Peculiar Tensile and Fracture Behaviors of Natural Silk Fiber in the Presence of an Artificial Notch

Abstract

Natural silk fibers achieve remarkable toughness by exploiting hierarchical structure organizations over many length scales. These hierarchical architectures are often decorated with defects that usually lead to catastrophic failure of artificial polymer materials. Silk fibers are self-tolerant of intrinsic/artificial defects to give surprising fracture toughness, but how they fulfill this function and the underlying mechanism remain elusive. Here, we unveil this puzzle by experimentally and theoretically investigating the tensile and facture behaviors of Antheraea pernyi (A. pernyi) silk monofilaments containing an artificial notch of controlled depth. The introduced transverse notch can be blunted effectively by ahead developed longitudinal crack through fibrillar separation. The notched silk fibers show ductile failure with tensile behavior dominated by the magnitude of longitudinal crack, which depends not only on the notch size but also on the interface interaction between nanofibrils. We propose that the highly oriented, disentangled nanofibrillar structure of A. pernyi silk offers it distinct tensile properties, path of crack propagation, and fracture mode in comparison with highly oriented synthetic fibers.