TY - JOUR

T1 - Fishnet model for failure probability tail of nacre-like imbricated lamellar materials

AU - Luo, Wen

AU - Bažant, Zdeněk P.

N1 - Funding Information:
Partial financial support under Army Research Office Grant W911NF-15-1-0240 and NSF Grant N00014-11-1-0515, both to Northwestern University, is gratefully appreciated.
Funding Information:
ACKNOWLEDGMENTS. Partial financial support under Army Research Office Grant W911NF-15-1-0240 and NSF Grant N00014-11-1-0515, both to North-western University, is gratefully appreciated.
Publisher Copyright:
© 2017, National Academy of Sciences. All rights reserved.

PY - 2017/12/5

Y1 - 2017/12/5

N2 - Nacre, the iridescent material of the shells of pearl oysters and abalone, consists mostly of aragonite (a form of CaCO3), a brittle constituent of relatively low strength (≈10 MPa). Yet it has astonishing mean tensile strength (≈150 MPa) and fracture energy (≈350 to 1,240 J/m2). The reasons have recently become well understood: (i) the nanoscale thickness (≈300 nm) of nacre’s building blocks, the aragonite lamellae (or platelets), and (ii) the imbricated, or staggered, arrangement of these lamellea, bound by biopolymer layers only ≈25 nm thick, occupying <5% of volume. These properties inspire manmade biomimetic materials. For engineering applications, however, the failure probability of ≤10−6 is generally required. To guarantee it, the type of probability density function (pdf) of strength, including its tail, must be determined. This objective, not pursued previously, is hardly achievable by experiments alone, since >108 tests of specimens would be needed. Here we outline a statistical model of strength that resembles a fishnet pulled diagonally, captures the tail of pdf of strength and, importantly, allows analytical safety assessments of nacreous materials. The analysis shows that, in terms of safety, the imbricated lamellar structure provides a major additional advantage - ∼10% strength increase at tail failure probability 10−6 and a 1 to 2 orders of magnitude tail probability decrease at fixed stress. Another advantage is that a high scatter of microstructure properties diminishes the strength difference between the mean and the probability tail, compared with the weakest link model. These advantages of nacre-like materials are here justified analytically and supported by millions of Monte Carlo simulations.

AB - Nacre, the iridescent material of the shells of pearl oysters and abalone, consists mostly of aragonite (a form of CaCO3), a brittle constituent of relatively low strength (≈10 MPa). Yet it has astonishing mean tensile strength (≈150 MPa) and fracture energy (≈350 to 1,240 J/m2). The reasons have recently become well understood: (i) the nanoscale thickness (≈300 nm) of nacre’s building blocks, the aragonite lamellae (or platelets), and (ii) the imbricated, or staggered, arrangement of these lamellea, bound by biopolymer layers only ≈25 nm thick, occupying <5% of volume. These properties inspire manmade biomimetic materials. For engineering applications, however, the failure probability of ≤10−6 is generally required. To guarantee it, the type of probability density function (pdf) of strength, including its tail, must be determined. This objective, not pursued previously, is hardly achievable by experiments alone, since >108 tests of specimens would be needed. Here we outline a statistical model of strength that resembles a fishnet pulled diagonally, captures the tail of pdf of strength and, importantly, allows analytical safety assessments of nacreous materials. The analysis shows that, in terms of safety, the imbricated lamellar structure provides a major additional advantage - ∼10% strength increase at tail failure probability 10−6 and a 1 to 2 orders of magnitude tail probability decrease at fixed stress. Another advantage is that a high scatter of microstructure properties diminishes the strength difference between the mean and the probability tail, compared with the weakest link model. These advantages of nacre-like materials are here justified analytically and supported by millions of Monte Carlo simulations.

KW - Biomimetic materials

KW - Failure probability

KW - Fracture mechanics

KW - Size effect

KW - Strength

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U2 - 10.1073/pnas.1714103114

DO - 10.1073/pnas.1714103114

M3 - Article

C2 - 29180402

AN - SCOPUS:85037040193

VL - 114

SP - 12900

EP - 12905

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 49

ER -