Modeling microarchitecture and mechanical behavior of nacre using 3D finite element techniques - Part I - Elastic properties

Three dimensional finite element models of nacre were constructed based on reported microstructural studies on the 'brick and mortar' micro-architectu re of nacre. 3D eight noded isoparametric brick elements were used to desig n the microarchitecture of nacre. Tensile tests were simulated using this m odel. The tests were conducted at low stresses of 2 MPa which occur well wi thin the elastic regime of nacre and thus effects related to locus and exte nt of damage were ignored. Our simulations show that using the reported val ues of elastic moduli of organic (0.005 GPa) and aragonitic platelets (205 GPa), the displacements observed in nacre are extremely large and correspon d to a very low modulus of 0.011 GPa. The reported elastic modulus of nacre is of the order of 50 GPa. The reason for this inconsistency may arise fro m two possibilities. Firstly, the organic layer due to its multilayered str ucture is possibly composed of distinct layers of different elastic moduli. The continuously changing elastic modulus within the organic layer may app roach modulus of aragonite near the organic-inorganic interface. Simulation s using variable elastic moduli for the organic phase suggest that an elast ic modulus of 15 GPa is consistent with the observed elastic behavior of na cre. Another explanation for the observed higher elastic modulus may arise from localized platelet-platelet contact. Since the observed modulus of nac re lies within the above two extremes (i.e. 15 GPa and 205 GPa) it is sugge sted that a combination of the two possibilities, i.e. a higher modulus of the organic phase near the organic-inorganic interface and localized platel et-platelet contact can result in the observed elastic properties of nacre. (C) 2001 Kluwer Academic Publishers.