The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


New developments in field mechanics

PETER W. LUCAS.

Bioclinical Sciences, Kuwait University

Thursday Afternoon, 200DE Add to calendar

The measurement of food material properties generally requires simultaneous monitoring of force and displacement while a specimen is loaded. The advent of the Darvell HKU portable mechanical tester about 20 years ago gave field researchers an opportunity for this on small specimens within a displacement-controlled framework. Yet some properties remain difficult to estimate with that tester, particularly via indentation, due to an inability to time loading ramps precisely. Recent developments have solved these issues by detaching force readings from increments in displacement. The result is a new range of possibilities, based largely around types of indentation. Blunt indentation is a relatively recent development in materials testing that can be applied to visco-elastic-plastic materials like soft foods. Force relaxation under a blunt probe (6 mm dia.) allows the modulus of even the ripest fruit flesh to be assessed in terms of two extremes: an instantaneous and an infinite value. The ratio of the two gives a quantitative estimate of how rate-sensitive such tissues are. The technique can also be adapted to obtain the modulus of the laminae of leaves, something not possible previously, via arranging for a blunt probe to deflect a circular portion of lamina that has been clamped evenly around its edges. This test offers insights into the mechanical behavior of leaf tissue, including the possibility that during their development, leaves transform from floppy sheets at flushing into stiff beams at maturity. This transformation has implications for primate feeding behavior, with respect to oft-stated preferences for ‘young’ leaves.

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