Nielsen, Michael Wenani8; Schmidt, Jacob Wittrup3; Høgh, Jacob Herold7; Waldbjørn, Jacob Paamand6; Hattel, Jesper Henri7; Løgstrup Andersen, Tom1; Markussen, Christen Malte1
1 Department of Wind Energy, Technical University of Denmark2 Composites and Materials Mechanics, Department of Wind Energy, Technical University of Denmark3 Department of Civil Engineering, Technical University of Denmark4 Section for Building Design, Department of Civil Engineering, Technical University of Denmark5 Wind Turbines, Department of Wind Energy, Technical University of Denmark6 Section for Structural Engineering, Department of Civil Engineering, Technical University of Denmark7 Department of Mechanical Engineering, Technical University of Denmark8 Manufacturing Engineering, Department of Mechanical Engineering, Technical University of Denmark
A holistic approach to strain monitoring in fibre-reinforced polymer composites is presented using embedded fibre Bragg grating sensors. Internal strains are monitored in unidirectional E-glass/epoxy laminate beams during vacuum infusion, curing, post-curing and subsequent loading in flexure until failure. The internal process-induced strain development is investigated through use of different cure schedules and tool/part interactions. The fibre Bragg grating sensors successfully monitor resin flow front progression during infusion, and strain development during curing, representative of the different cure temperatures and tool/part interfaces used. Substantial internal process-induced strains develop in the transverse fibre direction, which should be taken into consideration when designing fibre-reinforced polymer laminates. Flexure tests indicate no significant difference in the mechanical properties of the differently cured specimens, despite the large differences in measured residual strains. This indicates that conventional flexure testing may not reveal residual strain or stress effects at small specimen scale levels. The internal stresses are seen to influence the accuracy of the fibre Bragg gratings within the loading regime. This study confirms the effectiveness of composite life cycle strain monitoring for developing consistent manufacturing processes.
Journal of Composite Materials, 2013, Vol 48, Issue 3, p. 365-381