a1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
a2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
a3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of ∼95 wt% planar arrays of polygonal aragonite-based tablets (∼8 μm wide, ∼0.9 μm thick, stacked ∼40 nm apart) and ∼5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress σy were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, σy = 11 GPa (freshly cleaved samples) and E = 79 GPa, σy = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.
(Received January 27 2005)
(Accepted May 02 2005)
p1 Present address: Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309