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标题：Fishnet model for failure probability tail of nacre-like imbricated lamellar materials
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作者：Wen Luo ; Zdeněk P. Bažant
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2017
卷号：114
期号：49
页码：12900-12905
DOI：10.1073/pnas.1714103114
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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 > 10 8 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.
关键词：failure probability ; biomimetic materials ; fracture mechanics ; strength ; size effect