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Research Papers

High Strain Rate Tensile Behavior of Aluminum Alloy 7075 T651 and IS 2062 Mild Steel

[+] Author and Article Information
Jayaram R. Pothnis

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Indiajpothnis@gmail.com

Yernamma Perla

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Indiayernindh_p_h@yahoo.co.in

H. Arya

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Indiaarya@aero.iitb.ac.in

N. K. Naik1

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Indianknaik@aero.iitb.ac.in

1

Corresponding author.

J. Eng. Mater. Technol 133(2), 021026 (Mar 24, 2011) (9 pages) doi:10.1115/1.4003113 History: Received August 10, 2010; Revised November 17, 2010; Published March 24, 2011; Online March 24, 2011

Investigations on the effect of strain rate on tensile properties of two materials, namely, aluminum alloy 7075 T651 and IS 2062 mild steel, are presented. Experimental studies were carried out on tensile split Hopkinson pressure bar (SHPB) apparatus in the strain rate range of 54–164/s. Uncertainty analysis for the experimental results is presented. Johnson–Cook material constitutive model was applied to predict the tensile yield strength of the tested materials at different strain rates. It is observed that the tensile yield strength is enhanced compared with that at quasi-static loading. During tensile SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. An explanation to this is provided based on the increase in dislocation density and necking in the tested specimens during high strain rate loading and the consequent stress wave attenuation as it propagates within the specimen. The fracture behavior and effect of high strain rate testing on microstructure changes are examined. The peak force obtained based on strain gauge mounted on the transmitter bar is lower than the peak force obtained based on strain gauge mounted on the incident bar. There is an increase in tensile yield strength at high strain rate loading compared with that at quasi-static loading for both materials. The enhancement is more for IS 2062 mild steel than that for aluminum alloy 7075 T651. In the range of parameters considered, the strength enhancement factor was up to 1.3 for aluminum alloy 7075 T651 and it was up to 1.8 for IS 2062 mild steel. Generally, there was a good match between the experimental values and the Johnson–Cook model predictions.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

SHPB apparatus, tensile loading: (a) schematic arrangement and (b) photograph

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Figure 2

Arrangement of specimen and holders: (a) end-threaded cylindrical specimen (dimensions in mm) and (b) end-threaded cylindrical specimen with holders

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Figure 3

Deformation behavior of specimens: (a) end-threaded cylindrical calibration specimen with holders, (b) end-threaded cylindrical specimen with holders, (c) necking of the specimen during loading, and (d) idealized representation of necked specimen

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Figure 4

Tensile SHPB test results for Al alloy 7075 T651: dS=4 mm, lS=15 mm, and έ=109/s: (a) strain gauge signals on oscilloscope and (b) comparison of force versus time behavior, derived from strain gauge signals

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Figure 5

A typical yielded Al alloy 7075 T651 specimen

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Figure 6

High strain rate tensile test results for Al alloy 7075 T651: dS=4 mm, lS=15 mm, and έ=109/s: (a) time versus strain rate plot, (b) time versus strain plot, and (c) time versus stress plot

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Figure 7

Stress versus strain plot from high strain rate tensile test on SHPB for Al alloy 7075 T651: dS=4 mm, lS=15 mm, and έ=109/s

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Figure 8

Strain rate versus tensile yield strength plot, experimental and predicted using JC model for Al alloy 7075 T651

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Figure 9

Strain rate versus tensile yield strength plot, experimental and predicted using JC model for IS 2062 mild steel

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Figure 10

SEM images of Al alloy 7075 T651 specimen, tested at quasi-static strain rate: (a) specimen cross section (magnification=20X) and (b) central region of the specimen cross section showing dimples characteristic of ductile fracture (magnification=500X)

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Figure 11

SEM images of Al alloy 7075 T651 specimen, tested at high strain rate έ=77/s: (a) specimen cross section (magnification=20X) and (b) central region of the specimen cross section showing dimples, as well as flat regions, characteristic of ductile and brittle fractures, respectively (magnification=1000X)

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Figure 12

Photomicrograph of Al alloy 7075 T651 specimen, tested at quasi-static strain rate (magnification 500X)

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Figure 13

Photomicrograph of Al alloy 7075 T651 specimen, tested at high strain rate, έ=77/s (magnification 500X)

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