Identification of the material properties of a single crystal plasticity model with kinematic hardening based on cyclic micro-bending tests on single crystal IN718
The mechanical material properties of polycrystalline metallic materials strongly depend on the size, shape and orientation distributions of the single crystals in the aggregate. For the computational analysis of the correlations of these microstructural quantities and the mechanical material properties usually representative volume elements and homogenization methods are employed. The mechanical behaviour of the single crystals in the representative volume elements is described with single crystal plasticity models that give a continuum description of the slip of dislocations in discrete slip systems. To this end, the single crystal plasticity models include material properties like the critical resolved shear stress of the slip system and additional properties to describe hardening in each slip system as well as effects of latent hardening. The determination of the single crystal material properties can be challenging, especially if cyclic loading conditions and, hence, the Bauschinger effect, need to be considered.
It is the aim of this work to identify the material properties of a single crystal plasticity model for cyclic loading conditions based on available results of load-deflection curves of cyclic micro-bending tests done on IN718 single crystals at Institute of Ferrous Metallurgy (IEHK) of RWTH Aachen. The micro-cantilever beams were tested under single slip condition. The single crystal plasticity model uses a non-linear kinematic hardening rule in each slip system, so that the Bauschinger effect can be described, and includes latent kinematic hardening among the slip systems. For the validation of the single slip condition in the micro-cantilever beam and the identification of the material properties of the slip system of the single crystal plasticity model, a finite-element model of the micro-bending test is generated and the single crystal plasticity model with kinematic hardening is implemented as user subroutine in to the finite-element program ABAQUS. Prior to the experimental tests, the implemented model is used to determine the exact orientation of the micro-cantilever specimen in the single crystal to ensure that single slip occurs. Afterwards the material properties in the slip systems are determined such that the calculated load-deflection curves give a good description of the measured load-deflection curves. Stress-strain hysteresis loops of the IN718 single crystals are shown for single-slip and multiple-slip conditions.