Toughening Materials by Exploiting Soft-Hard Combination : From Nacre to Spider Webs

Abstract

Tough materials found in nature tend to have characteristic internal structures. For example, nacre which covers the surface of pearl possesses a layered structure composed of soft and hard elements. Nacre is not only beautiful but also strong! We review here a simple view on the toughening mechanism of nacre, together with that of spider webs which are also made up of soft and hard elements, i.e., hard radial threads and soft spiral threads. We begin our discussion with a review on the standard fracture mechanics, putting stress on dimensional analysis.