Experimental and numerical investigation into interlaminar toughening effect of chopped fiber-interleaved flax fiber reinforced composites

Effects of various chopped fiber (CF) interleaves, including CF type, CF length, and interleave areal density on mode I interlaminar toughening for flax fiber reinforced composites were studied via the double cantilever beam (DCB) experiment and simulation. The CF interleaved flax/epoxy composites were made by interleaving CFs randomly and uniformly in the mid-layer. A numerical model subject to the experiment was established involving the trilinear cohesive zone model (CZM) characterized by five parameters. The mode I interlaminar fracture toughness (G_IC) was furthest improved up to 2.322 kJ/m² by 80.7% using carbon CF interleave with 5 mm CF length and 25 g/m² areal density. The toughening mechanisms related to fiber bridging and flax multi-layer failure were discussed regarding different CF interleaves. Comparative analysis of numerical and experimental results revealed the quantitative relation between CZM parameters and CF interleave properties, providing guidance for designing CF interlaminar toughening.