Study On Mechanism Of Strength And Toughness Of Microstructure Of Bivalve Shell

Bivalve shell has excellent fracture strength and fracture toughness. The perfect mechanical properties are acquired from its excellent inner microstructures. The investigation on these microstructures can present the knowledge of its reinforced and toughness mechanisms, and provide beneficial guidance for designs of man-made ceramic materials or composites. The observation of scanning electron microscope shows that bivalve shell is a bio-ceramic composite consisting of thin sheets of aragonite and organic proteins. The shell possesses several typical sheet-shapes and laminated microstructures. Based on the observation, several microstructural models were built. The toughness mechanism of these microstructures was investigated based on fiber-pull-out theories, the knowledge of structural analysis and finite element method. Following conclusions were obtained.①In the microstructures of the aragonite-fiber overlapping of the shell, the overlapping ratio and length-thinness ratio of the fibers have greater influence on the composite material. The appropriate fiber-overlapping ratio and length-thinness ratio of the shell markedly improve the fracture toughness of the ceramic composite material.②The shell adopts curved aragonite sheets, and increase the length of the curved sheets and diminish its curvature radius markedly increase the pullout force of the sheets and improve the fracture toughness of the ceramic composite materials.③The shell also adopts large-end fiber in order to increase the pullout force, which enhances the fracture strength and fracture toughness of the shell.④The shell also adopts a kind of spiral structure of the aragonite fibers, which also increase the pullout force of the fibers compared to the parallel structure of the fibers, which obvious improve fracture toughness of the shell.⑤Curved aragonite sheets also are used by the shell for resisting the constringent stress compared to straight aragonite sheets, and the crisscrossing-tier structure of the shell can disperse concentrated force and reduce the internal maximal strain of the shell.Through the analysis on the microstructures of bivalve shell, the mechanism of the strength and toughness of the shell is revealed, which can provide profitable guidances for the design of man-made ceramic composites with high performance.