ROTATIONS WHICH MAKE STRAIN AND STRESS COAXIAL

At a material point of a hyperelastic anisotropic body the strain and the stress tensors do not share, in general, a common basis of proper vectors. It is shown that there are at least three rotations which, wh en applied to the reference configuration before a given deformation, yield a pair of coaxial strain and stress tensors. This is an improvem ent on a previous result, which showed such rotations to be no fewer t han two. The proof is based on the application of Milnor's theorem fro m differential topology.