Fatigue fracture of mother-of-pearl and its significance for predatory techniques



Specimens of nacre from the pearl oyster Pinctada margaritifera were loaded in bending to various fractions of the load needed to cause fracture. For a small number of cycles, less than about 1000, no changes in compliance or strength were found if the load was less than about 60% of the load necessary to cause failure. Above this fraction the compliance increased, the strength usually decreased but occasionally increased.

We conclude that, because the loading of a shell by a predator is likely to be far less controlled than loading by a machine, causing a shell to break by fatigue fracture is unlikely to be a tactic employed by a predator, though it may happen fortuitously.