Poisson's Ratio

The negative ratio of transverse (lateral) strain to axial (longitudinal) strain measured in a material subjected to uniaxial stress within its linear-elastic range; a dimensionless parameter that links lateral contraction to axial extension in isotropic elasticity and constrains relations among elastic constants (e.g., E = 2G(1+ν), K = E/[3(1−2ν)]).

The scalar ratio that quantifies the lateral (transverse) strain produced per unit axial strain under uniaxial stress in the linear elastic regime: ν = -ε_transverse / ε_axial. For homogeneous, isotropic, linear elastic solids ν links axial deformation to lateral deformation and influences volumetric response to loading.