Cyclic Polycrystalline Viscoplastic Model for Ratchetting of a Body Centered Cubic Metal

In the framework of crystal plasticity, a new cyclic polycrystalline viscoplastic model is constructed to describe the uniaxial ratchetting of a body centered cubic (BCC) metal. At the intra-granular scale, a combined kinematic hardening rule similar to the Ohno-Abdel-Karim model is employed to address the ratchetting within each single crystal grain; and two sets of slip systems with different resistances to dislocation slip, i.e., primary and secondary ones, are considered to capture the physical nature of dislocation slips in a body centered cubic (BCC) metal. At the inter-granular scale, an explicit transition rule is adopted to extend the single crystal approach into a polycrystalline version. It is shown that the proposed model describes the uniaxial ratchetting of annealed 42CrMo steel, a body centered cubic (BCC) metal, reasonably. Also, it is seen that the crystal orientation influences significantly the ratchetting of body-centered cubic (BCC) single crystals.