Model of the mechanical response of short flax fiber reinforced polymer matrix composites

Natural-fiber-reinforced short-fiber composites are finding more applications lately, therefore there is a need for estimation of the mechanical properties of such composites based on the properties of the constituents. The fibers themselves also possess complicated internal structure, resulting in anisotropy of their properties. Taking into account the internal structure of bast fiber, we evaluate the elastic properties of a composite unit cell, consisting of a fiber of average length and matrix according to the fiber volume fraction in the composite. The unit cell properties are used to estimate the stiffness of a misaligned short-fiber composite by means of orientation averaging. The results obtained are compared with the experimental stress-strain diagrams of short flax fiber/polypropylene matrix composite. Usually the mechanical response of short-fiber/polymer matrix composite is non-linear due to the inelastic matrix behavior. Accounting for the non-linear deformation of the matrix in the unit cell by modeling it as an elastic-plastic material, we also estimate its non-linear response under uniaxial loading.