Retroreflective sheeting materials as SHM passive strain sensors

Abstract
Highly reflective Retroreflective sheeting materials (RRSM) are widely used today for roadway signs and markings. Retroreflectivity (RR), defined as the portion of light re-turned to the light source as measured in candelas per lux per square meter, can be measured quite easily in the field using a handheld retroreflectometer. Tests show that as load is applied to RRSM, the retroreflection changes, and for many types of RRSM, RR decreases with increasing tension and has a mostly linear relationship to the material strain. This opens the possibility for using RRSM as a passive strain sensor for structural health monitoring, whereby measured changes in RR of RRSM mounted to a structure can be correlated to changes in strain. The sensor would be low cost, practical, and innovative. Tension test results show that a yellow-green type XI material produced by one manufacturer has one of the highest material sensitivities (ratio of retroreflectivity to strain) of the many the authors have tested. The sensitivity of the material, denoted here as A-TXIFYG, decreases linearly after it is strained past approximately 1000 microstrain (µε). This led to testing of the material after initial straining (pre-straining). Results show that for the material to have a similar sensitivity while mounted to that of the bare material tests, it must be externally clamped to the substrate.
Description
This book chapter was originally published in Bridge Maintenance, Safety, Management, Digitalization and Sustainability, by Jens Sandager Jensen, Dan M. Frangopol, and Jacob Wittrup Schmidt, 3765–72, 1st ed. London: CRC Press, 2024. https://doi.org/10.1201/9781003483755-444.. The version of record is available at: https://doi.org/10.1201/9781003483755-444. © 2024 The Author(s), ISBN 978-1-032-77040-6 Open Access: www.taylorfrancis.com, CC BY-NC-ND 4.0 license (https://creativecommons.org/licenses/by-nc-nd/4.0/)
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Citation
Power, Hannah M., and Harry W. Shenton. “Retroreflective Sheeting Materials as SHM Passive Strain Sensors.” In Bridge Maintenance, Safety, Management, Digitalization and Sustainability, by Jens Sandager Jensen, Dan M. Frangopol, and Jacob Wittrup Schmidt, 3765–72, 1st ed. London: CRC Press, 2024. https://doi.org/10.1201/9781003483755-444.