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TECHNICAL PAPERS

Effect of Strain Rate on the Dynamic Hardness in Metals

[+] Author and Article Information
Amin H. Almasri

Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803

George Z. Voyiadjis

Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803voyiadjis@eng.lsu.edu

J. Eng. Mater. Technol 129(4), 505-512 (Apr 09, 2007) (8 pages) doi:10.1115/1.2744430 History: Received August 24, 2006; Revised April 09, 2007

Traditionally, the hardness of materials is determined from indentation tests at low loading rates (static). However, considerably less work has been conducted in studying the dynamic hardness of materials using relatively high loading rates. In the present work, two models are used to predict strain rate dependency in hardness. The first model is a power law expression that is based on the dependence of the yield stress on the strain rate. This model is relatively simple in implementation, and it is quite easy to determine its parameters from simple uniaxial experiments. The second model is a micromechanical based model using Taylor’s hardening law. It utilizes the behavior of dislocation densities at high strain rates in metals in order to relate dynamic hardness to strain rates. The latter model also accounts for any changes in temperature that could exist. A finite element is also run and compared with the two models proposed in this work. Results from both models are compared with available experimental results for oxygen-free high-conductivity copper and 1018 cold rolled steel, and both models show reasonably good agreement with the experimental results.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Theoretical pressure-load characteristic of an ideally plastic metal deformed by a spherical indenter: OA: elastic deformation region, AB: transitional region, BC: fully plastic region

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Figure 2

Constraint factor versus σ0.08∕E obtained for different strain rates with typical values of n=0.5 and ε̇r=10,000

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Figure 3

Normalized flow stress versus strain rate of OFHC copper

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Figure 4

Hardness versus strain rate of OFHC copper

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Figure 5

Pressure distribution under the indenter impacting target at a velocity of 10m∕s (stresses are in Pa)

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Figure 6

Effect of temperature change on hardness behavior versus strain rate of OFHC copper

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Figure 7

Normalized flow stress versus strain rate for 1018 steel

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Figure 8

Hardness versus strain rate for 1018 steel

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Figure 9

Effect of temperature change on the hardness behavior versus strain rate for 1018 steel

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