Abstract
A direct numerical simulation of the cyclic response of a 250-grain polycrystalline aggregate over more than 1000 cycles is presented, being one of the few available simulations including a significant number of cycles. It provides unique results on the evolution of the accumulated plastic strain and ratcheting phenomena inside the grains. Even though the average stress–strain response stabilizes after 500 cycles, unlimited ratcheting is observed at some locations close to grain boundaries and triple junctions. A clear surface effect of the ratcheting behavior is evidenced based on an appropriate combination of Dirichlet, Neumann, and periodic boundary conditions. The magnitude of the ratcheting indicator is found to be significantly higher at the free surface than in the middle section of the aggregate. Both single- and polycrystalline samples of pure tantalum are tested at room temperature for identification of the parameters in the crystal plasticity model. Special attention is dedicated to modeling the static strain aging effects observed in this material.
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