Plastic spin and evolution of an anisotropic yield condition

Isotropic and anisotropic hardening will be combined with plastic spin in order to describe the microstructural behaviour of a polycrystalline metal in terms of continuum mechanics. In the present paper emphasis is given to the experimental procedure, based on previous work by Boehler and Koss and applied in order to verify that approach. Experimental results for aluminium sheets at small strain i.e., in the regime of elastic–plastic transition are described and compared with theoretical predictions. The agreement is fair to good although it will be seen that the generalised, linear Prager hardening rule does not fit the experimental data. In particular it is found that the plastic spin, understood as the difference between the classical local rotation, induced by the displacement field, and the local rotation of the granular lattice may differ considerably from zero.