Toughening mechanisms in bioinspired multilayered materials

Abstract

Outstanding mechanical properties of biological multilayered materials are strongly influenced by nanoscale features in their structure. In this study, mechanical behaviour and toughening mechanisms of abalone nacre-inspired multilayered materials are explored. In nacre's structure, the organic matrix, pillars and the roughness of the aragonite platelets play important roles in its overall mechanical performance. A micromechanical model for multilayered biological materials is proposed to simulate their mechanical deformation and toughening mechanisms. The fundamental hypothesis of the model is the inclusion of nanoscale pillars with near theoretical strength (s th E/30). It is also assumed that pillars and asperities confine the organic matrix to the proximity of the platelets, and, hence, increase their stiffness, since it has been previously shown that the organic matrix behaves more stiffly in the proximity of mineral platelets. The modelling results are in excellent agreement with the available experimental data for abalone nacre. The results demonstrate that the aragonite platelets, pillars and organic matrix synergistically affect the stiffness of nacre, and the pillars significantly contribute to the mechanical performance of nacre. It is also shown that the roughness induced interactions between the organic matrix and aragonite platelet, represented in the model by asperity elements, play a key role in strength and toughness of abalone nacre. The highly nonlinear behaviour of the proposed multilayered material is the result of distributed deformation in the nacre-like structure due to the existence of nano-asperities and nanopillars with near theoretical strength. Finally, tensile toughness is studied as a function of the components in the microstructure of nacre.

Role of the polymer phase in the mechanics of nacre-like composites

“…However, numerical simulations to determine the properties of the organic phase remain ambiguous. Commonly, the calculated elastic modulus ranges from one to several GPa, which is much closer to the experimental value of the dried matrix than to its natural humid form (Askarinejad and Rahbar, 2015;Bezares et al, 2010;Katti and Katti, 2001;.…”

Finite Element Analysis as a Method to Study Molluscan Shell Mechanics

“…Modulus values were calculated from the FEA by fitting to the Hertz contact model resulting in an elastic modulus of aragonite of 116 GPa, while the elastic modulus of the organic layer was calculated at 40 GPa . This value for the organic layer is much higher than previous measurements and estimations of the stiffness of the organic layer, which have been measured at: 2.84 ± 0.27 GPa, around 4.0 GPa, and 6.3 GPa . One attempt to reconcile this discrepancy by Xu et al used direct measurements of the organic phase through atomic force microscopy and inverse FEA.…”

“…Mineral bridges are thin mineral structures that connect tablets across the organic layer and have been implicated in the initiation of growth of new tablets . Mineral bridges tend to be concentrated towards the center of the tablets, can help reinforce the organic interface and central region of the tablet to prevent separation …”

Computational modeling of interfacial behaviors in nanocomposite materials

“…According to the material properties of aragonite crystal reported in the literatures (Askarinejad and Rahbar, 2015; Barthelat et al, 2006; Hrabanková et al, 2013; Zhang and Chen, 2013), the material properties of CaCO. were set to be: Young’s modulus E = 100GPa, Poisson’s ratio, mineral density ρ=3,190 kg/m 3 .…”