Ageing of autoclaved epoxy/flax composites: Effects on water absorption, porosity and flexural behaviour

• Published in: Composites. Part B, Engineering Vol. 202; p. 108380
• Main Authors: César dos Santos, Júlio, Ávila de Oliveira, Lívia, Panzera, Túlio Hallak, Remillat, Chrystel D.L., Farrow, Ian, Placet, Vincent, Scarpa, Fabrizio
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2020; Elsevier
• Subjects: Ageing process; Apparent porosity; Fibre orientation; Flax composite; Flexural properties; Mechanics; Physics; Prepreg; Water absorption; Fibre orientation; Ageing process; Prepreg; Flax composite; Water absorption; Apparent porosity; Flexural properties
• ISSN: 1359-8368; 1879-1069
• DOI: 10.1016/j.compositesb.2020.108380

This work investigates the effects of ageing on autoclaved composites made with unidirectional prepreg epoxy and flax tape in environments with 50% and 100% of relative humidity. A Design of Experiment (DoE) has been used first to determine the effect of the ageing time (0, 2, 4, 6, 8 and 16 days), type of bending (3-point and 4-point bending) and fibre orientation (longitudinal and transverse) on the water absorption and flexural properties of 50% saturated composites. A second experiment at 100% humidity has been also performed to further characterise the composites and to identify the equivalent ageing time that provides the mechanical behaviour of the 50% humidity samples after sixteen days. The water absorption and apparent porosity levels increase progressively with the ageing time, in particular for the case of transverse laminates; these features compromise the flexural properties of the composites. The laminates subjected to 4-point bending showed increased water absorption levels and improved flexural properties compared to the samples under 3-point bending. The flexural properties of flax composites at 50% humidity after 16 days are equivalent to those shown by composites immersed in water for less than one day.