On the improvement of strain measurements with FBG sensors embedded in unidirectional composites

Abstract

Optical fibre Bragg grating (FBG) sensors are now quite established and widely used in strain measurements of composites. However, insufficient understanding of the limitations of the embedment and measuring techniques often lead to inaccurate and inconclusive results. In this study, a novel method to improve the reliability and accuracy of the strain measurements on unidirectional composites using embedded FBG sensors was successfully developed. Using a carbon/epoxy prepreg system, test specimens were manufactured with longitudinally embedded FBG sensors. The combined behaviour of the sensors and the host material was characterized and a calibration rule (correction factor) was determined for the chosen material. The consistency of the results with both theoretical and empirical assumptions suggests that the proposed method is applicable to a wide range of FBG sensors and host materials.

Study of strain-transfer of FBG sensors embedded in unidirectional composites

“…This study is a continuation of a previous work [1], focused on the application of FBG sensors in unidirectional (UD) composites to measure the longitudinal strain. The objectives were:…”

“…To produce the unidirectional composite specimens the same procedure as in the previous work was used [1]. The specimens were produced with a free length of 100 mm, width of 20 mm and thickness of 1.5 mm.…”

“…However, the accuracy of the measurement in real applications strongly depends on the effectiveness of the strain transfer from the host material to the FBG sensors. Typically, the optical fibre and the host material in which it is embedded have different material properties (such as longitudinal stiffness) and, therefore, strain in both materials will not be equal when load is applied [1,9].…”

“…The experimental procedure to manufacture and test the specimens is the same as used in the previous study [1]. Also, the FBG sensors and the signal acquisition technology were the same as used in the previous study.…”

Analysis of Fibre Bragg Gratings Sensors Optimal Placement for Monitoring of Damage Propagation in Laminate Composites

“…There is a large number of research works were devoted to studying possibility of delamination and other defects detection using embedded FBG sensors [12][13][14][15][16]. However, due to limited sensibility of sensors, the results strongly depend on the distance between the defect and the sensor.…”