On the nature of the stiffness of nacre

The high stiffness of the biogenic composite nacre has to be attributed to the particular microstructure consisting of mineral platelets and the interfacial organic phase. In order to understand the mechanisms being responsible the elastic properties of nacre under tensile and shear loads have been studied and numerically simulated. It is found, that the thin layer of biopolymer plays a key role for the stress distribution in the composite. Two types of mechanisms of load transfer between the mineral platelets are discussed. Their plausibility is discussed for different levels of the Poisson's ratio of the biopolymer. Finite element calculations show, that the high stiffness of nacre determined experimentally is only approached if the organic layers participate as incompressible interphase on the deformation of the composite. In addition, mineral bridges between adjacent platelets enhance the stiffness of nacre under shear and transversal tension.