Abstract
The temperature response of fiber Bragg gratings (FBGs) embedded in carbon fiber reinforce polymers (CFRPs) is investigated in this paper. To provide strain-free temperature measurements, two pieces of anti-sticking materials are placed at both sides of the embedded optical fiber and between carbon fiber prepregs; thus, providing slippery surfaces that minimize the strain transfer to the FBG sensor. In particular, the impact of different anti-stick materials on the temperature and residual bending strain response of the embedded FBGs is experimentally investigated. Results demonstrate that although some materials can allow for minimum residual strain being transferred to the FBG, their thermal conductivity does not always fulfill the requirements for reliable temperature sensing. It is found out that, among the tested materials, aluminum and copper foils can provide both reliable temperature response (with negligible delay and bias) and minimum residual strain. Using such anti-stick materials, the error induced by the residual strain on FBG temperature measurements is also experimentally evaluated by applying temperature and bending loads (strain) simultaneously to the CFRP packaging. While the study is here performed for FBG-based point sensors, most of the results and conclusions are also expected to be valid for applications of embedded distributed optical fiber sensors being affected by strain-temperature cross-sensitivity issues.
Highlights
C ARBON fiber reinforced polymers (CFRP) have superior specific stiffness and strength over many other materials [1]
This paper presents, for the first time to the best of our knowledge, an experimental investigation of the effects that anti-stick materials have on the response of fiber Bragg gratings (FBGs) temperature sensorsloosely embedded in CFRP laminates
Experimental results demonstrate that the use of copper or aluminum foils between CFRP and the embedded FBG allows for the best thermal response among the studied materials, while they secure a significant reduction of the bending residual strain
Summary
C ARBON fiber reinforced polymers (CFRP) have superior specific stiffness and strength over many other materials [1]. This paper presents, for the first time to the best of our knowledge, an experimental investigation of the effects that anti-stick materials have on the response of FBG temperature sensors (quasi-)loosely embedded in CFRP laminates. Experimental results demonstrate that the use of copper or aluminum foils between CFRP and the embedded FBG allows for the best thermal response among the studied materials, while they secure a significant reduction of the bending residual strain Even though this experimental investigation is here carried out based on FBG point sensors, results are expected to be valid for large SHM systems involving the use of FBG arrays and distributed optical fiber sensors based on Brillouin or Rayleigh scattering
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