Distributed Strain Monitoring for Damage Evolution in CFRP Bolted Structures with Embedded Optical Fibers

Abstract

The authors proposed fiber-optic-based damage monitoring of carbon fiber reinforced plastic (CFRP) bolted joints. Optical fibers were embedded along bolt holes and strain change along the optical fiber induced by internal damage was measured by a Brillouin Optical Correlation Domain Analysis (BOCDA), which is a high spatial resolution distributed strain sensing system. This study began by investigating damage modes of CFRP bolted joints after bearing failure. Effective embedding positions of optical fibers were then proposed and their feasibility was evaluated by finite element analysis simulating the damage propagation in the bolted joint and consequent strain change. Finally, verification tests were conducted using specimens with embedded optical fibers at various positions. It was clearly shown that damage could be detected using residual strain due to fiber-microbuckling (kinking) damage or permanent deformation of neighboring plies. Furthermore, damage size and direction could be estimated from the change in the strain distribution. The system developed is quite useful for a first inspection of large-scale composite structures in aerospace applications.

Structural Health Monitoring of Gantry Girder using Fibre Bragg Grating Sensors

“…An optical fiber Bragg grating-strain sensor is used particularly for the strain-based SHM measurement (Takeda et al, 2013). The complex structures make use of advanced wireless sensor networks to mitigate the complications caused by the wired networks (Lynch and Loh, 2006).…”

Strain State Detection in Composite Structures: Review and New Challenges

“…In this large framework, many different sensing methodologies have thus been deployed for these structural monitoring applications. Many of these methods are based upon strain measurements, which can be detected by conventional gauges or other techniques [6]. Since 1940, the resistance strain gauges (SGs) exemplified the most powerful tool concerning the experimental stress evaluation, even today representing a common choice for monitoring material deformations and damage on in-service composite vehicles.…”

Structural health monitoring in aeronautical structures by means of distributed fibre optic sensing networks

“…Later, in 2003 the fuselage of a launch vehicle was monitored to analyse the deformations after curing (Murayama, Kageyama, Naruse, Shimada, & Uzawa, 2003). Other small-scale experiments were also carried out, thereby bolt holes were also successfully monitored after bearing failure by using a BOCDA system (Takeda, Minakuchi, & Nadabe, 2013). Some experiments have attempted to enhance this characteristic in terms of measurement range, strain and temperature accuracy.…”