Nanoscale Morphology and Indentation of Individual Nacre Tablets from the Gastropod Mollusc Trochus Niloticus

Abstract

The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of ∼95 wt% planar arrays of polygonal aragonite-based tablets (∼8 μm wide, ∼0.9 μm thick, stacked ∼40 nm apart) and ∼5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress σy were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, σy = 11 GPa (freshly cleaved samples) and E = 79 GPa, σy = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.

Hierarchical structure observation and nanoindentation size effect characterization for a limnetic shell

“…Simultaneously, many studies on the mechanical properties of nacre structures used the nanoindentation test [29][30][31][32][33][34]. Wang et al [29] studied a type of limnetic shell (Cristaria plicata) using the nanoindentation test and proposed several strengthening mechanisms based on their observations.…”

“…Li et al [30] investigated the mechanical properties of nacre structures for a type of red abalone by using the nanoindentation test; they measured the elastic modulus and hardness. Bruet et al [31] used the nanoindentation test to measure the average elastic modulus and hardness for the nacre structure of a Trochus niloticus shell. Katti et al [32] performed the nanoindentation test for measuring the mechanical properties of nacre platelets by using atomic force microscopy (AFM).…”

Micromechanics and Macromechanics of the Tensile Deformation of Nacre

“…Barthelat and Espinosa (2003) measured the nanoindentation properties of individual nacre tablets from Haliotis rufescens and through a comparison with finite element models suggested that the presence of intertablet organic material up to 3 layers below the tablet tested did not cause significant deviation on the elastic property of aragonite tablet measured. Bruet, et al (2005) conducted nanoindentation on individual aragonite tablets from the gastropod mollusk Trochus Niloticus and estimated a Young's modulus of ~ 90 GPa and a yield stress of ~ 10 GPa through a comparison with an elastic-perfectly plastic finite element model. AFM inspection of the indented region showed extensive pileup around the indentation zone and thus plastic deformation within the tablet; no micro/nanocracks were observed (Fig.…”

Composites, Multifunctional

“…Its high toughness is as a result of the duc tility of the organic matrix in connection with the re peated unfolding of the protein molecules. The nanostruc ture resembles a brickwork arrangement with a signifi cant overlap of the platelets and the organic matrix serv ing as the mortal [15]. This architecture is a critical fac tor that is responsible for the high fracture strength ob served in nacre [6,41].…”

“…In addition, Li et al [59] showed that the rotation of the nano-sized grain during loading is a key contributor to the high ductility. Many studies have been carried out on nacre using various experimental and modeling techniques to study its formation, its struc ture and morphology, and its deformation and properties, especially the mechanical properties [6,16,52,55,62,63,65,73,85].…”