Energy adaptation of non-associated plasticity tangent matrices for symmetric solvers

The behaviour of most civil engineering materials is considered by many to be best characterised by non-associated plasticity models which generate unsymmetric stiffness matrices. Various non-symmetric solution algorithms have been developed for solving such problems but these require large core storage, (approximately twice the size required for symmetric solution algorithms), and the computational process is consequently slowed down especially for very large problems. Two groups of eight symmetric solution techniques are proposed in this paper for non-associated plasticity problems using the total and plastic work done as scalar measures to adapt their tangent matrices for symmetric solvers. Five numerical examples are used to illustrate the performance and limitations of the techniques in terms of numerical stability, solution accuracy and computation times.