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The excellent mechanical properties of nacre with high-strength and high-toughness attract great attention, the mechanism discovery and biomimetic design are carried out by many researchers. The good fracture performance of nacre is mainly attributed to its internal sophisticated 'brick-mortar' structure. In this paper, two finite element models of classic rectangular brick-mortar structure and compared hexagons structure, under three-point bending loading at micron scale, are established respectively based on the interface cohesive model of the mortar. Their different mechanical behavior and fracture mechanism are studied.

Furthermore, the three-point bending experiments of corresponding nacre samples at millimeter scale are performed to verify the simulation, and the size effect is also studied by preparing samples with a series of thickness. The results indicate the fracture modes in the experiments are in agreement with the simulation. The cracking path along the mortar interface of the rectangular structure is more tortuous than that of the hexagons structure, and the more energy is dissipated for the rectangular structure during fracture. The bending strength and fracture energy of the rectangular structure are higher than those of the hexagons structure both in the experiments and the simulation. Moreover, both the bending strength and fracture energy increase with decreasing thickness of the samples. The corresponding theoretical analysis based on size effect model can explain the results well. The work is helpful to understand the trans-scale mechanism and for optimum design of biomimetic composites.

 

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