A simple constitutive law for artificial graphite-like materials

A plasticity theory capable of realistically describing non-linearly hardening material behaviour for multiaxial loadings with stress reversals, finds a particularly simple representation in the case of artificial graphite-like materials. The basic idea of the general theory is to include in the plastic strain rate constitutive relation parameters associated with the history of the most recent unloading-reloading in different directions. This is achieved indirectly by introducing in stress space the concept of the bounding surface which encloses the yield surface. The proximity of these two surfaces in the course of their simultaneous translation and possible deformation determined the value of the generalized plastic modulus. The special features of the model in the case of artificial graphite-like materials is that, due to the absence of pure elastic response, the yield surface shrinks to a single point, the point representing the stress rate itself. This implies many other simplifications of the general theory. Numerical examples show a good agreement with experimental results in a unaxial case. The model describes highly non-linear material response under stress reversal, and because of its simplicity is especially tractable for numerical applications. (Auth.)