To check for the limit of stability and for bifurcations of the response path, the tangential stiffness matrix is needed. The microplane model does not provide it directly, but it can always be computed by incrementing
the strain components (or the displacements) one by one and solving for the corresponding stress changes with the microplane model.
A greater insight into the microplane model, which may be useful for data fitting, can be achieved by separating the geometric aspect of damage (i. e., the effect of reduction of the stress-resisting cross section of the material) from other inelastic phenomena. This separation has been achieved in Carol, Bazant and Prat (1991). Correlation to plasticity models and continuum damage mechanics has been elucidated in Carol and Bazant (1997).