Titolo: Strain monitoring of composite elements by fibre Bragg grating sensors during a quasi-static indentation

Autori: V. Antonucci, M. Esposito, M.R. Ricciardi, M. Giordano, M. Zarrelli
Rivista: Composite Part B: Engineering
Anno di Pubblicazione: 2014
Volume: 56
Pagine: 34-41
Abstract: The damage resistance of a fibre reinforced composite materials subjected to a concentrated indentation force has been investigated. Composite samples were manufactured by vacuum infusion process and then tested according to the concentrated quasi-static indentation test standard (QSI). The composite coupons were sensorized with embedded Bragg grating fibres in various positions, to monitor the indentation-induced deformations during the loading event. Numerical simulations, performed by using a commercial FEM software, were carried out and predictions results compared with experimental data.

Final results showed that Bragg wavelength changes sensitively depending on the applied quasi-static forces and it identifies correctly the non-linear pattern of the force–displacement curve. It was determined that strain transfer to the Bragg fibre is strongly influenced by the embedding conditions and final location of the optoelectronic sensors in term of shifting and in-plane rotation. Comparison between simulated and experimental data showed some discrepancy mainly due to the displacement of the embedded fibre sensors from their original location, caused by the manufacturing. However, by an inverse procedure based on iso-strain curves both shifting and rotation of the FBG sensors respect to their original position could be evaluated.

This work confirms that although Bragg fibres are effective and reliable to monitor deformations of composite elements during an impact event but unwanted and unpredictable effects, due to manufacturing, should be carefully taking into account to analyse correctly the sensor signal and quantitatively evaluate the inter-laminar strains.