The role of water in the initial sliding of nacreous tablets: Findings from the torsional fracture of dry and hydrated nacre

Sliding Avalanches Between Nacreous Tablets

“…Nacre is a composite made from biogenic aragonite and organic matrices. The nano- and microscale brick-and-mortar structure enables nacre’s extraordinary strength and toughness, through which different toughening mechanisms are identified, including nanoscale mineral bridges, nanoasperities, protein chains, − and various microscale toughening mechanisms. , The nacreous tablets are composed of nanograins with diameters of 20–30 nm. − High-resolution transmission electron micrographs exhibited that aragonite crystals from the adjacent platelets share the same crystal orientations even though they are not connected sometimes. , Experimental observations through stress–strain curves have been obtained for the sudden breakage of mineral bridges, the initial sliding between tablet surfaces, and the unfolding of protein chains . Despite prior studies, limited research exists to elucidate how atomic interactions on nanograin surfaces evolve as nacreous tablets slide over each other.…”

“…In the linear increase stage, mineral bridges, nanoasperities, and organic matrices work together to resist the shear. Because of water, temporal stress redistribution paths are established between tablet surfaces and the more stabilized organic matrices . As the tablet slides, part of the shear resistance is transferred to the contacted nanoasperities (Figure c and Figure S2).…”

“…As the tablet slides, part of the shear resistance is transferred to the contacted nanoasperities (Figure c and Figure S2). The stress redistribution continues until all mineral bridges break and the contacted nanograins take over the entire shear resistance. Shear stress variations keep occurring intermittently until the critical sliding distance is achieved, at which the post-peak stress gradient of torsion enables cracks to propagate radially so that the nacre specimens fail catastrophically. ,,, During contact, the stress-drop rate temporarily exceeds the sliding rate imposed on the specimen, resulting in an avalanche with a certain stress drop size and slip size.…”

“… The stress redistribution continues until all mineral bridges break and the contacted nanograins take over the entire shear resistance. Shear stress variations keep occurring intermittently until the critical sliding distance is achieved, at which the post-peak stress gradient of torsion enables cracks to propagate radially so that the nacre specimens fail catastrophically. ,,, During contact, the stress-drop rate temporarily exceeds the sliding rate imposed on the specimen, resulting in an avalanche with a certain stress drop size and slip size. We measure stress drops by extracting a wide range of power laws and scaling functions using high-resolution temporal profiles, in which avalanche statistics and dynamics between sliding of hydrated nacreous tablets are identified.…”

“…11−13 High-resolution transmission electron micrographs exhibited that aragonite crystals from the adjacent platelets share the same crystal orientations even though they are not connected sometimes. 11,12 Experimental observations through stress−strain curves have been obtained for the sudden breakage of mineral bridges, 14 the initial sliding between tablet surfaces, 15 and the unfolding of protein chains. 16 Despite prior studies, limited research exists to elucidate how atomic interactions on nanograin surfaces evolve as nacreous tablets slide over each other.…”