Abstract
Due to the increasing ease of use and the superiority of the results, distributed strain measurements, utilizing Optical Backscatter Reflectometry (OBR), have become more important and widespread over the last few years. Strains are calculated from the difference between an actual optical Raleigh backscattering measurement and an initial reference value. However, under certain physical conditions, e.g., pinching or microbending of the optical fiber, no meaningful strain values are yielded by the commonly-used method to analyze OBR data. Such conditions were experienced in this study where the optical fiber was embedded into hardening epoxy for measuring shrinkage due to curing. In this work, it is shown that a new data analysis method called the “running reference analysis method” can overcome such obstacles and deliver meaningful strain values in circumstances in which the traditional method fails. In the new approach, each measurement is compared to the previous measurement, and the strain differences are added up to the absolute strain value. This method does not require a new experimental technique and will also work on old measurement files. It is also useful for other types of (OBR) strain measurements that contain many outliers and is not restricted to the investigation of cured epoxy.
Highlights
Many important large infrastructure components are created by pouring a liquid material into a mold and letting the material harden or cure
This method does not require a new experimental technique and will work on old measurement files. It is useful for other types of (OBR) strain measurements that contain many outliers and is not restricted to the investigation of cured epoxy
Optical Backscatter Reflectometry (OBR) has not been used so far to determine the internal shrinkage of, e.g., large cementitious or polymer structures. This may be due to the forces acting on the fiber during the curing process, which in return deteriorate the backscattered signal greatly, and only noise is extracted in traditional OBR analysis
Summary
Many important large infrastructure components are created by pouring a liquid material (e.g., cement or a polymer) into a mold and letting the material harden or cure. Digital image correlation tracks surface structures and allows one to determine two-dimensional local shrinkage on the surface of a sample [18,19] While this technique yields much more detailed information than the above methods, it can only be applied to rather small samples, with sizes of some centimeters. Backscattering happens at irregularities of the fiber material This means strains can be measured along the entire length of the fiber, allowing one to monitor large structures. OBR has not been used so far to determine the internal shrinkage of, e.g., large cementitious or polymer structures This may be due to the forces acting on the fiber during the curing process, which in return deteriorate the backscattered signal greatly, and only noise is extracted in traditional OBR analysis. The solutions will be useful for many applications of the OBR technique where local forces act on the fiber and high strain gradients occur
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