POISSON’S RATIO
It’s obvious that when an element is stretched linearly, it has a tendency to get thinner in the other
two directions. In simple words, the change in longitudinal and lateral strains are opposite generally opposite to each other.
Well, what is Poisson’s ratio? Denoted as ν, Poisson’s ratio is named after Simeon Poisson, which
is a measure of the tendency of both the strains acting opposite to each other. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. As most common materials become thinner in cross section on being stretched, Poisson’s ratio has a positive value for them. For a perfectly incompressible material, the Poisson’s ratio is exactly 0.5. Most basic engineering
materials have ν in the range between 0.0 and 0.5. Cork is around 0.0, most steels are about 0.3, and rubber is approximately 0.5. A Poisson’s ratio more than 0.5 can’t be managed for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material a negative volume.
Some materials, say the polymer foams, have a negative Poisson’s ratio; if these materials are
extended in one direction, they become thicker in perpendicular directions. Foams with negative Poisson’s ratios were made from conventional low-density open-cell polymer foams by causing the ribs of each cell to permanently extend inward, ensuing in a re-entrant structure. http://crbtech.in/Student-Reviews/Mechanical-Reviews
An example of the practical application of a particular value of Poisson’s ratio is the cork of a
beer bottle. The cork should be easily inserted and removed, moreover, it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, can’t be used for the same purpose because it would expand when compressed into the neck of the bottle and would jam the mouth. Cork, which has a Poisson’s ratio of nearly zero, is ideal for this application.
It is supposed that re-entrant foams can be used in such utilities as sponges,robust shock
absorbing material, air filters, and fasteners. Negative Poisson’s ratio materials can undergo slow decay of stress according to Saint-Venant’s principle. These materials are called anti-rubber, auxetics or dilatational and are an example of extreme materials. So we conclude here. If you want to do mechanical engineering courses in Pune , then our CRB Tech a name in this
field for you to consider and upskill yourself in CAD/CAM programs and continue your career. Our CAE training center provides the best career in the field of mechanical through our
mechanical engineering internships. http://crbtech.in/Student-Reviews/Mechanical-Reviews
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