Analytical stress analysis of a nuclear fuel pellet through mohr-coulomb yield criterion and linear workhardening law

Abstract

Closed-form solutions for the stresses and the displacements are obtained in a reactor fuel pellet of workhardenable material under operational conditions through Mohr-Coulomb yield criterion and its associated flow rule. Numerical integrations are generally necessary, but the solutions can be expressed explicitly when the workhardening law is linear. Yielding is found to initiate at the outer edge of the pellet, and a plastic zone propagates inward. When the pellet has completely yielded, there exsist three distinct plastic zones in the pellet corresponding to stress states of different facetes of the Mohr-Coulomb yield surface. The analysis is divided into three stages; fully elastic, partly plastic, and fully plastic stages. Primary concern is to analyze the plastic zone of the pellet. Numerical examples are given. In these, the effects of adopting the Mohr-Coulomb yield criterion and a linear workhardening law are shown. The stress levels of the Mohr-Coulomb yield criterion are relatively higher than those of Tresca. It is found that the effect of adopting the Mohr-Coulomb yield criterion becomes clear as the internal friction angle increases. And the workhardening effect is significant in the axial component of stress. Beyond the yield limit, considerable increase of the yield stress is found if workhardening is allowed.