Mineralized biological materials such as nacre and bone achieve remarkable
combinations of stiffness and toughness through staggered arrangements of
stiff components bonded by softer materials. These natural composites are
therefore substantial source of inspiration for emerging synthetic
materials. In order to gain new insights into structureperformance
relationships of these staggered structures, nacres from four species were
compared in terms of fracture toughness and damage propagation pattern.
Fracture tests revealed that all nacres display rising crack resistance
curves, but to different extents. Using in-situ optical and atomic force
microscopy, two distinct patterns of damage propagation were identified in
columnar and sheet nacre respectively. These two different patterns were
further confirmed by means of large scale numerical models of staggered
structures. Similar mechanisms possibly operate at the smallest scales of
the microstructure of bone.