Distributed optical sensing in composite laminates

Abstract

An optical fiber-based full-field strain measurement technique was used to investigate delamination growth in laminated composites. An experimental setup to load the test samples under idealized modes of delamination was used to investigate the ability to capture the shape and location of the delamination front. It is envisioned that the demonstrated approach has significant field applications in controlled laboratory settings where delaminations have to be located accurately. Furthermore, the ability of this measurement system to provide full-field strain measurements at any given preimplanted location through the thickness overcomes the surface strain measurements obtained by digital image correlation. In order to demonstrate the technique, distributed fiber optic sensing is used to monitor the propagation of delaminations under pure mode I and II loading. Optical fibers were embedded one ply from the crack plane of both double cantilever beam and end notch flexure specimens. To establish a repeatable fabrication methodology, manufacturing techniques for embedding the optical fibers during the laminate layup process were established. Specimens with and without embedded fibers were tested to verify the fibers did not affect measured fracture toughness values. Crack lengths measured with the optical fibers compared well with true crack lengths, and measured strain distributions compared well with results from finite element analysis.

Influence of cure parameters in polymer matrix composites using embedded optical fibers

“…13 However, other studies have shown that embedded optical fibers do not significantly impact properties such as mode II fracture toughness. 14 The embedding of fiber optic sensors allows monitoring of in-plane strains at selected locations and depths within a composite laminate. Embedded optical fibers can be used to monitor the degree of cure during processing, and if left intact, quasi-static events and transient events through the structure's service life.…”

“…It was determined that very low strains measured along the length of the 0 fiber direction were obtained in the unidirectional laminate, whereas most of the residual strains developed during cure were in the transverse direction and were spatially uniform, although researchers 16 have also determined that the residual strain is nearly 40% higher near the edge of the laminate and is primarily initiated by the resin-infusion process. Also, optical fibers have been widely used for damage detection [17][18][19][20] and monitoring crack growth 14,21 for structural health monitoring.…”

Distributed Strain Sensing from Different Optical Fiber Configurations

“…Near the ends of each bonded region, spikes occur (Points D, G) that may be associated with the overlapped regions of the optical fiber. During bonding of the optical fiber, the transverse regions (1)(2)(3)(4)(5)(6)(7)(8) were placed underneath the longitudinal fibers (A-H). This developed a distortion, or change in the radius, of the optical fiber at the ingress and egress of the bonded region as shown in Figure 6.…”

“…laminates. Meadows et al [7] used a looping configuration to estimate the shape of the crack front generated from end-notch flexural tests. A variety of configurations are being used to detect damage and determine residual stresses.…”

Impact response in polymer composites from embedded optical fibers

“…In this study, an optical fiber (OF)-based strain measurement technique was tested on laminated composites to estimate the damage area. Previous studies using embedded OFs have been used to determine delamination growth 12,13 and the strain distributions in composite bonded joints 14 and in composite repair patches. 15 Most studies using OFs use fiber Bragg grating sensors for delamination detection and location in composites [16][17][18] and metals.…”