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Research Papers

Strain Rate and Stress-State Dependence of Gray Cast Iron

[+] Author and Article Information
S. A. Brauer

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: sbrauer@cavs.msstate.edu

W. R. Whittington

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: wrw51@cavs.msstate.edu

K. L. Johnson

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: kyle@cavs.msstate.edu

B. Li

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: binli@cavs.msstate.edu

H. Rhee

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: hrhee@cavs.msstate.edu

P. G. Allison

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35406
e-mail: pallison@eng.ua.edu

C. K. Crane

Geotechnical and Structures Laboratory,
U.S. Army Engineer Research
and Development Center,
Vicksburg, MS 39180
e-mail: charles.k.crane@usace.army.mil

M. F. Horstemeyer

Center for Advanced Vehicular Systems,
Mississippi State University,
Starkville, MS 39759
e-mail: mfhorst@cavs.msstate.edu

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received April 27, 2016; final manuscript received December 3, 2016; published online February 9, 2017. Assoc. Editor: Xi Chen.This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government contributions.

J. Eng. Mater. Technol 139(2), 021013 (Feb 09, 2017) (11 pages) Paper No: MATS-16-1127; doi: 10.1115/1.4035616 History: Received April 27, 2016; Revised December 03, 2016

An investigation of the mechanical strain rate, inelastic behavior, and microstructural evolution under deformation for an as-cast pearlitic gray cast iron (GCI) is presented. A complex network of graphite, pearlite, steadite, and particle inclusions was stereologically quantified using standard techniques to identify the potential constituents that define the structure–property relationships, with the primary focus being strain rate sensitivity (SRS) of the stress–strain behavior. Volume fractions for pearlite, graphite, steadite, and particles were determined as 74%, 16%, 9%, and 1%, respectively. Secondary dendrite arm spacing (SDAS) was quantified as 22.50 μm ± 6.07 μm. Graphite flake lengths and widths were averaged as 199 μm ± 175 μm and 4.9 μm ± 2.3 μm, respectively. Particle inclusions comprised of manganese and sulfur with an average size of 13.5 μm ± 9.9 μm. The experimental data showed that as the strain rate increased from 10−3 to 103 s−1, the averaged strength increased 15–20%. As the stress state changed from torsion to tension to compression at a strain of 0.003 mm/mm, the stress asymmetry increased ∼470% and ∼670% for strain rates of 10−3 and 103 s−1, respectively. As the strain increased, the stress asymmetry differences increased further. Coalescence of cracks emanating from the graphite flake tips exacerbated the stress asymmetry differences. An internal state variable (ISV) plasticity-damage model that separately accounts for damage nucleation, growth, and coalescence was calibrated and used to give insight into the damage and work hardening relationship.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Polished GCI as observed under an optical microscope

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Fig. 2

Volume fraction of phases and phase identification

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Fig. 3

EDS images showing: (a) the original scanned image and elements, (b) iron, (c) manganese, and (d) sulfur

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Fig. 4

Sample image used for determining SDAS (etched with 2% nital)

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Fig. 5

Nearest neighbor distances when considering graphite only, particles only, and graphite and particles

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Fig. 6

(a) GCI plate labeled with directions used for testing and (b) triplanar micrograph illustrating the graphite orientations

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Fig. 7

Compression stress–strain behavior in the transverse and through-thickness directions at a strain rate of 0.001 s−1

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Fig. 8

Compression stress–strain behavior of GCI at three different strain rates for the transverse direction

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Fig. 9

Stress–strain response for GCI tested in tension

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Fig. 10

Stress–strain response for GCI tested in torsion

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Fig. 11

Scanning electron microscope images showing crack propagation from graphite flake to graphite flake for quasi-static compression tests. Void nucleation around the particle is apparent.

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Fig. 12

Scanning electron micrograph for GCI tested at a strain rate of 1600 s−1 for the transverse direction showing cracks and graphite debonding

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Fig. 13

Scanning electron micrograph of the failure surface for GCI tested in tension at quasi-static rates. Particle clusters were observed throughout the failure surface surrounded by the pearlitic matrix.

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Fig. 14

Quasi-static torsion sample as seen in a scanning electron microscope. Particle clusters, shown in the enlarged image, are found throughout the fracture surface.

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Fig. 15

Fracture surface for GCI tested in tension at high strain rate. Single particles were found on the fracture surface, but clusters were not evident.

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Fig. 16

Fracture surface of a torsion sample tested at high rate. Debonding of graphite from the pearlitic matrix dominates the fracture surface.

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Fig. 17

Mississippi State University (MSU) ISV Plasticity-Damage model calibrated model stress–strain curves as compared to experiment stress–strain curves

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