Fracture Toughness and Interfacial Design of a Biological Fiber‐Matrix Ceramic Composite in Sea Urchin Teeth

The working zone of a sea urchin tooth is a ceramic‐fiber‐reinforced ceramic‐matrix composite. It is composed of reinforcing calcitic fibers, a matrix of high‐magnesium‐containing calcite crystals, and organic material. It is much harder and tougher than most other calcitic materials. Fracture toughness and microhardness have been studied using microindentation. A comparison of fracture morphologies between intact teeth and teeth from which the organic component has been removed reveals that the thin organic sheath at the fiber/matrix boundary has an important contribution to the fiber pull‐out fracture behavior and, hence, to the toughness of the teeth.