Estimation of the Fracture Toughness of Leaves

Lucas, Peter W.; Pereira, Barry P.

doi:10.2307/2389448

Cited by 115 publications

(72 citation statements)

References 8 publications

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“…Toughness tests were carried out using instrumented scissors (Lucas & Pereira, 1990). Tests were designed to measure minimal toughness, so main veins were avoided as far as possible and leaf margins were excised.…”

Section: Methodsmentioning

confidence: 99%

Leaf fracture toughness and sclerophylly: their correlations and ecological implications

et al. 1992

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SUMMARYThe fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measured along a 'least tough' path using an instrumented cutting technique. Punch-and-die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration x 6-25) and the ratio of the two, the index of sclerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty-seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils).There was a highly significant positive correlation between fracture toughness and index of sclerophylly for the 42 species (R^ = 0 43, P < OOOl) brought about largely by a high correlation between toughness and crude fibre content. Fracture toughness was not correlated with lamina tissue dorsi-ventral thickness but high toughness was clearly associated with the presence of sclerenchyma bundle sheaths and sheath extensions. Analysis of the fracture path for 26 leaves of ten mangrove species showed a high correlation between the area fraction occupied by veins and fracture toughness if one species, Avicennia rumphiana, was excluded. The regression equation for the other nine species gave estimates of the fracture toughness of vein tissue and lamina matrix of 6053 and 327 J m~r espectively. Punch-and-die test results only correlated well with the cutting tests when values were divided by lamina thickness.The ratio of protein to fibre in a leaf (the reciprocal of the index of sclerophylly) has been established as a good predictor of leaf palatability and digestibility to generalist chewing folivores. The high correlation between fracture toughness and the index of sclerophylly for a large sample suggests that leaf toughness could be the factor used as a proximate cue for determining food quality in herbivore foraging strategies.

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Section: Methodsmentioning

confidence: 99%

Leaf fracture toughness and sclerophylly: their correlations and ecological implications

et al. 1992

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“…Cutting tests for estimating the fracture properties of plant and animal tissue (Eichhorn et al, 2007;Farren et al, 2004;Lucas and Pereira, 1990;Vincent, 1992) have usually involved placing a pair of scissors between the platform and the crosshead of a universal testing machine, and recording the work done to fracture or cut a specimen. The main limitation of this technique is that the frictional forces generated during the closing of the blades are not constant, thereby increasing the variability of the data .…”

Section: Clipper Cutting Testsmentioning

confidence: 99%

The effect of humidity on the fracture properties of human fingernails

Farran

Ennos²,

Eichhorn

2008

Journal of Experimental Biology

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SUMMARYFingernails are a characteristic anatomical feature of primates and their function is dictated by the environment in which they are utilised. The present study examined the mechanical properties of human fingernails as a function of relative humidity (RH) and the subsequent moisture content of the nail material. Nail clippings were stored at a range of RH values and then weighed in order to determine their moisture content. There was a non-linear relationship between the moisture content of nails and the RH of their local environment. The in vivo moisture content of nails, measured from 55% to 80% RH, was between 14% and 30%, similar to other keratinous materials such as claws, hooves and feathers. Cutting tests on the nail samples showed that the work of fracture was between 11 and 22 kJ m -2 , rising to a peak at 55% RH and falling at higher and lower humidities. At all RH values there was anisotropy within the nail between the proximal and lateral directions, the work of fracture being greater proximally. This anisotropy was greatest at 55% RH, at which point the proximal work of fracture was double the lateral value. These results suggest that the mechanical behaviour of human fingernails is optimised at in vivo conditions; they resist tearing most strongly under these conditions and particularly resist tearing into the nail bed. At more extreme humidity levels the fracture properties of the nail deteriorate; they are brittle when fully dry and fracture and split when wet.

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“…The scissor cutting tests were similar to those devised by Lucas and Pereira (1990), and widely used since to investigate the toughness of leaves and other plant tissues (Wright and Illius, 1995;Choong, 1996;Lucas et al, 1997Lucas et al, , 2000. A pair of precision scissors (Radio Spares model 539-609, Corby, UK) was mounted on the lower platform of a model 4301 universal testing machine (Instron, High Wycombe, UK), with its downward-pointing blade held rigid.…”

Section: Scissor Cutting Tests On Whole Nailsmentioning

confidence: 99%

The fracture properties and mechanical design of human fingernails

Farren

Shayler

Ennos

2004

Journal of Experimental Biology

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Fingernails are a characteristic feature of primates, and are composed of three layers of the fibrous composite keratin. This study examined the structure and fracture properties of human fingernails to determine how they resist bending forces while preventing fractures running longitudinally into the nail bed. Nail clippings were first torn manually to examine the preferred crack direction. Next, scissor cutting tests were carried out to compare the fracture toughness of central and outer areas in both the transverse and longitudinal direction. The fracture toughness of each of the three isolated layers was also measured in this way to determine their relative contributions to the toughness. Finally, the structure was examined by carrying out scanning electron microscopy of free fracture surfaces and polarized light microscopy of nail sections.When nails were torn, cracks were always diverted transversely, parallel to the free edge of the nail. Cutting tests showed that this occurred because the energy to cut nails transversely, at approximately 3·kJ·m -2 , was about half that needed (approx. 6·kJ·m -2 ) to cut them longitudinally. This anisotropy was imparted by the thick intermediate layer, which comprises long, narrow cells that are oriented transversely; the energy needed to cut this layer transversely was only a quarter of that needed to cut it longitudinally. In contrast the tile-like cells in the thinner dorsal and ventral layers showed isotropic behaviour. They probably act to increase the nail's bending strength, and as they wrap around the edge of the nail, they also help prevent cracks from forming. These results cast light on the mechanical behaviour and care of fingernails.

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Estimation of the Fracture Toughness of Leaves

Cited by 115 publications

References 8 publications

Leaf fracture toughness and sclerophylly: their correlations and ecological implications

Leaf fracture toughness and sclerophylly: their correlations and ecological implications

The effect of humidity on the fracture properties of human fingernails

The fracture properties and mechanical design of human fingernails

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