Measurement of Poisson's ratio using Newton's rings

A simple optical method of measuring Poisson's ratio is reported. It is most applicable to polymer spheres in circumstances where conventional nondestructive testing is not possible. The method relies on the use of microscopic investigations of Newton's rings to measure the radius of the Hertzian contact between the test sample and a flat glass plate. Measurement over a range of loads gives an estimate of Poisson's ratio provided that Young's modulus is known for the sample.