Twinning-Induced Plasticity (TWIP)
The proposed models treat deformation twinning as pseudoslip. Therefore, these models cannot accurately predict the formation of deformation twins with nanometer thickness, as observed in TWIP steels. Accordingly, a new crystal-plasticity framework at RVE level will be developed that can account for crystallographic slip, mechanical twinning, slip-twin interaction and twin-twin interactions. The constitutive model will introduce an energy-based criterion to accurately address the activation of mechanical twinning. In this new framework, element(s) of the FE model will be representing mechanical twins. Furthermore, the shear strain introduced by these types of twin interactions will also be incorporated into the kinematics of the formulation, via the deformation gradient,
where, P> considers only crystallographic slip; P∗ embodies exlastic deformation and rigid body rotations; and PRS represents shear strain (due to twinning), with kinematics similar to that of crystallographic slip.
Transformation induced plasticity (TRIP)
The research focus will be on the local strain partitioning among austenite, bainite, ferrite and martensite. Once the new numerical model is validated, simulations of various strain paths will be performed to investigate the effects of the volume fractions of different phases, the austenite distribution, nearest neighbors to austenite, and the austenite texture on the formability/performance of TRIP steels.
The numerical framework will include transformation kinetics and will be employed to investigate the dominant plastic deformation mechanisms during various strain paths. The transformation effect in the Q&P steels will be modelled by partitioning the deformation gradient into elastic, plastic and transformation parts, similar to equation 5. The transformation part of the deformation gradient can be obtained by using the shape strain vector and the habit plane of the transformation (dyadic product of the two vectors).