ Consi~tency in the force us~d to strike the rope 12
~ ¦ i6 d~irablç ~rom ono te6~ t~ a~o~h~r. Con~ en~y o~ ~t~king
5 1 ~o~ce permits dir~ct analytical comparisons to ~e made betw~en
~ data derived ~rom tests of the same rope at ~fferent poi~s in
7 the rope'~ 12 servic~ lif~, or from tests of dif~erent rope~.
8 Therefore, the te~ting apparatus 10 includes a striking
~ mechanism 14 whi~h consis~ently strikes the rope 12 with a
predetermined force. ~he s~iXing mechanism 14 of the
~1 i pre~erre~ embo~iment is a solenoid 16 with its plunger 1~ in a
12 1 position for striking the rope 12 when the solenoid 16 ~s
13 1 ac~v~ed (se~ Figure 3). Other desiyns for st~iking
¦¦ mechanisms 14 such ~s pneumatic devices o~ spring biased
16 ¦ devices (not hown) would be e~ually acceptable.
I lB ! It is noted that although any manner of s~riking the rope
: ¦ 12 is acceptabl~ fo~ any given ~e~t; a device provid~ng
l~ ¦ consis~ent stri~lng force is merety de ir~ble for ~e above-
¦ stated reasons On~ could, for instançe~ su~çes~fully conduct
a ~IV wave method test by st~iking ~he rope 12 with a ha~er
not Yhow~.
I Refer~ing a~ain to Figure 1, a s~nsor ~O is in~luded in
the testing appara~us 10 for ~ete~tin~ indi~idual vi~ratlon~l
: ,' waves in the rope 12 resulting ~rom the impact ~rom the
striking mechanism ~4. To permit testing of a wide range of
l! sizes and compositions o~ ~opes, cables, and strands, the
: 2~ 1
ensor 20 ~h~u1d b~ ~p~ble of di~ernillg in~ivi~ual
vibrational ~ves ranging in ~reqUenCy up to approximatQly
l lK~z
: 29
I Th~ pa~cular m~thod o~ de~ec~i~n for the sensor 20 ~s
SO l
l not important ~o long as th~ rela~iv~ amplitudes and sequential
51 ,
32 ~ 8
1~
I
' ~LZg~99
1 arrangement of vibr~tional wav~s in the rope 12 may be derlve~
2 from the ~ensor's 20 ou~put. The ~ensor 20 ~ay measure the
~pe's 12 actual ~isplacement, ve~ocity of displa~ement, or
4 acceleration of displacement.
Re~erring to Figure 2, one type of sensor 20 which has
~ ~en used for TI~ wave method comprises a co~l 22 and permanent
7 magnet ~4 com~ina~ion. Coil 22 is a~ache~ ~O the rope lZ, an~
~ I i~ placed between the positi~e pole 26 and the ~cgativ~ pola 2~
3 of the ma~net 24. The leads 30 of the coil 22 are att~ched to
the componen~s of the testing ~pp~r~tus 10 which proce~s the
¦ se~sor's 20 output. As the rope 12 vibrate~, it cause~ the
1~ 1 attached coil 22 to move rela~i~e to the ~ield o~ the ma~ne~
13 1 24. A voltage po~ential ~or each such movement is created, and
14 1 ~he resul~in~ electrical signals are detected and p~oce~eed ~y
1! 24. The relative motion of the coil 22 within the magnetic
¦¦ field created by magnet 24, induces a current to flow within the
¦ coil 22. This curren-t flow is in direct proportion to the
~7
magnitude of the relative motion of coil 22 within the magnetic
~3 1
,¦ field which is in turn directly related to the magnitude of the
¦¦ vi~rational wave within the rope 12. The induced current flow
21 ¦ within coil 22 thereby provides the necessary electrical signal
ll to be processed and analy~ed by the remaining components of the
a~ ~ testlng apparatus 10. Any other available electromagnetic
24 11 displacement sensor such as the Electro-Mike Displacement
25 1' ~ransducer manufactured by the Electro Corp. of Sarasota,
2~ I Florida, would likewise be appropriate.
27 ' Other designs for the sensor 20 are equally acceptable.
28 1 Devices which physically contact the rope 12 or which detect
a~ ~I vibrations by optical methods are examples. An optical sensor
~0 ¦¦ 20 such a~ a las~r vibration sensor is shown in Figure 3. An
31 ll optical sensor 20 has the advantage of not requiring any direct
32 li attachment to rope 12. Light may be directed at the vibrating
Il rope 12 from a dis-tance and may likewise be detected at a
1 ¦ distance as shown in Figure 3. Any available op-tical device
2 j capable of quantitatively detecting the vibrations of the rope
3 ll 12, such as the Laser Through Beam Photoelectric Sensor, LX
~ Series, manufactured by the Keyence Company, Ltd. of North
America, would likewise be appropriate.
~ ! Referrlng to Figure 1, the testing appara~us 10 ~nclu~es ~
7 !I signal amplifier 3~ whic~ is c~nnected to the ~ensor ~0. The
8 ~! 3ig~ mpli~icr 32 ~i~e~ the ~lectrio~l s~gn~l~ from the
sensor 20 and amplifies the signals to a level capable of beiny
detected and processed by ~he other components of the testing
apparatus 10. The amplitudes o~ the signals produced by the
.¦ signal ampllfier 32 are higher, but directly proportional to
I¦ the amplitudes of the electrical signals from the sensor 20.
¦¦ The signal amplifier'~ 32 output~ ~re, there~ore, propor~ional
¦ to the amplitude~ of the actu~l vibrational waves in the rope
i 12. ~he relAtive ~plitud~s o~ thc vi~rat~o~al wav~ ~n tn~
,I rope 12 are i~portan~ ~o ~IV wave me~hod analy~i~. The
7 !i frequency response of ~he signal amplifier 3~ should be at
I8 l le~st coex~ensive with the sensor 20.
9 i The testing apparatu~ 10 furthe~ in~ludes a signal
~ ~i condition~r 34 which is connected to the signal amplifier 32
2~ ~ for receivin~ the amplified signals. The signal conditioner 34
a2 j is ~ variable filter which filters signal ~requancies ~ro~ ~he
23 signal amplifier 32 falling within a user-defined range. This
24 ~ allows a user to filt~r sign~ls which are not useful ~or ~he
~ !! te~t ~eing condu~ted.
2B il Referring in combination to Figures 1 and ~, ~ digi~iæing
27 ¦ oscillos~ope 36 is believed to be the pre~erre~
2~ I reco~din~display ~evice for the testing apparatus 10. The
29 , oscilloscope 3 6 is connected to ~he signal conditioner 34 for
50 ¦ receiv~ng the signals ~rom the signal aondition~r 34. ~e
31 .
32 10
i.
~ ~2~ g
1 oscilloscope~s 36 ~isplay ~8 ~as a y-axis scale 40 measured in
2 amplitu~e units, and an x axis ~cale 42 measured in time units.
3 ~he oscilloscope 36 has calibration controls 43 ~or ad~usting
th~ display 38 to units appropriate to the particular rope 12
being te~ed.
~ he diglti~ing os~illo~cope 3~ not ~nl~ gi~eS a graph~c~l
r~p~esentatlon of the relatiYe ampli~udes and sequen~ial
ar~a~gemen~ o~ ~he signals rom the signal conditioner 34, and
S l consequently those o~ ~he actual vibrational waves in the rope
10 ¦ 12, but also records the signa~s for later re-display or
11 ¦ c~mputex analy~is.
12 Refexring agai~ to Figur~ 1, a trigger swit~h 44 activates
13 the striking mechanism 14 and provides a synchronization ~ignal
14 to start the digitizing oscilloscope ~6. Therefore, a user may
1~ 1 simply throw the switch 44, and the striking mechanism 14 will
13 !¦ strike the rope ~nd the electronic components of the tes~in~
17 l; apparatus lo will then p~OC2SS and record the resulting
~ vibrational waves. If a co~puter 58 is used (to be disc~s~ed
19 1l hereina~ter) t~e computer 58 may be interfaced with the swi~ch
20 1 44 and it may activate the co~ponent~ of the testing apparatus
~1 ! lo
2 3 1 Transverse impulse vibrational wave me~hod may be
2 ' conducted through anal~sig ~f data ~hich may be derived by the
~4 tes~ing apparatus 10 as just ~escribed. Transverse impulse
2B ~! vibrational wave m~a~hod is made po~sibl~ }:)ecause of the
i! measur~ble e~ect tha~ flaws and cension have on the
27 ¦ vibrational wave propaga~ion properties of oa~les, rop~s, and
2~ ¦ ~trands.
29 1 It is impo~ant ~o note tha~ TIV wave method may be
50, pe~ormed on fe~romagne~i~ and non-ferromagnetic metallic
31, materials as well as non-metallic materials aliXe. This ~iva~
32, !~ 11
~.2~
1 TlV wave me~hod a considera~le utill~arian advantage over
pre~ently used NDE methods. It is o~ furt~er impor~ance that
~ TIV wave method alone pe~n~ts testing an entire length of a
4 ~able, rope, or stran~ ~rom a single ~cess p~i~t at one end.
As previously men~loned t o~her ~D~ method~ ~e~uire passing ~he
~ tes~ing apparatus ove~ the enti~e length o~ a test sub~ect.
7 Re~erring to Figure 3, TIV wave method will normally be
8 per~ormed on ~bl~, rop~s, or metal strands which are in
~ ¦ service as ele~ator cables, ~uy wires, or in si~ilar hlgh-
10 ' stres~ and/or safety intensive applications. To perform a T~Vwave method tes~, the ~triking mechanism 14 is placed withi~ a
specified distan~e o~ the rope 12 whiCh ls to be tested.
13 ¦ Because a~alysis of the test results are simplified by having
~ the sensor 2a in close proxi~ity to the striking mechanism 14,
16 ¦¦ the s~xiking mechanism 14 and the ~ensor 20 are mounted on a
! slngle support stand ~6. The remaining compon~nt~ of the
~7 ¦ testing app~ratus 10 are connected as discus~ed abo~e. A
por~able power upply 40 is shown in ~i~ure 3 for Use in ar~a~
where electricity for the tes~ing apparatus 10 is not readily
¦ available.
~0 Ij
2L !I The ~triking mechanis~ 14 and the sensor 20 should be
¦ pl~ced near one end 50 o~ the ~ope 12. This simplifies
! analysis oY tests results because ~ wa~e approaGhes and then is
reflected by the end 50 of the rop~ 12 closest ~o t~e sensor
2~ i Z0. These waves will p~ss the sensor 20 a very shor~ tim~
2~ 1 apart. ~hereore, the two passages appear, and can be treated
27 as a single wave for p~rposes of TIV wave n~ethod.
28 ¦ For simplici~y~s sake, the vibrational ~aves ~reated by
29 ~ the impact of the ~trikin~ mecha~ism 14 will be ~eferred ~o as
30 1 a sLngle wave in the following dis~ussion.
51 1 Referring in ~ombination to Fi~re~ 1, 3, and 4, when
32 ~, 12
5.~,`` 1
I
1294699
1 ! test is conduc~ed ~ith the ~esting apparatus 10, -~he rope 12 is
a ¦, struck by the striking mechanism 14, and a vibra~ional wave is
3 ll propagated fro~ the point of i~pact. ~s the incideh~ wave
~ reaches an end 50 of the ~ope 12, it is reflected and travels
S towards the ~pposite end 50 where it is again r~lected, ~his
~ cycle continues until th~ energy in the rope 12 is completely
7 ~ dissipat~d, A flaw 52 in ~he rope 12 also re~lects vibrati~nal
waves, but to a lesser ex~ent t~lan ~he rope's 12 ends ~0.
9 ¦ TherP~ore, wave~ reflected by the flaw 5~ will have a lesser
amplitude than waves re~lecte~ by th~ rope's ends 50. Flaw-
eflected waves appear, in ~ime, between en~-re~lected waves
b~cause f~aw-re~lected waves travel a shor~er distance than
13 ~I end-reflected waves.
I
14 1 As disau~sed abo~e, the sensor 20 will produce an
16 electrical signal in response to each vibrational wave of
de~ectable amplitude which passes it. Each ele¢trical signal
¦ will have an amplitude proportional to the ~pli~ud~ o~ its
respec~ive vibrational wave. S~gnals from an ~nd-re~lec~d
¦ wave ~11, like the wave itself, ha~e a larger amplitude than
.¦ signals reflectin~ ~la~-~eflected wa~es. Flaws which are large
~i enough ~o pro~ide re~lected w~ves of measu~able amplitude are
il re~erred to as "discrete flaws."
! Flaws which are too small to reflect such Waves are
.! referred to as nnon-disc~e~e flaws" (not shown), ~hîle not
ind1vidually detectable, the presence o~ non-discrete flaw~ may
!! be recognized by me~hods which will be cliscussed hereina~ter.
xr l Referxing ~o Figure 4, a discrete flaw is indicate~ in the
1~ oscilloscope display ~a a~ a low amplitude ~law signal 54
intervenlng higher amplitude end signals 56. When a ~law
. signal 54 does appear, calculations Inay be conducted to locate
~ ' the discrete flaw 52 ~shown in Figure 3) which it represen~.
3~ 13
!
i. I
ll
1 i
I ~eferring ag~in to Figure 4, the pulse signal 55 i~ ~e
~ wav~ directly resul~ing from the imp~c~ ~rom the striking
4 ' ~.echanism 14, and may be t~ea~ed as ~n end signal 56.
6 The position of ea~h discrete ~law 52, the tension on ~he
6 rope, and the presence of non~di~cre~e ~law~ (hO~ shown) are
7 determined by formulae, one or more of whioh ~eguire the
8 ~ollowing var~ables whiGh may he derived rom the os~illosoope
! display 38-
10 1
~ r ~ the time lnterval between ad~acent end signals
11
12 ' 56.
15 ! t~ ~ the time interval between an end signal 56 and
ll the next subsequent ~law signal 54.
14 ',j
5 I Pi = the amplitude of an end sig~al 56 at point i.
¦¦ Pj ~ the ampli~ude o an end signal 56 at poin~ ;.
17 !I LLj = the ~raveliny distance of the wave between the
1~ two end signals shown by amplitudes Pi and P~.
;l
9 '¦ tr and t~ are determined simply by measuring the number o~
~ 'I time units between two adjacent end si~nals S6 as ind~cated by
21 ,I the x axis scale 42 ln the oscilloscope display 3B.
2~ ii Pi and Pj are determlned by resp~c~lvely mea~uring end
~3 i; signal~ 56 at poin~ 1 and ~ on th~ di~play 38 o~ the
~4 ii oscillo~cope 36 by referen~e ~o ~h~ y-axis 4 o . ~he at~enua~ion
~5, coef~ nt ~rmul~ tto be dis~usses he~eina~ter) in whi~h
2~ j these vaxiabl~ are used re~uires that Pi ~ Pj~
27 1 ~ij may be derivad by multiply~ng the leng~h (L) o~ the
28 1 rope 12 by twi~e the number of intervals between suc~s3slve e~
~9 si~nals 56 shown be~ween poin~s Pi and Pj on the di~play 3~.
The ~ollowing ~wo v~riables which are required by one or
S~ !1 14
11
ll
~ 9~6~3~
2 m~re of the tran~ver~e impul~e vibr~tlonal wavQ method formulae
must be independently determined;
L = th~ leng~h of the rope being t~sted.
= the mass per uni~ length o~ the rope being
7 ~e~ted.
I~ the entire length of a ~ope 12 may be vi~wed, as in
9 l
i Fiqure 3 wherein ~he rope 12 is used ag ~ gUy Wire~ ~he length
(~) may be determined by triangu~ation. If t~langulatlon is
1 1.
not possi~le, t~e length (L) o~ the rope 12 mu~t be de~2rmined
12 ,
13 ' by other means -- eithe~ by dire~t measurement, or ~y referen~e
' to ~lueprints, e~c.
: 14 j
The ma~s per unit length (C) o ~h~ ~ope 12 may be
: l6
~ a~quired ~rom the manu~a~turer of ~he rope 12, o~ may be
1~
l determined by analysis o~ a rope sample (no~ shvwn) li~e the
17 j
: Ij particular rope 12 which i~ ~o be tested.
~8
. ~aria~lPq WhiCh are derived ~y ~he me~hod ~o~ulae are as
~9 !
:j ~ollow~:
~1 1
: ,¦ D = the distance of a flaw fro~ the end 50 of the
~2 '~
~,i; rope 12 closest to the sensor 20.
23
v = propaga~ion ~eloci~y of vibrational waYes
~4 ;
¦¦ through ~he rope 12~
! T - ~he tensile load on the rope 12.
2~ !
¦ alpha- the attenuation coeff icien-t oE vibrational wave
27
in the ~ope 12.
~8 ~i
29
: ' The ~is~n~e (D) o~ a discrete flaw 52 from the~ end 50 o~
51 ,
~r~
11
i ~.29~6~
the rope 12 nearest the sensor 2 0 may be ne~rly approximated
aoc~ording to the following~ formula:
;S
4 D -- L(tf/~r)
~;
The flaw location aspect of the me~hod permits substantial ~me
7 savings in loc~ing a known di~rete flaw 52 for determining
8 the need fo~ the rope~s 12 replacement. ~his i.s a substantial
9 ¦ improvement over existing rope testing ~.etho~ Which require
0 1 passing the ~esting apparatus over the entirety of the rope 12
to dete~ and te locate a ~law 52.
~2 il During the time between two successive end signals 5~, and
13 j: consequently between two successi~e p~3~a~es of an ~nd
14 refleGted vibrational waves, the wave wlll have travelled the
length ~) of the rope 1~ twice. The~efore,:the propa~ation
: lg ¦ velocity (v) o~ vibratlonal waves in the rope 12 is determined
b~ the following fo~mula:
8~
~ = 2L/tr
~ ~ 20: il
~1 !IPropagation velocity (v) i5 a function o~ the tension (T~
,
~ a2 i on the rope 12 according to the following formula;
~ 23~
v -- ( Tf C ) 1/ 2
~ I!
2~ !1
¦The formula ~r calculating tensile load (T) when propagation
i
a7 ~v~3locity ~v) is known becomes:
28 !
29 T - ~:v2
;~ 30
~: :3L ¦1 5irice ~h~ t~sting apparatus 10 permi'cs cal~ula~ing th~
; S2 i, 1
~ : 11
~ !l
, j.
1 ¦ propagation velocity (v) kno~ing only the rope's 12 length (L)
2 1 and ~he cons~ant ~C,~ this formula of the ~ethod permits the
3 very simple determination of the tensile load on ~ rope 12.
4 Such ease of calculation has obvious pract~cal sa~ety
~ implications.
I ~ A~ briefly alluded to above, transverse impulse
. vibrational wave metllod includes steps Which, in some
instances, provide an indicia of non-discrete flaws (not shown)
, in the rope 12. This aspect of the method is based upon the
10 ~ fact that the rate at Whic~ energy in a vibra~ing rope 1~ is
11 dissipated is directly propor~ional to the populatioh of flaws
1~ ' in a rope 12.
13 Flaws, whether discrete or non-discrete, interrupt the
.¦ propagation of vibrational waves th~ough -the rope 12, and
Il energy ~s thereby dissipated more rapidly than in a rope havinq
¦¦ fewer ox no flaws. The rate of ene~gy dissipation in the rope
~ is shown by an a~tenuation coefficient (alpha~. ~he
1 ' attenuation coefficient is calculated by ~he following for~ula~
19~:
alpha = ~0 1~ ( )/Lij
~1
2 11 If the tested rop~ 12 shows a higher a~t~nuation co~fficient
23 ' talpha) than a ~ontrol rop~ (no~ shown) known to b2 flawle~s,
1 ~4 !! ~laws in the r~pe 12 are indicated.
As indicated abo~e, the v~iables necessary for
~B ~I calcula~ing the a~tenuation c~e~ficient ara easily derive~ ~rom
27 ! the dispIay 3~ of ~h~ os~illos~ope 36.
28 While t~ere is no way to distingui~h bet.ween discrete
29 flaws 52 and non-discrete flaws ~not shown) by calculating the
30 1 attenuation coeffici~n~, ~here is considerable value in making
1 Il the cal~ulation. This is pa~ticularly so when no discretQ
3~ I; 17
l ~z~6~
I
l j flaws S~ are de~e~ed. A high variance in the at~enuation
2 1 ooefficient o~ the rope 12 from that of a control rope (not
3 shown) would, in such a case, indicate a high n~n-discrete flaw
4 ¦ (not shown) population. such a rope sho~ld be investigated
5 1 ~urther.
~ I E~e~ when discrete flaws 52 a~e de.~ec~ed, an experien~ed
q u~er ~ay be able to recognize that the attenUAtiOn c~ef~iclent
8 ¦ f~r the rop~ 12 t~ not in line with t~e exp~c~ed value, i~
9 1 light of the severity, or la~k thereo~ of the known discret~
lO , ~laws 5Z. Such a disparity would be an indication of ~
l~ significant non-di~c~ete flaw popula~ion in add~ion to the
12 '! known discrete flaw~ 5
13 ~! ~e~erring again to Figures 1 and 4, as is apparent ~ro~
! the above discussion, proper analysis o~ the ~ignals ~om ~he
i! sensor 20 requires precise measurements oP time interval~
I between end signals 56 an~ flaw signals 54 and of the rela~ive
¦ amplitudes o~ adjacent end signals 56. C~lculations based upon
! the mea~red amplitudes and intervals are also requi~ed.
! There~ore, wh~l~ not neces~ar~v t~ prac~ic~ transverse impul~e
: ,. vibrational wave method, a computer ~8 for automa~ing
. measuremen~s and calculatiQns is desirable.
~ he compu~er 58 should be programed and equipped for the
~., following tasks:
24 1) ~o re.ceive and store data ~rom t~e digitiziny
oscilloscopc 36 representing ~he amplitude o~ and
2~ time intervals between the signa~ initially produced
27 I by the sensor 20;
2~ ¦ 2) To derive comparatlve amplitude~ of the signals;
3~ ~o mea~ure time between adjacen~ end signals 56, as
~ well as between a ~law ~ignal 54 and an adjacent end
31 `
32 1
469~
1 signal s6;
I ~ 4) To receive input of th~ rope's 12 lenyth rrOm the
3 user of the testing apparatus 10;
4 S) To receive input of the constan~ C for t~e particular
rope 12 being tested, which cons~ant, when multiplie~
~ by the propagation velocity squared, yields the
: i tensio~ on the rope 12, and ~o make the calculat~on;
7 ~) To divide the time be~ween the flaw signal 54 and the
~ ¦ adj~cen~ end signal 56 by the time betwesn adiacent
10 1 end ~ignals 5~ and to multiply the yuotien~ by the
11 rope's 12 length to calculate the discrete flaw's 52
a I po~ition on the rope;
~:13 7) To measure a di~ference in ampli~de between two
14 1 adjacent on~ sig~als 5~ and calculate the ~ttenuatio~
:~ lG ¦ coefficient for the rope 12; and
¦ 8) Most impor~a~tly, to provide the derived in~ormation
~17 ¦ ~ in a useful f~rmat.
¦ Fo~ producing permanent tes~ records, and particularly ~r
~, :
preparing :graph~al depictions o~ th~: testing apparatu3' 10
measurements a~: shown in Figure 4, a recorder ar grap~iag
~ ;prlnter 60 shauld ~e attached to ~he ~omp~er ~8.
The :testing apparatu~ 10 and fo~mulae juSt discussed
~ 2~ provide a method o~ tes~ing cable, syn~hetic rope, and m~tal
:z~ str~nd~whlch h~s~not ~een; previously known. No presently
2~ known tes~ing apparatus l~or method is ~pplicable to
2~ ferromagnetlc and:~non-ferromagnetic mat~rials, while at ~h~
7~1 same t ime~ permittlng full-léngth testing ~rom a sinql~ location
:28~¦ ~:~on a cable, rop~, or ~trand.
29~! ~ ~he abili~y to Ce~t syn~hetic ropes mad~ of such ma~erials
as nylon and ~VL~R~ will enable th~ use of the~e ropes ~or
3~ i
58 ~
:
~9~69g
1 applications previously reserved to metallic cahles because of
2 inade~uate testihg procedures . The ahil i~y to tes~ the f~
3 length o ;~ cable, rope, or ~;trand will greatly reduce the ti~e
4 and expense i~lvolved in testing ~;uch ~hings as elevator ca~les,
~ antenna guy wires, crane support cables, and the like.
8 1
11 1
12 !¦
13 11
lJ~ 1i
1~
77
18 i
~9
20 I
'i
22 ., -
23
~4
26
2~ 1.
27
~ 28 !1
29 I~
` ~'.~
! I
S2 ',
1~ 2Q
