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Link to original content: https://pubmed.ncbi.nlm.nih.gov/31645557
Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell - PubMed Skip to main page content
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. 2019 Oct 23;10(1):4822.
doi: 10.1038/s41467-019-12743-z.

Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell

Jiseok Gim  1 , Noah Schnitzer  1 , Laura M Otter  2 , Yuchi Cui  1 , Sébastien Motreuil  3 , Frédéric Marin  3 , Stephan E Wolf  4   5 , Dorrit E Jacob  2 , Amit Misra  1 , Robert Hovden  6   7
Affiliations

Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell

Jiseok Gim et al. Nat Commun. .

Abstract

The combination of soft nanoscale organic components with inorganic nanograins hierarchically designed by natural organisms results in highly ductile structural materials that can withstand mechanical impact and exhibit high resilience on the macro- and nano-scale. Our investigation of nacre deformation reveals the underlying nanomechanics that govern the structural resilience and absorption of mechanical energy. Using high-resolution scanning/transmission electron microscopy (S/TEM) combined with in situ indentation, we observe nanoscale recovery of heavily deformed nacre that restores its mechanical strength on external stimuli up to 80% of its yield strength. Under compression, nacre undergoes deformation of nanograins and non-destructive locking across organic interfaces such that adjacent inorganic tablets structurally join. The locked tablets respond to strain as a continuous material, yet the organic boundaries between them still restrict crack propagation. Remarkably, the completely locked interface recovers its original morphology without any noticeable deformation after compressive contact stresses as large as 1.2 GPa.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Highly deformed and recovered nacre. a Schematic of the inner shell surface of the bivalve mollusk P. nobilis, with the investigated area marked by a purple square. b HAADF STEM overview image of cross-sectional interface of nacre tablets before compression. c High-resolution STEM image of two tablets and their organic interface before compression. d Tablets heavily interlocked under 40 µN compressive load. e After indenter is retracted, tablets and organic interface have fully recovered their initial morphology. Insets show the movement of organic inclusions due to the deformation of the tablet and their complete recovery after removing the compressive load
Fig. 2
Fig. 2
Strain propagation confined by organic interfaces. a, b Bright-field TEM (with contrast inverted) on the cross-sectional nacreous region under low and high compressive contact stresses. Under low compressive stress, intra-tablet strain contours are generated, and strain propagates independently along each tablet. As the compressive stress is increased, nacre tablets interlock and larger inter-tablet strain contours propagate diagonally between tablets. c Tablet strain attenuation along the axis of the indentation source. The linear strain dissipation behavior indicates that the deformability of nacre is weakened as the applied stress is increased. Scale bar 200 nm
Fig. 3
Fig. 3
Recoverable mechanical strength of nacre and crack blunting within and between tablets. a Nine consecutive in situ TEM compression tests on the same nacreous tablet. Three different colors correspond to different contact areas during the series of the compressions. Stage drift caused changes to contact area between indentations. b ADF STEM images after the series of the indentation tests showing a crack blunted by an organic boundary. c ADF STEM image shows crack formed within tablet and blunted by an organic inclusion. d, e ADF STEM images of nacre tablet compressed by 47 µN (55% of σYield), corresponding to the non-linear elastic regime; structure remains fully recoverable—after deformation, nacre still preserves both its initial strength and structure. f Strength and elastic modulus of nacre from contact stress in nanoindentation on the thin cross-sectional specimen in this study and various types of testing—microscale tribology, tensile, compression, and bending—on bulk specimens in previous reports. Scale bar 50 nm
Fig. 4
Fig. 4
Toughening processes of nacre, prismatic calcite, and monolithic aragonite. a–c Bright-field TEM images of the cross-sectional nacreous region during in situ TEM indentation. The nacreous tablets made contact on the side of the tip (tip diameter: ~100 nm). Inset in c shows crack blunting at the organic interface. d–f Bright-field TEM images of the cross-sectional prismatic calcite region during indentation. g–i Bright-field TEM images of non-biogenic, monolithic aragonite during indentation. j Correlative compressive contact stress vs. displacement curve showing mechanical response of the nacreous, prismatic, and monolithic region. Stress herein is engineering stress calculated by dividing load by cross-sectional area contacted with tip. Total energy dissipation values (area under contact stress–displacement curves) marked. k Triboindentation on bulk specimens of nacre, prismatic calcite, and monolithic aragonite. Videos provided as Supplementary Material. (See Supplementary Movies 2, 3, and 4)
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