Poisson's ratio represents the ratio of which two types of strain?

Poisson's ratio is defined as the ratio of lateral strain to longitudinal strain in a material when it is subjected to uniform axial stress. This describes how much a material deforms in the transverse direction when it is stretched or compressed in the axial direction.

When a material is elongated (under tensile stress), it typically contracts in the directions perpendicular to the applied load, leading to lateral strain. Conversely, when a material is compressed, the same principle applies: it expands laterally while compressing longitudinally. The proportional relationship between these strains is what Poisson's ratio quantifies, providing insight into the material's ductility and ability to withstand different types of loading.

Understanding Poisson's ratio is crucial in engineering and material science because it helps predict how materials will behave under various stresses, which is vital for safe and effective design.