Local Ratcheting Phenomena in the Cyclic Behavior of Polycrystalline Tantalum

International audienceA direct numerical simulation of the cyclic response of a 250 grain polycrys-talline aggregate over more than 1000 cycles is presented, which belongs to the few available simulations including a significant number of cycles. It provides unique results on the evolution of accumulated plastic strain and ratcheting phenomena inside the grains. Even though the average stress strain response is stabilized after 500 cycles, unlimited ratchet-ing 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. The studied material is pure tantalum tested at room temperature for both single and polycrystalline samples used for parameter identification of the crystal plasticity model. Special attention is dedicated to the modeling of static strain aging effects observed in this material