A Method of Measuring Poisson's Ratio of Fibers1

An apparatus is described whereby Poisson's ratio may be measured for fibers whose diameter is approximately 250μ. The apparatus is used in conjunction with an Instron Testing Machine so that stress vs. strain measurements can be made at the same time Poisson's ratio vs. strain measurements are made. The measurements can be made statically or on fibers undergoing a constant rate of extension. Measurements on four different tilaments of drawn nylon 66 gave (above 1% strain) a constant value of 0.392 ± 0.025 for Poisson's ratio. (An extension rate of 0.02 in min. and an initial gauge length of about 40 cm. were used.) In general there is an increase of Poisson's ratio starting with about 0.34 at low strains and increasing to a final value of 0.392 at about 1% strain. Concurrent with the change in Poisson's ratio there is a change in the tangent modulus of the stress-strain curve.