Research Papers

Verification of a Thermoviscoplastic Constitutive Relation for Brass Material Using Taylor's Test

[+] Author and Article Information
Farid Abed

Department of Civil Engineering,
American University of Sharjah,
P.O. Box 26666,
Sharjah, UAE
e-mail: fabed@aus.edu

Tomasz Jankowiak

Institute of Structural Engineering,
Poznan University of Technology,
Piotrowo 5,
Poznan 60-965, Poland

Alexis Rusinek

Laboratory of Mechanics, Biomechanics,
Polymers and Structures,
National Engineering School of Metz,
1 route d'Ars Laquenexy,
Metz Cedex 03 57045, France

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 27, 2014; final manuscript received May 21, 2015; published online June 24, 2015. Assoc. Editor: Said Ahzi.

J. Eng. Mater. Technol 137(4), 041005 (Oct 01, 2015) (10 pages) Paper No: MATS-14-1206; doi: 10.1115/1.4030804 History: Received October 27, 2014; Revised May 21, 2015; Online June 24, 2015

This paper presents a methodology to define and verify the dynamic behavior of materials based on Taylor's test. A brass alloy with a microstructure composed mainly of two pure metals that have two different crystal structures, copper (face-centered cubic (fcc)) and zinc (hexagonal closed-packed (hcp)), is used in this study. A combined approach of different principal mechanisms controlled by the emergence and evolution of mobile dislocations as well as the long-range intersections between forest dislocations is, therefore, adopted to develop accurate definition for its flow stress. The constitutive relation is verified against experimental results conducted at low and high strain rates and temperatures using compression screw machine and split Hopkinson pressure bar (SHPB), respectively. The present model predicted results that compare well with experiments and was capable of simulating the low strain rate sensitivity that was observed during the several static and dynamic tests. The verified constitutive relations are further integrated and implemented in a commercial finite element (FE) code for three-dimensional (3D) Taylor's test simulations. A Taylor's test enables the definition of only one point on the stress–strain curve for a given strain rate using the initial and final geometry of the specimen after impact into a rigid surface. Thus, it is necessary to perform several tests with different geometries to define the complete material behavior under dynamic loadings. The advantage of using strain rate independent brass in this study is the possibility to rebuild the complete process of strain hardening during Taylor's tests by using the same specimen geometry. Experimental results using the Taylor test technique at a range of velocity impacts between 70 m/s and 200 m/s are utilized in this study to validate the constitutive model of predicting the dynamic behavior of brass at extreme conditions.

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Fig. 1

True stress versus true strain for the brass alloy at strain rate of 0.001 s−1 and different initial temperatures

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Fig. 2

True stress versus true strain for the brass alloy at an average strain rate of 3600 s−1 and room temperature

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Fig. 3

SEM images for the microstructure of brass for (a) undeformed and (b) deformed specimens

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Fig. 4

Athermal flow stress modeling for brass

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Fig. 5

Variation of the thermal flow stress with temperature at various plastic strains

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Fig. 6

Variation of the flow stress versus the strain rate

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Fig. 7

Comparisons of the stress–strain between experimental and FE results for brass at different initial temperatures and two strain rates of (a) 3600 s−1 and (b) 0.0001 s−1

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Fig. 8

Air gas gun used to launch the specimen and setup for impact velocity measurement

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Fig. 9

(a) Definition of the specimen geometry before and after impact to characterize the dynamic behavior of a material, (b) device used for the Taylor's test, and (c) sabot used for Taylor's test to ensure perpendicular impact

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Fig. 10

Equivalent plastic strains during the simulation of Taylor's test for the two methods at a time increment of 0.0001 s

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Fig. 11

Misses stresses during the simulation of Taylor's test for two methods at a time increment of 0.00005 s

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Fig. 12

The impact forces during the simulations of Taylor's test for the two FE methods

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Fig. 13

Comparisons of FE Taylor simulations with experiments for (a) strain and (b) strain rate conducted at room temperature and for different impact velocities

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Fig. 14

Comparisons of flow stress predicted by the FE Taylor simulations with experiments conducted at room temperature

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Fig. 15

FE Taylor simulation results showing the variation of (a) strain and (b) strain rate at different initial temperatures and impact velocities

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Fig. 16

Flow stress values predicted by the FE Taylor simulations at different velocity impacts and compared with experiments for high initial temperatures

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Fig. 17

Failure pattern of brass for initial velocities between 160 m/s and 200 m/s

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Fig. 18

FE simulation of failure mode of a brass specimen in Taylor test for initial velocity of 200 m/s

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Fig. 19

Failure criterion used in FE Taylor test simulations




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