A symmetrisation method for non-associated unified hardening model

This paper presents a simple method for symmetrising the asymmetric elastoplastic matrix arising from non-associated flow rules. The symmetrisation is based on mathematical transformation and does not alter the incremental stress-strain relationship. The resulting stress increment is identical to that obtained using the original asymmetrized elastoplastic matrix. The symmetrisation method is applied to integrate the Unified Hardening (UH) model where the elastoplastic matrix is asymmetric due to stress transformation. The performance of the method is verified through finite element analysis (FEA) of boundary value problems such as triaxial extension tests and bearing capacity of foundations. It is found that the symmetrisation method can improve the convergence of the FEA and reduce computational time significantly for non-associated elastoplastic models.