International audienceExperimental investigations on flax and glass fabrics reinforced epoxy specimens, i.e. FFRE and GFRE, submitted to fatigue tests are presented in this paper. Samples having [0/90](3S) and [+/- 45](3S) stacking sequences, with similar fibre volume fractions have been tested under tension-tension fatigue loading. The specific stress-number of cycles to failure (S-N) curves, show that for the [0/90](3S) specimens, FFRE have lower fatigue endurance than GFRE, but the [+/- 45](3S) FFRE specimens offer better specific fatigue endurance than similar GFRE, in the studied life range (<2 x 10(6)). Overall, the three-stage stiffness degradation is observed in all cases except for [0/90](3S) FFRE specimens, which present a stiffening phenomenon of around 2-3% which could be related to the straightening of the microfibrils

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. lay-ups. The Probabilized Stress-Number of cycles (P-S-N) curves have been determined for each laminate type. The measured stress and strain data allowed to quantify the evolution of the mechanical properties, i.e. stiffness, damping and permanent strain as a function of imposed cycles. Especially, the stiffening phenomenon of flax reinforcements oriented parallel to the loading direction has been confirmed. However, due to the competition between damage development and the fibre stiffening, the increase in the longitudinal Young's modulus was noticed on the composites depending on the ratio of fibres parallel to load direction.

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Experimental investigations were conducted on flax and E-glass fibres reinforced epoxy matrix composites subjected to quasi-static loadings. Flax/epoxy samples having [0] 12 , [90] 12 , [0/90] 3S and [±45] 3S stacking sequences, with a fibre volume fraction of 43% have been tested under tension, compression and in-plane shear loadings. Overall, the compression strength of glass/epoxy was 76% greater than for the flax/epoxy composite. The damage evolution of flax/epoxy of [0/90] 3S and [±45] 3S samples has been evaluated in terms of transverse crack densities with respect to the load increment. The crack density exhibited a classical ''S'' shaped pattern for [0/90] 3S and linearly for [±45] 3S specimens versus the applied load. The final crack densities were respectively of 32/cm and 25/cm for the [0/90] 3S and [±45] 3S samples.