Behavior of a silkworm silk fiber web structure under wind load

Abstract

Optimized by Nature for millions of years, silk is one of the strongest biomaterials with outstanding mechanical properties, it is both extensible and tough in order to ensure specific functions. In particular, protein-based Bombyx mori silkworm silk's stiffness is originated from the crystalline region of the semi-crystalline fibroin and the extensibility from the length hidden within the amorphous region. The silk fiber is coated with sericin which acts as a glue connecting fibers together and as a matrix in the three-dimensional nonwoven multi-layer composite structure of the cocoon. These properties can be engineered and enhanced with forced reeling silk: fast spun silks are stiffer and less extensible than slow reeled silk. For this study, two-dimensional single cocoon layer webs are created by silkworms and tested under an increasing wind load until failure, the deflections are recorded. To complement the experimental results, the web's structure is generated in two different models: straight fiber web and wavy fiber web models. Both models are studied under constant wind load for four type of fibers with different reeling speeds thus different mechanical properties. These tests indicate that the deflection increases with wind load for both the experiments and the simulations, but also that webs composed of fibers with different mechanical properties are not necessary stiffer and less extensible as the material they are composed of are stiffer and less extensible because of the high redundancy and randomness of the web structure. The divergence in results between the experiments and the simulations suggests the need to improve the models to be more in accordance with the real webs.