IEC TR 62048:2014
(Main)Optical fibres - Reliability - Power law theory
Optical fibres - Reliability - Power law theory
IEC TR 62048:2014(E) is a guideline that gives formulae to estimate the reliability of fibre under a constant service stress based on a power law for crack growth. This third edition cancels and replaces the second edition published in 2011, and constitutes a technical revision. The main changes with respect to the previous edition are listed below:
- correction to the unit of failure rates in Table 1;
- correction to the FIT equation for instantaneous failure rate [19] in addition to all call-outs and derivations;
- insertion of a new note about fibre length dependency of failure rates;
- addition of informative Annex A and relevant reference;
- editorial corrections of inconsistencies. Keywords: reliability of fibre, service stress, power law for crack growth
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IEC TR 62048 ®
Edition 3.0 2014-01
TECHNICAL
REPORT
colour
inside
Optical fibres –
Reliability – Power law theory
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IEC TR 62048 ®
Edition 3.0 2014-01
TECHNICAL
REPORT
colour
inside
Optical fibres –
Reliability – Power law theory
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
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XB
ICS 33.180.10 ISBN 978-2-8322-1369-8
– 2 – TR 62048 © IEC:2014(E)
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Symbols . 8
4 General approach . 10
5 Formula types . 10
6 Measuring parameters for fibre reliability . 11
6.1 Overview . 11
6.2 Length and equivalent length . 11
6.3 Reliability parameters . 12
6.3.1 Overview . 12
6.3.2 Proof-testing . 12
6.3.3 Static fatigue . 12
6.3.4 Dynamic fatigue . 13
6.4 Parameters for the low-strength region . 13
6.4.1 Overview . 13
6.4.2 Variable proof test stress . 13
6.4.3 Dynamic fatigue . 14
6.5 Measured numerical values. 17
7 Examples of numerical calculations . 17
7.1 Overview . 17
7.2 Failure rate calculations . 18
7.2.1 FIT rate formulae . 18
7.2.2 Long lengths in tension . 18
7.2.3 Short lengths in uniform bending . 20
7.3 Lifetime calculations . 22
7.3.1 Lifetime formulae . 22
7.3.2 Long lengths in tension . 22
7.3.3 Short lengths in uniform bending . 23
7.3.4 Short lengths with uniform bending and tension . 25
8 Fibre weakening and failure . 26
8.1 Crack growth and weakening . 26
8.2 Crack fracture . 28
8.3 Features of the general results . 29
8.4 Stress and strain . 30
9 Fatigue testing . 30
9.1 Overview . 30
9.2 Static fatigue . 30
9.3 Dynamic fatigue . 32
9.3.1 Overview . 32
9.3.2 Fatigue to breakage . 32
9.3.3 Fatigue to a maximum stress . 34
9.4 Comparisons of static and dynamic fatigue . 34
9.4.1 Intercepts and parameters obtained . 34
9.4.2 Time duration . 34
TR 62048 © IEC:2014(E) – 3 –
9.4.3 Dynamic and inert strengths . 35
9.4.4 Plot non-linearities . 36
9.4.5 Environments. 36
10 Proof-testing . 37
10.1 Overview . 37
10.2 The proof test cycle . 37
10.3 Crack weakening during proof-testing . 38
10.4 Minimum strength after proof-testing . 39
10.4.1 Overview . 39
10.4.2 Fast unloading . 39
10.4.3 Slow unloading . 40
10.4.4 Boundary condition . 41
10.5 Varying the proof test stress . 41
11 Statistical description of strength by Weibull probability models . 41
11.1 Overview . 41
11.2 Strength statistics in uniform tension . 41
11.2.1 Unimodal probability distribution . 41
11.2.2 Bimodal probability distribution . 43
11.3 Strength statistics in other geometries . 43
11.3.1 Stress non-uniformity . 43
11.3.2 Uniform bending . 44
11.3.3 Two-point bending . 45
11.4 Weibull analysis for static fatigue before proof-testing . 45
11.5 Weibull analysis for dynamic fatigue before proof-testing . 47
11.6 Weibull distribution after proof-testing . 49
11.7 Weibull analysis for static fatigue after proof-testing . 51
11.8 Weibull analysis for dynamic fatigue after proof-testing . 53
12 Reliability prediction . 54
12.1 Reliability under general stress and constant stress . 54
12.2 Lifetime and failure rate from fatigue testing . 55
12.3 Certain survivability after proof-testing . 56
12.4 Failures in time . 57
13 B-value: elimination from formulae, and measurements . 58
13.1 Overview . 58
13.2 Approximate Weibull distribution after proof-testing . 58
13.2.1 Overview . 58
13.2.2 "Risky region" during proof-testing . 58
13.2.3 Other approximations . 59
13.3 Approximate lifetime and failure rate . 61
13.4 Estimation of the B-value . 62
13.4.1 Overview . 62
13.4.2 Fatigue intercepts . 62
13.4.3 Dynamic fatigue failure stress . 62
13.4.4 Obtaining the strength . 62
13.4.5 Stress pulse measurement . 63
13.4.6 Flaw growth measurement . 63
– 4 – TR 62048 © IEC:2014(E)
Annex A (informative) Statistical strength degradation map. 64
Bibliography . 65
Figure 1 – Weibull dynamic fatigue plot near the proof test stress level . 16
Figure 2 – Instantaneous FIT rates of 1 km fibre versus time for applied stress/proof
test stress percentages (bottom to top): 10 %, 15 %, 20 %, 25 %, 30 % . 19
Figure 3 – Averaged FIT rates of 1 km fibre versus time for applied stress/proof test
stress percentages (bottom to top): 10 %, 15 %, 20 %, 25 %, 30 % . 19
Figure 4 – Instantaneous FIT rates of bent fibre with 1 m effective length versus time . 21
Figure 5 – Averaged FIT rates of bent fib
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