The dislocation configurational energy density in discrete dislocation plasticity

Dislocation configurational energy is the term assigned to describe the elastically-stored energy associated with the interaction of dislocations and their structures. It is the energy which is over and above that from the summation of the dislocation line energies when considered isolated and non-interacting. It is therefore different to the free energy and the stored energy. This paper presents a formulation for its determination utilising discrete dislocation plasticity. The total geometrically necessary (GND)and statistically stored dislocation density mean free distance allows the configurational energy density to be determined, thus providing a length scale over which the configurational energy is stored. This quantity is assessed in polycrystals undergoing fatigue loading showing that clear microstructural locations, often associated with high GND density, become established at which the progressive, cyclic, increasing configurational energy occurs. A higher length scale crystal plasticity stored energy density has recently been introduced which attempts to capture local dislocation configurational energy density as an indicator of fatigue crack nucleation and growth. The former is compared and assessed against the dislocation configurational energy density in this paper.