A Running Reference Analysis Method to Greatly Improve Optical Backscatter Reflectometry Strain Data from the Inside of Hardening and Shrinking Materials

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.

In-Situ Strain Measurements in Large Volumes of Hardening Epoxy Using Optical Backscatter Reflectometry

“…The actual strain value at a given time is then calculated by adding up these strain differences. The running reference method was used to obtain the strain values presented in this work and the method is to be published [29].…”

“…The second steep strain gradient at the exit point of the fiber has a further reduction of the backscatter signal as result and no meaningful strain values can be determined afterwards from the raw data. This mechanism however is outside the scope of this paper and interested readers are referred to the discussion of the details of the applied method in [29]. However, since this affects the strain values just after it exits the structure, it has no influence on the general application of the measurement method.…”

A Review of Recent Distributed Optical Fiber Sensors Applications for Civil Engineering Structural Health Monitoring

“…Instead, the novel but more computationally taxing one (Polynomial Interpolation Comparison Method) provided much smoother and reliable output plots as evident in Figure 74. In Heinze and Echtermeyer [27], a novel post-processing methodology was introduced as a solution to the issue of "meaningless results" (SRAs) being reported by OBR analyses whenever OFDR DOFS pinching or micro-bending occurred. The latter reportedly is the typical case for DOFS embedded inside hardening and shrinking materials.…”

“…Finally, Song et al [174] argued that whenever BOTDA DOFS are employed for the detection of large cracks inside any study material, these lead by definition to large Crack Opening Displacements which can be easily detected in the fiber's output as strain peaks or singularities. Yet, when it comes to microcracks, their formation does not bring along In Heinze and Echtermeyer [27], a novel post-processing methodology was introduced as a solution to the issue of "meaningless results" (SRAs) being reported by OBR analyses whenever OFDR DOFS pinching or micro-bending occurred. The latter reportedly is the typical case for DOFS embedded inside hardening and shrinking materials.…”

A Sensitive and Fast Fiber Bragg Grating-Based Investigation of the Biomechanical Dynamics of In Vitro Spinal Cord Injuries

“…By measuring strain, we can quantify their elasticity and health, among others [ 1 ]. A number of techniques have already been proposed for the mechanical characterization, such as indentation probes [ 2 ], tension testers [ 3 ], compression techniques or rotatory shear techniques [ 4 , 5 ], and optical backscatter reflectometry [ 6 ]. All these techniques have common drawbacks, such as their inability to measure low-strain values and their slow response time.…”