Figure 2.

Nonlinear elasticity of material in large deformation. The relationship between the normalized true stress and stretch ratio for a neo-Hookean bar subjected to uniaxial tensile force T is shown. The dashed line represents the prediction of the linear small-strain theory (Hooke's law). The solid line represents the nonlinear response of the material. The inset shows the geometry and loading. The tension bar has a cross-section area of A₀ and length of L₀ before deformation. After deformation, the cross-section area shrinks to A and the length extends to L. The true stress σ is defined by T/A, whereas the extension ratio λ is L/L₀.