TY - JOUR

T1 - Lower hardness than strength

T2 - The auxetic composite microstructure of limpet tooth

AU - Wurmshuber, Michael

AU - Wilmers, Jana

AU - Kim, Jongil

AU - Oh, Sang Ho

AU - Bargmann, Swantje

AU - Kiener, Daniel

N1 - Publisher Copyright: © 2023

PY - 2023/4/29

Y1 - 2023/4/29

N2 - The limpet tooth is widely recognized as nature's strongest material, with reported strength values up to 6.5 GPa. Recently, microscale auxeticity has been discovered in the leading part of the tooth, providing a possible explanation for this extreme strength. Utilizing micromechanical experiments, we find hardness values in nanoindentation that are lower than the respective strength observed in micropillar compression tests. Using micromechanical modeling, we show that this unique behavior is a result of local tensile strains during indentation, originating from the microscale auxeticity. As the limpet tooth lacks ductility, these tensile strains lead to microdamage in the auxetic regions of the microstructure. Consequently, indentation with a sharp indenter always probes a damaged version of the material, explaining the lower hardness and modulus values gained from nanoindentation. Micropillar tests were found to be mostly insensitive to such microdamage due to the lower applied strain and are therefore the suggested method for characterizing auxetic nanocomposites.

AB - The limpet tooth is widely recognized as nature's strongest material, with reported strength values up to 6.5 GPa. Recently, microscale auxeticity has been discovered in the leading part of the tooth, providing a possible explanation for this extreme strength. Utilizing micromechanical experiments, we find hardness values in nanoindentation that are lower than the respective strength observed in micropillar compression tests. Using micromechanical modeling, we show that this unique behavior is a result of local tensile strains during indentation, originating from the microscale auxeticity. As the limpet tooth lacks ductility, these tensile strains lead to microdamage in the auxetic regions of the microstructure. Consequently, indentation with a sharp indenter always probes a damaged version of the material, explaining the lower hardness and modulus values gained from nanoindentation. Micropillar tests were found to be mostly insensitive to such microdamage due to the lower applied strain and are therefore the suggested method for characterizing auxetic nanocomposites.

UR - http://www.scopus.com/inward/record.url?scp=85158029848&partnerID=8YFLogxK

U2 - 10.1016/j.actbio.2023.04.035

DO - 10.1016/j.actbio.2023.04.035

M3 - Article

VL - 2023

SP - 447

EP - 453

JO - Acta biomaterialia

JF - Acta biomaterialia

SN - 1742-7061

IS - 166

ER -