Table 3.—Tensile test data for typical sample

Stress, Strain, Torque, Load, Elongation,
kip/in’ pet infin lbfeft Kips in
4.420 0.008 128.5 8.207 0.014
13.471 A127 372.8 25.011 234
27,732 256 764.6 51.489 470
44.624 384 1246.8 82.852 704
61.674 512 1734.0 114.509 940
75.777 642 2129.7 140.694 1.178
88.722 .769 2497.3 164.728 1.412
101.457 902 2854.8 188.373 1.654
113.718 1.030 3194.5 211.138 1.890
125.716 1.160 3536.7 233.414 2.129
137.188 1.292 3850.9 254.714 2.370
147.765 1.420 4144.8 274.352 2.605
157.500 1.553 A419 (292.427 2.849
166.131 1.684 4649.8 308.452 3.001
174.077 1.816 4848.3 323,205 3.332
181.023 1.949 5032.8 336.102 3.576
187.127 2.082 5180.3 347.435, 3.820
192.337 2213 5307.6 357.108 4.061
197.195 2.348 5409.0 366.128 4.309
201.230 2.481 5502.3 373.620 4.552
204.861 2618 5582.3 380.361 4.804
207.808 2751 5630.7 385.833 5.048
210.544 2.886 5679.1 390.913 5.296
212.860 3.021 5707.0 395.213 5.544
214.912 3.158 5735.0 399.023 5,795,
216.596 3.292 5745.2 402.149 6.041
217.964 3.428 5752.8 404.689 6.290
219.280 3.563 5756.7 407.133 6.538
220.122 3.697 5745.2 408.696 6784
220.911 3.832 5738.8 410.161 7.032
221.542 3.968 57185 411.333 728
221.911 4.105 5698.2 412.018 7.532
222.272 4.241 5679.1 412.688 7.782
222.437 4374 5654.8 412.994 8.026
222.700 4.419 5652.3 413.483 8.109
222.648 4.432 5644.7 413.386 8.133

Table 4.—Measured tensile test data

Cycle Breaking
Position, ft multiplier Load, Elongation, Load loss, 4
kips in pet

T10to 127... 1 3764 «4.16 9.04 . |
165 to 182 3 3805 3.88 5.88 =
190 to 207 3 3853 3.71 687 a
245 to 262 5 4154 4.02 -40 g J
300 to 317 7 418.1 4.13 1.04 a
355 to 372 8 = 3860 8.82 671
380 to 397 8 «3878 8.2 8.69 4
408 to 425 8 = 3648 8.08 11.83
431 to 447 8 «381.9 2.62 14.96
456 to 472 8 6B 2.08 10.96 n
480 to 497 8 3369-2738 18.58 2 4 6 8 10
oe ee rt ys 4 ELONGATION, in
onto oes $ bred en a Figure 9.—Typlcal test-toad versus elongation. Breaking
775 to 792 0 413.5 8.13 07 13.5 Kips.
830 to 847! . ) 413.8 7.70 00

\Best piece.


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

With Factors for Conversion to Units of the International System of Units (SI)

Abbreviation Unit of measure To convert to— Multiply by—
deg degree
ft foot meters 0.3048
ft/min foot per minute meters per second 00508
gpm. gallon per minute 10 liters per second 0631
h hour
hp horsepower kilowatts .7457
in inch centimeters 2.54
in/min inch per minute meters per second 06096
kip 10° pound (force) newtons 444.8
kip/in? kip per square inch megapascals 6894.8
Ibf pound (force) newtons 4.448
Ibfeft pound force per foot newton-meters 1.3558
Ibf- ft/kip pound force per foot per kip newton-meters per kilonewtons 3048
min minute
pet percent
pet in/in strain, inch per inch+0.01 strain, meter per meter+0.01 1
psi pound (force) per square inch kilopascals 6.8948

second



The criterion of a maximum of 10 pct strength loss can
only be determined from destructive testing of the worst
section, which obviously cannot be measured until the rope
is retired. NDT devices measure loss of metallic area and
local faults (broken wires), however, results are not nec-
essarily proportional to strength because they do not
include changes in the hardness of the wires.

Destructive tests are sometimes made on the "cut-offs"
which result from the periodic necessity to reterminate the
attachment to the cage or skip. However, this section is
not representative of the condition of the rope. Until sev-
eral cut-offs are made, this part of the rope has not been
over the sheave and so has experienced no bending fa-
tigue. It is subjected to some degree of corrosion, but may
not have received the same lubrication as the rest of the
rope. Depending on the type of termination used, the cut-
off probably has experienced much different stresses. For
example, when U-bolt clips are the means of termination,
there are high local stresses at each clamp. Experience
with testing field samples of cut-offs and retired rope sec-
tions has confirmed that tensile tests on cut-offs will not
provide an accurate measurement of strength loss.

The criterion of rope diameter loss greater than 6 pet
can only be determined by physical measurements. These
are time consuming and reflect only the strength loss due
to surface wear and internal nicking. Diameter measure-
ments, however, cannot provide any indication of strength
loss due to embrittlement.

B

Loss of one-third of the diameter of outer wires, a third
criterion, is extremely hard to measure. It is not possible
to get a caliper under a crown wire to make a diameter
measurement. The possibility of measuring the width of
the flat portion, assuming it to be the chord of the wear
arc, to calculate the area of the wear arc has several prob-
lems: First, high precision is required in measuring width
of the flat, and second, the flat is not flat, but a curve.
Third, sometimes peening occurs which causes a "wire
edge" burr that distorts the width measurement. Fourth,
in “flattened strand” construction, which is increasingly
popular, the outer wires are swaged flat during fabrication
and true wire diameter cannot be measured. Furthermore,
this method yields only an estimate of loss of strength due
to wear, but not due to fatigue.

The number of broken wires is useful in that it is an
indication of the fatigue state of the rope. However, there
are some anomalies in the effectiveness of this criterion,
too. First, at present, the correlation between the number
of broken wires and the degree of fatiguing is unknown.
Second, embrittlement can exist before the wires begin to
break. It is expected that future testing under this project
will quantify such relationships.

The test data relating to these criteria were extracted
from tables 4, 6, and 7, and compared in table 8.

Table 8.—Retirement criteria for test rope

Position, Cycle Breaking load Rope diam Outer wire diam Broken wires
ft multiplier loss, pet loss, pet oss, pet per lay
Oo. 0 NA 0.14 1.2 0
50 i] NA 1.82 147 0
100 . 1 NA WT 14.3, 0
105 to 127 .. 1 9.04 NA NA 0
150 ..... 0 1 NA 2.49 20.1 0
160 to 182 .. 3 5.88 NA NA 0
185 to 207 .. 3 6.87 3.84 WE t)
240 to 262 .. 5 40 5.42 * 436 0
300 to 325... 7 “1.04 5.37 * 43.2 0
350 to 372... 8 671 * 614 * 49.4 4
375 to 397 .. 8 8.69 NA NA 5
400 to 425... 8 * 11,83 * 6.23 * 50.1 4
425 to 447 .. 8 * 14.95 NA NA "7
450 to 472 .. 8 * 10.96 * 6.23 * 50.1 * 2B
475 to 500... 8 * 18.58 * 6.23 * 50.1 17
525 to 550 .. 7 7 5.52 * 443 1
575 to 600 .. 5 66 5.28 * 424 0
640 to 662 .. 3 5.53 5.04 * 40.5 0
700... eee 1 NA 3.50 28.1 0
725 to 750... 1 6.02 cal 27 ty)
775 to 800... 0 07 0 0 0
825 to 847 . 0 ) NA NA 0

NA Not available.


shutdown. The main means of changing the drum rotation
is through a regenerative braking system in the drive, thus
the hydraulically actuated friction brakes are a backup
system, The friction brakes can stop the drum in about
three-fourths of one rotation from maximum speed. The
computer is programmed to recognize and react to emer-
gency situations, via a variety of sensors, such as when
the tension cylinder runs out of travel, when the rope is
nearing the end on the drum, or if the rope should break.
Operations are monitored continuously throughout a test.

The drum liner can be replaced with other surface
materials such as urethane-coated materials or grooved
liners for tracking and wear studies. The sheaves are all
built with bolt-on segments that are replaceable for shape
and wear studies, as well as for accommodation of differ-
ent rope diameters.

An environmental chamber is mounted at one location
on the rope travel path. It can provide sprays of water,
corrosives, and dirt to simulate environmental effects. The
chamber is not intended for simulation of particular mine
environments because they are so highly variable from
mine to mine and seasonally as well.

Provision is also made for mounting nondestructive
testing devices along the rope path to evaluate their
effectiveness in measuring deterioration of the rope such

as broken wires and loss of metallic area due to wear and
corrosion. One model is presently being used as a normal
part of the testing procedure and a second is on order.

‘The specifications for the bending fatigue machine are
given in table 1,

Table 1.—Bending fatigue machine specifications

Maximum rope tension . . . tbf.. 300,000

Maximum rope speed ft/min .. 1,000
Maximum fleet angle . . deg. 29
Maximum rope stretch (without regripping) ... ft. . 20
Rope diameter . ving. — 1t0.21/2
Rope length . ft.. up to 1,100
Drum diameter . 1 ft. 10
Drum width . . ft.. 84
Tension sheave diameter . ft 10
Idler sheave diameter . . ft. 8
Drum drive motor hp. 500
Hydraulic system:

Flow rate. 30

Pressure 3,000

TENSILE TEST MACHINE

The second major piece of equipment in the laboratory
is the tensile machine (fig. 5). Although this facility is

Figure 5.—Tensile and axial fatigue testing machine.



INTRODUCTION

The Wire Rope Research Laboratory is located at the
US. Bureau of Mines’ Pittsburgh Research Center in
Bruceton, PA (figs, 1-2). The laboratory was setup as part
of the Hoisting System Development project, which has
been a continuing effort by the Bureau for several years.
Since personnel hoists carry many people at a time, the
failure of a rope could result in a catastrophic accident.
While focusing on the hoisting of personnel and materials
in shafts and slopes of underground mines, the products of
this research will apply to draglines for surface mining and
to wire ropes for guying, guidance, staying, and for general
use in the industry.

Essentially, the objective of the project is to improve
the safety and economics of hoisting systems by quantifying
the degradation process, The research approach is to de-
velop accurate data on the factors that reduce wire rope
strength, such as fatigue (both bending and axial), wear,
and corrosion. This data can also be used to improve non-
destructive testing equipment for better measurement of
rope condition, It can be seen that the safety and eco-
nomic concerns are interrelated, and that the potential
benefits of such research are high.

Figure 1.—Wire Rope Research Laboratory.



WIRE ROPE RESEARCH: ANALYSIS OF BENDING FATIGUE
IN A 2-INCH IWRC WIRE ROPE

By A. J. Miscoe’ and W. M. McKewan”

ABSTRACT

A unique machine for inducing bending fatigue in wire ropes was built at the U.S. Bureau of Mines’
Pittsburgh Research Center. This machine can produce nine levels of degradation through repetitive
cycling of long samples of wire ropes of the types used in the mining industry. This report provides an
analysis of the results of the first wire rope to be fatigued on this machine. These results have indicated
that as a wire rope accumulates bending cycles, its strength first decreases because of wear and then in-
creases due to cold working of the wires. As the amount of cold working increases, more and more of
the embrittled wires break and the strength of the rope decreases rapidly. In this test, application of

several of the regulatory retirement criteria to various sections of the rope suggests that there may be
some inconsistency among them.

Supervisory physical scientist.
2Metallurgist.
Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.


4

In the case of this rope, the 450- to 500-ft zone had so
many broken wires that the LF trace from the Magno-
graph was unintelligible. It did indicate severe damage,
but individual wire breaks could not be distinguished.
Normally, of course, a rope would be retired long before
that many wires were broken. It would appear from these
data that measurement of metal hardness, which is indica-
tive of cold working, could be a valuable supplement in
assessing the condition of wire rope.

The four criteria were applied to the data in table 8.
As indicated by the asterisks, there is some variation in
the retirement range of the criteria under discussion.

Considering breaking strength loss of 10 pet, a hoist rope
having a section like the test rope’s 400- to 500-ft sec-
tion would be retired. For the criterion of rope diam-
eter loss of 6 pet, a section like the 350- to 500-ft part
would cause retirement. Considering outer wire diameter
loss of one-third, a hoist rope with a section like the 240-
to 662-ft piece would be retired. And for broken wire per
lay length, a section like the 425- to 500-ft section would
cause retirement. It is expected that further research
under this project will confirm and quantify these
conclusions, providing data for support of any regulatory
changes,

CONCLUSIONS

The most significant finding is that the data pro-
vide evidence that the rope goes through three phases of
degradation: strength reduction due to the loss of metal
area, strength increase due to cold working, and finally,
rapid strength loss due to the fatigue failure of the wires.
Degradation is not quite symmetrical about the middle
of the rope due to inherent differences in the design of
the machine. Test results indicate that nondestructive

measurement of metal hardness, which is an effect of cold
working, would be a valuable supplement to current in-
spection methods in assessing the condition of wire rope.

Another conclusion that can be drawn from this test is
that there is some variation among the current retirement
criteria. Further research is needed to define the varia-
tions and to establish a better understanding of wire rope
behavior.

INT.BU.OF MINES,PGH.,PA 29763


Figure 3.—Bending fatigue machine.

Overall control of the machine is provided by a com-
puter that permits unmanned operation over extended pe-
riods since fatigue life will be tested to many thousands of
cycles. At the maximum speed of 1,000 ft/min, a machine
cycle takes about 1 min; since the center of the rope is
cycled eight times for each machine cycle, 1,000,000 rope
bending cycles would require 24-h operation for about
87 days. It is not planned to run the ropes to destruction
since the objective is to measure remaining strength at cer-
tain intervals of load, speed, and number of rope bending
cycles, The computer manages the hydraulic system as
well as the drive system. The hydraulic system, through
the ram, maintains constant rope tension and compensates
for stretch in the rope. It also manages the braking sys-
tem used for changing the direction of drum rotation dur-
ing cycling as well as the friction brakes for emergency

MACHINE CYCLE MULTIPLIER

3 dead wraps
each end

=rwyura on oo

co) 100 200 300 400 500 600 700 800 900
DISTANCE ALONG ROPE, ft

Figure 4.—Test rope fatigue cycle profile.



RI

9466

REPORT OF INVESTIGATIONS/1993

Wire Rope Research: Analysis of Bending
Fatigue in a 2-Inch IWRC Wire Rope

By A. J. Miscoe and W. M. McKewan

ny: United States Department of the Interior

Bureau of Mines


TEST PROCEDURE

BENDING FATIGUE MACHINE

For the bending fatigue test, the rope specimen was
reeved through the machine and wound onto the drum.
The rope was 847 ft long. It was the first rope to be run
on this machine and was used for shakedown of the equip-
ment. Consequently, it had a highly varied history of loads
and speeds. After the shakedown was completed, the rope
was run until 28 broken wires were counted in the middle
section, The rope was removed from the machine and cut
into 25-ft samples for further testing. These samples were
cut into three sections: a 17-ft piece for a tensile destruc-
tive test; a 5-ft piece for wire-by-wire examination; and a
3-ft section for metallographical analysis. The location of
the sample cuts to be used for tensile tests was determined
by the cycle pattern in figure 4.

TENSILE TEST MACHINE

The 17-ft samples were terminated with resin-filled,
standard closed sockets. This resulted in a finished speci-
men gage length of about 15 ft. This length was chosen

based on the results of a baseline testing program de-
scribed in the previously mentioned publication.

NONDESTRUCTIVE TESTERS

The instrument was mounted on the rope next to
the drum and operated according to the manufacturer’s
directions. To make a test, the rope is run through the
instrument once to properly magnetize it. The sensor
head is removed during rewinding to prevent a change in
the magnetic polarity of the rope and then it is remounted.
The rope is then run through the instrument while the
data is being recorded. The Magnograph was not avail-
able when this rope was new, so the determination of rope
condition was based on the end sections of the rope that
never left the drum. While this section experienced load-
ing and unloading stresses, no bending cycles occurred.
These "best pieces" amounted to about 90 ft on each end
of the rope.

Sections of typical chart records for a best piece and
for the most deteriorated part of the rope are shown in
figure 7. There are two traces for each chart; the lower

crown wir

0.7% metal ar

DISTANCE, ft

Figure 7.-Typical data from electromagnetic nondestructive test Instrument. Anno-
tated chart records show data for a best piece (top) and a badly deteriorated part of rope

(bottom).



planned primarily for tensile strength tests on wire rope
specimens in support of bending fatigue research, it also
has the versatility to create fatigue under a cyclic axial
force. The bending fatigue machine is not capable of ap-
plying cyclic tensile forces. Axial fatigue work is planned
to occur later in the program. The main application of the
tensile machine is to measure actual breaking strengths of
ropes as received for comparison with similar measure-
ments made after the rope has been degraded on the
bending fatigue machine. These measurements provide
quantitative data to establish the effects of service condi-
tions on the life of wire ropes. The performance of this
machine was reported in a previous publication?

New and used ropes from mine hoists, obtained through
cooperative agreements with mining companies, are also
tested to assess the effects of real-life use.

The machine is essentially a hydraulically actuated ten-
sile testing machine in a horizontal position rather than
the usual vertical position to reduce vertical height require-
ments and for ease of access. It is composed of three ele-
ments: the load frame, the electrical console, and the hy-
draulic power supply, all operating in conjunction, The
load frame contains the hydraulic actuator assembly and
the load cell. The moveable crosshead containing the
torque sensor cell has hydraulic positioners and locks. The
locks sustain full-rated load in either direction. Safety
enclosures for the specimen are provided for operator pro-
tection during testing. As a further protection, the build-
ing is locked and personnel are cleared from the area.

The load is applied through a closed-loop servohydrau-
lic system in which high-pressure hydraulic fluid, under the
precise control of a servovalve, is provided to the actuator.
To accomplish this, the system controller compares a con-
trol signal with feedback signals from the transducer.
Error signals control the servovalve. The controllable

parameters are displacement of the actuator, load applied
to the specimen, and torque generated by the wire rope
specimen as axial load is applied.

The electronic control console contains all the necessary
analog components for servo control, hydraulic power
control, programming, signal conditioning, test parameter
readout, and interlock functions. It also contains a digital
computer and necessary interface to control, record, and
plot the testing data. System specifications are listed in
table 2.

Table 2.—Tensile and axial fatigue machine specifications

Rope tension .
Actuator speed

NONDESTRUCTIVE TESTERS

A commercially available electromagnetic nondestruc-
tive tester (EM NDT), the Magnograph,t Model MAG-1,
purchased for laboratory use is shown in figure 6.

Such devices are useful because they can examine the
interior of a wire rope. They operate on the principle of
magnetically saturating the test rope and then measuring
any changes in the saturation level. As a rope wears,
metal is lost and thus will show a lower level of saturation.
The measuring sensors thus indicate the loss of metallic
area (LMA). Because broken wires create magnetic poles,
they are recorded as a spike on the chart and can be
counted. These are known as local faults (LF) and are an
indication of brittleness in the rope.

3McKewan, W. M., and A. J. Miscoe. Baseline Tensile Testing at the
Wire Rope Research Laboratory. BuMines IC 9255, 1990, 23 pp.

igiverseseserertens
EE
ee Py

fe
ee,
aa ie

He

eee
Lie

‘Reference to specific products does not imply endorsement by the
ULS. Bureau of Mines.

Figure 6.—Magnograph nondestructive sensor.



FTL
Office, Contall] Test [tr] Office,
8- ft rollup door: Room ) Room R
. IR oom
15-ft rollup door. 108 "a || 107 103
ety? rea
Room i £3 Storage |
m =|-Storage £3 Platform
| platform Tensile and axial 3 i
Room: 1 fatigue machine 3!
2 UL 7
Lav Term shop area 15-ft
13 Laboratory, rollup
Room 101 Reel handler door
UY, a
1 Winch H Hl
\ | Reel |
f
bird i ' Bending fatigue machine ; sera |
be
Mot
a)
8-ft rollup door. Room
100
Figure 2.Layout of laboratory.
EQUIPMENT

BENDING FATIGUE MACHINE

Because the primary mode of wire rope degradation is
fatigue from bending under high stresses on sheaves and
drums, the principal machine in the laboratory is one de-
signed to cause fatigue damage in varying degrees in a
long sample (about 1,000 ft) of wire rope. By using a long
sample, the possible variation among short samples is
avoided. These variations include differences in samples
obtained at different times and from different manufac-
turers, as well as changes in machine operations due to
such things as sheave wear. The bending fatigue machine
is shown in figure 3,

The "three-sheave” configuration not only shortens the
load frame, but also is a convenient means of accommo-
dating a range of sheave diameters without affecting the
maximum fleet angle when sheaves are changed. Fleet
angle is the angle made by the rope at any wrap on the
drum and the line made when the rope is in a plane

perpendicular to the drum axis through the plane of the
sheave. Another important benefit of this configuration is
that there are up to eight rope-bending cycles for each
machine cycle, This benefit is important to the test plan
because it increases the number of tests that can be ac-
complished in any given period and greatly improves the
statistical significance of the resulting experimental data.
Perhaps the most interesting result of the three-sheave
configuration is how the specimen is degraded, Because
of the different number of bends experienced by adjacent
segments of the rope, a staggered degradation profile re-
sults, Thus, in a single specimen and a single test period,
there will be available for further examination multiple
samples of rope at each of nine different levels of degrada-
tion (fig. 4). This feature is very advantageous when doing
studies relating to service life and establishing new or re-
vised retirement criteria, because it reduces the test time
requirements as compared to an ordinary test machine.


CONTENTS

Abstract .
Introduction .
Equipment . bbe eee e eens
Bending fatigue ‘machine .
Tensile test machine . .
Nondestructive testers
Test procedure ......
Bending fatigue machine .
Tensile test machine . .
Nondestructive testers . .
Test rope description .
Results ....
Conclusions

ILLUSTRATIONS

Wire Rope Research Laboratory .
Layout of laboratory ..
Bending fatigue machine .
Test rope fatigue cycle profile ....
Tensile and axial fatigue testing machine ..
Magnograph nondestructive sensor ..... . .
Typical data from iectromagnetic ns nondestructive test instrument .
Test rope construction .
9. Typical test—load versus elongation
10. Typical test—stress versus strain .

11. Typical test—torque versus load ... .
12. Effect of distance along rope on breaking strength ..... aeons
13. Effect of number of bending cycles on breaking strength . . .
14. Effect of distance along rope on breaking strain .. .
15. Effect of number of bending cycles on breaking strain .
16. Effect of number of bending cycles on Torque K ........
17, Area losses from NDT charts and diameter measurements .

SPAAwWAYNE

TABLES

Bending fatigue machine specifications .
Tensile and axial fatigue machine specifications .
Tensile test data for typical sample .
Measured tensile test data ..
Calculated tensile test data . . :
Diameter and NDT measurements .

Broken wires .
. Retirement criteria for test rope ..

PAKVSYYP

Page

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50 /
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() 1 2 3 4 5

STRAIN, pet in/in

Figure 10.—Typical test—stress versus strain. Yield = 170.8
kip/in’; breaking stress = 222.7 kip/in?; modulus = 10.67 x 10°
psi.

TORQUE, 105 Ibf-ft

200 = 300
LOAD, kips —_
LOAD ips
Figure 11.—Typical test—torque versus load. Torque K =
14.81 Ibfeft/kip.

400 500

Figure 14 shows that initially the breaking strain fol-
Jowed a pattern similar to that of the breaking strength in
figure 12. Figure 15 shows the same degree of symmetry
as in figure 13, The significance of decreased strain is that
cold working occurred with increased cycling.

Figure 16 shows that Torque K is also sensitive to in-
creased cycling, although not to a great extent.

Table 5 shows the data calculated from the measure-
ments made during the tensile tests. Breaking stress and
strain are computed by the operating program when the
rope specifications are inserted, The beginning of the
plastic deformation is determined by inspection. The mod-
ulus of elasticity is then determined by linear regression
analysis. The yield stress and strain are then calculated
from the 0.2 pet offset line (fig. 9). These calculations
were described in the previously mentioned publication.
Graphs of these relationships versus distance and cycles
are not shown since they are derived from the same data
as in table 4 and thus would be similar.

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MACHINE CYCLE MULTIPLIER

Figure 13.—Etfect of number of bending cycles on breaking
strength.

ROPE POSITION, ft

Figure 12.—Effect of distance along rope on breaking strength.

£5 - :
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ROPE POSITION, ft

Figure 14.—Effect of distance along rope on breaking strain.



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MACHINE CYCLE MULTIPLIER

Figure 15.~Effect of number of bending cycles on breaking
strain.

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MACHINE CYCLE MULTIPLIER

Figure 16.—Etfect of number of bending cycles on Torque K.

5 T T T T T T T
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5 °
g 3 ee “8,
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0 100 200 300 400 500 600 700 800
ROPE POSITION, ft

Figure 17.—Area losses from NDT charts and diameter meas-
urements. NDT Is nondestructive tester.

The current regulations regarding retirement of hoist
ropes* include four criteria that pertain to the ropes tested
at the Wire Rope Research Laboratory:

Strength loss exceeding 10 pct as determined by
NDT tests.

¢ Rope diameter loss exceeding 6 pct of the baseline
measurement,

© Outer wire diameter loss of more than one-third.

¢ Number of broken wires in one lay length in excess
of 5 pet of the number of load-bearing wires in the rope
(six for this rope) or 15 pet of the number of load-bearing
wires in a strand (two to three for this rope).

Failure to pass any of these criteria is cause for a rope to
be retired from service.

Table 7 shows the tabulation of a visual count of the
number of broken wires per lay on the surface of the rope.
These were the averages for three lay lengths.

SUS. Code of Federal Regulation. Title 30-Mineral Resources;
Chapter I-Mine Safety and Health Administration, Department of La-
bor; Subchapter N—Metal and Nonmetal Mine Safety and Health:
Subpart R, Article 56, and Subpart R, Article 57, Subchapter O—Coal
Mine Safety and Health; Subpart O, Article 75, and Subpart O, Article
‘77; July 1, 1992.

Table 7.~Broken wires
Position, ft Cycle muttiplier Broken wires per lay
105to 110 .... 1 0
160 to 165 . 3 0
185 to 190. . 3 0
240 to 245 . 5 0
320 to 325 . 7 0
350 to 355 . 8 4
375 to 380 .... 8 5
400 to 405... 8 4
425 to 430 .... 8 7
450 to 455. 8 2B
478 to 480 . 8 7
545 to 550 . 7 1
575 to 580 . 5 0
640 to 645. 3 0
745 to 750 . 1 0
795 to 800 .... 0 0
825 to 830 .... 0 0



Library of Congress Cataloging in Publication Data:

Miscoe, Anthony J.
Wire rope research : analysis of bending fatigue in a 2-inch IWRC wire rope / by
AJ. Miscoe and W.M. McKewan.

P. em. — (Report of investigations; 9466)
Includes bibliographical references.
1. Mine hoisting—Equipment and supplies—Testing. 2. Wire rope—Fatigue—

Testing. I. McKewan, William M. I. Title. III. Series: Report of investigations
(United States. Bureau of Mines); 9466.

TN23.U23  [TN339] 622 s—de20_[622’.6] 92-37417 CIP.



Report of Investigations 9466

Wire Rope Research: Analysis of Bending
Fatigue in a 2-Inch IWRC Wire Rope

By A. J. Miscoe and W. M. McKewan

UNITED STATES DEPARTMENT OF THE INTERIOR
Bruce Babbitt, Secretary

BUREAU OF MINES


one shows the LMA, and the upper one shows the LF.
Comparing like traces for the two samples, the LMA line
is lower, indicating a metal loss of about 5 pet. The LF
trace for the best piece shows only normal variations due
to the passing of rope-lay peaks and to the high signal

magnification, The LF trace for the most deteriorated
piece shows large disturbances from the faults. Proper
interpretation of such a chart requires highly skilled
operators.

TEST ROPE DESCRIPTION

The test rope was of 2-in-diam, 6x25 filler wire con-
struction, with a right regular lay of 12.15 in, and an
independent wire rope core (IWRC). In this construction
(fig. 8), there are 6 strands containing 19 wires (of ap-
proximately the same diameter) with 6 filler wires for
spacing; the filler wires are not considered load bearing.
The core is composed of seven strands, each containing
seven smaller wires having approximately the same di-
ameter. The wire rope core contributes about 15 pct of
the total strength of the rope.

Although not identified when purchased, it is be-
lieved that the wires were of extra improved plow (EIP)
steel based on the data obtained from the "best pieces."
As such, the rope had a nominal breaking strength of
396 kips. IWRC rope was chosen because of availability
at the time of startup. Such rope is stiff compared to fiber
core rope, and so is seldom used for hoist rope in U.S.
underground mines,

RESULTS

Two tensile tests were made on samples that were
taken from the drum (dead wrap) portion of the rope.
These samples had no bending cycles and were used as
base tests for comparison. The data from one of the tests
are shown in table 3 and figures 9 through 11. Figure 9 is
a plot of load versus elongation. Figure 10 is a plot of
stress versus strain. From this plot the modulus of elas-
ticity, the breaking stress and strain, and the yield stress
and strain are calculated. Torque K is the slope of the
line in a plot of the torque generated by a rope sample
during a tensile test versus the load (fig. 11). The slope is
a straight line until just before rupture.

The data obtained from tensile tests on the rope sam-
ples are shown in table 4 and figures 12 through 15.

In table 4, the number listed under "cycle multiplier" is
the ratio of machine (or drum) cycles to the number of
rope bending cycles. Owing to the nature of shakedown
testing, the number of machine cycles was not available
from the trial period data. This multiplier was described
previously under EQUIPMENT. The final column is the
percentage loss of breaking strength based on the 830- to
847-ft drum sample ("best piece").

Figure 12 shows that the rope goes through three
phases of degradation: strength reduction due to metal
area loss, strength increase due to cold working, and fi-
nally, serious strength loss due to the fatigue failure of
the wires. The degree of symmetry is indicated in fig-
ure 13, As can be seen, there is some scatter in the data,

indicating that the machine does not degrade the rope in
exact symmetry. The relationship between the machine
cycle multipliers in figure 13 and the distance along the
rope in figure 12 is shown in figure 4 and table 4.

Figure 8.—Test rope construction.


Table 6 contains data from other physical measure-
ments that were made two days before the rope was re-
moved from the bending fatigue machine. The first two
columns list the linear locations and the cycle multiplier at
that location, The next column shows the rope diameter,
as measured by a caliper, averaged from three positions
around the rope. The next two columns are computations
of the percent reduction in diameter and metallic area
compared to the best pieces. The loss of area is obtained
from an in-house computer program that will be reported

i

in the near future. The area computed by measurement
is compared to the LMA determined by the NDT sensor
(column 6) in figure 17. This comparison shows that the
largest difference on the first half of the rope is 1.7 pet,
but only 0.3 pct on the second half. This indicates that
both methods give comparable accuracy. The final column
shows the percent loss of diameter of the outer wires of
the rope, which also was determined by the previously
mentioned computer program.

Table 5.—Calculated tensile test data
Cycle Breaking Yield Modulus of Torque K,
Position, ft multiplier Stress, ‘Strain, ‘Stress, Strain, elasticity, Ibfeft/kip
kip/int pet infin —_kip/int- pet infin 10° pel
Ti0t a7... 1 2027 230 1747 148 138 147
165 10 182 3 200.7 215 185.4 1.38 158 139
190 to 207 . 3 2075 2.06 1858 1.41 155 139
245 to 262 . 5 2237 2.23 190.4 1.43 162 13.0
300 to 317 7 225.1 2.30 2020 147 158 13.4
355 to 972 . 8 2079 1.84 194.2 1.45 157 132
380 to 397 . 8 208.5 1.73 194.0 1.48 152 13.4
408 10 425 8 196.5 1.85 187.0 1.42 155 13.2
431 to 447 . 8 189.5 1.52 1859 1.43 15.1 13.2
486 10 472. 8 198.4 1.78 1859 1.42 152 133
480 to 497 . 8 178 1.43 176.1 1.39 148 133
525 to 542 . 7 2206 2.18 199.3 1.45 16.1 13.2
580 to 597 . 8 2214 2.16 199.5 1.43 159 132
645 to 662 . 3 2105 1.85 1955 1.45 187 135
725 t0 742 . 1 209.4 2.32 183.0 1.42 150 142
77510792 .... 0 2227 443 1708 177 107 148
890 to 847 .... 0 2228 4.19 1724 1.80 10.4 148
Table 6.—Diameter and NDT measurements
Position, ft Cycle Rope diam ‘Area loss, pot Wire diam
multiplier in Toss, pot Calc NDT loss, pet
0 2.082 Or oot 00 12
0 2.047 1.82 36 0 147
1 2.048 17 3 (10 143
: 1 18
: 1 2.033 2.49 7 18 204
: 3 35
200 . 3 2,005 3.84 14832 308
250 5 1.972 5.42 30838 436
300 7 1.973 8.37 30140 43.2
350 8 1.987 6.14 38838 49.4
400 . 8 1.955 6.23 39740 50.1
440. 8 46
450. 8 1.985 6.23 397 36 50.1
500. 8 1.955 623 397-38 50.1
550 7 1.970 5.52 3168.4 44.3
600 . 8 1.975 5.28 29 28 42.4
650 . 3 1.980 5.04 2650-25 405
700 . 1 2.012 3.50 120 15 28.1
750 . 0 2.078 34 03 0 27
800 0 2.085 00 00 ) 0