SIST EN 60793-1-33:2004
(Main)Optical fibres -- Part 1-33: Measurement methods and test procedures - Stress corrosion susceptibility
Optical fibres -- Part 1-33: Measurement methods and test procedures - Stress corrosion susceptibility
Describes methods for the determination of stress corrosion susceptibility parameters of optical fibres. Dynamic fatigue and static fatigue tests are used to determine stress corrosion susceptiblity parameters, dynamic n-value and static n-value. Five test methods are described: Dynamic and static n-value by axial tension, dynamic and static n-value by two-point bending, and static n-value by uniform bending. These tests provide values of the stress corrosion parameter, n, used for reliablilty calculations in EN 62048.
Lichtwellenleiter -- Teil 1-33: Messmethoden und Prüfverfahren - Spannungskorrosionsempfindlichkeit
Fibres optiques -- Partie 1-33: Méthodes de mesure et procédures d'essai - Résistance à la corrosion sous contrainte
Décrit des méthodes d'essai pour la détermination de la résistance à la corrosion sous contrainte des fibres optiques. Des essais de fatigue dynamique et de fatigue statique sont utilisés pour déterminer les paramètres de résistance à la corrosion sous contrainte, la valeur n de fatigue dynamique et la valeur n de fatigue statique. Cinq méthodes sont décrites: Valeur n de la fatigue dynamique et de fatigue statique par tension axiale, valeur n de la fatigue dynamique et de fatigue statique par flexion en deux points, et valeur n de fatigue statique par courbure uniforme. Ces essais fournissent les valeurs du paramètre de corrosion sous contrainte, n, utilisées dans les calculs de fiabilité de la EN 62048.
Optična vlakna – 1-33. del: Metode merjenja in preskusni postopki – Dovzetnost na napetostno korozijo (IEC 60793-1-33:2001)*
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SIST EN 60793-1-33:2004SLOVENSKIseptember 2004
STANDARDOptična vlakna – 1-33. del: Metode merjenja in preskusni postopki – Dovzetnost na napetostno korozijo (IEC 60793-1-33:2001)*Optical fibres - Part 1-33: Measurement methods and test procedures - Stress corrosion susceptibility (IEC 60793-1-33:2001)©
Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljenoReferenčna številkaSIST EN 60793-1-33:2004(en)ICS33.180.10
EUROPEAN STANDARDEN 60793-1-33NORME EUROPÉENNEEUROPÄISCHE NORMApril 2002CENELECEuropean Committee for Electrotechnical StandardizationComité Européen de Normalisation ElectrotechniqueEuropäisches Komitee für Elektrotechnische NormungCentral Secretariat: rue de Stassart 35, B - 1050 Brussels© 2002 CENELEC -All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.Ref. No. EN 60793-1-33:2002 EICS 33.180.10English versionOptical fibresPart 1-33: Measurement methods and test procedures -Stress corrosion susceptibility(IEC 60793-1-33:2001)Fibres optiquesPartie 1-33: Méthodes de mesureet procédures d'essai -Résistance à la corrosion sous contrainte(CEI 60793-1-33:2001)LichtwellenleiterTeil 1-33: Messmethodenund Prüfverfahren -Spannungskorrosionsempfindlichkeit(IEC 60793-1-33:2001)This European Standard was approved by CENELEC on 2002-03-05. CENELEC members are bound tocomply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration.Up-to-date lists and bibliographical references concerning such national standards may be obtained onapplication to the Central Secretariat or to any CENELEC member.This European Standard exists in three official versions (English, French, German). A version in any otherlanguage made by translation under the responsibility of a CENELEC member into its own language andnotified to the Central Secretariat has the same status as the official versions.CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EN 60793-1-33:2002- 2 -ForewordThe text of document 86A/688/FDIS, future edition 1 of IEC 60793-1-33, prepared by SC 86A, Fibresand cables, of IEC TC 86, Fibre optics, was submitted to the IEC-CENELEC parallel vote and wasapproved by CENELEC as EN 60793-1-33 on 2002-03-05.The following dates were fixed:–latest date by which the EN has to be implementedat national level by publication of an identicalnational standard or by endorsement(dop)2002-12-01–latest date by which the national standards conflictingwith the EN have to be withdrawn(dow) 2005-03-01Annexes designated "normative" are part of the body of the standard.Annexes designated "informative" are given for information only.In this standard, annexes A, B, C, D, E and ZA are normative and annexes F, G and H areinformative.Annex ZA has been added by CENELEC.Compared to IEC 60793-1:1989 and IEC 60793-2:1992, IEC/SC 86A has adopted a revised structureof the new IEC 60793 series: The individual measurement methods and test procedures for opticalfibres are published as "Part 1-XX"; the product standards are published as "Part 2-XX".The general relationship between the new series of EN 60793 and the superseded EuropeanStandards of the EN 188000 series is as follows:ENTitlesupersedesEN 60793-1-XXOptical fibres -- Part 1-XX: Measurement methodsand test proceduresIndividual subclauses ofEN 188000:1992EN 60793-2-XXOptical fibres -- Part 2-XX: Product specificationsEN 188100:1995EN 188101:1995EN 188102:1995EN 188200:1995EN 188201:1995EN 188202:1995EN 60793-1-3X consists of the following parts, under the general title: Optical fibres:- Part 1-30: Measurement methods and test procedures – Fibre proof test- Part 1-31: Measurement methods and test procedures – Tensile strength- Part 1-32: Measurement methods and test procedures – Coating strippability- Part 1-33: Measurement methods and test procedures – Stress corrosion susceptibility- Part 1-34: Measurement methods and test procedures – Fibre curl__________Endorsement noticeThe text of the International Standard IEC 60793-1-33:2001 was approved by CENELEC as a EuropeanStandard without any modification.__________
- 3 -EN 60793-1-33:2002Annex ZA(normative)Normative references to international publicationswith their corresponding European publicationsThis European Standard incorporates by dated or undated reference, provisions from otherpublications. These normative references are cited at the appropriate places in the text and thepublications are listed hereafter. For dated references, subsequent amendments to or revisions of anyof these publications apply to this European Standard only when incorporated in it by amendment orrevision. For undated references the latest edition of the publication referred to applies (includingamendments).NOTEWhen an international publication has been modified by common modifications, indicated by (mod), the relevantEN/HD applies.PublicationYearTitleEN/HDYearIEC/TR 62048- 1)The law theory of optical fibre reliability--
1) To be published.
NORMEINTERNATIONALECEIIECINTERNATIONALSTANDARD60793-1-33Première éditionFirst edition2001-08Fibres optiques –Partie 1-33:Méthodes de mesures et procédures d'essai –Résistance à la corrosion sous contrainteOptical fibres –Part 1-33:Measurement methods and test procedures –Stress corrosion susceptibility Commission Electrotechnique Internationale International Electrotechnical CommissionPour prix, voir catalogue en vigueurFor price, see current catalogue IEC 2001
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Geneva, SwitzerlandTelefax: +41 22 919 0300e-mail: inmail@iec.ch IEC web site
http://www.iec.chCODE PRIXPRICE CODEW
60793-1-33 © IEC:2001– 3 –CONTENTSFOREWORD.5INTRODUCTION.91Scope and object.112Normative references.113Apparatus.134Sampling and specimens.135Reference test method.136Procedure.157Calculations.158Results.159Specification information.15Annex A (normative)
Dynamic n value by axial tension.17Annex B (normative)
Dynamic n value by two-point bending.31Annex C (normative)
Static n value by axial tension.41Annex D (normative)
Static n value by two-point bending.47Annex E (normative)
Static n value by uniform bending.51Annex F (informative)
Considerations for dynamic fatigue calculations.57Annex G (informative)
Considerations for static fatigue calculations.65Annex H (informative)
Considerations on stress corrosion susceptibility parametertest methods.67Bibliography.75Figure A.1 – Schematic of translation test apparatus.17Figure A.2 – Schematic of rotational test apparatus.19Figure A.3 – Schematic of rotational test apparatus with load cell.19Figure A.4 – Representation of dynamic fatigue graph.29Figure B.1 – Schematic of two-point bending unit.37Figure B.2 – Schematic of surface platen.39Figure B.3 – Dynamic fatigue data schematic.39Figure C.1 – Schematic of possible static fatigue (tension) apparatus.45Figure D.1 – Schematic of possible static fatigue (two-point bending) apparatus .49Figure E.1 – Schematic of possible static fatigue (uniform bending) apparatus.55Figure H.1 – The results of the round robin fracture strength versus time.73Figure H.2 – The results of the round robin fracture strength versus time.73Table F.1 − 95 % confidence interval for nd.59
60793-1-33 © IEC:2001– 5 –INTERNATIONAL ELECTROTECHNICAL COMMISSION____________OPTICAL FIBRES –Part 1-33: Measurement methods and test procedures –Stress corrosion susceptibilityFOREWORD1)The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprisingall national electrotechnical committees (IEC National Committees). The object of the IEC is to promoteinternational co-operation on all questions concerning standardization in the electrical and electronic fields. Tothis end and in addition to other activities, the IEC publishes International Standards. Their preparation isentrusted to technical committees; any IEC National Committee interested in the subject dealt with mayparticipate in this preparatory work. International, governmental and non-governmental organizations liaisingwith the IEC also participate in this preparation. The IEC collaborates closely with the InternationalOrganization for Standardization (ISO) in accordance with conditions determined by agreement between thetwo organizations.2)The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, aninternational consensus of opinion on the relevant subjects since each technical committee has representationfrom all interested National Committees.3)The documents produced have the form of recommendations for international use and are published in the formof standards, technical specifications, technical reports or guides and they are accepted by the NationalCommittees in that sense.4)In order to promote international unification, IEC National Committees undertake to apply IEC InternationalStandards transparently to the maximum extent possible in their national and regional standards. Anydivergence between the IEC Standard and the corresponding national or regional standard shall be clearlyindicated in the latter.4)
The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for anyequipment declared to be in conformity with one of its standards.5)
Attention is drawn to the possibility that some of the elements of this International Standard may be the subjectof patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.International Standard IEC 60793-1-33 has been prepared by subcommittee 86A: Fibres andcables, of IEC technical committee 86: Fibre optics.This standard, together with the other standards in the IEC 60793-1-3X series, cancels andreplaces the second edition of IEC 60793-1-3, of which it constitutes a technical revision.The text of this standard is based on the following documents:FDISReport on voting86A/688/FDIS86A/727/RVDFull information on the voting for the approval of this standard can be found in the report onvoting indicated in the above table.This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.Annexes A, B, C, D, E form an integral part of this standard.Annexes F, G, H are for information only.
60793-1-33 © IEC:2001– 7 –IEC 60793-1-3X consists of the following parts, under the general title Optical fibres:• Part 1-30: Measurement methods and test procedures: Fibre proof test• Part 1-31: Measurement methods and test procedures: Tensile strength• Part 1-32: Measurement methods and test procedures: Coating strippability• Part 1-33: Measurement methods and test procedures: Stress corrosion susceptibility• Part 1-34: Measurement methods and test procedures: Fibre curlThe committee has decided that the contents of this publication will remain unchangeduntil 2003. At this date, the publication will be•reconfirmed;•withdrawn;•replaced by a revised edition, or•amended.
60793-1-33 © IEC:2001– 9 –INTRODUCTIONPublications in the IEC 60793-1 series concern measurement methods and test procedures asthey apply to optical fibres.Within the same series several different areas are grouped, as follows:–parts 1-10 to 1-19: General–parts 1-20 to 1-29: Measurement methods and test procedures for dimensions–parts 1-30 to 1-39:Measurement methods and test procedures for mechanical charac-teristics–parts 1-40 to 1-49:Measurement methods and test procedures for transmission andoptical characteristics–parts 1-50 to 1-59:Measurement methods and test procedures for environmental charac-teristics.
60793-1-33 © IEC:2001– 11 –OPTICAL FIBRES –Part 1-33: Measurement methods and test procedures –Stress corrosion susceptibility1 Scope and objectThis part of IEC 60793 contains descriptions of the five main test methods concerning thedetermination of stress corrosion susceptibility parameters.The object of this standard is to establish uniform requirements for the mechanicalcharacteristic stress corrosion susceptibility. Dynamic fatigue and static fatigue tests are usedin practice to determine stress corrosion susceptibility parameters, dynamic n-value and staticn-value.Any fibre mechanical test should determine fracture stress and fatigue properties underconditions that model the practical application as close as possible. Some appropriate testmethods are available:–A:
Dynamic n value by axial tension (see annex A);–B:
Dynamic n value by two-point bending (see annex B);–C:
Static n value by axial tension (see annex C);–D:
Static n value by two-point bending (see annex D);–E:
Static n value by uniform bending (see annex E).These methods are appropriate for types A1, A2 and A3 multimode and type B1 single-modefibres.Static and dynamic fatigue test methods show comparable results if both tests are performedin the same effective measuring time. For dynamic fatigue tests this means a measuring timewhich is (n + 1) times larger than the measuring time of static fatigue tests.When using static fatigue test methods, it has been observed that for longer measuring timesand consequently lower applied stress levels, the n-value increases. The range of measuringtimes of the static fatigue tests, given in this standard, approaches the practical situationbetter than that of the dynamic fatigue tests, which in general are performed in relatively shorttime-frames.These tests provide values of the stress corrosion parameter, n, that can be used forreliability calculations according to IEC 62048.2 Normative referencesThe following referenced documents are indispensable for the application of this document.For dated references, only the edition cited applies. For undated references, the latest editionof the referenced document (including any amendments) applies.IEC 62048, The law theory of optical fibre reliability 1_________1
To be published.
60793-1-33 © IEC:2001– 13 –3 ApparatusSee annexes A, B, C, D, and E for each of the layout drawings and other equipmentrequirements for each of the methods respectively.4 Sampling and specimensThese measurements are statistical in nature. A number of specimens or samples from acommon population are tested, each under several conditions.Failure stress or time statistics for various sampling groups are used to calculate the stresscorrosion susceptibility parameters.4.1 Specimen lengthSpecimen length is contingent on the test procedure used. See the respective annexes A, B,C, D and E for the length required for the test method. For tensile tests, the length rangesfrom 0,5 m to at most 5 m. For two-point bending tests, the actual length tested is less than1 cm and for uniform bending tests about 1 m.4.2 Specimen preparation and conditioningAll of the test methods shall be performed under constant environmental conditions. Unlessotherwise specified in the detail specification, the nominal temperature shall be in the range of20 °C to 23 °C with a tolerance of ±2 °C for the duration of the test. Unless otherwisespecified in the detail specification, the nominal relative humidity (RH) shall be in the range of40 % to 60 % with a tolerance of ±5 % for the duration of the test.Unless otherwise specified, all specimens shall be pre-conditioned in the test environment fora minimum period of 12 h.The use of stress corrosion susceptibility (and proof stress) parameters for reliabilityestimates is still under consideration. A method for extrapolating such parameters to serviceenvironments different from the default environment specified above has not been developed.It has been observed that the value of n produced by these tests can change after even briefexposure of the fibre to elevated temperature and humidity. A guide for the use of thesemethods is documented in IEC 62048.The observed value of stress corrosion susceptibility parameter, n, may differ between fatiguetest methods. Influences on the results have been observed concerning the measuring timeand the applied stress level. Care should be taken in the choice of test method. This shouldbe agreed between the user and manufacturer.5 Reference test methodMethod A is the reference test method and shall be used to resolve disputes because it yieldsminimal values compared to the others and may be completed in a duration practical fordispute resolution.
60793-1-33 © IEC:2001– 15 –6 ProcedureSee annexes A, B, C, D and E, respectively, for the individual test methods.Each of several samples (consisting of a number of specimens) is exposed to one of anumber of stress conditions. For static fatigue tests, a constant stress is applied from sampleto sample and time to failure is measured. For dynamic fatigue tests, the stress rate is variedfrom sample to sample and the failure stress is measured.The following is an overview of the procedures common to all methods:–complete pre-conditioning;–divide the specimens into sample groups;–apply the specified stress conditions to each sample group;–measure time or stress at failure;–complete calculations7 CalculationsThe calculations for each individual test method are found respectively in annexes A, B, C, Dand E.8 Results8.1 The following information shall be reported with each test:–fibre identification;–test date;–stress corrosion susceptibility parameter;–test method.8.2 The following information shall be provided upon request:–specific information as required by the test method;–any special pre-conditioning.Clauses A.5, B.5, C.5, D.5, and E.5 have results that apply respectively for each specificmethod.9 Specification informationThe detail specification shall specify the following information:–information to be reported;–any deviations to the procedure that apply;–failure or acceptance criteria.
60793-1-33 © IEC:2001– 17 –Annex A (normative)Dynamic n value by axial tensionThis method is designed for determining the dynamic stress corrosion susceptibility parameter(dynamic n value, nd) of optical fibre at specified constant strain rates.This method is intended only to be used for use with those optical fibres of which the medianfracture stress is greater than 3 GPa at the highest specified strain rate. For fibres withmedian fracture stress less than 3 GPa, the conditions herein have not demonstratedsufficient precision.This method is intended to test fatigue behaviour of fibres by varying the strain rate. The testis applicable to fibres and strain rates for which the logarithm of fracture stress versus thelogarithm of strain rate behaviour is linear.A.1 ApparatusThis clause describes the fundamental requirements of the equipment used for dynamicfracture stress testing. There are several configurations that meet these requirements.Examples are presented in figures A.1 to A.3. Unless otherwise specified in the detailspecification, use a gauge length of 500 mm for tensile test specimens.Speed-controldeviceMotorVariable
speeddriveCapstan diameter(50 mm min.)To load cellTo cross headFibreFibre
holders(capstans)Load cellGauge length(500 mm min.)IEC
1385/01Figure A.1 – Schematic of translation test apparatus
60793-1-33 © IEC:2001– 19 –FibreNon-rotating capstanRotating capstanwith torsion sensorIEC
1386/01Figure A.2 – Schematic of rotational test apparatusLoad cellVertical non-rotatingcapstanRotating capstanFibreIEC
1387/01Figure A.3 – Schematic of rotational test apparatus with load cellA.1.1 Support of the specimenGrip the fibre length to be tested at both ends and subject the fibre to tension until fractureoccurs in the gauge length section of the fibre. Minimize the fibre fracture at the grip byproviding a surface friction that prevents excessive slippage.Do not include breaks that occur at the grip in the sample or use them in the calculations.Use a capstan, optionally covered with an elastomeric sheath, to grip the fibre. Wrap asection of the fibre that will not be tested around the capstan several times and secure it atthe end with, for example, an elastic band or masking tape. Wrap the fibre with no crossovers.The gauge length is the length of fibre between the axes of the gripping capstans before it isstretched.
60793-1-33 © IEC:2001– 21 –Use a capstan and pulley diameter so that the fibre is not subjected to a bending stress thatcauses the fibre to break on the capstan. For typical silica based fibres, the bending stressesshall not exceed 175 MPa when the fibre is wrapped as shown in the figures or traverses apulley. (For 125/250 µm – cladding/coating – silica fibre, the minimum capstan diameter isthen 50 mm.) Provide a capstan surface tough enough that the fibre does not cut into it whenfully loaded. This condition can be determined by pre-testing.A.1.2 Stressing applicationElongate the fibre at a fixed strain rate until it breaks. The rate of elongation is expressed aspercentage per minute, relative to the gauge length. Two examples for doing this are asfollows:a)increase the separation between the gripping capstans by moving one or both of thecapstans at a fixed rate of speed, with the starting separation equal to the gauge length(figure A.1); orb)rotate one or both of the gripping capstans, to take up the fibre under test (see figures A.2and A.3).The strain rate is the change in length between the two locations, in per cent, divided by thetime.If method b) is used, ensure that the fibre on the capstan does not cross over itself as it iswrapped.If fibres are tested simultaneously, protect each fibre from adjacent fibres so that whiplash atfracture does not damage other fibres under test.A.1.3 Fracture force measurementMeasure the tensile stress during the test and at fracture for each test fibre by a load cell,calibrated to within 0,5 % (0,005) of the fracture or maximum load, for each range of fracturestress. Calibrate the load cell while oriented in the same manner as when testing the fibreunder load. For method b), use a light, low-friction pulley (or pulleys) in place of the non-rotating capstan (see figure A.2), or the rotating capstan (see figure A.3), when calibratingload cells with a string and calibration weight.Use a string, attached at one end to the load-measuring device (or its capstan), to duplicatethe direction of an actual test fibre and be of a thickness or diameter comparable to that of atest fibre. A minimum of three calibration weights are recommended for load cell calibrationwhich bracket the typical fracture or maximum load (50 % below maximum, maximum and50 % above maximum).Recording the maximum tensile load at the time of fracture may be obtained for example by astrip chart recorder. The response time shall be sufficient to report the fracture stress within1 % of the actual value.NOTE
Frictional effects from the pulleys can lead to substantial errors in the load cell calibration of rotatingcapstan testers for horizontally mounted fibre.A.1.4 Strain rate controlDetermine the setting for the speed control unit by trial in order to meet the specified strainrates. Express the strain rate as a percentage of gauge length per unit time. Unless otherwisespecified in the detail specification, the maximum strain rate shall be
equal to or less than100 %/min. Select the actual maximum strain rate by taking into account aspects of the test
60793-1-33 © IEC:2001– 23 –method such as equipment considerations, material properties of the samples, etc. In additionto the maximum rate, use three additional strain rates, each reduced sequentially by roughly apower of 10 from the maximum.It is possible to minimize test duration by using a faster strain rate in conjunction with areduced load. For example, if a strain rate of 0,025 %/min is specified, test some specimensat the next fastest rate (0,25 %/min) to establish a range of fracture stress. Then pre-load to alevel equal to or less than 80 % of the lowest fracture stress found for the initial trialspecimens at the next fastest rate.A.1.5 Stress rate characterizationThe stress rate may vary with fibre type, equipment, breaking stress, fibre slippage, and strainrate. Characterize the stress rate, aσ&, at each strain rate used in the fatigue calculationaccording to:)8,0()(2,0fffaσσσσ×−×=tt&(A.1)whereσfis the fracture stress;t(σf)is the time to fracture;t(0,8 × σf)is the time at 80 % of the fracture stress.A.2 Test sampleA.2.1 Sample sizeBecause of the variability of test results, test a minimum of 15 specimens for each strain rate,and drop the lowest breaking fracture stress data point for each strain rate. Alternatively, ifthe standard error of estimate of slope σf vs. aσ& is 0,0017 or greater (as explained in F.2),test a minimum of 30 specimens for each strain rate and drop the lowest two breaking fracturestress data points for each strain rate.A.2.2 Sample size (optional)As explained in clause A.2.1, additional specimens may be required for some applications inwhich the confidence interval on the estimate of the dynamic (tension) stress corrosionsusceptibility parameter, nd needs to be known. Refer to table F.1 for various sample sizes,depending upon the expected dynamic Weibull slope, md. Appropriate use of the algorithm inclause F2 is restricted to tests in which the same sample size is specified for each strain rate.A.3 ProcedureThis procedure describes how to obtain fibre fracture stress on a given sample set tested at agiven strain rate. Calculations of population statistics are presented in clause F.2.A.3.1Set and record the gauge length (see A.1.2).
60793-1-33 © IEC:2001– 25 –A.3.2Set and record the strain rate (see A.1.4).A.3.3If method a) of A.1.4 is used, return the gripping capstans to the gauge lengthseparation.A.3.4Load the test specimen in the grips, one end at a time. The tangent point of the fibreshall be in the same location as that for the load calibrations. Guide each specimen so thatthe fibre makes at least the required number of turns around the capstan without crossingover itself.A.3.5Re-set the load recording instrument.A.3.6Start the motor to stress the fibre. Record the stress vs. time until the fibre breaks.Stop the motor.A.3.7Repeat steps A.3.3 through A.3.6 for all fibres in the sample set.A.3.8Calculate the fibre fracture stress, σf, for each break. Use equation (A.2).A.3.9Calculate the stress rate, aσ&.A.3.10Complete the required population statistic calculations. Use equations (A.3) to (A.6).A.4 CalculationsA.4.1 Fracture stressThe following method can be used to calculate the fracture stress, σf, when the coatingcontribution is negligible (less than 5 %), such as on common 125 µm diameter fibre with acoated diameter of 250 µm (polymer coating):σf = T/Ag(A.2)whereTis the force (tension) experienced by the composite specimen at fracture;Agis the nominal cross-sectional area of the glass fibre.A more complete method is given in clause F.3 for use when the coating contribution isimportant.A.4.2 Fracture stress at a gi
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