Characterization of process-induced defects in automated fiber placement manufacturing of composites using fiber Bragg grating sensors

Abstract

With the increasing use of automated fiber placement method for manufacturing highly precise bespoke composite components in the aerospace industry, the level of manufacturing defects within the laminate structure needs to be monitored and minimized for structural integrity. One of the main common defects in automated fiber placement process is misalignment between the tape paths in successive courses which leads to non-integrity of laminate and consequently significant reduction in mechanical strength of the laminate. Therefore, it is necessary to find an appropriate inspection method to monitor and identify these processing defects at the earlier stages of manufacturing. Since optical fiber Bragg grating sensors are being increasingly utilized for structural health monitoring in composite materials and as they were successfully implemented by Oromiehie et al. in their earlier work for on-line lay-up process monitoring, the same methodology is once again tried for identifying the misalignment defects in automated fiber placement process. The experiments are carried out on glass-fiber/nylon laminate with embedded fiber Bragg gratings for the automated tape placement method. The defects due to misalignment are identified by the fiber Bragg grating sensors through their reflected wavelength changes during the automated manufacturing process. The analysis of results indicates that the fiber Bragg grating sensors can be reliably implemented for on-line defect monitoring during the automated fiber placement process to ensure the quality of final product and maintain the expected design life.

In-situ simultaneous measurement of strain and temperature in automated fiber placement (AFP) using optical fiber Bragg grating (FBG) sensors

“…The measured wavelength during the placement of remaining plies were also monitored and recorded in real time. In another experimental program, [19][20][21] the application of optical FBG sensors for identifying misalignment defects within the laminate have also been demonstrated through the embedment of three different artificial defects within the laminate. It was found that depending on the type of defects in terms of material and size, three different changes in the wavelength profiles could be observed.…”

A literature review of quality control for automated lay-up processes

“…Due to the limited measurement speed, an online quality control system is not possible at the moment. Fiber Bragg grating Oromiehie [32,38,110] has been investigating Fiber Bragg grating (FBG) sensors for online monitoring during lay-up since 2016. The Fiber Bragg grating technology consists of an optical fiber with a periodical reflective index along the longitudinal direction of the fiber core creating a wavelength-specific dielectric mirror.…”

“…The first step towards monitoring the AFP process was done by just monitoring process parameters, such as the induced strain during the lay-up process of glass fiber/high-density polyethylene material [32,114]. A silica optical FBG system [110] was implemented for online monitoring of defects during the TPC AFP. The tested material was thermoplastic glass fiber nylon.…”

Structural health monitoring for woven fabric CFRP laminates

“…This makes CFRP an inherently smart material, as changes in the electrical conductivity will occur as deformation or damage occur within the structure [29][30] [31]. It also means that electrical conductivity measurements in CFRP laminates have the potential to out-perform other methods, such as fibre optics, thermography, and acoustic methods, as it employs carbon fibres themselves as the sensing element, removing the need for additional sensors to be added [32,33,5].…”