Sliding Avalanches Between Nacreous Tablets

Abstract

Nacre, also known as mother of pearl, possesses extraordinary mechanical properties resulting from its intriguing hierarchical brick-and-mortar microstructures. Despite prior studies, interactions between nanoasperities during sliding still need to be elucidated. In this study, we measure slip events between nanograins of microlayers at high temporal resolution during torsion-induced sliding. We model the slips as avalanches caused by interactions of atoms on nanograin surfaces, from which power laws and scaling functions describing statistics and dynamics of slip events are studied. The largest avalanche occurs when nanograins leave each other after the maximum contact. The agreement between measurements and predictions shows that avalanches act essentially in the inhomogeneous sliding of nacreous tablets. Further insights into nanofriction provided in this work may lead to the development of nanoscale tribological systems.

Interfacial Mechanical Behavior in Nacre of Red Abalone and Other Shells: A Review

“…Before the specimen fails, the shear stresses increase linearly from zero in the center to the maximum on the outer surface because of the transversely isotropy of nacreous microstructure. 13,56,87,88 The shear stress in torsion is described by…”

“…102−106 In addition, large stress gradients along the radius drove the cracks so quickly that there was little chance to trigger microscale toughening mechanisms resulting from tablet sliding. 13,56,87,88 While excellent work has been achieved using in situ SEM or TEM to probe the mechanical properties of individual tablets, research on the intertablet properties is limited, maybe because it is difficult to handle the tiny intertablet space and preserve the original microstructures of nacre. 107 Furthermore, it will trigger the tablet sliding mechanisms in mode II condition such as in tension, compression, bending, or direct shear.…”

“…Even though the vertical spacing between tablets is limited (∼30 nm), the tests successfully exposed interfacial connections between nacreous tablets to continuous shear planes (Figure ). Before the specimen fails, the shear stresses increase linearly from zero in the center to the maximum on the outer surface because of the transversely isotropy of nacreous microstructure. ,,, The shear stress in torsion is described by Where τ is the shear stress on the horizontal plane of the gauge section, T is the torque, r is the gauge section radius, ρ is the distance between an arbitrary point on the cross section to the center varying from 0 to r , J = 0.5π r 4 is the polar moment of inertia. In Figure , τ b represents the shear stress distribution before the specimen failure.…”

“…A high temporal resolution system (∼100 kHz sampling rate) was created to probe the interfacial behavior of nacreous materials, ,,, via which the minute variations between nacreous interfaces during sliding were recorded. For dry nacre under torsion, the measured shear strength was 45.2 ± 16.0 MPa at 2.0 ± 0.8% shear strain of failure.…”

“…Profiles are averaged over avalanches with similar durations T . Images reproduced with permission from ref . Copyright 2020 American Chemical Society.…”