High Strain Measurement Using Fiber Bragg Grating Sensors

Fiber Bragg Grating-based (FBG) strain sensors have been widely used in engineering applications requiring small size, light weight, amenability to multiplexing, and very fast response times. State-of-the-art FBG interrogators are capable of measuring as low as sub micro strains and as high as 1% fiber strain in tension and higher still under compression. In this paper, we will discuss the development of an FBG based real-time instrumentation system to conduct highly dynamic strain measurements during an impact. A high-speed FBG interrogation system was used along with an FBG sensor data analysis software for efficient post-processing. In order to capture high strain data during an impact event, one needs to conduct measurements at very fast speeds and simultaneously to maintain FBG sensor survivability. A high strain FBG fixture was designed accordingly. Such high strain fixture allows the FBG strain sensor to measure the actual field strain with a reduction factor K in order to expand the strain measurement range. Numerical simulation results using finite element analysis (FEA) were used to validate the high strain fixture design analysis. Finally, a proof-of-concept FBG-based high strain measurement system has been demonstrated to measure dynamic strain data under impact tests. Experimental strain reduction factors were determined from the strain data and correlated well with FEA predicted values.