Poison Ratio and Area reduction of materials

Poison ratio is the measure of poison effect which describes the expansion or contraction of a material in direction perpendicular to the direction of loading. When we apply stress longitudinally  to any material (Copper/Aluminium) it deforms the material. Any stress in longitudinal will result change in lateral axis of that material. Suppose we take a wire with diameter "D" and apply longitudnal stress on it. Longitudnal stress will results in longitudnal strain. The new diameter of wire will be "d". Now to find the reduction in diamter from "D" to "d" we use poison ratio. According to poison ratio

An area reduction of 22-22 % for copper and 26% for Aluminum can be achieved using poison ratio.