IEC 60793-1-31:2019

Optical fibres - Part 1-31: Measurement methods and test procedures - Tensile strength

IEC 60793-1-31:2019 provides values of the tensile strength under dynamic loading of optical fibre samples. The method tests individual lengths of uncabled and unbundled glass optical fibre. Sections of fibre are broken with controlled increasing stress or strain that is uniform over the entire fibre length and cross section. The stress or strain is increased at a nominally constant rate until breakage occurs. The distribution of the tensile strength values of a given fibre strongly depends on the sample length, loading velocity and environmental conditions. The test can be used for inspection where statistical data on fibre strength is required. Results are reported by means of statistical quality control distribution. Normally, the test is carried out after temperature and humidity conditioning of the sample. However, in some cases, it can be sufficient to measure the values at ambient temperature and humidity conditions. This method is applicable to categories A1, A2, and A3, and classes B and C optical fibres. The object of this document is to establish uniform requirements for the mechanical characteristic: tensile strength. This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) correction of Formulae (3b) and (4b) and renumbering of formulae.
Keywords: tensile strength under dynamic loading of optical fibre samples

Fibres optiques - Partie 1-31: Méthodes de mesure et procédures d'essai - Résistance à la traction

IEC 60793-1-31:2019 donne les valeurs de résistance à la traction des échantillons de fibre optique, soumis à une charge dynamique. Cette méthode soumet à essai des longueurs individuelles de fibre optique en verre, non câblées et non groupées en faisceau. Des sections de fibre sont rompues en les soumettant à une contrainte ou une déformation croissante et contrôlée, uniforme sur toute la longueur et la section transversale de la fibre. La contrainte ou la déformation augmente à une vitesse nominalement constante jusqu’à ce que la rupture se produise. La distribution des valeurs de résistance à la traction pour une fibre donnée dépend étroitement de la longueur des échantillons, de la vitesse d’application de la force et des conditions d’environnement. L’essai peut s’appliquer à titre d’examen lorsque des données statistiques sur la résistance des fibres sont exigées. Les résultats sont déclarés sous forme d’une distribution statistique de contrôle de qualité. Habituellement, l’essai est réalisé après un conditionnement en température et en humidité de l’échantillon. Cependant, dans certains cas, la mesure des valeurs à la température et à l’humidité ambiantes peut être suffisante. Cette méthode s’applique aux fibres optiques de catégories A1, A2 et A3, et de classes B et C. L’objet du présent document est de déterminer des exigences uniformes relatives à la caractéristique mécanique: la résistance à la traction. Cette troisième édition annule et remplace la deuxième édition parue en 2010. Cette édition constitue une révision technique. Cette édition inclut les modifications suivantes par rapport à l’édition précédente:
a) correction des Formules (3b) et (4b) et renumérotation des formules.
Mots clés : résistance à la traction des échantillons de fibre optique

General Information

• Status: Published
• Publication Date: 05-Feb-2019
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: SC 86A - Fibres and cables
• Drafting Committee: WG 1 - TC 86/SC 86A/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 06-Feb-2019
• Completion Date: 08-Mar-2019

Relations

• Revises: IEC 60793-1-31:2010 - Optical fibres - Part 1-31: Measurement methods and test procedures - Tensile strength
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60793-1-31 ®
Edition 3.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-31: Measurement methods and test procedures –Tensile strength

Fibres optiques –
Partie 1-31: Méthodes de mesure et procédures d’essai –Résistance à la traction
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IEC 60793-1-31 ®
Edition 3.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-31: Measurement methods and test procedures –Tensile strength

Fibres optiques –
Partie 1-31: Méthodes de mesure et procédures d’essai –Résistance à la traction

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-6529-1

– 2 – IEC 60793-1-31:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Hazards . 7
5 Apparatus . 8
5.1 General . 8
5.2 Gripping the fibre at both ends . 8
5.3 Sample support . 8
5.4 Stretching the fibre . 8
5.5 Measuring the force at failure . 9
5.6 Environmental control equipment . 9
6 Sample preparation . 10
6.1 Definition . 10
6.2 Sample size and gauge length . 10
6.3 Auxiliary measurements . 11
6.4 Environment . 11
7 Procedure . 11
7.1 Preliminary steps . 11
7.2 Procedure for a single specimen . 11
7.3 Procedure for completing all samples for a given nominal strain rate . 12
8 Calculations . 12
8.1 Conversion of tensile load to failure stress . 12
8.2 Preparation of a Weibull plot . 13
8.3 Computation of Weibull parameters . 13
9 Results . 14
9.1 Details to be reported . 14
9.2 Details to be recorded . 15
10 Specification information . 15
Annex A (informative) Typical testing apparatus of tensile strength under dynamic
loading . 16
Annex B (informative) Guidelines on gripping the fibre . 18
Annex C (informative) Guidelines on stress rate . 22
Bibliography . 24

Figure 1 – Bimodal tensile strength Weibull plot for a 20 m gauge length test set-up at
5 %/min strain rate . 10
Figure A.1 – Capstan design . 16
Figure A.2 – Translation test apparatus . 16
Figure A.3 – Rotating capstan apparatus . 17
Figure A.4 – Rotating capstan apparatus for long lengths . 17
Figure A.5 – Ganged rotating capstan tester . 17
Figure B.1 – Gradual slippage. 18

Figure B.2 – Irregular slippage . 18
Figure B.3 – Sawtooth slippage . 19
Figure B.4 – Acceptable transfer function . 19
Figure B.5 – Typical capstan . 20
Figure B.6 – Isostatic compression . 20
Figure B.7 – Escargot wrap . 21
Figure C.1 – System to control stress rate . 22
Figure C.2 – Time variation of load and loading speed . 23

– 4 – IEC 60793-1-31:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-31: Measurement methods and test procedures –
Tensile strength
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60793-1-31 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) correction of Formulae (3b) and (4b) and renumbering of formulae.

The text of this International Standard is based on the following documents:
FDIS Report on voting
86A/1908/FDIS 86A/1926/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60793 series, published under the general title Optical fibres, can
be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60793-1-31:2019 © IEC 2019
INTRODUCTION
Failure stress distributions can be used to predict fibre reliability in different conditions.
IEC TR 62048 shows mathematically how this can be done. To complete a given reliability
projection, the tests used to characterize a distribution are controlled for the following:
• population of fibre, for example coating, manufacturing period, diameter;
• gauge length, i.e. length of section that is tested;
• stress or strain rates;
• testing environment;
• preconditioning or aging treatments;
• sample size.
This method measures the strength of optical fibre at a specified constant strain rate. It is a
destructive test, and is not a substitute for proof-testing.
This method is used for those typical optical fibres for which the median fracture stress is
greater than 3,1 GPa (450 kpsi ) in 0,5 m gauge lengths at the highest specified strain rate of
25 %/min. For fibres with lower median fracture stress, the conditions herein have not
demonstrated sufficient precision.
Typical testing is conducted on "short lengths", up to 1 m, or on "long lengths", from 10 m to
20 m with sample size ranging from 15 to 30.
The test environment and any preconditioning or aging are critical to the outcome of this test.
There is no agreed upon model for extrapolating the results for one environment to another
environment. For failure stress at a given stress or strain rate, however, as the relative
humidity increases, failure stress decreases. Both increases and decreases in the measured
strength distribution parameters have been observed as the result of preconditioning at
elevated temperature and humidity for even a day or two.
This test is based on the theory of fracture mechanics of brittle materials and on the power-
law description of flaw growth (see IEC TR 62048). Although other theories have been
described elsewhere, the fracture mechanics based on power-law theory is the most generally
accepted.
A typical population consists of fibre that has not been deliberately damaged or
environmentally aged. A typical fibre has a nominal diameter of 125 mm, with a 250 mm or less
diameter acrylate coating. Default conditions are given for such typical populations. Non-
typical populations might include alternative coatings, environmentally aged fibre, or
deliberately damaged or abraded fibre. Guidance for non-typical populations is also provided.

__________
kpsi = kilopounds per square inch.

OPTICAL FIBRES –
Part 1-31: Measurement methods and test procedures –
Tensile strength
1 Scope
This part of IEC 60793 provides values of the tensile strength under dynamic loading of
optical fibre samples. The method tests individual lengths of uncabled and unbundled glass
optical fibre. Sections of fibre are broken with controlled increasing stress or strain that is
uniform over the entire fibre length and cross section. The stress or strain is increased at a
nominally constant rate until breakage occurs.
The distribution of the tensile strength values of a given fibre strongly depends on the sample
length, loading velocity and environmental conditions. The test can be used for inspection
where statistical data on fibre strength is required. Results are reported by means of
statistical quality control distribution. Normally, the test is carried out after temperature and
humidity conditioning of the sample. However, in some cases, it can be sufficient to measure
the values at ambient temperature and humidity conditions.
This method is applicable to categories A1, A2, and A3, and classes B and C optical fibres.
The object of this document is to establish uniform requirements for the mechanical
characteristic: tensile strength.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60793-1-20, Optical fibres – Part 1-20: Measurement methods and test procedures –
Fibre geometry
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Hazards
This test involves stretching sections of optical fibre until breakage occurs. Upon breakage,
glass fragments can be distributed in the test area. Protective screens are recommended.
Safety glasses shall be worn at all times in the testing area.

– 8 – IEC 60793-1-31:2019 © IEC 2019
5 Apparatus
5.1 General
Clause 5 specifies the fundamental requirements of the equipment used for dynamic strength
testing. There are many configurations that can meet these requirements. Some examples are
presented in Annex A. The choice of a specific configuration will depend on such factors as
• the gauge length of a specimen,
• the stress or strain rate range,
• the environmental conditions, and
• the strength of the specimens.
5.2 Gripping the fibre at both ends
Grip the fibre to be tested at both ends and stretch it until failure occurs in the gauge length
section. The grip shall not allow the fibre to slip out prior to failure and shall minimize failure
at the grip.
Record a break that occurs at the grip, but do not use it in subsequent calculations. Since
fibre strain is increasing during the test, some slippage occurs at the grip. At higher stress
levels, associated with short gauge lengths, slippage can induce damage and cause gripping
failures that are difficult to ascertain. The frequency of such failures can often vary with stress
or strain rate. Careful inspection of the residual fibre pieces, or other means, is required to
prevent the possibility of including gripping failures in the analysis.
Use a capstan, typically covered with an elastomeric sheath, to grip the fibre (see Figure A.1).
Wrap a section of fibre that will not be tested around the capstan several times and secure
the fibre at the ends with, for example, an elastic band. Wrap the fibre with no crossovers.
The capstan surface shall be tough enough so that the fibre does not cut into it when fully
loaded. The amount of slippage and capstan failures depends on the interaction of the fibre
coating and the capstan surface material, thickness, and number of wraps. Careful preliminary
testing is required to confirm the choice of a capstan surface.
Design the diameter of the capstan and pulley so that the fibre does not break on the capstan
due to bend stress. For typical silica-clad fibres, the bend stresses shall not exceed
0,175 GPa.
EXAMPLE For a typical 125 µm cladding/250 µm coating silica fibre, the minimum capstan diameter is 50 mm.
A particular gripping implementation is given in Annex B.
5.3 Sample support
Attach the specimen to the two grips. The gauge length is the length of fibre between the axes
of the gripping capstans before it is stretched. To reduce the space required to perform the
test on long gauge lengths, one or more pulleys may be used to support the specimen (see
Figure A.4). The pulleys shall be designed, and their surfaces kept free of debris, so the fibre
is not damaged by them. The remainder of the fibre, away from pulleys and capstans, shall
not be touched.
When multiple fibres are tested simultaneously, as in Figure A.5, a baffle arrangement is
required to prevent a broken fibre from snapping into, or otherwise perturbing the other fibres
under test.
5.4 Stretching the fibre
Stretch the fibre at a fixed nominal strain rate until it breaks. The nominal strain rate is
expressed as the percent increase in length per minute, relative to the gauge length.

There are two basic alternatives for stretching the fibre.
– Method A: Increase the separation between the gripping capstans by moving them apart at
a fixed rate of speed, with the starting separation equal to the gauge length (Figure A.2).
– Method B: Rotate a capstan at a fixed rate to take up the fibre and strain the section
between capstans (Figures A.3 to A.5). The rotation shall not result in crossovers on the
capstan.
Calibrate the strain rate to within ±10 % of the nominal strain rate. Some equipment
configurations are computer-controlled and allow dynamic control of the capstan motion to
produce a constant stress rate. A particular implementation of this is given in Annex C.
The strain rate shall be agreed between customer and supplier. A strain rate range of either
2,5 % to 5 % or 15 % to 25 % is typically used.
5.5 Measuring the force at failure
Measure the tensile load (force in tension) at failure for each specimen by a calibrated load
cell, to within ±1 % of the actual load. This can be done with a variety of methods:
• strip chart recorder;
• peak and hold meter;
• computer sampling.
Provide a means of measuring the tensile load as a function of time to determine the stress
rate. This is not required for each individual test, but shall be done occasionally.
Calibrate the load cell to within 0,5 % of the failure, or maximum load, for each range of
failure loads, while it is oriented in the same manner as when testing a fibre. Do this by
substituting a string attached to a known weight for the test specimen. For method B, a light,
low-friction pulley can be used in place of the capstan that is not attached to the load cell. The
string, with one end attached to the load cell capstan and the other end attached to a known
weight, shall duplicate the direction of a test specimen and be of a diameter comparable to
that of a test specimen. A minimum of three calibration weights, bracketing the typical failures,
is recommended.
5.6 Environmental control equipment
Measured failure stress and fatigue characteristics are known to vary with temperature and
humidity of the fibre, both of which shall be controlled during both preconditioning and test.
Many equipment configurations can be used to provide the required controls, including
controls on the entire room in which testing is conducted.
The following are the typical control requirements:
• temperature: 23 °C ± 2 °C;
• relative humidity: 50 % ± 5 %.
Alternative test environments, such as high non-precipitating humidity, can be achieved by
enclosing the test specimen and injecting water vapour into the enclosure. Figure A.5 shows a
ganged tester that includes an enclosure over a circulating water bath.

– 10 – IEC 60793-1-31:2019 © IEC 2019
6 Sample preparation
6.1 Definition
A sample is one or more fibres from a population. Each sample provides a result by cutting it
into smaller lengths called specimens. Testing results on these specimens are combined to
yield an overall result for the sample. The term "sample size" is used to indicate the number
of specimens tested in the rest of the document.
For ribbonized fibre, select the specimens uniformly across the ribbon structure. Exercise
caution in removing fibre from the ribbon to avoid inadvertent strength reduction.
6.2 Sample size and gauge length
The result of testing is a statistical distribution of failure stress values. Hence all reported
parameters are statistical in nature, with inherent variability that is a function of the sample
size and the variability of the flaw size within the sample. The weakest site, or largest flaw,
within a specimen will fail, and the typical failure stress decreases as gauge length increases.
A given population can have flaws generated from multiple causes. An example is a bi-modal
aggregate distribution as shown in the Weibull plot of Figure 1 (see also 8.2) obtained for a
20 m gauge length set-up. The narrow near vertical distribution on the right (around 5 GPa) is
called the intrinsic region; the wider distribution below this 5 GPa is the extrinsic region.

Figure 1 – Bimodal tensile strength Weibull plot for a 20 m
gauge length test set-up at 5 %/min strain rate
Testing on gauge lengths of 0,5 m does not typically result in measuring flaws from the
extrinsic region. From time to time, however, the failure stress of an extrinsic flaw is
measured and appears as an "outlier". If the outlier is included in the data analysis, errors in
the parameters will occur. For typical testing, uniform outlier removal techniques are
recommended.
For tests which are designed to measure the characteristics of the extrinsic region, large
sample sizes (hundreds of specimens) and long gauge lengths (20 m) are recommended. For
characterization of the intrinsic region as per this document, a gauge length of 0,5 m is often
used. For the dynamic strength, a sample size of 30 is often used. Any deviation from these
values is to be specified in the detail specification.
Statistical analysis can be performed to determine whether a given precision has been
achieved.
6.3 Auxiliary measurements
Failure stress calculations require a conversion of tensile load to the stress on the cross
section of the glass portion of the fibre. The cladding diameter, as measured by
IEC 60793-1-20, shall be used in this calculation to compute the cross sectional area. The
coating also bears part of the tensile load that decreases the stress on the glass cross section.
Subclause 8.1 contains formulae for stress calculations.
The coating correction factor is a function of the coating thickness, measured by IEC 60793-1-
21 and Young's modulus of each coating layer and the modulus of the glass. The modulus of
cured coating is often characterized by the manufacturer. For typical fibre, the contribution of
coating effects is less than 5 % of total load, and compensation (hence measurement) for
coating is not required (see 8.1). When this is done, the reported failure stress is larger than
the actual by a fixed percentage. When coating effects are compensated, average or nominal
values may be used for all specimens. The contribution of the coating modulus to failure
stress can change with the stress or strain rate. If the contribution at any stress or strain rate
is greater than 5 % of the total load, then the coating effect shall be included in the
computation.
6.4 Environment
There are two key environmental considerations: aging environment and test environment.
Fibre aging is sometimes required. Even brief accelerated aging can produce increases or
decreases in the measured strength of some fibres. The causes of these phenomena are not
well understood. As a consequence, extrapolation methodologies from accelerated aging
environments to other environments are under study.
After extensive aging, the coating surface friction can be altered. After any aging and before
any testing, fibre specimens should be pre-conditioned in the test environment for at least
12 h.
The typical test environment is 23 °C ± 2 °C and 50 % ± 5 % RH. Alternative environments,
such as high non-precipitating relative humidity, can yield significantly different failure stress
values.
7 Procedure
7.1 Preliminary steps
1) Age the specimens if required.
2) Precondition the specimens.
7.2 Procedure for a single specimen
1) Mount the specimen in the capstans, making sure the fibre does not cross over itself or
become damaged in the gauge length by mounting.
2) Verify equipment settings for the desired nominal strain rate.
3) Reset the tension recording display.

– 12 – IEC 60793-1-31:2019 © IEC 2019
4) Begin capstan motion. For nominal strain rates of 0,03 %/min or less, the specimen may
be pre-loaded at 0,3 %/min to about half of the expected failure stress at the slower rate.
The expected failure stress may be projected from results at higher strain rates. When
testing damaged fibre, pre-loading is not recommended unless the expected time to failure
is in excess of 4 h.
5) At failure, stop the capstan and record the failure load and, if necessary, the stress rate.
6) Verify that the break did not occur on the capstan. If it did, mark the measurement so it
will not be used in calculations.
7) Remove the residual fibre from the capstans and complete any auxiliary measurements, if
necessary, as in 6.3.
7.3 Procedure for completing all samples for a given nominal strain rate
1) Record the nominal strain rate and any population identifications.
2) Determine if coating effects will be compensated. If so, record the appropriate coating
parameters (see 8.1). Record the nominal cladding diameter if the nominal value is used
to compute stress.
3) Complete 5.2 for each specimen.
4) Using 8.1, compute the failure stress for each specimen, and sort in increasing order.
5) Complete the Weibull plot (see Figure 1), if required, using 8.2. If required, compute the
Weibull parameters, m and S , using 8.3.
d 0
6) If required for handleability requirements, compute the median failure stress σ and the
15-percentile failure stress σ according to 8.2.
8 Calculations
8.1 Conversion of tensile load to failure stress
The following symbols and units are used:
• fibre dimensions: mm;
• gauge length: m;
• stress σ and failure stress σ : GPa;
f
• tension T and failure tension T N.
f
Method A
When the load is substantially aligned with the tension T and D is the cladding diameter,
g
Formula (1) provides the stress without compensating for the coating:
4×10 T
σ= in GPa (1)
πD
g
Method B
When coating is compensated, the following formulae are used. Calculate the fraction
EA
R= ,
(2)
N
E A + EA
00 ∑ jj
j=1
where
E is Young's modulus of the glass, typically 70,3 GPa for silica;
A is the cross sectional area of the glass fibre.
For N coating layers indexed with j, E and A are the Young's modulus and layer cross
j j
sectional area, for each layer, respectively.
The coating compensated stress is given by
σσ= R (3)
c
8.2 Preparation of a Weibull plot
Figure 1 shows a typical Weibull plot, where the line drawn through the data represents an
ideal Weibull distribution. While Weibull plots are typically used to display the data for a given
nominal strain rate, the actual distribution may not be Weibull.
1) Sort the failure stress values in order of increasing value.
2) Let k represent the rank of a given failure stress, for example, k = 1, 2, 3., N, and σ be
fk
th
the k failure stress.
3) Let
x = lnσ (4)
k fk
and
k− 0,5
 
y=ln−−ln 1 (5)
k 
 
N
 

4) Plot y versus x . Label the axes with the associated probability levels and failure stress
k k
values.
NOTE The median failure stress σ and the 15-percentile failure stress σ are calculated if applicable.
50 15
If 0,5N + 0,5 is an integer, σ = σ . Otherwise, σ is determined by an appropriate interpolation between
50 0,5N + 0,5 50
σ and σ .
0,5N 0,5N + 1
If 0,15N + 0,5 is an integer, σ = σ . Otherwise, σ is determined by an appropriate interpolation between
15 0,15N + 0,5 15
σ and σ , where square brackets stand for the greatest integer function.
[0,15N + 0,5] [0,15N + 0,5] + 1
8.3 Computation of Weibull parameters
The Weibull distribution cumulative frequency function is given by:
m
 d
 
σ
 
F=1− exp− (6)
 
 S 
 0
 
k− 0,5
where F corresponds to of Formula (5). Consequently,
N
σ

fk
(7)
ym= ln

k d

S

– 14 – IEC 60793-1-31:2019 © IEC 2019
Method A – Simple rank method
For the sample sizes that are typically used (see 6.1), the following method can be used.
Determine the values
kN0,15+ 0,5
k 0,85N+ 0,5 (8)
kN0,5+ 0,5
Compute
yy−
kk
(9)
m =
d
xx−
kk
and
 
0,366512
(10)
Sxexp +
0  k 
m
 d 
Method B – Maximum likelihood estimation (MLE) method
The logarithm of the likelihood function is
N N
−mm
dd
lnL m ,S Nln m−Nm ln S+−m 1 lnσσ−S (11)
( ) ( ) ( ) ( )
( )
d0 d d 0 d ∑∑fk
 0 fk
kk1 1
Select m and S to maximize Formula (11). For a given value of m , the optimal value for S
d 0 d 0
is
N
m
d
S = σ (12)
0 ∑
fk
N
k=1
The optimum value for m is determined by an iterative method.
d
9 Results
9.1 Details to be reported
Report the following information for each test:
– fibre identification;
– date and title;
– strength values – report the stress value under which the fibre breaks as the strength of
fibre (Weibull plot and, if applicable, Weibull parameters m and S ).
d 0
==
=
=
=
=
=
9.2 Details to be recorded
Provide the following information for each test:
– length of sample;
– pulling speed (strain rate);
– type of clamping fixtures;
– relative humidity and ambient temperature;
– any special conditioning.
10 Specification information
The detail specification shall specify the following information:
– any deviations from the procedure that apply;
– failure or acceptance criteria.

– 16 – IEC 60793-1-31:2019 © IEC 2019
Annex A
(informative)
Typical testing apparatus of tensile strength under dynamic loading

Figure A.1 – Capstan design
Figure A.2 – Translation test apparatus

Figure A.3 – Rotating capstan apparatus

Figure A.4 – Rotating capstan apparatus for long lengths

Figure A.5 – Ganged rotating capstan tester

– 18 – IEC 60793-1-31:2019 © IEC 2019
Annex B
(informative)
Guidelines on gripping the fibre
The uniform transfer of force from the capstan to the glass fibre is essential for obtaining good
measurements of failure stress. Both the coating and the stress rate can alter this transfer
function, depending on the capstan surface and mechanical characteristics. The quality of the
transfer function can be assessed by inspecting the plot of measured force (stress) versus
applied strain (time under increasing load). Figures B.1 to B.3 show results that are not
acceptable. Figure B.4 shows a result that is acceptable.
NOTE Time and force (strength) scale are not indicated since these figures are only qualitative illustrations.

Figure B.1 – Gradual slippage
Figure B.2 – Irregular slippage

Figure B.3 – Sawtooth slippage

Figure B.4 – Acceptable transfer function
These results are affected by the surface of the capstan, the capstan diameter, the number of
wraps around the capstan, and the clamping mechanism. For some coatings, the typical
capstan shown in Figure B.5 does not provide acceptable results. Alternative capstan
surfaces, such as silicone, can improve the results, but subtle batch changes can lead to the
results shown in Figure B.1.
– 20 – IEC 60793-1-31:2019 © IEC 2019

Figure B.5 – Typical capstan
Other methods have been tried. Figures B.6 and B.7 show two approaches that were found to
yield better results, but which did not provide uniformly acceptable force rate plots and low
incidence of gripping failures.

Figure B.6 – Isostatic compression

Figure B.7 – Escargot wrap
– 22 – IEC 60793-1-31:2019 © IEC 2019
Annex C
(informative)
Guidelines on stress rate
Fibre slippage or loading system compliance can be compensated for by using a servo control
system similar to the one shown in Figure C.1. The fibre is attached at one end to a capstan
mounted on a translation stage. The stage is moved by a computer-controlled stepper motor.
The load applied to the fibre is monitored by the computer using an A/D data acquisition
system. The computer software can then continuously modify the stepper motor speed to
maintain the specified loading rate.
A double-sided adhesive foam tape is recommended for covering the capstans. Any slippage
of the fibre then tends to be steady due to the viscous nature of the adhesion. Non-adhesive

friction tape can lead to stick-slip conditions, and it is then difficult for the computer software
to compensate for the abrupt changes in load that occur.
Load cell
Fibre
Stepper
Translation stage
motor
3 500 Hz Interface Motor
A/D board logic drive
Proportional
servo control
IEC
Figure C.1 – System to control stress rate
Figure C.2 shows a comparison of the load profile and translation stage speed for
experiments run at a constant speed of 2 μm/s and at a constant stress loading rate of
0,3 MPa/s. That speed corresponds to a nominal stress rate of 0,29 MPa/s, yet the measured
stress rate is only 0,18 MPa/s. In contrast, the servo-controlled result is a loading stress rate
very close to the specified value. To achieve this, the loading speed was continuously varied
as shown in the right hand figure.

Figure C.2 – Time variation of load and loading speed

– 24 – IEC 60793-1-31:2019 © IEC 2019
Bibliography
IEC 60793-1-21:2001, Optical fibres – Part 1-21: Measurement methods and test procedures
– Coating geometry
IEC 60793-2-10:2017, Optical fibres – Part 2-10: Product specifications – Sectional
specification for category A1 multimode fibres
IEC 60793-2-20:2015, Optical fibres – Part 2-20: Product specifications – Sectional
specification for category A2 multimode fibres
IEC 60793-2-30:2015, Optical fibres – Part 2-30: Product specifications – Sectional
specification for category A3 multimode fibres
IEC 60793-2-40:2015, Optical fibres – Part 2-40: Product specifications – Sectional
specification for category A4 multimode fibres
IEC 60793-2-50:2015, Optical fibres – Part 2-50: Product specifications – Sectional
specification for class B single-mode fibres
IEC 60793-2-60:2008, Optical fibres – Part 2-60: Product specifications – Sectional
specification for category C single-mode intraconnection fibres
IEC TR 61649:2008, Weibull analysis
IEC TR 62048:2014, Optical fibres – Reliability – Power law theory

_____________
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SOMMAIRE
AVANT-PROPOS . 28
INTRODUCTION .
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