Remarks on the Theory of Elasticity

In compressible Neohookean elasticity one minimizes functionals which are composed by the sum of the L2 norm of the deformation gradient and a nonlinear function of the determinant of the gradient. Non–interpenetrability of matter is then represented by additional invertibility conditions. An existence theory which includes a precise notion of invertibility and allows for cavitation was formulated by Müller and Spector in 1995. It applies, however, only if some L p-norm of the gradient with p > 2 is controlled (in three dimensions). We first characterize their class of functions in terms of properties of the associated rectifiable current. Then we address the physically relevant p = 2 case, and show how their notion of invertibility can be extended to p = 2. The class of functions so obtained is, however, not closed. We prove this by giving an explicit construction. Mathematics Subject Classification (2000): 74B20, 35D05, 46E35 (primary), 49J45 (secondary).