FRACTURE MECHANISMS OF THE STROMBUS-GIGAS CONCH SHELL - IMPLICATIONS FOR THE DESIGN OF BRITTLE LAMINATES

Flexural strength, crack-density evolution, work of fracture, and crit ical strain energy release rates were measured for wet and dry specime ns of the Strombus gigas conch shell. This shell has a crossed-lamella r microarchitecture, which is layered at five distinct length scales a nd can be considered a form of ceramic ''plywood''. The shell has a pa rticularly high ceramic (mineral) content (99.9 wt%), yet achieves unu sually good mechanical performance. Even though the strengths are mode st (of the order 100 MPa), the laminated structure has a large strain to fracture, and a correspondingly large work of fracture, up to 13 kJ m(-2). The large fracture resistance is correlated to the extensive m icrocracking that occurs along the numerous interfaces within the shel l microstructure. Implications of this impressive work of fracture for design of brittle laminates are considered.