1. Istituto di Scienza e Tecnologie dell’Informazione, “Alessandro Faedo”, Consiglio Nazionale delle Ricerche, Via G. Moruzzi, 1, San Cataldo, 56124, Pisa, Italy 2. Institute of Mathematics ASCR, ?itná 25, 115 67, Prague 1, Czech Republic
Abstract:
For an anisotropic no-tension material there exist at least two rotations such that stress and strain become coaxial. The same result holds for any hyperelastic material whose response is expressed in terms of the small strain tensor and whose stress function is a continuous positively homogeneous degree 1 function.