A Standard Test Method for Evaluating Crack Monitoring Performance of Distributed Fiber Optic Sensors

In this paper, a standard test method of evaluating the measurement performance of distributed sensors such as Brillouin scattering based fiber optic sensors (FOSs) and other long gauge sensors for monitoring cracks is proposed. The performance evaluation of two types of Brillouin scattering based DFOSs named as BOTDR(Brillouin Optical Time Domain Reflectometry) and PPP-BOTDA (Pulse Pre-Pump Brillouin Optical Time Domain Analysis) are then performed based on the proposed test method. Experimental results illustrate that for Brillouin scattering based distributed sensing techniques with 10cm-1m spatial resolution, the FOSs installed with the overall bonding (OB) method can hardly measure the crack width with a quantitative manner, while FOS installed with the point fixation (PF) method can be used to measure the crack width with a great performance. For BOTDR sensing technique, with a limitation of 1m-order spatial resolution, loop installation of FOS is the best way to accurately and stably monitor crack width. For PPP-BOTDA sensing technique, in despite of possessing 10cm-order spatial resolution, if the gauge length of FOS is shorter than the critical effective sensing length (CESL), the measurement accuracy is significantly affected by the slippage between the core and coating layer of FOS.