Surface-Mounted Bare and Packaged Fiber Bragg Grating Sensors for Measuring Rock Strain in Uniaxial Testing.

Balarabe Wada Isah,Hisham Mohamad

doi:10.3390/s21092926

Abstract

The paper explores the possibility of using high-resolution fiber Bragg grating (FBG) sensing technology for on-specimen strain measurement in the laboratory. The approach provides a means to assess the surface deformation of the specimen, both the axial and radial, through a chain of FBG sensor (C-FBG), in a basic setup of a uniaxial compression test. The method is cost-effective, straightforward and can be commercialized. Two C-FBG; one was applied directly to the sample (FBGBare), and the other was packaged (FBGPack) for ease of application. The approach measures the local strain with high-resolution and accuracy levels that match up to the existing local strain measuring sensors. The approach enables the evaluation of small-strain properties of the specimen intelligently. The finite element model analysis deployed has proven the adaptability of the technique for measuring material deformation. The adhesive thickness and packaging technique have been shown to influence the sensitivity of the FBG sensors. Owing to the relative ease and low-cost of instrumentation, the suggested method has a great potential to be routinely applied for elemental testing in the laboratory.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Total of specimens were tested, readings from all sensors were periments performed on limestone specimens equipped with C-fiber Bragg grating (FBG) sensors
FBG sensors consisting of two packaged (FBGPack),in and strain gauges (SG) are toresponse the sample for measuring distinct color.(Local) strain, while linear variable differential transformer (LVDT) is attached to the upper loading plate to measure on-specimen the crosshead deformation

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The study of the mechanical behavior of rocks provides solutions to engineering problems related to a wide range of human activities, especially with the evolvement of large geotechnical engineering structures, such as deep tunnels, boreholes for oil and gas, and tunnels for storage of radioactive waste. Analyzing the mechanical behavior of rocks requires strain measurement. Most rocks are very stiff, and their strain response to loading is minimal (microstrain) [1]. It requires a very accurate and high-resolution device to obtain a realistic stress-strain relationship of the rocks

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Conclusion