Microstructure-Related Mechanical Properties of Nacre in Pinctada Shell

Biological materials with various outstanding properties have been studied for a long time by investigators.As a kind of natural biological material,sea shells exhibiting the complexity and unique architectures have drawn much attention in recent years.In the present work,Pinctada shell was selected as the target material,and its

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

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∼2.5mm.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 2.5mm 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.

A high-strength and high-toughness nacreous structure in a deep-sea Nautilus shell:Critical role of platelet geometry and organic matrix

To explore the differences in mechanical behavior of nacre between shells that live in different water depths,the microstructures,phase composition and related mechanical properties of nacre under indentation,three-point bending and shear tests in deep-sea Nautilus and freshwater Cristaria plicata shells were systematically investigated.It is found that the nacreous structure in Nautilus shell exhibits an outstanding combination of high strength and high toughness compared with that in C.plicata shell,attributing to its larger aspect ratio of platelet and interfacial shear resistance.Specifically,the interfacial resistance is mainly generated from the adhesion of organic matrix and friction caused by nano-asperities on platelet surfaces.According to the interfacial resistance model,the stiction force originated from organic matrix adhesion is sensitive to its content,and the friction force produced by nano-asperities presents a positive correlation with their distribution density and dimension.Hence,the higher content of organic matrix of nacre with denser and larger nano-asperities on platelet surfaces in Nautilus shell contributes to a higher interfacial resistance.Therefore,it is the coupled effects of platelet geometries(i.e.aspect ratio and nano-asperity)and organic matrix that result in the high-strength and high-toughness nacreous structure in Nautilus shell,which is thus more conductive to inhabit in the deep sea with extremely high pressure.The present research findings are expected to provide beneficial references for the design of strong and tough nacre-inspired materials with appropriate platelet geometry and content of soft phase.