Where
Fs : Rate of fiber rupture after application of a proof test
with a tension σP for tP and then σs for ts [Fs = 0.01]
σP : Strain[%] given to the fiber in the proof test.
σs : Strain[%] given to the fiber after the installation of cable
tp : Time applied stress to the fiber in the proof test.
ts : Lifetime of the fiber after the installation of cable.
Np : Number of ruptures in the unit length of fiber given a tension of σP for tP seconds. [NP = 0.03/km]
L : Length of fiber [L=1000km]
m : Index of Weibull distribution [m=10]
n : Constant [Fatigue value]
2. Calculation
Fig.1 is shown relation between the allowable stress time [ts], Life time of the
optical fiber and strain given to the fiber[Service strain] after the installation
of the cable at different fatigue value[n] and proof strain[σp].
In generally, the service strain is 0.1% to 0.2%. So when the proof strain is 1%
and the fatigue value[n] is 20, the lifetime of the optical fiber is to be 25 years at least.
Fig 1.on between the of allowable strain[s] and allowable stressing tmetsat the different proof strain [%on between the allowable strain and allowable stressing tme at the different fatgue value [n]
