The critical role of size effect on internal damage and mechanical properties of flax fiber reinforced composites

The effect of the size on the strength of laminated artificial fiber reinforced composites has been extensive discussed during the design of large composites structure. With the trial as the structures in aerospace, civil engineering, automobile industry, the scaling of the properties of plant fiber reinforced composite should be studied. In this paper, the size effect and failure mechanism of tensile and impact properties of flax fiber reinforced composites were valuated. The effects of different area, thickness and volume on the tensile properties of composites were explored. Additionally, the failure mechanism of size effect on tensile specimens was proposed through the damage morphologies of composites. It is found that the twist of fiber bundle plays an important role in the size effect of composite thickness. Besides, the relationship between impact properties and size effect of composites was conducted, including the size of hammer, different impact energy and sample size. The curves of different types of impact samples were normalized to verify the linear rule in response stage. The crack length after impact was measured and the size effect of crack length was discussed. The size effect of crack area was studied by calculating the crack area with ultrasonic C-scan. Different "size effects" between flax fibers and artificial fibers were explored. The results are expected to provide a theoretical basis for the structural design of plant fiber reinforced composites.