Modeling mechanical responses in a laminated biocomposite Part II Nonlinear responses and nuances of nanostructure

Accurate pseudo-hexagonal nanoarchitecture of nacre was used to design three dimensional finite element models of nacre, the inner layer of mollusk shells. Tensile tests were simulated introducing linear and nonlinear material properties in these models. Material parameters of components of nacre (aragonitic bricks and the complex organic phase) such as elastic modulus and hardness were obtained from bulk measurements reported in literature. In addition, nanoscale experiments conducted using atomic force microscopy and nanoindentation provided mechanical properties of aragonite platelets and organic phase. Linear simulations in the elastic regime at low stresses (2 MPa) was conducted on the new models. Our simulations indicate that a high modulus of organic phase (∼20 GPa) is necessary to obtain the experimentally obtained bulk phase elastic response of nacre. Our nanoindentation experiments also confirmed the simulations. Further nonlinear simulations were conducted under the assumption of a fully elastic behavior of aragonite and an elastoplastic model for the organic phase. Further the yield stress of the organic phase is varied over a wide range from 40 to 400 MPa. The resulting yield stress of nacre was compared to experimentally obtained value. Again ou