A New Stored Energy Model Based on Plastic Work of Back Stress during Cyclic Loading in Polycrystalline Metal

Two mesomechanics models were analyzed in an attempt to reveal the relationship between stored energy and back stress. It has been indicated that the portion of elastic stored energy due to residual microstresses (E(SR)) is closely related to intergranular back stress (X(inter)), and the stored energy of dislocations inside grains (E(SD)) can be estimated with the plastic work of intragranular back stress (X(intra)). Then, the evolution of back stress during cyclic loading was studied, and the plastic work of back stress (W(pB)) was calculated with the low cycle fatigue experimental data of Ti-6Al-4V. The result shows that W(pB) is partially released at every reverse loading, sufficient to reproduce the evolution of stored energy correctly under cyclic loading. The study also reveals that partially released energy is related to the decrease of X(inter) at the initial state of reversal loading resulting from the reduction of the plastic strain incompatibility between grains.