Research paper of the month
January 2012 – Poisson’s and modern materials
Poisson’s ratio is well known for measuring the resistance of a material to distort under mechanical load rather than to alter in volume. It is two centuries old, and now, with the benefit of the accumulation of measurements on new as well as traditional materials, offers a universal metric to compare their differing performance when strained elastically. This is because Poisson’s ratio falls between narrow numerical limits, whether materials are soft or stiff, in contrast to elastic moduli which are widely scattered over many decades. The invited review takes a radical look at Poisson’s ratio for the first time, not just in the way the idea has inspired new materials but also in how it has brought new insight to understanding existing ones.
The figure shows the utility of Poisson’s ratio in embracing the mechanical performance all stable materials in isotropic form (click on image to enlarge).This encompasses critical fluids, Bose Einstein condensates, cork, bone, glass, steel, dental amalgam, lead, rubber and liquids – to pick out just a few – all contained between the numerical bounds of -1 and +1/2. Poisson’s ratio n is plotted against the ratio of the bulk and shear elastic moduli, B and G, which measure respectively the responses to volume and shape change that lie at the heart of the concept. The graph sets the scene for explaining how packing and connectivity on many different length scales influence Poisson’s ratio. The narrative then leads on to reconciling overarching empirical relationships recently discovered between Poisson’s ratio and the relaxation of supercooled antecedents, and also between fracture and elasticity in the solids state – all phenomena occurring beyond the elastic limit where the ratio might not be expected to apply.
Neville Greaves, Lindsay Greer, Rod Lakes & Tanguy Rouxel, Nature Materials, published on line: 24 October 2011.
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