Why poission ratio is between 5 and -5?

Answer 1

10

Answer 2

Poisson ratio for all materials lies between -1 and +.5, with most between 0 ( like cork) and 0.5 ( like rubber). It cannot be greater than 0.5 as that is the limit of being incompressible, no change in volume. If greater than 0.5, volume would decrease in tension which is unlikely to ever occur.

If poisson ratio is 0, that is max volume change; when axially put in tension it does not change its dimension in the lateral direction and increases in volume..

If less than zero, to theoretical -1, it actually bulges out laterally ( in tension) in the opposite direction you would expect, increasing its volume further (it gets longer and fatter). Such materials are rare but have been developed.