Abstract
The design of optical fibre cables currently preferred by BICC ordinarily produces little or no tension or torsion in the fibres. Bending them into helical form, however, causes a permanent stress which couid give rise to static fatigue. In a recent paper, the probability that a bent fibre will fail owing to static fatigue was calculated. The calculation is extended in the present paper to take account of proof-testing. Assuming reasonable values for the parameters, it appears that a fibre of 125μm diameter, proof-tested at 0.5% strain and subsequently bent to a radius not less than 25 mm, would certainly survive for 40 years.
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Abbreviations
- A :
-
constant of the material and the environment; surface area (possibly elementary)
- A 0 :
-
surface area of a gauge length
- a :
-
radius of fibre
- B :
-
constant of the material and the environment
- E :
-
Young's modulus
- F :
-
cumulative probability of failure
- F p :
-
failure probability on proof test
- F s :
-
failure probability in service
- F(ts):
-
failure probability in service, referred to the number of fibres surviving the proof test
- K I :
-
stress intensity factor for mode I failure
- K Ic :
-
critical stress intensity factor
- L :
-
length of fibre
- L 0 :
-
gauge length
- M :
-
modified Weibull shape parameter
- m :
-
Weibull shape parameter
- n :
-
stress corrosion susceptibility
- p :
-
stress corrosion susceptibility for environment of proof test
- q(M) :
-
a function (see text)
- R :
-
radius of curvature
- S :
-
applied stress
- S eq :
-
equivalent stress (whereS varies with time)
- S i,S′ i :
-
inert strength
- S 0 :
-
Weibull scale parameter
- S p :
-
maximum stress during proof test
- S s :
-
service stress
- s :
-
stress corrosion susceptibility for service environment
- t :
-
time
- t eq :
-
equivalent duration (whereS varies with time)
- t f :
-
time to failure
- t 0 :
-
scale time
- t p :
-
equivalent duration of proof test
- t s :
-
service life
- Y :
-
a geometrical constant
- δ, δ0, δ′0 :
-
size of flaw
- θ :
-
azimuth measured from neutral plane
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Fox, M. Theoretical fatigue life of helically stranded optical fibres. Opt Quant Electron 15, 253–260 (1983). https://doi.org/10.1007/BF00619936
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DOI: https://doi.org/10.1007/BF00619936