Abstract
A bottom-up material modeling based on a nonlocal crystal plasticity model requires information of a large set of physical and phenomenological parameters. Because of the many material parameters, it is inherently difficult to determine the nonlocal crystal plasticity parameters. Therefore, a robust method is proposed to parameterize the nonlocal crystal plasticity model of a body-centered cubic (BCC) material by combining a nanoindentation test and inverse analysis. Nanoindentation tests returned the load–displacement curve and surface imprint of the considered sample. The inverse analysis is developed based on trust-region-reflective algorithm, which is the most robust optimization algorithm for the considered non-convex problem. The discrepancy function is defined to minimize both the load–displacement curves and the surface topologies of the considered material under applying varied indentation forces obtained from numerical models and experimental output. The numerical model results based on the identified material properties show good agreement with the experimental output. Finally, a sensitivity analysis performed changing the nonlocal crystal plasticity parameters in a predefined range emphasized that the geometrical factor has the most significant influence on the load–displacement curve and surface imprint parameters.
Highlights
Nanoindentation is a technique for testing the mechanical properties of materials in the nanometer scale utilizing instruments with high precision
The considered material behavior is described by the nonlocal crystal plasticity model formerly defined and by a user-defined material subroutine (UMAT), which is coupled to the finite element model to simulate the nanoindentation test
Discrepancy functions from different initial sets approximately reached to the same quantity at the end displacement curvesObviously, and onthe surface imprints bybased analyzing the numerical model based of procedure
Summary
Nanoindentation is a technique for testing the mechanical properties of materials in the nanometer scale utilizing instruments with high precision. Density tensor [24,25,26] These nonlocal crystal plasticity models consist of numerous physical and phenomenological parameters, and characterizing these parameters directly from experimental tests is inherently difficult and makes it necessary to use inverse analysis technique to obtain these parameters. Inverse analysis by iterative finite element simulations requires two main prerequisites: precision and uniqueness The former means that the model is sufficiently accurate and representative of the real experiment. This study focused on the inverse analysis technique by iterative finite element simulations because of its simplicity for modeling of the nanoindentation test. The combination of material properties used in the finite element model that results in the simulated load–depth curve and in the surface imprint matching the experimental output is assumed to represent the nonlocal crystal plasticity properties being investigated.
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