A new hardening law is introduced into the classical incremental theor
y of plasticity for initially isotropic solids allowing us not only to
rigidly translate, transversely isotropically deform and rotate, but
also to distort the yield surface. The law, on the whole, can satisfac
torily describe modifications of the surface experimentally obtained b
y other authors in complex biaxial tension-torsion Loading of thin-wal
led tubular specimens of pure aluminum.