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Parameterization of a nonlocal crystal plasticity model by nanoindentation and inverse modeling

By Jenni Engels (Ruhr Universität Bochum)
Co-authors: Napat Vajragupta (Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)/ Ruhr-Universität Bochum)
Soheil Rooein (Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)/ Ruhr-Universität Bochum)
Siwen Gao (Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)/ Ruhr-Universität Bochum)
Waseem Amin (Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)/ Ruhr-Universität Bochum)
Alexander Hartmaier (Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)/ Ruhr-Universität Bochum)


With the extensive demand for an approach describing the relationship between microstructural features and mechanical properties, several crystal plasticity models have been proposed in the recent decades. These constitutive models take the crystallographic orientations on deformation of both single crystal and polycrystal into account. However, these models neglect the influence of deformation gradient, which is fundamentally important as observed in several experiments. To incorporate this influence, advanced nonlocal constitutive models which are derived based on the concept of the geometrically necessary dislocations (GND) density tensor have been introduced. One major drawback of the nonlocal model and other micromechanical models is rather large number of material parameters necessary to describe material specific behavior. Furthermore, guidelines to determine all these material parameters are still limited. Therefore, a standardized parameterization technique should be discussed in the micromechanics community to promote applications of the nonlocal crystal plasticity models. This study aims to propose a parameterization technique for the nonlocal crystal plasticity model using a combination of nanoindentation and inverse modeling. Because of its large grain diameter, tempered Armco Iron is chosen as the material for investigation in this study. In the first step, series of nanoindentation test using cone-spherical indenter tip are performed on the selected grain with different indentation loads in order to investigate their influences on pile-up and sink-in behavior. Afterwards, the resulting surface topologies are then characterized. In the second step, simulation of the indentation process with approximated parameters is performed and the experimental and simulated surface topologies and force-displacement curves are compared. With an iterative procedure, the model parameters are adapted to yield an optimal agreement between experiment and simulation. Consequently, this proposed parameterization technique of the nonlocal crystal plasticity model could be further developed into a general protocol, which would then be applicable for other microstructures.

Ⓒ Photos:Toerisme Leuven