IEC 60793-1-31:2010

IEC 60793-1-31


®


Edition 2.0 2010-05



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


IEC 60793-1-31:2010

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---------------------- Page: 2 ----------------------
IEC 60793-1-31


®

Edition 2.0 2010-05



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
PRICE CODE
INTERNATIONALE
S
CODE PRIX
ICS 33.180.10 ISBN 978-2-88912-562-3
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – 60793-1-31  IEC:2010



CONTENTS

FOREWORD . 4


INTRODUCTION . 6

1 Scope . 7

2 Normative references . 7


3 Apparatus . 7

3.1 General . 7

3.2 Gripping the fibre at both ends . 8

3.3 Sample support . 8
3.4 Stretching the fibre . 8
3.5 Measuring the force at failure . 9
3.6 Environmental control equipment . 9
4 Sample preparation . 9
4.1 Definition . 9
4.2 Sample size and gauge length . 9
4.3 Auxiliary measurements . 10
4.4 Environment . 11
5 Procedure . 11
5.1 Preliminary steps . 11
5.2 Procedure for a single specimen . 11
5.3 Procedure for completing all samples for a given nominal strain rate . 11
6 Calculations . 12
6.1 Conversion of tensile load to failure stress . 12
6.2 Preparation of a Weibull plot . 13
6.3 Computation of Weibull parameters . 13
7 Results . 14
7.1 The following information should be reported for each test: . 14
7.2 The following information should be provided for each test: . 14
8 Specification information . 14
Annex A (informative) Typical dynamic testing apparatus . 15
Annex B (informative) Guideline on gripping the fibre. 17
Annex C (informative) Guideline on stress rate . 21

Bibliography . 22

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 . 15
Figure A.2 – Translation test apparatus . 15
Figure A.3 – Rotating capstan apparatus . 16
Figure A.4 – Rotating capstan apparatus for long lengths . 16
Figure B.1 – Gradual slippage . 17
Figure B.2 – Irregular slippage . 17
Figure B.3 – Sawtooth slippage . 18
Figure B.4 – Acceptable transfer function . 18
Figure B.5 – Typical capstan . 19

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60793-1-31  IEC:2010 – 3 –


Figure B.6 – Isostatic compression . 19

Figure B.7 – Escargot wrap . 20


Figure C.1 – System to control stress rate . 21

Figure C.2 – Time variation of load and loading speed . 21

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– 4 – 60793-1-31  IEC:2010


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
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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 second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
The main change with respect to the previous edition is the addition of comprehensive details,
such as examples of fibre clamping as given in Annexes A, B and C.

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60793-1-31  IEC:2010 – 5 –


This bilingual version, published in 2011-07, corresponds to the English version.


The text of this standard is based on the following documents:

CDV Report on voting

86A/1285/CDV 86A/1308/RVC



Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.


The French version of this standard has no been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60793-1 series, published under the general title Optical fibres –
Measurement methods and test procedures, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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– 6 – 60793-1-31  IEC:2010


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 shall be controlled for the following:


• Population of fibre, e.g., 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 prooftesting.
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 is 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/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 µm, with a 250 µm or less
nominal diameter acrylate coating. Default conditions are given for such typical populations.
Atypical populations might include alternative coatings, environmentally aged fibre, or
deliberately damaged or abraded fibre. Guidance for atypical populations is also provided.

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60793-1-31  IEC:2010 – 7 –


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 of optical fibre samples and
establishes uniform requirements for the mechanical characteristic – tensile strength. 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 may be sufficient to measure
the values at ambient temperature and humidity conditions
This method is applicable to types A1, A2, A3, B and C optical fibres.
Warning – 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 should be worn at all times in the testing area.
2 Normative references
The following referenced documents are indispensable for the application 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
IEC 60793-1-21, Optical fibres – Part 1-21: Measurement methods and test procedures –

Coating geometry
3 Apparatus
3.1 General
This clause prescribes 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:
• gauge length of a specimen
• stress or strain rate range
• environmental conditions
• strength of the specimens.

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– 8 – 60793-1-31  IEC:2010


3.2 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. (For typical 125/250 µm silica fibre, the minimum capstan diameter is then 50 mm.)
A particular gripping implementation is given in Annex B.
3.3 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.
3.4 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
of Annex A).
– 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 of Annex A). 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.

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60793-1-31  IEC:2010 – 9 –


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.


3.5 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.
3.6 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 might be used to provide the required controls, including
controls on the entire room in which testing is conducted.
Typical control requirements are:
• Temperature: 23 ± 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.
4 Sample preparation

4.1 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 this standard.
For ribbonized fibre, select the specimens uniformly across the ribbon structure. Exercise
caution in removing fibre from the ribbon to avoid inadvertent strength reduction.
4.2 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 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.

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– 10 – 60793-1-31  IEC:2010


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 6.2) 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.


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 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 standard, 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.

98
90
70
50
20
5
1
0,7 1 2 4 7 10
σ (GPa)
f   IEC  853/10



Figure 1 – Bimodal tensile strength Weibull plot for a 20 m
gauge length test set-up at 5 %/min strain rate
Statistical analysis can be performed to determine whether a given precision has been
achieved.
4.3 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
...