Mechanical Strength Characteristics Of Optical Fibers In The High-Temperature Environments

The use of optical fibers as strain sensors to monitor the health and integrity of high temperature structures is a current research focus. However, it is found that the optical fiber is fragile and easy to fracture when the sensors based on the optical fibers are used in high-temperature environments, which reduced the service life of sensors. Therefore, it is necessary to investigate mechanical strength of the optical fibers at high temperature in order to predict and extend the service life of sensors based on the optical fibers. In this thesis, the mechanical strength characteristics of the optical fibers in high-temperature environments are investigated by dynamic tensile fracture tests. A high-temperature tensile testing system is designed to obtain the fracture strength of the optical fibers under the conditions of various temperatures and various tensile rate. The fracture mechanisms of the optical fibers at high temperature are discussed from the fracture strength and the surface state, which provides the basis of theoretical mechanics for the research and development of high-temperature fiber optical sensors. The experimental results indicate that the designed fiber tensile testing system at high temperature can achieved the tests well. The fracture strength of the optical fiber at high temperature suffer from attenuation relative to room temperature. The fracture strength decrease with the temperature increasing. At room temperature and300℃, with the improvement of the tensile rate, the fracture strength of the optical fiber reduce continuously. At540℃, with the improvement of the tensile rate, the fracture strength of the optical fiber increase instead.Meanwhile, the fracture strength of the annealed fibers is tested and the annealing process of optical fibers is expounded. The results indicate that the fracture strength of annealed fibers suffers from great attenuation. At the tensile rate of30mm/min, the fracture strength is101.7MPa, which drops by97.8%compared to the strength of bare fibers at room temperature. By the observation of the surface morphology, the reason is that crystallization occurs at the surface of the fibers at high temperature. During the annealing process, a large number of cracks are formed at the crystallization layer, which affects the fracture strength of the optical fibers significantly.