Abstract
Software packages are being developed for automated extraction of plasticity parameters from indentation data (primarily load-displacement plots, although residual indent dimension data are also likely to be useful). Their design must be closely integrated with the associated experimental measurements. The procedure involves iterative FE simulation of the penetration of a spherical indenter into a sample, with automated convergence on a best-fit set of parameter values characterizing the yielding and work hardening response of the material (in a constitutive law). This paper outlines the main issues involved in optimization of experimental conditions and model formulation. Illustrative experimental data are presented from extruded rods of 5 metallic materials. Experimental issues include the dimensional scales of the indenter radius, R, and the depth of penetration, δ, with δ/R (the “penetration ratio”) being of particular significance. A brief study is presented of the potentially conflicting requirements of deforming a volume large enough to represent the response of the bulk and having a value of δ/R that creates plastic strains in a range that will adequately capture the work hardening response. A key conclusion of this study is that a “mid-range” indentation facility is likely to be optimal, with a load capability of at least a few kN, able to create δ/R values up to ∼40%, with R ∼0.5–2 mm. Other experimental issues include displacement measurement techniques, calibration of machine compliance and the possibility of material anisotropy (due to crystallographic texture). Issues related to formulation of the FE model include specification of the domain and mesh, selection of the constitutive plasticity law and simulation of interfacial friction. The convergence algorithm used is also described.
Highlights
There has been increasing focus over the past decade or two on obtaining stress-strain curves from outcomes of instrumented indentation experiments
It would be possible to include in this set other parameters that influence the indentation process, such as the coefficient of friction, that has not been done for the results presented here
While the present work is focused on plasticity, the approach is applicable to others, such as creep and superelasticity
Summary
There has been increasing focus over the past decade or two on obtaining (true) stress-strain curves (well beyond the elastic limit) from outcomes of instrumented indentation experiments (mainly load-displacement plots, residual indent shapes can be used). The stress and strain fields beneath an indenter, even one with a simple shape such as a sphere, are complex and change with penetration depth, making it very difficult to identify realistic analytical relationships The prospects for this approach, certainly in terms of having a robust procedure that can be applied to a wide range of materials, are not promising. The present paper is aimed at examining all of the main issues in some detail, including the relationships between the experimental procedures and the numerical simulations This is done using a wide range of experimental indentation data, illustrating how they are used in an automated way within software packages to obtain the values of parameters in constitutive stress-strain laws
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
