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Johnson-Cook parameter evaluation from ballistic impact data via iterative FEM modelling

Published version
Peer-reviewed

Type

Article

Change log

Authors

Burley, M 
Campbell, JE 
Dean, J 
Clyne, TW 

Abstract

A methodology is presented for evaluating a strain rate sensitivity parameter for plastic deformation of bulk metallic materials. It involves ballistic impact with a hard spherical projectile, followed by repeated FEM modeling, with predicted outcomes (displacement-time plots and/or residual indent shapes) being systematically compared with experiment. The “correct” parameter value is found by seeking to maximize the value of a “goodness of fit” parameter (g) characterizing the agreement between experimental and predicted outcomes. Input for the FEM model includes data characterizing the (temperature-dependent) quasi-static plasticity. Since the strain rate sensitivity is characterized by a single parameter value (C in the Johnson-Cook formulation), convergence on its optimum value is straightforward, although a parameter characterizing interfacial friction is also required. Using experimental data from (both work-hardened and annealed) copper samples, this procedure has been carried out and best-fit values of C (~0.016 and ~0.030) have been obtained. The strain rates operative during these experiments were ~104 – 106 s-1. Software packages allowing automated extraction of such values from sets of experimental data are currently under development.

Description

Keywords

Indentation, High strain rates, Impact indentation, Finite element analysis, Plasticity

Journal Title

International Journal of Impact Engineering

Conference Name

Journal ISSN

0734-743X
1879-3509

Volume Title

112

Publisher

Elsevier BV
Sponsorship
Engineering and Physical Sciences Research Council (EP/I038691/1)
EPSRC (1504177)
EPSRC (EP/K503757/1)