Strength and failure mechanisms of polyimide-coated optical fibers

Arne Skontorp

doi:10.1117/12.388112

12 June 2000 Strength and failure mechanisms of polyimide-coated optical fibers

Arne Skontorp

Proceedings Volume 3986, Smart Structures and Materials 2000: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials; (2000) https://doi.org/10.1117/12.388112
Event: SPIE's 7th Annual International Symposium on Smart Structures and Materials, 2000, Newport Beach, CA, United States

Abstract

Embedded optical fibers and sensors must survive and remain functional for the lifetime of the structure being monitored, as repairs are generally impossible. Thus, the feasibility of an embedded optical fiber monitoring concept depends heavily on the durability of the optical fiber. Processes that degrade the mechanical properties of these fibers are therefore of great concern. During the process of writing a Bragg grating sensor in a fiber, the polyimide coating is damaged locally by ablation, making the fiber vulnerable to moisture degradation. To rectify this situation, the coating in the area around the grating is commonly removed and the fiber is recoated. However, this procedure itself makes the fiber susceptible to degradation by moisture and handling. Tensile experiments were conducted on both virgin fiber and on fibers that had been recoated to study deterioration related to the recoating process. Weibull theory was used to model the strength distributions and a fracture mechanics approach was used in conjunction with microscopy to study failure initiation and to evaluate the relative significance of coating defects. The results indicated that two independent flaw populations existed in the fibers, one associated with manufacturing defects and the other with inherent flaws on the surface of the glass fiber. The failure was always initiated on the glass surface, not in the coating, and the condition of the coating did not effect the failure location. The recoated fibers always failed in the recoated section at a significantly reduced load, due to degradation after exposure of the glass to the environment. This suggested that the recoating process might actually worsen the situation.

Citation Download Citation

Arne Skontorp "Strength and failure mechanisms of polyimide-coated optical fibers", Proc. SPIE 3986, Smart Structures and Materials 2000: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (12 June 2000); https://doi.org/10.1117/12.388112

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