Influence of hydrothermal ageing on the fatigue behaviour of a unidirectional flax-epoxy laminate

Although the research and development in plant fibre composites is growing rapidly, these materials still require specific considerations before being adopted by industry in structural applications. One of the main issue is related to their durability. The objective of this study is to investigate the influence of hydrothermal ageing on the fatigue behaviour of an unidirectional flax-epoxy laminated composite by implementing the fatigue tests in a water bath. Results show that while the quasi-static strength and rigidity are significantly affected by the ageing, the fatigue strength is however improved. The fatigue strength coefficient is more than two times lower after ageing, indicating a lower decrease of the maximum stress with the increasing number of cycles. After ageing, the maximum stress level for an expected lifetime of 5.3 106 cycles is approximately 90 MPa, which is comparable to the one of unaged specimens. It is also pointed out that the remaining quasi-static tensile properties and behaviour of the aged specimen are not significantly affected after 1.3 106 cycles at a stress level of 90 MPa.