Thickness-dependent mechanical properties of nacre in Cristaria plicata shell: Critical role of interfaces

Abstract

The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests. The results show that the mechanical behavior of nacre exhibits a strong thickness dependence. The bending strength firstly increases with the increase of specimen thickness and then becomes roughly constant as the thickness reaches a certain value of ∼2.5 mm. However, the mean value of work per unit volume increases constantly with increasing specimen thickness; meanwhile, the cracking mode changes from penetration into the platelets to deflection along the interfaces. The theoretical analyses indicate that the thickness-dependent mechanical properties of nacre are mainly caused by the variation in the number of inter-lamellar interfaces. The more the number of inter-lamellar interfaces is, the higher the strength and work of fracture of nacre under bending tests will be. However, as the number of inter-lamellar interfaces reaches a certain value (e.g., in the present specimen with 2.5 mm thickness), the strength tends to remain constant, while the work of fracture still increases. Therefore, the present research findings are expected to provide a valuable guidance for the interfacial design of nacre-like materials with high strength and toughness.