Finite element modeling of banded structures in Bombyx mori silk fibres

Transmission electron microscopy studies have shown curved bands of contrast in degummed Bombyx mori fibres. This contrast implies a molecular difference between the light and dark bands, which in turn implies a periodic variation in mechanical properties along the fibre axis. Finite element modeling was used to compare the mechanical behaviour of fibres with various banded geometries. Lateral, longitudinal and diagonal lamellae were compared with V-shaped and parabolic cupped lamellae. The simulation results from the lamellar models were compared to laminar composite theory. The cupped parabolic and V-shaped geometrics both showed a redistribution of the axial stresses from the centre toward the edge of the fibre. This redistribution allowed for a substantial increase in the toughness compared to simple lateral lamella as well as a moderate increase in the initial modulus without a significant change in the yield strength.