Enhanced energy of parallel fractures in nacre-like composite materials

Physique de la Matière Condensée, Collège de France 11 place Marcelin Berthelot, 75231 Paris cedex 05, France and Department of Physics, Graduate School of Humanities and Sciences Ochanomizu University - 2-1-1, Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan

Corresponding author: okumura@phys.ocha.ac.jp

Received: 28 November 2002
Accepted: 23 June 2003

Abstract

Nacre, often found inside sea shells such as oysters, has a spectacular resistance to fracture, which results from their construction out of alternating layers of soft and hard material. The fracture resistance is greatest for cracks moving perpendicular to the layers, but cracks parallel to the layers also have difficulty in progressing, and this fact has not been well explained. In this letter, we consider small parallel fractures in nacre-like material and show the possibility that the fracture energy is increased over a value due to the near-tip processes by a factor λ that is given by the ratio of short- and long-time viscoelastic moduli of the soft matter. Small cracks running along the layers take a scaling form we call a “lenticular trumpet” that has not previously been observed.