Constitutive Equations

The differential system of balance laws, both in Eulerian form ( 5.31 ) and in Lagrangian forms ( 5.48 ) and ( 5.56 ), contains more unknown functions than equations. Therefore, it is necessary to close the system, i.e., balance the number of unknowns with the number of equations, by adding new equations that characterize the constitution of the materials. These equations are called for this reason constitutive equations.