MECHANICAL BEHAVIOUR OF DAMAGED CENTRAL CORE STRAND CONSTITUTING A STEEL WIRE ROPE HOIST UNDER THE EFFECT OF A STATIC LOAD

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 7, Issue 3, May–June 2016, pp.360–367, Article ID: IJMET_07_03_033
Available online at
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=7&IType=3
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ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
MECHANICAL BEHAVIOUR OF DAMAGED
CENTRAL CORE STRAND CONSTITUTING
A STEEL WIRE ROPE HOIST UNDER THE
EFFECT OF A STATIC LOAD
E. Boudlal and M. Barakat
ISEM/Higher Institute of Maritims Studies, Laboratory of Mechanics, Km 7 Road El
Jadida Casablanca Morocco
N. Mouhib, M. Lahlou, and M.El Ghorba
Laboratory of Control and Mechanical Characterization of Materials and Structures,
National Higher School of Electricity and Mechanics, BP 8118 Oasis, Hassan II
University, Casablanca, Morocco
H. Ouaomar
Faculty of Sciences and Technics, Mghilat, Beni Mellal, Morocco
ABSTRACT
The main objective of this study is to predict the evolution of damage of the
central core (strand) that represent the heart of a wire rope, based on simple
experimental tensile test conducted on virgin samples and others artificially
damaged by breaking wires constituting the samples at different percentages.
The experimental results obtained have allowed us to follow the evolution of
the damage and quantify it. Thereafter, it was possible to identify three stages
of damage. Therefore, be able to intervene in time for predictive maintenance.
This study also includes a correlation between two methods of calculating the
damage namely static damage and damage by unified theory and this by
analogy to cyclical behavior. The comparison shows good agreement.
Keywords: Central Core Strand, Damage, Predictive Maintenance, Tensile
Test, Wire Rope.
Cite this Article: E. Boudlal, M. Barakat, Mouhib, M. Lahlou, M.El Ghorba
and H. Ouaomar, Mechanical Behaviour of Damaged Central Core Strand
Constituting A Steel Wire Rope Hoist Under The Effect of A Static Load.
International Journal of Mechanical Engineering and Technology, 7(3), 2016,
pp. 360–367.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=7&IType=3

E. Boudlal, M. Barakat, Mouhib, M. Lahlou, M.El Ghorba and H. Ouaomar
1. INTRODUCTION
Wire ropes are belonging to the class of complex systems due to the large number of
components that build them and their complicated processes of operations. It is
generally a set of multiple strands wound around a central core strand and each strand
is comprised of several wires helically wound [1] (Fig.1).
Figure 1 Basic components of a typical wire rope
This specific structure permits the wire ropes to resume loads despite the break of
one or more wires. Furthermore, they are able to carry loads in the longitudinal
direction while being flexible in the lateral direction [2].
Despite all the advantages that this conception represents, it is an accepted fact
that wire ropes are consumable with a limited life and it should be replaced before the
risk of failure becomes unfortunate. Industrial experience shows that sudden breaking
of a large part of wire ropes in service is most often due to the cumulative damage of
wires [3][4]. This is particularly insidious because of its hidden nature, which may
lead to serious accidents.
As part of this problem, this study focuses on the mechanical behaviour of one of
the components of the wire rope which is the central core strand of which several lots
were artificially damaged at different percentages (14%, 28%, 42%, 57% and 71%
broken wires). Based on an experimental tensile tests, the evolution of damage is
determined and subsequently the critical life fraction βc is defined. Such a study could
be beneficial for manufacturers because of its low cost and speed.
2. MATERIAL & EXPERIMENTAL METHODS
2.1. Material
In this study, we consider a Steel Wire Rope of type 19x7 and antigyratory
construction (1x7 + 6x7 + 12x7) (Figure 2), with a diameter of 7mm mainly used as a
rigging wire rope for all types of cranes and for exploring in the high seas due to its
excellent resistance to deformation.
The considered central core strand is composed of 7 individual wires, a core wire
(core of the central core) and 6 peripheral wires helically arranged around.

Mechanical Behaviour of Damaged Central Core Strand Constituting A Steel Wire Rope
Hoist Under The Effect of A Static Load
Figure 2 Steel Wire Rope of type 19x7 and antigyratory construction (1x7 + 6x7 + 12x7)
2.2. EXPERIMENTAL METHODS
As mentioned before, the goal is to follow the damage of central core strand extracted
from steel wire rope. For this, static tests were performed on artificially damaged
specimens at different levels of damage by cutting some wires (14%, 28%, 42%, 57%
and 71% broken wires).
To obtain specimens of central core strand, a suitable length of the cable was cut
and strands were de-wiring (wiring off). The minimum length of the samples is equal
to the length of the test plus the necessary for the mooring. Therefore, a length of 300
mm is anticipated as the length of the test. The measurements tolerance in the length
is ± a millimeter for all samples [5].
To break wires manually, a tip was inserted carefully through the number of wires
to cut and lift carefully by turning the tip in the direction of wiring then cut using a
diagonal cutting pliers.
All specimens were tested in tension according to DIN EN 10002-1 with imposed
displacement corresponding to a strain rate of 2mm / min. The tests were carried out
under the conditions of air and room temperature (≈ 20-24 ° C) on a Zwick Roell type
of machine with a force cell ± 10 kN. Figure 3 shows the assembly with a close view
of the sample placed between the mooring jaws.
The fixation of the samples is performed by means screwed wedges on both ends of
the strand in order to prevent sliding of the samples during the tests.
Figure 3 Experimental setup of a central core sample extracted from wire rope

3. RESULTS & DISCUSSION
3.1. Mechanical characterization
All the tests leading to the rupture of central core specimens has allowed to trace the
shape of tensile curve representing the evolution of stress applied to the virgin
specimen strand (MPa) versus strain (%) (Figure4) and subsequently extract the
mechanical characteristics summarized in table 1 (the values given are average
values).
Figure 4 Stress-Strain curve of the extracted virgin central core strand
The mechanical properties of the virgin specimen are reported in the table1.
Table 1 The mechanical properties of central core strand
Mechanical
properties
Tensile
strength
Elastic
limit
Young
modulus
Poisson’s
ratio
Value 1561 MPa 1367 MPa 189 GPa ν = 0,3
3.2 Tensile tests of tested specimens of the extracted central core strand at
different percentages of damage
Experimental results according to the number of broken wires (virgin, 14%, 28%,
42%, 57% and 71% broken wires) are given in Figure 5. The curves describe on 3D
the evolution of strength (N) versus displacement (mm).

Figure 5 Evolution of the strength (N) versus displacement (mm) for different levels of
damage
When carrying out the tests and according to the results shown in Figure 5, it was
found that the ultimate strength drop depending on the number of broken wires.
Therefore, following this reaction of studied strand (central core), it was possible to
assess the damage at each level of damage by similarity to the behavior of a material
under cyclic loads
3.3. Quantification of static damage
The model of static damage (Ds) is to determine the evolutions of forces whose
variations are mainly due to damage. Then we quantify the damage by the variable Ds
expressed as [6]:
Where:
Fu: Value of the maximum ultimate strength
Fur: Value of the ultimate strength
Fa: Force just before the final break
The evolution of central core damage is followed at several levels of degradation
starting with its virgin state until failure. This phenomenon is described by the
damage parameter Ds Equation (1) by the following limits:
 In the initial state: → Fur = Fu → D = 0
 In the final state: → Fur = Fa →D = 1
The variation of the static damage according to the life fraction is illustrated by
the curve in figure 6:
(1)

Figure 6 Evolution of the static damage depending on the life fraction 
Increased damage means the increase in strength loss in static tensile samples.
This loss changes when artificial damage becomes more important.
The curve in Figure 6. allowed us to identify three stages of damage using the
curvature change [7]. The first stage corresponds to its initiation; until β= 2/7 broken
wires (28% damage), damage grows relatively slowly. Then there is the stage II
which is within the range of β = [28%, 71%] when the damage becomes progressive
and predictive maintenance is essential to industrial. The critical life fraction βc =71%
is the bridge between the progressive damage of stage II and stage III where the
damage is accelerating sharply and the break could be brutal. This means that from
71% of broken wires, the central core strand, the heart of wire rope, is declared in
default.
3.4. Quantification of damage using unified theory
The damage of the strand being progressive, its variation is influenced by the level of
loading. Various representative theories of this damage are given initiated by the
linear of Miner law; finding that the damage changes linearly depending on the
fraction of life. [8]
By analogy with the unified theory, an empirical relationship describing the
damage is proposed:
Where: β = , γ = and γu =
F0 is the residual endurance limit that could be determined by multiplying the
ultimate residual force by a coefficient α (for n = 0; F0 = α Fu).
For a coefficient α =
(2)

The variation of the damage according to β with γ as a parameter and that of the
linear Miner rule is shown in Figure7. Each curve is associated to a loading level.
Figure 7 Evolution of Damage by unified theory and Miner law in function of the life
fraction
It is noted that the damage curve approaches gradually the bisector (the linear
Miner law) versus β for high levels of loading.
Arguably Miner law provides greater safety and simplicity for the user that the
unified theory. It is for this reason that many researchers adopt this law for damage
study of wire ropes.
3.5. Comparison of the two methods of damage calculation
The correlation between the damage calculated from equation (1) of static damage
and that of the equation (3) of the unified theory appears on the curves in Figure 8.
Figure 8 Comparison of damage according to the unified theory and the Miner law with static
damage

Comparing the damage curves of two calculation methods and the curve of the
cumulative damage (Miner law), we see that the curve of static damage is similar to
that of the damage according to the theory unifies for loading levels = 2.26 and
=2.14 in the predefined stage I (β = [0%, 28%]). However, it is clear that the curve
deviates from static damage in stage II (β = [28%, 71%] ) and stage III (β = [71, 1%])
to lie beyond Miner.
4. CONCLUSION
Concerning the study of central core strand extracted from wire rope hoist, it was
possible to follow the evolution of damage to each percentage of damage based solely
on easy tensile tests. Two damage quantification methods were used for this study: the
method of calculation of static damage and the method of calculation by unified
theory. Comparisons of results have shown good agreement. Three stages of damage
were determined; Stage I [0, 28%] corresponding to the initiation of the damage, stage
II [28%, 71%] for the progressive damage that requires predictive maintenance and
stage III [71%, 1] where the damage is brutal, so the strand (central core) is declared
in default. Furthermore, a study of the behavior of an entire wire rope is being
established with data the cable geometry and the damage of the coiled strand and the
central core.
REFERENCES
[1] Canadian Centre for Occupational Health and Safety, Wire rope lifting in
February 2010.
[2] Yujie Yu, Finite element study of behavior and interface force conditions of
seven-wire strand under axial and lateral loading” Construction and Building
Materials66 (2014) 10–18
[3] Brevet. P : Pathologie des suspensions. la corrosion - la fatigue. Rapport
technique PB/MMC 2005-254, Laboratoire Central des Ponts et Chaussées, 2005.
[4] Ponthiaux. P., Wenger. F. et Richard. C.: Tribocorrosion. Techniques de
l'Ingénieur, COR 60:1_22, Dec. 2007.
[5] EN 10002-1: Metallic materials – Tensile testing-Part 1: Method of test at
ambient temperature”: European Standard: 2001 has the status of a DIN
Standard.
[6] Mouhib. N., Ouaomar. H., Lahlou. M., El Ghorba. M, Characterization of
residual energy loss and Damage Prediction of 7-wire strand extracted from a
steel wire rope and subjected to a static test, International Journal of Research
2(06), June 2015.
[7] Mouhib. N., Etude multi-échelles du comportement mécanique d'un câble
métallique de levage de type antigiratoire (19x7) soumis à des chargements
statiques et prédiction de sa durée de vie: expérimentale, analytique et numérique.
Phd thesis, ENSEM. MOROCCO. 2015.
[8] C. Bathias, J. Bailon, La fatigue des matériaux et des structures, pp. 328–330.
1980.
[9] P. Govindarao, Dr. P. Srinivasarao, Dr. A. Gopalakrishna and C V Sriram,
Improvement of Tensile Strength of Butt Welded Joints Prepared by Vibratory
Welding Process. International Journal of Mechanical Engineering and
Technology, 4(4), 2013, pp. 53–61.

MECHANICAL BEHAVIOUR OF DAMAGED CENTRAL CORE STRAND CONSTITUTING A STEEL WIRE ROPE HOIST UNDER THE EFFECT OF A STATIC LOAD

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MECHANICAL BEHAVIOUR OF DAMAGED CENTRAL CORE STRAND CONSTITUTING A STEEL WIRE ROPE HOIST UNDER THE EFFECT OF A STATIC LOAD