Dynamic mechanical loss in keratin at low temperatures

Druhala, M.; Feughelman, M.

doi:10.1007/bf01387962

Cited by 27 publications

(5 citation statements)

References 16 publications

(9 reference statements)

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“…The strain limit of covalent bond stretching (after that molecular fracture occurs) in a single tropocollagen molecule is 0.5 [35]. This is consistent with macroscopic tensile stress-strain measurements on protein tissues such as horn (mainly keratin), tendon and ligament (mainly collagen), where the tensile strain limit is usually 0.5 or less [36][37][38]. The above calculated values are much higher than this elastic limit of 0.5.…”

Section: Non-linear Extension Of Protein Layerssupporting

confidence: 86%

Size-dependent elastic/inelastic behavior of enamel over millimeter and nanometer length scales

et al. 2010

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The microstructure of enamel like most biological tissues has a hierarchical structure which determines their mechanical behavior. However, current studies of the mechanical behavior of enamel lack a systematic investigation of these hierarchical length scales. In this study, we performed macroscopic uni-axial compression tests and the spherical indentation with different indenter radii to probe enamel's elastic/inelastic transition over four hierarchical length scales, namely: 'bulk enamel' (mm), 'multiple-rod' (10's microm), 'intra-rod' (100's nm with multiple crystallites) and finally 'single-crystallite' (10's nm with an area of approximately one hydroxyapatite crystallite). The enamel's elastic/inelastic transitions were observed at 0.4-17 GPa depending on the length scale and were compared with the values of synthetic hydroxyapatite crystallites. The elastic limit of a material is important as it provides insights into the deformability of the material before fracture. At the smallest investigated length scale (contact radius approximately 20 nm), elastic limit is followed by plastic deformation. At the largest investigated length scale (contact size approximately 2 mm), only elastic then micro-crack induced response was observed. A map of elastic/inelastic regions of enamel from millimeter to nanometer length scale is presented. Possible underlying mechanisms are also discussed.

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Section: Non-linear Extension Of Protein Layerssupporting

confidence: 86%

Size-dependent elastic/inelastic behavior of enamel over millimeter and nanometer length scales

et al. 2010

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“…The dynamic mechanical properties of a-keratin have been investigated in human stratum corneum [30], horse hair [31], and wool [14]. There is a strong correlation between the humidity/water content and the viscoelastic property values.…”

Section: Resultsmentioning

confidence: 98%

Effects of humidity on the mechanical properties of gecko setae

et al. 2011

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“…An up to 10µm long zone means that multiple crystallite nanofibers or even multiple enamel rods are included in the inelastic process and the bridging stress is not only caused by protein bridging alone. Experimental studies showed that the ultimate stress of proteins such as ligaments (mainly collagen), tendon (mainly collagen) and horn (mainly keratin) are 2.5-7MPa, 70MPa and 260MPa respectively (Sikoryn and Hukins, 1990;Bigliana et al, 1992, Meyers et al, 2008Druhala and Feughelman, 1974) and are generally lower than the calculated 163-770MPa Secondly, the stress intensity shielding contributed by the protein bridging can be estimated by using a Dugdale-zone model, K p =2*σ p *f p *(2*l p /π) 0.5 with K p the stress intensity due to protein bridging, σ p =2.5-260MPa the yield strength of protein, f p =0.1 the area fraction of protein bridging ligaments (estimated based on the volume fraction of protein in enamel), l p =1-10µm the protein bridging zone length (Evans and McMeeking, 1986). K p is calculated as 0-0.13MPa.m 0.5 and is much smaller than the crack tip toughness.…”

Section: Discussionmentioning

confidence: 99%

Sub-10-micrometer toughening and crack tip toughness of dental enamel

Ang

Schulz

Fernandes

et al. 2011

Journal of the Mechanical Behavior of Biomedical Materials

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In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip toughness (K I0, K III0 ), the crack closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K I0 of cracks along enamel rod boundaries and across enamel rods exhibit similar range of values: K I0,Ir =0.5-1.6MPa.m 0.5 (based on Irwin's 'nearfield' solution) and K I0,cz =0.8-1.5MPa.m 0.5 (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K III0,Ir was computed as 0.02-0.15MPa.m 0.5 . The crack-closure stress at the crack tip was computed as 163-770MPa with a cohesive zone length and width 1.6-10.1µm and 24-44nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro-and nanometer scale) as well as microcracks were identified.

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Dynamic mechanical loss in keratin at low temperatures

Cited by 27 publications

References 16 publications

Size-dependent elastic/inelastic behavior of enamel over millimeter and nanometer length scales

Size-dependent elastic/inelastic behavior of enamel over millimeter and nanometer length scales

Effects of humidity on the mechanical properties of gecko setae

Sub-10-micrometer toughening and crack tip toughness of dental enamel

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