Stiffening effect of fatigue and creep loading in unidirectional flax fibre/epoxy composites

A study related to the fatigue behaviour of natural fibre composites was conducted to expand their industrial applications. Unidirectional flax/epoxy composites were fabricated, and their fatigue and creep behaviour was investigated by applying a range of different testing conditions. Stiffness was found to increase during fatigue loading, and this was accompanied by accumulation of residual strain.

By arranging the results in a stiffness-strain diagram, a linear trend was established with a positive slope representing the stiffening effect. A similar linear trend was obtained for creep loading, however, with a larger stiffening effect. For fatigue loading, the stiffening effect was found to be changed by the applied cycle frequency.

The combined findings in the study suggest that stiffness change in the composites is reflecting a balance between stiffening due to residual strain, and softening due to fatigue damaging.