This paper investigates the influence of the stress level and hygrothermal conditions on the creep/recovery behaviour of three high-grade composites made of GreenPoxy and flax and hemp fibres. The results show that the levels of instantaneous, time-delayed and residual strains increase with the applied load and the severity of the environment. The time-delayed strains of the materials are higher in the creep phase than in the recovery phase. A stiffening effect is also observed during the recovery phase. The post-creep viscoelastic properties are then identified using an anisotropic viscoelastic law from the recovery function. The relaxation time function is independent of the stress level and the environmental conditions. The viscous parameter varies with the stress level and increases substantially with severe environmental conditions. The dependence of the creep/recovery behaviour on the stress level is due to the dependence of the stiffening phenomenon and irreversible mechanisms rather than to the viscoelastic behaviour.

This study focuses on the development and mechanical testing of a quasi-unidirectional woven hemp fabric for composite applications. The fabric is designed to combine the advantages of easy handling, impregnability by resin and fiber alignment. In this sense, low twisted rovings, low crimping characteristics and a high roving density in the main direction were used. The results show that the manufacturing process proposed for this highly unbalanced woven fabric is less aggressive than that for a balanced pattern, and the effective tensile properties of the fibers are preserved. This innovative hemp fabric is also used to manufacture unidirectional and cross-ply laminated composites. The results indicate competitive properties relative to those of commercial flax-based reinforcements with rigidities similar to those of composites made with quasi-unidirectional woven fabrics, non-crimp fabrics and tapes.