How does it determine the expected lifespan of an optical fiber under constant tension?
The static fatigue coefficient, or n-value, is a critical parameter for determining the expected lifespan of an optical fiber under constant tension. It quantifies the susceptibility of the fiber to strength degradation over time due to stress corrosion, which is a process accelerated by the presence of moisture and sustained mechanical load.
How it determines lifespan:
The n-value is used in empirical models, often described by the following relationship:
log(t_f) = -n * log(σ_a) + log(K)
Where:
t_fis the time to failure (expected lifespan)nis the static fatigue coefficient (n-value)σ_ais the applied stress (constant tension)Kis a material constant
A higher n-value indicates greater resistance to static fatigue, meaning the fiber can withstand a given stress for a longer period, or a higher stress for the same period, before failing. In essence, it describes how rapidly the fiber’s strength degrades under sustained load and environmental conditions. Engineers use the n-value, along with initial fiber strength and operational stress levels, to predict the reliability and expected service life of optical fibers in various applications, particularly those involving long-term tensile loads.
For applications requiring high reliability under sustained tension, such as in structural health monitoring or in demanding industrial environments, OFSCN offers specialized solutions. For instance, our OFSCN® High-Strength Fiber Bragg Gratings / Fiber Bragg Grating Strings (Bare) utilize screened high-strength polyimide-coated optical fibers, providing enhanced durability and resistance to static fatigue.
Here is an image illustrating the type of fiber used in such applications:
You can find more technical details about our high-strength fiber products here: