Equations governing a linearelastic boundary value problem are based on three tensor partial differential equations for the balance of linear momentum and six
their (linear) elastic properties fully described by two elastic moduli, and one may choose any pair. Given a pair of elastic moduli, all other elastic moduli
generally exhibits a very linear stress–strain relationship up to a well defined yield point. The linear portion of the curve is the elastic region, and the slope
rod of any elastic material may be viewed as a linear spring. The rod has length L and cross-sectional area A. Its tensile stress σ is linearly proportional