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Research Papers

Dynamic Fracture of Aluminum-Bonded Composites

[+] Author and Article Information
Prasenjit Khanikar

Department of Mechanical Engineering,
Indian Institute of Technology,
Guwahati 781039, India

Qifeng Wu

Department of Mechanical and
Aerospace Engineering,
North Carolina State University,
Raleigh, NC 27695-7910

M. A. Zikry

Department of Mechanical and
Aerospace Engineering,
North Carolina State University,
Raleigh, NC 27695-7910
e-mail: zikry@ncsu.edu

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received September 30, 2015; final manuscript received March 2, 2016; published online May 10, 2016. Assoc. Editor: Ghatu Subhash.

J. Eng. Mater. Technol 138(3), 031009 (May 10, 2016) (13 pages) Paper No: MATS-15-1247; doi: 10.1115/1.4033036 History: Received September 30, 2015; Revised March 02, 2016

A dislocation density-based crystal plasticity framework, a nonlinear computational finite-element methodology adapted for nucleation of crack on cleavage planes, and rational crystallographic orientation relations were used to predict the failure modes associated with the high strain rate behavior of aluminum-bonded composites. A bonded aluminum composite, suitable for high strain-rate damage resistance application, was modeled with different microstructures representing precipitates, dispersed particles, and grain boundary (GB) distributions. The dynamic fracture approach is used to investigate crack nucleation and growth as a function of the different microstructural characteristics of each alloy in bonded composites with and without pre-existing cracks. The nonplanar and irregular nature of the crack paths were mainly due to the microstructural features, such as precipitates and dispersed particles distributions and orientations, ahead of the crack front. The evolution of dislocation density and the subsequent formation of localized plastic slip contributed to the blunting of the propagating crack(s). Extensive geometrical and thermal softening resulted in localized plastic slip and had a significant effect on crack path orientations and directions along cleavage planes.

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Figures

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Fig. 1

Scanning electron micrograph of crack formation in the AA2195 layer in a bonded composite of AA2139 and AA2195

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Fig. 2

Schematic of the finite-element model, showing the microstructure with a representative grain in each layer of the bonded composite

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Fig. 3

Normalized normal stress contours (normalized by matrix yield strength) for the bonded composite, with a pre-existing crack, subjected to tensile strain rate of 50,000 s−1: (a) high stresses at crack arrest position (1.1% nominal strain), (b) the crack blunting at crack arrest position (3.9% nominal strain), and (c) almost complete rupture (4.8% nominal strain)

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Fig. 4

Crack extension plot

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Fig. 5

Normalized immobile dislocation density contours (normalized by saturated immobile dislocation density) for the bonded composite, with a pre-existing crack, subjected to tensile strain rate of 50,000 s−1 (a) on the most active slip system of the matrix, (1 1¯ 1)[0 1 1] and (b) on the most active slip system of the θ/ precipitates, (1¯ 1 2)[1 1¯ 1] (both at 4.8% nominal strain)

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Fig. 6

(a) Normalized immobile dislocation density (normalized by saturated immobile dislocation density) on six active slip systems of the matrix near the blunted crack tip at the final stage of the crack arrest (3.9% nominal strain), (b) immobile dislocation density on the most active slip system of the matrix ((1 1¯ 1)[0 1 1] at the initial stage of the crack arrest (1.3% nominal strain), and (c) immobile dislocation density on the most active slip system of the matrix ((1 1¯ 1)[0 1 1] at the final stage of the crack arrest (3.9% nominal strain)

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Fig. 7

(a) Crystallographic lattice rotation at 4.8% nominal strain, (b) accumulated plastic strain at 4.1% nominal strain, and (c) temperature rise due to adiabatic heating at 3.9% nominal strain for the bonded composite, with a pre-existing crack, subjected to tensile strain rate of 50,000 s−1

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Fig. 8

Normalized normal stress contours (normalized by matrix yield strength) for the bonded composite, without any pre-existing crack, subjected to a tensile strain-rate of 50,000 s−1: (a) crack nucleation (3.5% nominal strain), (b) the major crack at 4.0% nominal strain, and (c) after complete failure (6.0% nominal strain)

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Fig. 9

Normalized immobile dislocation density (normalized by saturated immobile dislocation density) on the most active slip systems of the matrix, (1 1¯ 1)[0 1 1] for the bonded composite, without any pre-existing crack, subjected to tensile strain rate of 50,000 s−1 (a) at 2.8% nominal strain and (b) at 6.0% nominal strain

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Fig. 10

(a) Crystallographic lattice rotation at 4.0% nominal strain, (b) accumulated plastic strain at 4.0% nominal strain, (c) temperature rise due to adiabatic heating at 4.0% nominal strain, and (d) normalized pressure (normalized by Young's Modulus of matrix) at 3.0% nominal strain for the bonded composite, without a pre-existing crack, subjected to tensile strain rate of 50,000 s−1

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Fig. 11

Stress–strain curves for the bonded aluminum composite with a pre-existing crack at strain rates of 50,000 s−1 and 30,000 s−1

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Fig. 12

Comparison of normalized normal stress contours (normalized by matrix yield strength) at 3.5% nominal strain under strain-rates of (a) 30,000 s−1 and (b) 50,000 s−1 and at 4.3% nominal strain under strain rates of (c) 30,000 s−1 and (d) 50,000 s−1

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Fig. 13

Comparison of normalized normal stress contours (normalized by matrix yield strength) at a tensile strain-rate of 50,000 s−1 for AA2195–AA2139-bonded composite, with a pre-existing crack, at 4.8% nominal strain for the cases (a) with microstructure and (b) without microstructure

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Fig. 14

Comparison of normalized normal stress contours (normalized by matrix yield strength) at a tensile strain rate of 50,000 s−1 for AA2195–AA2139-bonded composite, without any pre-existing crack, at 4.4% nominal strain for the cases (a) with microstructure and (b) without microstructure

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